VSEBINA – CONTENTS
IZVIRNI ZNANSTVENI ^LANKI – ORIGINAL SCIENTIFIC ARTICLES
Selective oxidation of manganese in molten pig iron
Selektivna oksidacija mangana v staljenem grodlju
D. Pihura, M. Oru~, J. Lamut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
The corrosion behaviour of ferritic stainless steels in alkaline solutions
Korozijsko vedenje feritnih nerjavnih jekel v alkalnih raztopinah
A. Kocijan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
Numerical design of a hot-stretch-reducing process for welded tubes
Numeri~no na~rtovanje vro~e raztezne redukcije varjenih cevi
S. Re{kovi}, R. Kri`ani}, F. Vodopivec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Preparation and study of Mg2Sn-based composites with different compositions
Priprava in karakterizacija lastnosti kompozitov na osnovi Mg2Sn
V. Kevorkijan, S. D. [kapin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
Osseointegration and rejection of a titanium screw
Oseointegracija in zavrnitev titanovega vijaka
G. Klan~nik, M. Zdovc, U. Kov{ca, B. Pra~ek, J. Kova~, J. Rozman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
Corrosion investigation of the Pre{eren monument in Ljubljana
Korozijska preiskava Pre{ernovega spomenika v Ljubljani
M. Bajt Leban, V. Kuhar, T. Kosec, A. Legat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
The microflora and physico-chemical properties of lignite from the Mirash mine, near Kastriot
Mikroflora in fizikalno-kemijske lastnosti lignita iz rudnika Mirash pri Kastriotu
F. Plakolli, L. P. Beqiri, A. Millaku . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
Cadmium and lead accumulation in Alfalfa (Medicago Sativa L.) and their influence on the number of stomata
Akumulacija kadmija in svinca v rastlini Lucerna (Medicago Sativa L.) in njun vpliv na {tevilo listnih por
A. Bytyqi, E. Sherifi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
STROKOVNI ^LANKI – PROFESSIONAL ARTICLES
The selection and development of tribological coatings
Izbira in razvoj tribolo{kih prevlek
Y. Kharlamov, V. Dal, I. Mamuzi}, L. Lopata, G. S. Pisarenko. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
Recycling of steel chips
Recikliranje jeklenih ostru`kov
M. Torkar, M. Lamut, A. Millaku . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
18. MEDNARODNA KONFERENCA O MATERIALIH IN TEHNOLOGIJAH, 15. – 17. november, 2010, Portoro`, Slovenija
18th INTERNATIONAL CONFERENCE ON MATERIALS AND TECHNOLOGY, 15–17 November, 2010, Portoro`, Slovenia . . . . . . 293
ISSN 1580-2949
UDK 669+666+678+53 MTAEC9, 44(5)233–292(2010)
MATER.
TEHNOL.
LETNIK
VOLUME 44
[TEV.
NO. 5
STR.
P. 233–292
LJUBLJANA
SLOVENIJA
SEP.–OCT.
2010

D. PIHURA et al.: SELECTIVE OXIDATION OF MANGANESE IN MOLTEN PIG IRON
SELECTIVE OXIDATION OF MANGANESE IN MOLTEN
PIG IRON
SELEKTIVNA OKSIDACIJA MANGANA V STALJENEM GRODLJU
Dervi{ Pihura1, Mirsada Oru~1, Jakob Lamut2
1University of Zenica, Metallurgical institute "Kemal Kapetanovi}", Travni~ka c. 7, 72000 Zenica, B&H
2University of Ljubljana, FNT, Department for materials and metallurgy, A{ker~eva c. 12, 1000 Ljubljana, Slovenia
dervis.pihura@gmail.com
Prejem rokopisa – received: 2008-09-22; sprejem za objavo – accepted for publication: 2010-03-15
An examination of the process of selective oxidation for molten pig iron indicates the possibility of lowering the content of
unwanted or harmful elements. This process makes it possible to achieve the optimum Mn content in pig iron (hot metal)
without any oxidation of the other elements present, such as carbon, etc. Several variants of oxygen blowing with the addition of
a slag-forming component were checked. The final element content in the hot metal depends on the initial Mn content, the
oxygen blowing and on the added slag components. The lowering of the Mn content in the hot metal to the limit solves the
problems of converter processing, lowers the slag quantity, increases the yield of steel by more 4 % and improves the
steel-making process.
Key words: selective oxidation, hot metal, high manganese content
Analiza procesa selektivne oksidacije teko~ega grodlja daje mo`nost, da odstranimo ne`elene in {kodljive elemente. Proces
omogo~a, da dose`emo optimalno vsebnost mangana v surovem grodlju (vro~a kovina) brez oksidacije drugih elementov,
ogljika in drugih. Preizku{enih je bilo ve~ variant vpihovanja kisika z dodatki za tvorbo `lindre. Kon~na vsebnost mangana v
grodlju je odvisna od za~etne vsebnosti, vpihovanja kisika in od dodatkov za `lindranje. Zmanj{anje vsebnosti mangana do meje
re{uje probleme konvertorskega procesiranja, zmanj{a koli~ino `lindre, pove~a izkoristek jekla za ve~ od 4 % in izbolj{a proces
izdelave jekla.
Klju~ne besede: selektivna oksidacija, grodelj, visoka vsebnost mangana
1 INTRODUCTION
Only in some countries metallurgists face the
problem of a large content of manganese in molten pig
iron (hot metal) of above 4.00 % 1,2,3,4,5. The higher Mn
content in hot metal during the oxidation, i.e., during
steel-making, influences the formation of slag and causes
serious problems for the technology. For this reason, the
reaction between manganese and oxygen in hot metal is
still being investigated. There are particular problems
with hot metal that has a manganese content above 1 %.
The process of manganese oxidation was investigated
from the points of view of the reaction mechanism, the
thermodynamics and the kinetics, and different con-
clusions were proposed. The majority of investigations
were performed on hot metal with a low manganese
content, below 1.00 %. Only rarely was the object of the
examination some hot metal with a high manganese
content, higher than 4 %, as the initial content. Only on
the basis of investigations with a high manganese iron
can the present misunderstandings and confusion about
results be solved, with the condition that the effect of the
method of introducing the oxygen into the hot metal on
the evolution of reactions is also considered.
During the processing of hot metal with a high
manganese content to steel, a large quantity of slag is
obtained that decreases the yield and increases the
splashing 5,6. So far, no process for the selective oxida-
tion of manganese from hot metal before pouring into a
steel-making furnace was developed and attempts to
decrease the manganese content in hot metal were not
successful. In fact in Austria, steel-makers gave up on
the use of iron ore with a high content of manganese 1,5.
In Russia and Bulgaria trials of the oxidation of
manganese were not successful and it was only possible
to produce FeMn from slag with a high percentage of
MnO 3,4,7. The treated hot metal had a low carbon content
and was not suitable for the making of steel with less
than 2.00 % of manganese.
New technical solutions and equipment for the
processing of hot metal in a ladle offer the possibility of
decreasing some harmful or unwanted elements with
selective oxidation 6,7,8 before tapping the hot metal into
the steel furnace. In this work we ordered the problem of
lowering the manganese content, combining the
introduction of oxygen with the use of an appropriate
slag. Specifically, the influence of the addition of
slag-forming oxides, especially SiO2, was investigated.
The performed experiments indicate that it was possible
to decrease the manganese content in the hot metal from
4.00 % or more to below 1.00 at 1773 K.
In this article the metallurgical and technological
aspects of the selective oxidation of manganese with
oxygen and slag formation on a pilot-plant scale are
presented that offer the possibility of applications on an
industrial scale.
Materiali in tehnologije / Materials and technology 44 (2010) 5, 235–238 235
UDK 669.1:669.046-547:546.711 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 44(5)235(2010)
2 METALLUGICAL CHARACTERISTICS OF
SELECTIVE OXIDATION
Selective oxidation has to be carried out only with a
sufficient supply of oxygen as well as with a slag that is
rich in FexO. The multi-reaction equilibrium of the
selective oxidation of manganese can be deduced using a
suitable method; however, a more reliable method of
calculation is based on the equilibrium principle and a
change of the Gibbs’ free energy of the formation of
oxides (Go) for different reactions. It is important to
calculate the conditions for the selective oxidation of
manganese with no change in the initial carbon content
and with the minimal oxidation of silicon. For the three
elements carbon, silicon and manganese, three equations
can be written showing a mutual equilibrium between
any of two, with only two independent equations. The
equilibria for the systems Mn-C and Mn-Si are solved
with numerical iteration.
It is assumed that the change of the manganese
content for low and higher initial contents does not have
corresponding changes in the decreasing part of the
curves in Figure 1, especially for the case of the
Mn–humpback 3,9. The changes in the manganese content
at the lower part of the curves at 1873 K do not occur
below the of Mn–humpback in melts without carbon
content and for hot metal melts with 4.00 % or more C at
1573 K 1. This strengthens the importance of clarifying
the mechanism of the reactions in the systems Mn–{O2}
and Mn–FexO.
It is assumed that the mechanism of the reactions of
selective oxidation of manganese with oxygen in the
presence of FexO slag components occurs as shown in
Figure 2. It is important that in the processing the
continuity of the reactions fields is maintained: 1 – initial
reactions (1st field), 2 – transition reactions (2nd field) and
3 – stable reactions (3rd field). It is further concluded that
oxygen blown into the field of the initial reactions (mark
1) can react with iron, silicon, manganese and carbon.
On the base of the Go – T dependences it is possible to
expect that at 1573 K only the manganese is oxidised. It
is assumed that the oxidation of carbon is damped
because of the influence of a ferro-static pressure deep
into the melt. In the second field (number 2 in Figure 2),
the formed FexO is reduced with silicon. It is assumed
that additional reactions occur in the third field of
permanent reactions (number 3). The process of selective
oxidation of manganese is achieved with a transition
through all three fields in Figure 2, only.
The eij values for the temperature of 1573 K are
calculated by applying two approaches: from the
obtained data or from values for 1873 K, considering the
difference in temperature.
The calculation of the free energy Go at different
stages of the manganese’s selective oxidation leads to a
236 Materiali in tehnologije / Materials and technology 44 (2010) 5, 235–238
D. PIHURA et al.: SELECTIVE OXIDATION OF MANGANESE IN MOLTEN PIG IRON
Figure 3: Dependence of the coeficient of manganese distribution LMn
= w(Mn)/w[Mn] of melt temperature and the (FeO) content in the slag
Slika 3: Odvisnost koeficienta porazdelitve mangana LMn = w(Mn)/w
[Mn] od temperature taline in vsebnosti FeO v `lindri
Figure 1: Change of the different initial Mn content during the
oxidation process: (•) 0.20 % Mn; () 0.40 % Mn; () 0.5 % Mn; (x)
1.2 % Mn; (x) 2.0 % Mn; (•) 4.00 % Mn; 4. (+) 8.00 % Mn
Slika 1: Sprememba razli~ne za~etne vsebnosti mangana med
procesom oksidacije: (•) 0.2 % Mn; () 0.4 % Mn, ()0.5 % Mn, (x)
1.2 % Mn, (x) 2.0 % Mn, (•) 4.0 % Mn, (+) 8.0 % Mn
Figure 2: Mechanism of reaction blowing oxygen and slag
components 1. initial reactions.; 2. transition reactions; 3. permanent
reactions; 4. hot metal; 5. slag; 6. oxygen; 7. argon
Slika 2: Mehanizem reakcijskega vpihovanja kisika in komponente
`lindre. 1 – za~etne reakcije, 2 – prehodne reakcije, 3 – permanentne
reakcije, 4 – teko~i grodelj, 5 – `lindra, 6 – kisik, 7 – argon
different equilibrium situation. The possibility of prior
silicon oxidation at 1573 K, thus, before the oxidation of
manganese and carbon, is dependent on other
influencing factors; firstly, of the slag composition. The
equilibrium between the silicon and the manganese is
reached at the beginning of the oxidation process and
both elements are oxidized in parallel in preference to
the carbon until the ternary equilibrium silicon, manga-
nese and carbon is achieved. The content of carbon has
to remain constant at the initial level or changed
insignificantly. Thus, the final equilibrium composition
of the hot metal depends not only upon the temperature
and the initial composition, but also upon the activity of
the oxides aSiO2 and aMnO.
3 THE OXIDATION OF MANGANESE, THE
PRINCIPLE AND THE EXPERIMENTAL
PROCEDURE
The solution to the problem of a high manganese
content of about 4.00 % in the hot metal produced in
Zenica could be found by considering the system
Fe-Mn-Si-C-O at 1573–1673 K for Go – T dependences
that offer the possibility of irreversible reactions. In this
temperature range it is possible to achieve the value for
the wMn/wC ratio of 0.10, which allows the success-
ful selective oxidation of manganese. The measure of the
rate of accelerated reactions of manganese oxidation,
which determines the degree of reaction, is the mass
transport coefficient (kMn). A significant decrease in the
content of one element (X1) by a sufficient decrease of
the second (X2) can be achieved on the condition of kX1 >
kX2 and for the ratio of the distribution coefficient LX1 >
LX2. The most important is the distribution of elements,
and especially manganese, between the hot metal and the
slag (LMn = wMn/w(Mn)) (Figure 3).
The experiments were performed in the ladle with a
porous plug with a charge of hot metal with the
composition in mass fractions: (4.03 ± 0.25) % C, (3.80
± 0.52) % Mn and (0.56 ± 0.10) % Si. The oxidation was
carried out with oxygen blowing and the addition of 6 %
of FexO for the slag formation. The experiments were
performed in three variants of the lance blowing of
oxygen: 1. on the slag surface, 2. in the hot metal and 3.
in the metal being rinsed with argon. The temperature of
the hot metal was, in all cases, 1573 K.
For the existence of all three reactions fields, only the
role of FexO as an oxidation intensifier and the control of
the oxidation of silicon with the present component SiO2
were assumed. If all the reaction fields are reduced to
one field of permanent reaction, it would be difficult, or
even impossible, to control the selective oxidation of
iron, silicon, manganese, carbon, etc. The decrease of
manganese content to the equilibrium value excludes it
from the oxidation process and the content of manganese
at the start of the oxidation of carbon and iron is
considered as critical [Mn]c.
4 EXPERIMENTAL RESULTS
The obtained experimental results show that the most
successful manganese oxidation process occurs during
the blowing of oxygen with parallel argon rinsing
(variant 3) without the oxidation of carbon, and accept-
able kinetics of silicon oxidation. Data on the oxidised
quantity of manganese and the losses of silicon and
carbon are presented in Figures 4 and 5. It is obvious
that already after 7.5 min. of oxidation in the variant 3,
the final manganese content of 0.10 % Mn was achieved
with the oxidation rate of vMn = 0.39 % Mn/per min,
which is higher than that quoted rate of vMn = 0.35 %
Mn/per min 3. With the variant 2, the final manganese
content was <1.00 %. The slag with the optimal charac-
teristics was obtained with the largest additions of FexO
and SiO2. In spite of the large oxygen supply, the average
free oxygen content in the hot metal is (3 ± 2) μg/g.
Materiali in tehnologije / Materials and technology 44 (2010) 5, 235–238 237
D. PIHURA et al.: SELECTIVE OXIDATION OF MANGANESE IN MOLTEN PIG IRON
Figure 5: Average oxidised elements quantity of carbon (), silicon
() and manganese () during oxidation for variants: 1 – blowing to
surface; 2 – blowing into melt; 3 – blowing into melt with argon
rinsing
Slika 5: Povpre~na koli~ine oksidiranih elementov ogljika (),
silicija () in mangana () med oksidacijo mangana za variante: 1 –
vpihovanje na povr{ino, 2 – vpihovanje v talino in 3 – vpihovanje v
talino z izpiranjem z argonom
Figure 4: Oxidation of manganese at 1573 K for variants: 1. ()
blowing on melt surface; 2. () blowing in melt; 3. () blowing in
melt and rinsing through a porous plug
Slika 4: Oksidacija mangana pri 1573 K za variante: () vpihovanje
na povr{ino taline, () vpihovanje v talino, () vpihovanje v talino in
izpiranje z argonom skozi porozen ~ep
In the hot metal at 1573 K, the oxidation of manga-
nese alone is connected to the effect of the high carbon
content and to interaction parameters with a value
different to that at 1873 K. The composition and activity
of slag formed with lance oxygen blowing on the melt
top, in the melt, as well as for argon rinsing are different
for the same slag addition. For instance, the activities
aMnO and aFeO at 1573 K are for oxygen top blowing,
0.234 and of 0.642, into melt blowing, 0.395 and of
0.464, and blowing with argon rinsing, 0.474 and of
0.459.
5 CONCLUSIONS
1. On the basis of the thermodynamics, kinetics, mecha-
nism and mass transfer conditions as well as the
effect of slag addition it was concluded that it was
possible to ensure the selective oxidation of manga-
nese in hot metal without significantly affecting the
content of the other elements.
2. Through the pilot-plant oxidation of only manganese
at 1573 K it was possible to determine suitable values
of the technological and metallurgical parameters to
achieve an optimal decrease for the high initial
manganese content in the hot metal.
3. Considering the influence of oxygen and FexO for the
checked oxidation variants, it is obvious that the
optimal mechanism of selective oxidation of the
manganese is connected with the kinetics of the
supply of oxygen. The decrease of the manganese
content is only achieved if the selective oxidation
occurs in three reaction fields.
4. During the oxidation of manganese, other elements
are maintained at the initial contents or are minimally
oxidised, as carbon, or silicon, depending on the SiO2
in the slag.
5. The obtained results of the manganese oxidation do
not lead to a secondary increase in the content of
manganese in the hot metal.
6. From the environmental point of view, of all the
checked variants, the variant 3 is the most acceptable,
as in the processing no brown fumes are produced.
6 REFERENCES
1 Pihura D.: Pregled procesa oksidacije Si, Mn, P i S (Survey of the
process of oxidation of Si, Mn, P and S); Metalur{ki institut, Zenica,
1989
2 Lamut J, Pihura D, Selektivna oksidacija mangana (Selective
oxidation of manganese), Project, Slovenia – BiH, 2004
3 Kvitko, M. F., Afanasjev, S.G., Kislorodno-konvertorni proces (The
oxigen convertor proces) Moskva, Metallurgija, 1974
4 Mal~eva, N., Kacareva, I., Savov, P., Rudodobiv i metalurgija (1969)
5, 23
5 Kammerhofer Van E, Dobrowsky F et al., BHM, 113 (1986),
444–449
6 Ohkotskij, V. B. et al., Steel in USSR 20 (1990) 7, 317/20
7 Vincent D. i Makin S.B., A New Concept in Liquid Metal Treatment
ISID Ltd, 1999
8 Deo B, Boom R. Fundamentals of Steelmaking Metallurgy, London
1993
9 Koch K et al. Stahl u. Eisen 104 (1984), 767
D. PIHURA et al.: SELECTIVE OXIDATION OF MANGANESE IN MOLTEN PIG IRON
238 Materiali in tehnologije / Materials and technology 44 (2010) 5, 235–238
A. KOCIJAN: THE CORROSION BEHAVIOUR OF FERRITIC STAINLESS STEELS IN ALKALINE SOLUTIONS
THE CORROSION BEHAVIOUR OF FERRITIC
STAINLESS STEELS IN ALKALINE SOLUTIONS
KOROZIJSKO VEDENJE FERITNIH NERJAVNIH JEKEL V
ALKALNIH RAZTOPINAH
Aleksandra Kocijan
Institute of Metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenia
aleksandra.kocijan@imt.si
Prejem rokopisa – received: 2010-03-11; sprejem za objavo – accepted for publication: 2010-04-07
The corrosion resistances of X6Cr17 and X2CrTi17 ferritic stainless steels and cold-rolled, low-carbon steel, as well as circular
and transversal welds of X6Cr17 ferritic stainless steel, were investigated in a non-phosphate detergent with a solution pH of
10.5 and at a temperature of 60 °C. The second investigated solution contained the non-phosphate detergent and sodium
perborate tetrahydrate at pH 11 and was at a temperature of 90 °C. The potentiodynamic measurements showed that the
corrosion resistance decreased from X2CrTi17 and X6Cr17 to the welded specimens and the cold-rolled, low-carbon steel in
non-phosphate detergent at the lower temperature. At the elevated temperature and with the addition of sodium perborate
tetrahydrate the corrosion stability of all the investigated materials decreased significantly.
Keywords: ferritic stainless steel, potentiodynamic, alkaline solution, corrosion
Preu~evali smo korozijsko odpornost vzorcev X6Cr17, X2CrTi17 feritnih nerjavnih jekel, hladno valjanega malooglji~nega
jekla in kro`nega ter pre~nega zvara X6Cr17 feritnega nerjavnega jekla v raztopini nefosfatnega detergenta pri pH 10,5 in
temperaturi 60 °C. Druga preiskovana raztopina je vsebovala nefosfatni detergent in natrijev perborat tetrahidrat pri pH 11 in
temperaturi 90 °C. Rezultati potenciodinamskih meritev so pokazali, da sta korozijsko najbolj obstojna materiala X2CrTi17 in
X6Cr17, manj pa obe vrsti zvarov in hladno valjano malooglji~no jeklo. Pri povi{ani temperaturi in z dodatkom natrijevega
perborata tetrahidrata se je korozijska odpornost vseh petih vzorcev izrazito zmanj{ala.
Klju~ne besede: feritna nerjavna jekla, potenciodinamske, alkalna raztopina, korozija
1 INTRODUCTION
Ferritic steels with about 17 % Cr (e.g., X6Cr17,
AISI 430, and EN 1.4016) are of interest as they are
some of the most widely used stainless engineering
materials and offer an attractive alternative to the more
expensive austenitic stainless-steel grades.1 X6Cr17 is a
ferritic, straight chromium, non-hardenable grade, com-
bining good corrosion resistance and formability
characteristics with useful mechanical properties.1 It has
a good resistance to a wide variety of corrosive media,
including nitric acid and some organic acids. It attains its
maximum corrosion resistance in the highly polished or
buffed condition. In general, its resistance to pitting and
crevice corrosion resistance is close to that of the steel
grade 304.2 The stress-corrosion cracking resistance of
Grade X6Cr17 is very high, as it is for all ferritic
grades.3,4 Typical applications for the X6Cr17 grade
include the linings for dish washers, refrigerator-cabinet
panels, automotive trim, lashing wire, element supports,
stove trim rings, fasteners and chimney liners.1
The ferritic stainless steel X2CrTi17 stabilised with
titanium has a very good resistance to intergranular
corrosion.5 Furthermore, titanium also binds sulphur and
leads to improved pitting corrosion. All ferritic stainless
steels are also resistant to stress-corrosion cracking and
have a good corrosion resistance to mineral acids, cold
dilute organic acids and cold oxidizing and alkaline salt
solutions, to atmospheric corrosion, to high-temperature
oxidation and to hot water.5 Stabilisation with titanium
results in a good toughness and ductility for the welds.
The corrosion resistance of the welds is similar to that of
the base metal. The typical applications of this grade are
in domestic appliances, such as the tubs and drums of
washing machines.
The aim of the present study was to evaluate the
corrosion resistance of X2CrTi17 and X6Cr17 ferritic
stainless steels as well as circular and transversal welds
of X6Cr17 ferritic stainless steel in alkaline solutions
using potentiodynamic measurements in order to esta-
blish an appropriate substitution of X2CrTi17 with
X6Cr17 for washing machines. A cold-rolled, low-
carbon steel was also investigated.
2 EXPERIMENTAL
The nominal values of the chemical composition of
the investigated materials are shown in Table 1.
The experiments were carried out in two solutions.
The first solution consisted of 10 g/L 2508 SDC IEC
non-phosphate detergent, allowed for use in the inter-
national standard "ISO 6330:2000 Domestic Washing
and Drying Procedures for Textile Testing" and contains
fluorescent brightening agents, with a pH of 10.5 at a
temperature of 60 °C.
Materiali in tehnologije / Materials and technology 44 (2010) 5, 239–242 239
UDK 620.193:669.14.018.8 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 44(5)239(2010)
The second solution was prepared by the dissolution
of 8 g of 2508 SDC IEC non-phosphate detergent and 2
g of sodium perborate tetrahydrate per litre of H2O at pH
11 and a temperature of 90 °C. Sodium perborate tetra-
hydrate is a reagent allowed in the international stan-
dards "ISO 105 C06, C08 and C09" and "ISO 6330:
2000". It acts as a bleaching agent and is incorporated
into the latest standards to replicate modern commercial
laundry products.
The test specimens were cut into discs of 15 mm
diameter. The specimens were then embedded in a
Teflon PAR holder and employed as a working electrode.
The reference electrode was a saturated calomel elec-
trode (SCE, 0.242 V vs. SHE) and the counter electrode
was a high-purity graphite rod. All the potentials
described in the text are stated with respect to SCE.
The potentiodynamic measurements were recorded
using an EG&G PAR PC-controlled potentiostat/galva-
nostat Model 263 with M252 and Softcorr computer
programs. For the potentiodynamic measurements the
specimens were immersed in the solution 1 hour prior to
the measurement in order to stabilize the surface at the
open-circuit potential. The potentiodynamic curves were
recorded starting from a potential that was 250 mV more
negative than the open-circuit potential. The potential
was then increased using a scan rate of 1 mV s–1, until
the transpassive region was reached.
3 RESULTS AND DISCUSSION
The corrosion-current density (icorr) and the potential
at zero current (E(I = 0)) values were calculated from
linear polarization measurements and Tafel plots using
the equation:
Rp = a c / (2.3 Icorr (a + c))
The corrosion current, Icorr, is calculated from Rp, the
least-squares slope, and the Tafel constants, a and c, of
the 100 mV decade–1. The value of E(I = 0) is calculated
from the least-squares intercept.
The potentiodynamic behaviours of the investigated
materials in two testing solutions are shown in Figures 1
and 2, accompanied by calculated values of the corro-
sion rates, the corrosion-current densities (icorr), the
potentials at zero current (E(I = 0)) and the polarisation
resistances (Rp) (Tables 2 and 3). The differences in the
alloys’ composition affected the polarisation and the
passivation behaviours of the tested materials.
Figure 1 compares the potentiodynamic polarisation
curves for the X6Cr17 and X2CrTi17 ferritic stainless
steels and the cold-rolled, low-carbon steel as well as
circular and transversal welds of X6Cr17 ferritic stain-
less steel in the phosphate detergent at 60 °C. After 1 h
of stabilization at the open-circuit potential, the E(I = 0)
for X6Cr17 in the non-phosphate detergent at 60 °C was
approximately –0.15 V. Following the Tafel region, the
alloy exhibited a semi-passive behaviour with three
active-passive transition zones. The breakdown potential
(Eb) for the X6Cr17 was approximately 0.75 V. For the
case of X2CrTi17, the E(I = 0) was approximately equal
to –0.24 V. The range of passivation was similar to that
for the X6Cr17 specimen without the active-passive
A. KOCIJAN: THE CORROSION BEHAVIOUR OF FERRITIC STAINLESS STEELS IN ALKALINE SOLUTIONS
240 Materiali in tehnologije / Materials and technology 44 (2010) 5, 239–242
Table 1: The nominal values of chemical composition of X6Cr17, X2CrTi17 ferritic stainless steels and cold rolled low-carbon steel (w/%)
Tabela 1: Nominalne vrednosti kemijske sestave X6Cr17, X2CrTi17 feritnih nerjavnih jekel in hladno valjanega malooglji~nega jekla (w/%)
C Si Mn Cr S P N Ti
X6Cr17 0.12 max 1.00 max 1.00 max 14–18 0.03 max 0.040 max – –
X2CrTi17 0.025 max 0.50 max 0.50 max 16–18 0.015 max 0.040 max 0.015 max 0.35 max
DC01 EN10130 0.12 max – 0.60 max – 0.045 max 0.045 max – –
Table 2: Calculated values of corrosion rates (vcorr), corrosion current
densities (icorr), potentials at zero current (E(I = 0)) and polarisation
resistances (Rp) for X6Cr17, X2CrTi17 ferritic stainless steels and
cold rolled low-carbon steel as well as circular and transversal welds
of X6Cr17 ferritic stainless steel in non phosphate detergent at 60 °C.
Tabela 2: Izra~unane vrednosti korozijske hitrosti, gostote koro-
zijskega toka, potenciala pri ni~elnem toku in polarizacijske upornosti
za vzorce X6Cr17, X2CrTi17 feritnih nerjavnih jekel hladno valjanega
malooglji~nega jekla in kro`nega ter pre~nega zvara X6Cr17 feritnega
nerjavnega jekla v raztopini nefosfatnega detergenta pri 60 °C
Sample vcorr /(mm/year)
E(I = 0)
/mV
icorr /
(μA/cm2)
Rp
/k
X6Cr17 0.0013 151.3 0.120 277.0
X6Cr17
(circular weld) 0.036 242.1 3.282 13.16
X6Cr17
(transversal weld) 0.015 281.5 1.399 27.26
DC01 EN10130 0.059 340.5 6.132 5.382
X2CrTi17 0.0013 240.8 0.116 310.5
Table 3: Calculated values of corrosion rates, corrosion current
densities (icorr), potentials at zero current (E(I = 0)) and polarisation
resistances (Rp) for X6Cr17, X2CrTi17 ferritic stainless steels and
cold rolled low-carbon steel as well as circular and transversal welds
of X6Cr17 ferritic stainless steel in non phosphate detergent with the
addition of sodium perborate tetrahydrate at 90 °C.
Tabela 3: Izra~unane vrednosti korozijske hitrosti, gostote koro-
zijskega toka, potenciala pri ni~elnem toku in polarizacijske upornosti
za vzorce X6Cr17, X2CrTi17 feritnih nerjavnih jekel hladno valjanega
malooglji~nega jekla in kro`nega ter pre~nega zvara X6Cr17 feritnega
nerjavnega jekla v raztopini nefosfatnega detergenta z dodatkom
natrijevega perborata tetrahidrata pri 90 °C
Sample vcorr /(mm/year)
E(I = 0)
/mV
icorr /
(μA/cm2)
Rp
/k
X6Cr17 0.059 21.62 5.442 6.063
X6Cr17
(circular weld) 0.411 40.08 37.77 1.137
X6Cr17
(transversal weld) 0.351 78.87 32.22 0.781
DC01 EN10130 8.167 434.4 847.4 0.0565
X2CrTi17 0.049 4.851 4.568 7.700
transition zones and an Eb of 0.75 V. The corrosion-
current densities in the passive range had lower values
for the X2CrTi17 specimen. The E(I = 0) values for the
circular and transversal welds of X6Cr17 ferritic stain-
less steel in the non-phosphate detergent at 60 °C were
–0.24 V and –0.28 V, respectively. The corrosion-current
densities for both welded specimens increased signifi-
cantly in comparison to the non-welded sample. The
cold-rolled, low-carbon steel was the least corrosion
resistant of all the investigated samples, with an E(I = 0)
value of –0.34 V and a corrosion-current density of
6 μA/cm2. The calculation of the polarisation resistance
(Rp) showed that the corrosion stability of the X2CrTi17
specimen was the greatest of all the tested materials,
with an Rp value of approximately 300 k. The second
most stable specimen was the steel X6Cr17 with an Rp
value of approximately 280 k. The welded specimens
and the cold-rolled, low-carbon steel exhibited a signi-
ficant decrease in Rp values, indicating a lower corrosion
resistance of these specimens compared to the steels
X6Cr17 and X2CrTi17 (Table 2).
In Figure 2 the potentiodynamic polarisation curves
for the X6Cr17 and X2CrTi17 ferritic stainless steels,
and the cold-rolled, low-carbon steel, circular and
transversal welds of X6Cr17 ferritic stainless steel in the
non-phosphate detergent with the addition of sodium
perborate tetrahydrate at 90 °C are shown. The corrosion
resistance of all the investigated samples decreased con-
siderably, compared to the results in the non-phosphate
detergent at lower temperatures. The steels X2CrTi17
and X6Cr17 exhibited improved corrosion characteristics
compared to the other three samples, although the
difference with the welded specimens was not so pro-
nounced as in the first solution due to the aggressiveness
of the second solution (Table 3). The corrosion stability
of the cold-rolled, low-carbon steel decreased a great
deal with the addition of sodium perborate tetrahydrate
and the higher temperature (Table 3).
4 CONCLUSION
The present electrochemical study was conducted in
order to determine the corrosion performance of different
ferritic stainless steels in a specific alkaline environment;
the influence of welding and the chemical composition
of the selected materials on the corrosion characteristics
was evaluated, also.
The potentiodynamic measurements were performed
with the investigated steels and welds in a non-phosphate
detergent at 60 °C and with the addition of sodium
perborate tetrahydrate at 90 °C. The results showed the
superior corrosion stability of the X2CrTi17 and X6Cr17
ferritic stainless steels in comparison to the welded
X6Cr17 ferritic stainless steel and the cold-rolled, low-
carbon steel at the lower temperature. The corrosion
resistance of all the investigated materials decreased
significantly at the elevated temperature and with the
addition of sodium perborate tetrahydrate. The
X2CrTi17 and X6Cr17 ferritic stainless steels showed
comparable electrochemical characteristics, while the
corrosion stability of the circular and transversal welds
of the X6Cr17 ferritic stainless steel was similar. The
resistance of the cold-rolled, low-carbon steel to
corrosion in the alkaline solution was significantly
diminished in comparison with the other investigated
materials.
The results of the present study indicate that the
electrochemical characteristics of the X6Cr17 and
A. KOCIJAN: THE CORROSION BEHAVIOUR OF FERRITIC STAINLESS STEELS IN ALKALINE SOLUTIONS
Materiali in tehnologije / Materials and technology 44 (2010) 5, 239–242 241
Figure 2: Potentiodynamic polarisation curves for X6Cr17, X2CrTi17
ferritic stainless steels and cold rolled low-carbon steel as well as
circular and transversal welds of X6Cr17 ferritic stainless steel in non
phosphate detergent with the addition of sodium perborate tetra-
hydrate at 90 °C.
Slika 2: Potenciodinamske krivulje vzorcev X6Cr17, X2CrTi17 ferit-
nih nerjavnih jekel hladno valjanega malooglji~nega jekla in kro`nega
ter pre~nega zvara X6Cr17 feritnega nerjavnega jekla v raztopini
nefosfatnega detergenta z dodatkom natrijevega perborata tetrahidrata
pri 90 °C
Figure 1: Potentiodynamic polarisation curves for X6Cr17, X2CrTi17
ferritic stainless steels and cold rolled low-carbon steel as well as
circular and transversal welds of X6Cr17 ferritic stainless steel in non
phosphate detergent at 60 °C.
Slika 1: Potenciodinamske krivulje vzorcev X6Cr17, X2CrTi17
feritnih nerjavnih jekel hladno valjanega malooglji~nega jekla in
kro`nega ter pre~nega zvara X6Cr17 feritnega nerjavnega jekla v
raztopini nefosfatnega detergenta pri 60 °C
X2CrTi17 ferritic stainless steels in alkaline media at
elevated temperatures are similar. This allows the
substitution of X2CrTi17 with X6Cr17 ferritic stainless
steel in the fabrication of washing machines.
5 REFERENCES
1 B. Marian, C. Aurel, Metalurgia International, 13 (2008) 6, 55–59
2 I. Tikhovskiy, D. Raabe, F. Roters, Materials Science and Engi-
neering a-Structural Materials Properties Microstructure and
Processing, 488 (2008)1–2, 482–490
3 I. Tikhovskiy, D. Raabe, F. Roters, Scripta Materialia, 54 (2006) 8,
1537–1542
4 F. Gre{ovnik, Mater. Tehnol. 34 (2000) 5, 289–293
5 J. Charles, J.-D. Mithieux, P.-O. Santacreu, L. Peguet, Rev. Met. 3,
(2009) 124–139
A. KOCIJAN: THE CORROSION BEHAVIOUR OF FERRITIC STAINLESS STEELS IN ALKALINE SOLUTIONS
242 Materiali in tehnologije / Materials and technology 44 (2010) 5, 239–242
S. RE[KOVI] et al.: NUMERICAL DESIGN OF A HOT-STRETCH-REDUCING PROCESS FOR WELDED TUBES
NUMERICAL DESIGN OF A HOT-STRETCH-REDUCING
PROCESS FOR WELDED TUBES
NUMERI^NO NA^RTOVANJE VRO^E RAZTEZNE REDUKCIJE
VARJENIH CEVI
Stoja Re{kovi}1, Rade Kri`ani}1, Franc Vodopivec2
1University Zagreb, Faculty of Metallurgy, Aleja narodnih heroja 3, 44103 Sisak, Croatia
2Institute of metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenia
reskovic@simet.hr
Prejem rokopisa – received: 2009-12-21; sprejem za objavo – accepted for publication: 2010-05-18
During stretch reducing, steel is submitted to complex stressing and straining processes. This paper gives a theoretical model of
a heat-stretch-reducing process for the relation between the tube diameter and the wall thickness. The design is verified by a
determination of the number of revolutions of rolls with every caliber for specific tubes on an industrial mill. The control of the
rolled-tube dimensions confirmed the accuracy of the design.
Key words: hot-stretch reducing, welded tubes, numerical model of design, calibrate, coefficient of plastic extension of the steel
Pri raztezni redukciji je jeklo izpostavljeno kompleksni napetostni in deformacijski obremenitvi. V ~lanku je predstavljen
teoreti~en model procesa vro~e raztezne redukcije za razmerje med premerom cevi in debelino njene stene. Na~rt je preverjen z
dolo~itvijo {tevila vrtljajev valjev na industrijski valjarni za vsak kaliber za dolo~ene dimenzije cevi. Kontrola dimenzij cevi je
potrdila natan~nost izra~una.
Klju~ne besede: vro~a raztezna redukcija, varjene cevi, numeri~no na~rtovanje, kalibracija, koeficient plasti~nega iztezanja
1 INTRODUCTION
With the technology of stretch reducing, previously
manufactured tubes are transformed in several passes
into tubes with a selected diameter and wall thickness.1,2,3
In the processing, the tube is submitted to strong
compression and tensile stresses during the reduction of
the diameter and the decrease of the tube wall with
stretching and tensile stressing. Both the types of
stressing are mutually dependent, complex and very
high.2,3 The extent of stretching is defined by the
coefficient of plastic extension and it is regulated by the
number of revolutions of the rolls during every pass.4
This coefficient is the ratio of the reduction of the tube
diameter and wall, and the ratio of the compression and
tensile stresses in the tube. The number of passes
depends, on the one hand, on the required reductions of
the tube diameter and the wall, and on the other hand, on
the lowering of the temperature from the first to the last
reduction pass. The quality of the processed steel is of
great importance, since it determines the temperature
range of the processing. For this reason, theoretically, the
number of passes of the stretch-reducing mill depends on
the total size of the reduction and the decrease of the
temperature in all the reducing passes.
The model design of the stretch-reducing parameters,
mainly reductions, stretchings, and temperature, is
relatively complex and depends on several mutually
related parameters. The improper selection of the
stretch-reducing parameters leads to deviations between
the planned and the obtained tube dimensions and the
failure of the tubes’ walls and a non-uniform defor-
mation over the tube length may also occur.5 In
comparison to other processes of tube rolling, stretch
reducing has some advantages, probably the most
important is that it enables the manufacturing of several
finished tubes from the same initial tube diameter and
wall thickness.2,9 Also, better accuracy is achieved for
the final tube diameter and the wall thickness. And
finally, for stretch reducing no internal tool is necessary
and welded tubes can be processed without prior removal
of the welded beard, while the quality of the tube surface
is improved. The technology of stretch reducing is very
specific and the number of rolling mills is relatively low.
Accordingly, the number of references related to the
process is also small. In this work, a theoretical model of
the design of the hot-stretch reducing of tubes is
presented, which was used to establish the number and
the form of the passes for the industrial rolling of tubes
of final diameters in the range ¾ inch to 3 inch from an
initial tube of 4 inch.
2 THE PROCESS OF STRETCH REDUCING
The stretch-reducing mill consists of a line of several
passes–stands, and as example in Figure 1 a three-stands
rolling mill is shown.3 The number of rolls per caliber is
two up to four, with an optimum of three, and any caliber
can have an individual drive or all the calibers can have a
shared drive. All the calibers have an oval, and only the
last one has a circular shape. The rolls are inclined at
Materiali in tehnologije / Materials and technology 44 (2010) 5, 243–250 243
UDK 621.771.28:621.791 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 44(5)243(2010)
120° and the passes at 60° (Figure 1). The number of
passes depends on the tube dimensions and the
maximum reduction of the tube diameter and wall
thickness. To lower the processing temperature and make
possible the use of a greater number of passes in the
prescribed temperature range, the intercaliber distance
must be as small as possible.2,3,4
A schematic of the work of the stretch-reducing mill
is shown in Figure 2. No change of the wall thickness
occurs in the first pass, while the reduction of the
diameter is 3 % to 5 %. The friction coefficient is
negative and has the role of driving the processed tube.
In the following two to three passes the diameter
reduction is 12 %, the coefficient of plastic extension is
below 0.5 and the tube-wall thickness is increased. In the
middle passes the diameter reduction is up to 12 %, the
extension coefficient is 0.75 and the reduction of the tube
diameter and the wall thickness is achieved. In the last
two passes the accuracy of the final product is ensured
with a diameter reduction of 3 % to 1.5 % and with a
constant wall thickness The rate of the processed tube
increases from pass to pass.4,5
The number of passes, the dimensions of the
reduction rolls and the rate of the roll revolutions are
given. The calculation model is based on two basic laws:
the law of the constancy of the pass rate and of the
constancy of volume. When designing the successions of
passes on the continuous processing line it is necessary
to consider that on the same time, the tube is in several
passes. To maintain the continuity of the processing, the
same volume of material has to pass through every
processing pass. If this continuity is not respected, the
movement of the tube may be affected and by greater
differences, disturbances or even breaking of the rolling
may occur.2,5,6
The as-welded tube enters the stretch-reducing mill
with an initial outside tube diameter of d0 and a tube-wall
thickness of s0, which are reduced to the final dimensions
of dn and sn in a determined number of passes. For the
decrease of the tube wall to the required thickness, in
relation to the initial, a sufficient tensile stressing (v) is
required2,6,7 it is necessary that for the part of the
processed tube between two following passes. For this
reason, the rotation rate of the following rolls is greater
than that of the precedent, thus (nn >… > n2 > n1). The
increase in the rotational rate in every pass depends on
the reduction of tube diameter and the wall thickness in
the pass.
For the simplified design model of the process passes
of the tubes, the stretch-reducing equations (1) to (6) are
used. For the number of passes n the relations (1) and (2)
must be fulfilled, such that:
v v v constn1 1 1 2 1( ) ( ) ( )= = = = (1)
or
A v A v A v Cn	 
 ⋅ = ⋅ = = ⋅ =1 1 1 2 1( ) ( ) ( ) (2)
where C is the rolling constant, v1 is the tube exit rate
from the pass and A is the area of the tube section
The circumferential velocity of the rolls is:
v D n0 = ⋅ ⋅π (3)
Because of acceleration, the tube rate v1 is greater
during the pass exit than the circumferential rolls’
velocity. For a simplification of the calculation of the
passes, the difference is generally neglected and it is
assumed that vi = vo. On the basis of this supposition, the
constant C is calculated from equation (4):
A D v A D v A D v Cn n n	 
⋅ ⋅ = ⋅ ⋅ = = ⋅ ⋅ =1 1 1 2 1 2 1( ) ( ) ( ) (4)
where D is the rolls’ working diameter inside the pass
and n is the revolution rate of the rolls.
The calculation is necessary for every new dimension
of tube manufactured. After every calculation, the
working diameter of the rolls is deduced with relation to
the first or the final pass and the rolling constant is
determined.7,9 The number of revolutions for the other
rolls is then calculated according to equation (5):
N
C
A D
=
⋅
(5)
On the basis of the constant C the working diameters
of all the rolls are calculated using equation (6):
D
C
A N
=
⋅
(6)
The rolls’ diameter is a variable only in the projects
of a new rolling mill. For mills in operation, the rolls’
diameter depends on the diameter of the rolls for
standardised types of mill stands.
The explained calculation is very much simplified
and it could be applied only for checking in cases when
S. RE[KOVI] et al.: NUMERICAL DESIGN OF A HOT-STRETCH-REDUCING PROCESS FOR WELDED TUBES
244 Materiali in tehnologije / Materials and technology 44 (2010) 5, 243–250
Figure 2: Scheme of the work of the stretch reducing mill2
Slika 2: Shema delovanja raztezne valjarne
Figure 1: Flow chart of a three-calibers stretch-reducing rolling mill
(3)
Slika 1: Preto~na shema trikalibrne raztezne valjarne
the mill constant is determined with a detailed calcu-
lation in which the compression stresses generated by the
simultaneous reduction of tube diameter and of tube wall
with tensile stresses are considered.
For a detailed calculation it is necessary to first
determine the elements of the deformation zone. The
reduction of the area is determined for the transverse
tube section in every pass opening caliber (reduction of
diameter), and the rate of the rolls’ revolution (the
reduction of the tube wall with elongation). The relation
of both reductions depends on the coefficient of the
plastic extension, which also represents the relation of
the compression and tensile stresses.
3 ELEMENTS OF THE DEFORMATION ZONE
For the calculation of the reduction and the rate in the
deformation zone the elements of this zone need to be
determined according to Figure 3. The zone is defined
by the angle of contact , the neutral angle 
, the
gripping length between the surface of the rolls and the
tube as well as the tube diameter and the wall thickness.
With the stretch reducing of the tubes, the defor-
mation zone consists of two parts. In the first part with
the compression stresses the tube diameter is decreased,
and in the second part with the tensile stresses the wall
thickness is decreased. Both parts are connected at the
neutral angle 
. The total length of the deformation zone
ld from the gripping point to the exit of the tube
represents the line of contact between the rolls and the
processed tube. The neutral angle 
 is calculated with the
equation:


 

= ⋅ −
⎛
⎝
⎜
⎞
⎠
⎟
2
1
2
(7)
The angle of contact  is calculated from:


= −⎛⎝
⎜ ⎞
⎠
⎟arccos 1
d
R
(8)
and
R
D b
=
−w
2
2
(9)
With the parameters d, Dw and b showed in Figure
3.10
The friction angle  depends on the temperature Ti,
the rolls type ml, the rolling rate m2 and the type of the
steel processes m3, and it is calculated from equation
(12):
 = arctan (10)
 = ⋅ ⋅ ⋅ − ⋅m m m Ti1 2 3 105 0 005( . . ) (11)
Figure 4 shows that the neutral angle  determines
the point where the tube rate in the rolling direction is
equal to the horizontal component of the circumferential
roll velocity on the transport radius (v
 = v cos 
), the
point where the tube rate at the exit of the deformation
zone (v1) becomes greater than the circumferential roll
velocity on the transport line.6,10
According to this analysis v1 > v
 > v0 and with the
dependence of the observation point, in the deformation
zone the relative positive and negative motion occurs
with respect to the roll circumferential velocity.
4 ROLLING RATE
To achieve the reduction of the tube diameter and
wall thickness it is necessary to establish the proper
relation of the rates in all the phases of the stretch
reducing. The proper relation of the rates ensures the
continuous processing of the changes of the diameter and
the wall tube section area. As for other continuous
rolling processes, the law of constant volume must be
respected. For different points of the deformation zone,
this law is given by the relations (12) and (13):
a) At the exit of the deformation zone
A v A v A vn n	 
⋅ = ⋅ = = ⋅1 1 1 2 1( ) ( ) ( ) (12)
The law of constant volume requires that in the first
pass the initial rate is smaller than the pass exit rate. The
Materiali in tehnologije / Materials and technology 44 (2010) 5, 243–250 245
S. RE[KOVI] et al.: NUMERICAL DESIGN OF A HOT-STRETCH-REDUCING PROCESS FOR WELDED TUBES
Figure 4: Tube and roll rates and point of the neutral angle in the
deformation zone
Slika 4: Hitrost cevi in valjev na to~ki nevtralnega kota deformacijske
zone
Figure 3: Elements of the deformation zone (10)
Slika 3: Elementi zone deformacije
pass exit rate is increased with the decrease of the
section of the tube wall until the rolling is ended.
At the neutral point of the deformation zone
A v A v A vn n
	 
 

 
 
 
⋅ = ⋅ = = ⋅( ) ( ) ) ( )1 2  (13)
The distribution of the rates and their relative place in
the deformation zone for the tube rolling in a three-rolls
oval pass is shown in Figure 4. The tube rate is equal to
the horizontal component of the circumferential roll
velocity and the tube rate at the exit of the deformation
zone is greater than the circumferential roll velocity on
the transport radius. For an angle lower than 
, a rela-
tively positive tube motion occurs (the zone of over-
taking), while, for the angle lower than 
 a relatively
negative motion of the tube occurs (the tube straggling
zone), Figure 5.
The overtaking, i.e., the difference in the roll circum-
ferential velocity and the tube exit rate, is given in
equations (14), (15) and (16).
s
v v
vi
i i
i
=
−1 tr
tr
( ) ( )
( )
(14)
s
A
v v
vi
i
i
i i i
i
=
−





( )
( )
( ) ( ) ( )
( )
costr tr
tr
(15)
s /
A
i
i
i
i% cos
( )
( )
( )= −
⎛
⎝
⎜
⎞
⎠
⎟



 1 (16)
The tube exit rate from the pass deformation zone
according to equations (7) and (8) and with respect to the
neutral angle (Figure 4) is calculated according to
equations (17), (18) and (19).
v
A v
i
i i
i
=

 


( ) ( )
( )
(17)
v vi i i
 
( ) ( ) ( )cos= tr (18)
v
A
vi
i
i
i i	




( )
( )
( )
( ) ( )cos= tr (19)
The tube exit rate is deduced from the mill constant C
in equation (4) according to equation (20).
v
C
i
i
	 ( ) ( )
= (20)
The number of revolutions of the rolls is calculated on
the basis of the transport radius and the circumferential
velocity in this radius from equation (21).
N
v
Di
i
i
= tr
tr
( )
( )π
60 (21)
The number of revolutions of the rolls for every pass
in the stretch-reducing mill Ni, depends on the initial
rate, thus the number of revolutions of the first pass n1; it
depends on the number of revolutions for every caliber
and it is calculated using equations (22) and (23).
n n Ni i= 1 (22)
With a multiplication of the number of stands with
the number of revolutions of the first pass the number of
revolution is obtained for every pass.
N
A D
A Di i i i
=








( ) ( ) ( )
( ) ( ) ( )
cos
cos
1 1 1tr
tr
(23)
The number of revolutions of the first pass depends
on the tube entering rate, i.e., the rate of tube welding.
5 DETERMINATION OF THE SECTION
AREA OF THE TUBE DURING THE
STRETCH-REDUCING PROCESS
By continuous rolling of the tubes on the stretch-
reducing mill the mutual relation of the rates is defined
as the change of the area of the tube section in the
deformation zone.11,12 The base equation for the
calculation of the section area is:
A s d si i i i= ⋅ −π ( )sr (24)
As the tubes are rolled with three rolls oval calibers,
the calculation of the section area is complex, especially
if the point in the deformation zone is also considered.
With standard processing, the reduction diameter is
equal for all the passes with the exception of the first and
the two last passes. The average relative reduction dia-
meter without elongation is in the range of 3 % to 5 %,
and in the range 7 % to 12 % if the elongation s is also
considered. With practical technology, the diameter
reduction is given by the dimension of the caliber of pass
size6,7 (Figure 6).
The basic caliber dimensions are the width a and the
height b (Figure 6). With relation to the previous, in the
following stand the caliber is changed for an angle of
120° and the width (ai-1) becomes the height with the size
S. RE[KOVI] et al.: NUMERICAL DESIGN OF A HOT-STRETCH-REDUCING PROCESS FOR WELDED TUBES
246 Materiali in tehnologije / Materials and technology 44 (2010) 5, 243–250
Figure 5: Processing rates in the deformation zone (10)
Slika 5: Hitrosti preoblikovanja v coni deformacije (10)
decreased by the reduction in this pass (bi) (Figure 6).
Simple equations for the calculations of the change of
diameter di and wall thickness si are the relations (25)
and (26).
Δd a bi i= −−1 1 (25)
s s
s s
d d
d di i
i i
i i
i= −
−
−
−−
−
−
−1
1
1
1( )
 (26)
The average outside tube diameter dsri is determined
by the dependence of the dimensions of the three-rolls
oval caliber according to Figure 6 by applying equation
(27):
d
b a b a
b ai
i i i i
i i
sr =
⋅ − ⋅ − ⋅ ⋅
−
2865 0365 05
2
2 2. . .
(27)
According to2,6,8 it is possible to determine the tube
dimensions accurately. The tube section outside the
deformation zone is calculated using equations (28) and
(29).
[ ]A R R si i i= − − −3 2 1 1 1 2 2 ( ) ( )
[ ]− − −3
2
3 1 1 2
e
R R s
i
i i i icos ( ) cos( ) ( )  (28)
d
A
s
si
i
i
isr = +π
(29)
At the neutral angle of the deformation zone, the
outside tube diameter is:
d
A
i
i
sr = 2
( )

π
(30)
The area of the section of the tube wall in the neutral
position of the deformation zone is:
A s d si i i1 ( ) ( ) ( ) ( )( )
 
 
 
= −π (31)
The area of the tube at the exit from the deformation
zone is:
A R
a
R
a e
i k i
i
i
i i
( ) arcsin= −
⎛
⎝
⎜
⎞
⎠
⎟3
3
2
3
2
2 (32)
6 TUBE-WALL-STRETCHING REDUCTION
For proper stretch reducing of the tubes it is of basic
importance to know the maximum allowed changes of
the tube-wall thickness and diameter. The tube reduction
from the initial to the end size is defined by the maxi-
mum deformation and stressing of the material at the
processing temperature for every phase of the pro-
cessing.2,9,11
The wall reduction is defined by the coefficient of
plastic elongation. The maximum value of this
coefficient determines the limit value of the reduction of
the wall thickness. On the other hand, the maximum wall
reduction thickness also depends on the maximum
drawing force and on the material deformation resistance
at the processing temperature. For this reason, it is
necessary to determine, for every phase of stretch
reducing, the maximum value of the coefficient of plastic
extension to prevent the tube tearing. Theoretically, the
maximum value of the coefficient of plastic extension is
1, while the practical value is in the range 0.1 to 1. The
coefficient is calculated for the design of the passes for
every step of the processing and the related changes to
the tube diameter and the wall thickness. The calculation
is performed by assuming that the deformation is
uniform over the whole tube section and that the
elongation is equal for all the passes.2,6,8
With the analysis of the coefficient of plastic
elongation, it is necessary to consider the following:
a) the coefficient for the total elongation (average per
pass) zu makes it possible to determine the total elon-
gation of the tube. From the physical point of view, zu
exists only for ideal cases, when the coefficient of
plastic extension is equal for all the passes and it is
equal to zu. This cannot be achieved during practical
processing, as, in the first and in the last stands of the
processing line the possibility of drawing with the
rolls is limited and zi < zu. For this reason, the
elongation is greater in the middle caliber than zu.
b) In theory, the initial and the end extension coeffi-
cients exist; however, the values of both are not
clearly defined and as the average elongation
coefficient the arithmetical value of both coefficients
is calculated:
S. RE[KOVI] et al.: NUMERICAL DESIGN OF A HOT-STRETCH-REDUCING PROCESS FOR WELDED TUBES
Materiali in tehnologije / Materials and technology 44 (2010) 5, 243–250 247
Figure 6: a) reduction of tube diameter, b) dimensions of the three
rolls caliber
Slika 6: a) redukcija premera cevi, b) dimenzije kalibra s tremi valji
z
z z
i
i i
sr
=
+−1
2
(33)
This value is then used to calculate the decrease of
wall thickness. Theoretically, the value of the coefficient
of extension could be between 0.0 and 1.0.
For zteor < 0.5 the wall thickness is increased and the
diameter reduction of 3 % to 5 % is achieved. The
increase of thickness of the tube wall is necessary to
obtain in the following pass a homogenous decrease of
tube diameter and to maintain, in a safe range, the
material stressing.
For zteor = 0.5 the wall thickness is unchanged and
practice shows that it remains unchanged also for z =
0.55
For zteor., max = 1.0 in parallel, the tube diameter in and
the wall thickness are decreased. It cannot be achieved in
practice because it leads to tearing of the rolled tube. The
maximum practically used extension coefficient is of z =
0.7 to 0.8.
Theoretically, the coefficient is the ratio of axial
stress and the deformation resistance of the material,
such that:
z
k
i=

f
(34)
The analytical dependence of the stress and deforma-
tion is given by the equations:
 

 

 

r sr
r
l sr
l
t sr
t
−
=
−
=
−
(35)
( ):( ):( ) : :        r sr l sr t sr r l t− − − = (36)
The average stress also depends on the type of the
processed material. In equation (37) the dependence
upon the deformation resistance kf is:
    sr 1 f r l t= ⋅ ⋅ − = ⋅ + +
1
3
2
1
3
( ) ( )k (37)
On the other hand, the stress depends also on the
relation of the wall thickness and the tube diameter:
 sr
sr
= ⋅ ⎛⎝
⎜ ⎞
⎠
⎟s
d
(38)
k f l t= −  (39)



r
t sr
sr
sr
sr
= ⎛⎝
⎜ ⎞
⎠
⎟ =
s
d
(40)
The solution of equations (35) and (36) given in
equation (41) is obtained by applying the equations (34),
(37), (38), (39) and (41):
2 1 1 2⋅ ⋅ − + − ⋅z ( ) ( ) 
 r
=
z ⋅ − + +( ) ( ) 

1 1
l
=
=
z ⋅ − + −( ) ( ) 

1 2
t
(41)
Equation (41) is the basis for equation (42), which is
used for the calculation of the plastic extension by
stretch reducing the tubes:
z =
⋅ − + +
⋅ −
   
   
l t
l t
( ) ( )
) (
2 1
1
(42)
The coefficient "" obtained from (40) cannot be
used in practice, and it is corrected by considering the
uniform tube deformation "T" deduced from equation
(43).
T =
−


sr
sr1
(43)
Applying the corrected value "T", the relation for the
average coefficient of plastic extension is calculated
from equation (44).
z
T T
Tsr
l t
l t
=
⋅ − + +
⋅ −
 
   
( ) ( )
) (
2 1
1
(44)
The values for the coefficient zisr obtained from
equation (42) are appropriate to those obtained from
equation (44). However, the calculation is simpler by
applying equation (42), and this equation is
recommended for use in practice. The values of "zisr"
calculated from the equations (42) and (44) differ only in
the second decimal2.
The coefficient "T" calculated from equation (43) is
reliable for the relation (s/d)sr in the range from 0.27 to
0.275. If the relation differs from this range and it is not
constant during the processing, the correction of the
coefficient "T" becomes necessary. For this reason, an
additional coefficient "k" is used that considers the effect
of the diameter reduction on the thickness reduction. For
the three rolls the caliber the coefficient "k" is calculated
from equation (45).
ki
i
=
1
	

(45)
Finally, for the coefficient "T" the following equation
is obtained:
T
i
=
⋅ + ⋅
−
⎡
⎣⎢
⎤
⎦⎥
+0868 0 264
1
1
1 0 70. . . 

 

sr sr
2
sr
(46)
From equations (46) and (44) the average value of the
coefficient of extension is calculated and used for the
determination of the tube-wall reduction in the i-pass.
In equation (44) the logarithmic values for the axial,
tangential and radial deformations are included, which
are calculated from equations (47), (48) and (49).
a) li – lg of axial deformation from equation (47).
 li
i i i
i i i
s d s
s d s
=
⋅ −
⋅ −
⎡
⎣⎢
⎤
⎦⎥
− − −( ) ( ) ( )
( ) ( )( )
1 1 1
(47)
b) ti – lg of tangential deformation from equation (38).
S. RE[KOVI] et al.: NUMERICAL DESIGN OF A HOT-STRETCH-REDUCING PROCESS FOR WELDED TUBES
248 Materiali in tehnologije / Materials and technology 44 (2010) 5, 243–250
 ti
i i
i i
d s
d s
=
−
−− −
ln
( ) ( )1 1
(48)
c) ri – lg of radial deformation from equation (49).
 ri
i
i
l
s
s
=
−( )1
(49)
The diameter reduction "i" per pass in equations (45
and 46) is calculated from equations (50):
 i
i i
i
d d
d
=
−−
−
( )
( )
1
1
(50)
From equation (43) the coefficient "T" is deduced for
the case when:
a) sr  for thin tube wall as (51)
T ≈  sr (51)
b) sr  for the full section of the rolled tube according
to (52)
T ≈ ⋅2  sr (52)
The parameters affecting the maximum value of the
coefficient of plastic extension are2,7:
• the material plasticity at the processing temperature
considering the strain hardening in the deformation
zone and the softening between the rolling passes that
depends on a given tube rate on the distance between
the rolling stands,
• the diameter reduction,
• the total previous deformation,
• the rolling rate,
• the uniformity of the temperature over the tube
length.
7 VERIFICATION OF THE CALCULATION
The calculation was verified on an industrial stretch-
reducing mill with 18 three-rolls passes. The possibility
to change the number of revolutions (minimum and
maximum for every pass) of the mill are shown in
Figure 7.
On the mill, the welded tubes of 117.3 mm × 3.8
mm are rolled to tubes of size from  17.1 mm × 2.0 mm
to  114.3 mm × 4.5 mm. The pass designing was
verified for the tubes  21.3 mm × 2.65 mm and  48.3
mm × 3.25 mm. The rolling of tubes  21.3 mm × 2.65
mm is carried out in 18 passes and of the tubes  48.3
mm × 3.25 mm in 12 passes. For both tube dimensions
and for each pass the minimum and maximum number of
revolution was calculated, which is shown in Figure 8. It
is clear from this figure that the calculated values were
achieved and the design verified. All the produced tubes
have the required mechanical and technological pro-
perties and the required dimensional accuracy, thus
confirming that the pass design is also reliable for
industrial production.
8 CONCLUSION
In this article the process of the design of passes is
given for the hot-stretch reducing of tubes. The calcu-
lations are based on data from references and our own
S. RE[KOVI] et al.: NUMERICAL DESIGN OF A HOT-STRETCH-REDUCING PROCESS FOR WELDED TUBES
Materiali in tehnologije / Materials and technology 44 (2010) 5, 243–250 249
Figure 8: Number of revolutions calculated for the tubes: a)  21.3
mm × 2.65 mm and b)  48.3 mm × 3.25 mm
Slika 8: [tevilo vrtljev, izra~unanih za cevi: a)  21,3 mm × 2,65 mm
in b)  48,3 mm × 3,25 mm
Figure 7: Maximum and minimum number of revolutions at the
industrial stretch-reducing mill
Slika 7: Najve~je in najmanj{e {tevilo vrtljajev na industrijski valjarni
za raztezno reduciranje
industrial data. The mutual dependence of the processing
parameters is also considered, and the calculation of the
tube rate and the reduction for every processing step is
explained. Since the reduction of the tube-wall thickness
is achieved with stretching, the processing rate and the
reduction of the wall thickness are mutually dependent
and determine the extent of the internal stresses in the
processed material. The corresponding parameters are
related through the coefficient of plastic extension,
which was also calculated.
The processing parameters are calculated and verified
for two tube dimensions in current industrial production.
The agreement between the calculated and the obtained
dimensions of the tubes confirms the accuracy and the
reliability of the designed passes. The rolled tubes have
the properties required by the standards and confirm that
the relation between the reduction of the wall and the
tube diameter as well as the processing rate and the
extent of stresses were considered with sufficient
accuracy.
i – number of passes of the stretch-reducing mill
d0 – external tube diameter
dn – external tube diameter in the i – pass
d – reduction of tube diameter
s – tube-wall thickness
si – tube-wall thickness in the i – pass
C – rolling constant
V1 – tube exit rate from the rolls
A – pass surface
D – working diameter of rolls (bottom of passes)
Dw – ideal rolls diameter
Dtr – transport diameter of rolls
a – pass width
b – pass height
n – number of revolutions of the rolls
A – area of tube section
 – angle of contact

 – neutral angle in the deformation zone
 – angle change in the deformation zone
 – angle of friction
μ – friction coefficient
v – circumferential velocity of rolls
v0 – tube rate in the deformation zone
v
 – tube rate in the deformation zone at the neutral angle


vt – tube rate at the exit of deformation zone
m1 – coefficient dependent on rolls quality
m2 – coefficient dependent on rolling rate
m3 – coefficient dependent on steel microstructure
z – coefficient of plastic extension
zi – coefficient of plastic extension in the i- pass
zku – total coefficient of plastic extension
zsr – average coefficient of plastic extension
kf – deformation resistance of the rolled material
l – axial stress
r – radial stress
t –tangential stress
sr – total average stress
l – lg of axial deformation
t – lg of tangential deformation
r – lg of radial deformation
 – coefficient of the relation of reduction of tube wall
and diameter
T – coefficient of correction of the coefficient z
k – coefficient of correction of the coefficient z with
respect to the diameter reduction
9 REFERENCES
1 S. Re{kovi}, F. Vodopivec; Mater. Tehnol., 42 (2008) 6, 257–262
2 R. Kri`ani}: Technology of stretch reducing, geometrical characte-
ristics of passes and parameters of the manufacturing of tubes,
Institute of Metallurgy, Sisak, 1978, 1–24
3 K. H. Staat: Streckreduzierwalzwerk, Metalurgija, 10 (1971), 13–22
4 H. Molther: Rolling line for the stretch-reducing for tubes,
www.freepatententsoline.com
5 R. Kri`ani}, S. Re{kovi}: Pass determination of rolls for IRS; Pro-
ceedings of the Symposium, VII Symposium of roling-mill worker of
Yugoslav, OUCM, Beograd, Mavrovo, 1985
6 A. A. [ev~enko: Continous rolling of tubes, Metalurgizdat, Moskva
1954, p. 188
7 R. Kri`ani}, M. [indler, S. Re{kovi}: Development of the IRS com-
puter program, II – Optimisation of the production of small wall
welded tubes, Institute of Metallurgy, Sisak, 1979
8 G. I. Guljajev, P. I. Iv{in: Technology of continuous rolling of tubes
without, Metalurgizdat, Moskva 1975, p. 145
9 S. Re{kovi}: Parameters of working for IRS, Instruction book for the
Rolling mill, Ironwork Sisak, Sisak, 1999
10 R. Kri`ani}: Metalurgija, 26 (1987) 4, 109–116
11 I. Horvat: Calculation of the contact area on the three rolls stretch
reducing stand, degree thesis, Faculty of Metallurgy, Sisak, 1983
12 R. Kri`ani}: Metalurgija, 26 (1987) 1/2, 3–11
13 R. Kri`ani}: Metalurgija, 24 (1988) 2, 49–55
14 W. Demny, H. Molther, H. Gerhards: Process and rolling mill for
stretch reducing of tubes, www. freepatententsoline.com
15 D. Pavli}: Study of the hot rolling of welded tubes on the stretch
reducing mill, Degree Thesis, FSB, Zagreb, 1998
16 R. Kri`ani}: Technology of stretch reducing and geometrical charac-
teristics of passes in the production of welded tubes in the Rolling
mill for welded tubes, Institute of Metallurgy, Sisak, 1978
S. RE[KOVI] et al.: NUMERICAL DESIGN OF A HOT-STRETCH-REDUCING PROCESS FOR WELDED TUBES
250 Materiali in tehnologije / Materials and technology 44 (2010) 5, 243–250
V. KEVORKIJAN, S. D. [KAPIN: PREPARATION AND STUDY OF Mg2Sn-BASED COMPOSITES ...
PREPARATION AND STUDY OF Mg2Sn-BASED
COMPOSITES WITH DIFFERENT COMPOSITIONS
PRIPRAVA IN KARAKTERIZACIJA LASTNOSTI KOMPOZITOV NA
OSNOVI Mg2Sn
Varu`an Kevorkijan1, Sre~o Davor [kapin2
1zasebni raziskovalec, Betnavska cesta 6, 2000 Maribor, Slovenia
2Sre~o Davor [kapin, Institut "Jo`ef Stefan", Jamova 39, 1000 Ljubljana, Slovenia
varuzan.kevorkijan@impol.si
Prejem rokopisa – received: 2010-02-22; sprejem za objavo – accepted for publication: 2010-03-15
Single-phase Mg2Sn powders were successfully reaction-synthesized from the elements and applied for the preparation of
Mg2Sn-based composites with different natures, microstructures and combinations of properties. These were fully dense (95
% T.D.) Mg- and Al-metal-matrix composites (MMCs) reinforced with either Mg2Sn particles or mixtures of Mg2Sn with TiC or
TiB2 particulates by the infiltration of porous Mg2Sn preforms with molten magnesium or aluminium; and (ii) Mg2Sn
intermetallic matrix composites discontinuously reinforced with TiC and TiB2 particles by pressureless sintering.
The microstructures of the composite samples were examined using scanning electron microscopy (SEM-EDS) and X-ray
powder diffraction (XRD). The mechanical properties were evaluated by Vickers hardness measurements performed at room
temperature, while the fracture toughness of the specimens was determined by applying the indentation method.
Based on the data accumulated, an evaluation of the mechanical properties of these composites on the basis of the volume
content of different constituents was performed.
Moreover, the ability of various microstructures obtained with pressureless infiltration and sintering for tailoring the desired
combination of mechanical properties. (e.g., toughening in combination with hardness) was also investigated and reported.
Thus, the infiltration led to MMCs with different microstructures and mechanical properties, depending on the infiltrant applied.
The samples infiltrated with molten magnesium possessed a characteristic lamellar, sometimes referred to as "Chinese script",
eutectic microstructure and thereby an enhanced fracture toughness (up to 7.7 MPa m1/2 in non-reinforced and 5.8 MPa·m1/2 in
reinforced counterparts), in combination with a Vickers hardness superior to those of conventional Mg-Sn alloys. On the other
hand, although the mechanical response (Vickers hardness) of the samples infiltrated with aluminium was even better than in the
counterparts infiltrated with magnesium, the absence of the "Chinese script" microstructure was observed to have a detrimental
influence on the fracture toughness, which was significantly lower in these samples.
The densification of intermetallic matrix composites (IMCs) with a Mg2Sn matrix discontinuously reinforced with TiC or TiB2
ceramic reinforcement performed by non-reactive, solid-state sintering resulted in samples with a high density (95% T.D.) and
different combinations of mechanical properties compared to MMCs obtained by infiltration. The Vickers hardnesses of the
sintered IMCs were much better than in the MMCs obtained by infiltration, with the exception of the fracture toughness, which
was reduced below 1.8 MPa m1/2.
Key words: Mg2Sn powder, synthesis, Mg2Sn-based composites, sintering, infiltration, microstructure development, hardness,
fracture toughness
Z reakcijo v trdnem smo iz elementov sintetizirali Mg2Sn. Spojino smo zdrobili in prah uporabili za pripravo vrste kompozitov z
razli~nimi mikrostrukturnimi in mehanskimi lastnostmi. Pripravili smo goste kompozite (95 % T. G.): (i) na osnovi kovinske
matrice Mg in Al tako, da smo v porozne predoblike spojine Mg2Sn ter predoblike razli~nih sestav na osnovi Mg2Sn in TiC
oziroma TiB2 infiltrirali teko~i Mg oziroma Al, in (ii) na osnovi intermetalne spojine Mg2Sn, ki smo jih pripravili s sintranjem
Mg2Sn z dodatkom oja~itvene faze trdin TiC oziroma TiB2.
Mikrostrukturno analizo pripravljenih kompozitov smo opravili z vrsti~nim elektronskim mikroskopom in elementno
spektroskopsko disperzijsko analizo (EDS) ter z rentgensko pra{kovno difrakcijo. Mehanske lastnosti, trdoto po Vickersu in
zlomno `ilavost smo merili pri sobni temperaturi.
Dobljene rezultate smo razlo`ili glede na fazno sestavo pripravljenih kompozitnih vzorcev. Opisali smo odvisnost mehanskih
lastnosti infiltriranih in sintranih vzorcev v odvisnosti od mikrostrukturnih karakteristik.
Pri infiltraciji nastajajo kompoziti s kovinsko matrico (KKM) z razli~no mikrostrukturo in mehanskimi lastnostmi, kar je
odvisno od uporabljene kovine, ki jo infiltriramo. Kompoziti na osnovi Mg izkazujejo lamelarno evtekti~no mikrostrukturo
(kitajska pismenka) in izbolj{ano zlomno `ilavost (do 7,7 MPa m1/2 neoja~ani materiali in 5,8 MPa m1/2 oja~ani kompozitni
materiali) in tudi vi{jo trdnost po Vickersu glede na komercialne Mg-Sn zlitine. Kompoziti na osnovi infiltriranega Al izkazujejo
vi{jo trdnost kot Mg kompoziti, vendar pa ni`jo zlomno `ilavost, ker ne tvorijo lamelarne mikrostrukture.
Pri sintranju kompozitov na osnovi intermetalne Mg2Sn-matrice, ki so bili oja~ani s TiC oziroma TiB2 nastajajo gosto sintrani
kompozitni materiali (95 % T. G.) z razli~nimi mehanskimi lastnostmi. Trdota teh materialov je ve~ja, kot jo izkazujejo
kompoziti na osnovi kovinske matrice, vendar pa imajo manj{o zlomno `ilavost, manj kot 1,8 MPa m1/2.
Klju~ne besede: Mg2Sn-prah, priprava, kompoziti na osnovi Mg2Sn, sintranje, infiltracija, razvoj mikrostrukture, trdota,
prelomna `ilavost
1 INTRODUCTION
Current applications of magnesium stannide (Mg2Sn)
are limited to the optimisation of the microstructure and
mechanical properties of magnesium 1–7 and in lead-free
aluminium alloys 8. In the Mg-Sn and Mg-Sn-Ca creep-
resistant magnesium alloys, Mg2Sn precipitates are
applied as a thermally stable intermetallic phase for
suppressing the grain-boundary sliding and dislocation
movement, resulting in an improvement of the creep
properties.
Materiali in tehnologije / Materials and technology 44 (2010) 5, 251–259 251
UDK 621.762:669.018.9 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 44(5)251(2010)
However, due to its high melting point (770 °C),
relatively low density (3.59 g/cm3 – about half that of the
density of tin), excellent compressibility (2.83 10–11
m2/N, approximately 50 % higher than for Mg2Si) and a
thermal expansion coefficient (9.9 10–6 K–1) similar to
some borides and carbides 9,10, magnesium stannide is a
promising structural material, particularly in combina-
tion with magnesium and aluminium alloys and
composites. The Vickers hardness of Mg2Sn is about 1.2
GPa 7, significantly lower than for Mg2Si (3.5–7.0 GPa),
but still twice as high in comparison with the hardness of
Mg-Sn alloys.
In addition, Mg2Sn is a stoichiometric compound
suitable for achieving characteristic eutectic microstruc-
tures (i.e., "Chinese-script") and therefore for tailoring
the properties of composites (particularly the fracture
toughness) with Mg2Sn appearing as a matrix or a rein-
forcement phase.
In contrast to numerous investigations carried out in
developing Mg-Sn alloys with Mg2Sn precipitates
formed in situ, only a limited number of investigations
were concerned with the synthesis of Mg2Sn powder 11
and, to the best of our knowledge, none with its densifi-
cation, alone or with some other reinforcing phases, i.e.,
as a matrix for high-temperature composites or as
particulate reinforcement in metal matrix composites.
Hence, in the present study, the following investi-
gations were performed in order to demonstrate the
potential of Mg2Sn as an advanced composite matrix or
discontinuous reinforcement: (i) the synthesis of Mg2Sn
single-phase powder from the elements; (ii) pressureless
sintering and characterisation of Mg2Sn-based inter-
metallic matrix composites discontinuously reinforced
with TiC or TiB2 particles, and (iii) the formation and
characterisation of Mg- or Al-metal matrix composites
reinforced with either Mg2Sn particles or mixtures of
Mg2Sn with TiC or TiB2 particulates by the infiltration of
porous Mg2Sn preforms with molten magnesium and
aluminium.
2 EXPERIMENTAL
In the first part of the experimental work, Mg2Sn
powder was synthesized with a reaction synthesis from
the elements. As the source of magnesium and tin,
cylindrical samples machined from pure magnesium and
tin rods were used. Magnesium and tin samples in three
different molar ratios (stoichiometric, with 5 % and 10 %
excess of magnesium) were placed in a platinum crucible
and heated in a vacuum furnace (for 2 h at 660 °C or for
1 h at 700 °C) in a static atmosphere of argon. This was
followed by cooling to room temperature and characte-
risation of the as-obtained product with optical and
scanning electron microscopy (OM and SEM) and X-ray
diffraction (XRD). After that, the product was milled in
an attrition mill for various milling times (0.5–2 h) in
order to achieve the desired morphology of the Mg2Sn
particles. The as-milled Mg2Sn powders were then
applied for various infiltration and sintering experiments.
The infiltration was performed by using porous pre-
forms made from laboratory synthesized Mg2Sn powder
of grade C (Table 1) and mixtures of Mg2Sn powder
grade C and commercially available TiC (99.5 %, d50 =
4 μm) and TiB2 powders (99.5 %, d50 = 6 μm), as listed in
Table 2. The preforms were isostatically pressed at
various pressures (from 80 MPa to 150 MPa) in order to
achieve samples with different porosities. The samples
obtained were cylinders, 50 mm high and 20 mm in
diameter. As infiltrant, Al-xSn and Mg-xSn (x = 3%,
5 %) alloys were applied. Al-xSn and Mg-xSn alloys
necessary for infiltration were prepared from pure
aluminium or magnesium and pure tin powders melted in
a graphite crucible with the protection of a fusing agent.
The melt was then stirred to ensure homogeneity and,
finally, it was cast into a preheated mould. The as-cast
ingots were cut and machined into thin cylindrical plates
having the same diameter as the Mg2Sn preforms (20
mm). Finally, a preform sandwiched between two Al-xSn
or Mg-xSn plates was placed in a ceramic crucible using
the following procedure: the first Al-xSn or Mg-xSn
plate was placed on the bottom of crucible and the pre-
form was fixed on it using upper and lower preformatted
steel plates. After that, the upper Al-xSn or Mg-xSn plate
was placed on it. The volume of the Al-xSn or Mg-xSn
plates was calculated to be approximately 50 % higher
than the volume of the pores in the preform. The infiltra-
tion was conducted by heating the assembly in a vacuum
furnace at 730 °C for 1 h, under a static atmosphere of
argon.
After completion of the infiltration, the assembly was
cooled to room temperature, and then the infiltrated
preform was removed from the furnace. The green sam-
ples for sintering experiments were formulated by
blending the synthesized Mg2Sn powder (grade C, Table
1) with commercial ceramic powders (TiC and TiB2) in
appropriate amounts to create IMCs with mass fractions
w = (10, 30 and 50) % of TiC or TiB2 reinforcement. The
powder blends were thoroughly mixed in a planetary mill
and subsequently cold compacted. In all cases, the
sintering of the compacts was conducted at 750 °C for
1 h in a static atmosphere of argon using a vacuum
furnace. The as-synthesized composite samples were cut,
machined and polished in accordance with standard
procedures.
Microstructural characterization of the fabricated
composites was performed with OM and SEM, whereas
XRD measurements were applied to the samples to
identify the phases and their crystal structure. A quanti-
tative determination of the volume percentage of Mg2Sn
and ceramic particles in the matrix, as well as the
retained porosity, was performed with an assessment of
optical and scanning electron micrographs of polished
composite bars using the point-counting method and
image analysis and processing software. The composite
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density measurements were carried out using Archi-
medes’ principle, applying absolute ethanol as the
immersion fluid. The initial density of the green com-
pacts (preforms and tablets) was calculated from the
mass and geometry of the samples.
Vickers hardness (HV) measurements were per-
formed at room temperature on polished composite
samples and calculated as the average of six indenta-
tions. These measurements were made with a conven-
tional Vickers tester (load: 9.8–24.5 N for 15 s).
Due to their small dimensions and high brittleness,
the fracture toughness of the specimens obtained was
determined by applying the indentation method 12. The
KIC of the composite samples was determined from sub-
micron-derived indentation cracks and calculated
according to the equations proposed by Niihara et al. 13.
3 RESULTS AND DISCUSSION
3.1 Mechanism of the formation, chemical composition and
morphology of laboratory-prepared Mg2Sn powder
Depending on the initial composition of the reaction
mixture and the heating conditions, the concentration of
Mg and Sn impurities in the synthesized Mg2Sn phase
varied significantly.
On applying reaction mixtures with a stoichiometric
ratio of elemental magnesium and tin, more than w = 5
% of the tin remained in the reaction product obtained
(Mg2Sn powder grade A, Table 1), which was most pro-
bably caused by a loss of magnesium. This assumption
was additionally confirmed by the experimental finding
that the amount of non-reacted tin increased with the
increasing temperature of the synthesis.
Table 1: Phase composition and morphology of laboratory-prepared
Mg2Sn powders
Tabela 1: Fazna sestava in morfologija laboratorijsko izdelanih
Mg2Sn prahov
Powder (Mg2Sn)/% (Sn)/% d50/ìm
Grade A 95 5 3.3
Grade B 97 3 2.4
Grade C 99.8 0.2 2.1
On the other hand, by applying a reaction mixture
with a small (x = 5 %) excess of magnesium, the amount
of non-reacted tin was reduced below 5 % or even below
w = 3 % (mass fractions) (grade B, Table 1) at a lower
temperature of synthesis (660 °C).
Finally, by using a reaction mixture with the mol
fraction x = 10 % excess of magnesium, single-phase
Mg2Sn (grade C, Table 1) with no Mg or Sn peak
detected in the XRD pattern was prepared at 700 °C.
The investigation of the solidified product samples
indicated that the reaction mechanism of the Mg2Sn
synthesis is homogeneous nucleation and growth. Based
on the phase diagram of the Sn-rich corner in the Mg-Sn
binary system 14, it is evident that Mg will start to
dissolve into the liquid phase immediately after the
temperature exceeds the melting point of Sn (505 K).
With increasing temperature, a greater amount of Mg
will be dissolved and, after melt saturation, the Mg2Sn
will start to nucleate according to reaction 1:
Mg(s) + Sn(l) = Mg2Sn(s) (1)
Above the melting point of magnesium (923 K), the
nucleation of Mg2Sn will continue by nucleation from
the saturated liquid phase according to reaction 2:
Mg(l) + Sn(l) = Mg2Sn(s) (2)
Thus, to achieve the complete conversion of reactants
into Mg2Sn, it is important to preserve a permanent
excess of magnesium (approximately w = 10 %) in the
system up to the end of the synthesis. The morphology
of the laboratory-prepared Mg2Sn powder, obtained with
milling the solidified sample from reactive synthesis, is
presented in Figure 1. As is evident, the powder ob-
tained is non-agglomerated, with well-shaped individual
particles with a size below 5 μm.
The typical phase composition in the synthesized
Mg2Sn powders is reported in Table 1. The compositions
of various Mg2Sn-TiC and Mg2Sn-TiB2 mixtures used for
preforms in the infiltration experiments are listed in
Table 2.
Table 2: The composition of various Mg2Sn-TiC and Mg2Sn-TiB2
mixtures used for preforms preparation in the infiltration experiments
Tabela 2: Sestava razli~nih zmesi Mg2Sn-TiC in Mg2Sn-TiB2,
uporabljenih za pripravo predoblik
Mixture Initial composition, /%
#1 100 % Mg2Sn (grade C)
#2 75 % Mg2Sn (Grade C)–25 % TiC
#3 75 % Mg2Sn (Grade C)– 25 % TiB2
#4 70 % Mg2Sn (Grade C)–30 % TiC
#5 70 % Mg2Sn (Grade C)–30 % TiB2
3.2 Composites made by pressureless infiltration
3.2.1 Al-Mg2Sn(p) and Mg-Mg2Sn(p)
The infiltration of porous Mg2Sn preforms (compo-
sition #1, Table 2) with molten Al resulted in fully dense
composite samples with a continuous aluminium-based
matrix, reinforced with Mg2Sn particles and Mg2Sn
precipitates appearing near the primary Mg2Sn particles,
Figure 2a.
On the other hand, samples fully infiltrated with
molten magnesium have a characteristic lamellar "Chi-
nese script" eutectic microstructure, Figure 3a, and com-
pletely different mechanical properties, Table 3.
In both cases, due to the complete and non-reactive
wetting of the Mg2Sn preform skeleton with molten Mg
or Al, under atmospheric pressure the infiltration pro-
ceeded spontaneously. The absence of chemical reactions
between the preform skeleton and the molten infiltrants
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254 Materiali in tehnologije / Materials and technology 44 (2010) 5, 251–259
Figure 4: a) SEM micrograph and b) XRD spectrum of pressureless
infiltrated Al-Sn-Mg2Sn(p)-TiC(p) composite sample with an initial
composition of the preform skeleton of  = 69 % Mg2Sn,  = 29 %
TiC and  = 2 % Al (volume fraction /%)
Slika4: a) SEM posnetk in b) XRD difraktogram vzorca Al-Sn-
Mg2Sn(p)-TiC(p) – kompozita, izdelanega z infiltriracijo predoblike na
osnovi 69 % Mg2Sn, 29 % TiC in 2 % Al (volumenski dele` /%)
Figure 2: a) SEM micrograph and b) X-ray powder-diffraction pattern
of the pressurelessly infiltrated Mg2Sn-Al composite sample
Slika 2: a) SEM-posnetek in b) XRD-difraktogram Mg2Sn-Al-kom-
pozita, pripravljenega z infiltracijo
Figure 3: a) SEM micrograph and b) X-ray powder diffraction pattern
of the Mg2Sn-Mg composite sample infiltrated at 730 °C showing a
lamellar structure consisting of Mg2Sn "Chinese-script" in a matrix of
magnesium
Slika 3: a) SEM-posnetek in b) XRD-difraktogram Mg2Sn-Mg-kom-
pozita, infiltriranega pri 730 °C z zna~ilno lamelarno mikrostrukturo
oja~itve v Mg matriki
Figure 1: a) SEM micrograph of Mg2Sn powder (grade B) after
milling, b) SEM micrograph of as-synthesized Mg2Sn and c) X-ray
powder diffraction pattern of the prepared compound Mg2Sn: A –
grade B powder (Table 1), and B – grade C powder (Table 1)
Slika 1: a) SEM-posnetek Mg2Sn prahu (tip B) po mletju, b) SEM-
posnetek vzorca Mg2Sn pred mletjem in c) XRD-difraktogram sinte-
tizirane Mg2Sn-spojine: A – tip B (Tabela 1) in B-tip C (Tabela 1)
was proved with the corresponding X-ray diffraction
patterns, Figures 2b and 3b.
As evident from Tables 3 and 4, the Vickers hard-
nesses of the Al-Mg2Sn and Mg-Mg2Sn MMCs are im-
proved with increasing the amount of Mg2Sn particulate
reinforcement. However, regarding the fracture tough-
ness, quite the opposite behaviour was observed. The
fracture toughness of Al-Mg2Sn and Mg-Mg2Sn MMCs
decreases with an increasing amount of Mg2Sn particu-
lates.
Comparing the mechanical properties of the
Al-Mg2Sn and Mg-Mg2Sn MMCs, it is found that the
Vickers hardness is evidently better in the samples
infiltrated with aluminium. However, the fracture tough-
ness is an exception, becoming greater (almost doubled)
in the samples infiltrated with magnesium.
The extraordinary fracture toughness of Mg-Mg2Sn
MMCs is caused by their characteristic lamellar structure
consisting of Mg2Sn "Chinese script" in a matrix of a
magnesium solid solution.
3.2.2 Al-Mg2Sn(p)-TiC(p) and Al-Mg2Sn(p)-TiB2(p)
Preforms made from mixtures of laboratory-synthe-
sized Mg2Sn powder and commercially available TiC
and TiB2 powders (compositions #1, #2, #3 and #4),
were also successfully pressurelessly infiltrated with
molten aluminium, resulting in samples with almost
theoretical density and interesting combinations of
mechanical properties.
The microstructure of infiltrated samples consisted of
a co-continuous network of Mg2Sn phase interpenetrated
by an aluminium matrix with finely dispersed TiC or
TiB2 particles, Figures 4 and 5. The absence of secon-
dary phases, Figure 5b, indicates that in this case the
spontaneous infiltration also proceeded as a non-reactive
process.
The reinforcement of an Al matrix with TiC or TiB2
particles resulted in a marked improvement in the
Vickers hardness. As evident from Table 5, the Vickers
hardness of Al-Mg2Sn-TiC and Al-Mg2Sn-TiB2 compo-
sites was approximately 50 % higher than in non-rein-
forced Al-Mg2Sn samples, Table 3.
An examination of the fracture toughness, Table 5,
revealed that the toughness of the MMCs was inversely
proportional to the total amount of reinforcing phase.
Moreover, it became lower when replacing some of the
Mg2Sn particles with more brittle TiC or TiB2 particu-
lates. This is well documented in Tables 3 and 5 for
samples with approximately the same total amount of
particulate reinforcement.
3.2.3 Mg -Mg2Sn(p)-TiC(p) and Mg-Mg2Sn(p)-TiB2(p)
The experiments showed that the infiltration of
Mg2Sn-TiC and Mg2Sn-TiB2 preforms with molten mag-
nesium proceeded spontaneously, without a chemical
reaction between the preform skeleton and the molten
magnesium. By adjusting the porosity of the preforms
within the range the volume fractions of 30 % to 35 %,
composites with different compositions listed in Table 6
were routinely fabricated. At 900 °C, the infiltration was
complete within 1h, resulting in composite samples with
less than  = 5 % of retained porosity.
The resulting composite samples have a typical
eutectic microstructure showing a lamellar structure
consisting of Mg2Sn "Chinese script" in a matrix of
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Table 3: Average room-temperature Vickers hardness and fracture toughness of Al-Mg2Sn composites prepared by pressureless infiltration
Tabela 3: Povpre~ne vrednosti trdote po Vickersu in prelomne `ilavosti, izmerjene pri sobni temperaturi na vzorcih Al-Mg2Sn-kompozitov, izde-
lanih s postopkom infiltracije
Composite composition
/%
Retained porosity
/%
Density
/(g/cm3)
Vickers hardness
(GPa)
KIC/
(MPa m1/2)
18 % Al-82 % Mg2Sn 2.2 ± 0.2 3.5 ± 0.4 0.87 ± 0.09 3.4 ± 0.4
29 % Al-71 % Mg2Sn 3.5 ± 0.4 3.4 ± 0.3 0.82 ± 0.08 4.7 ± 0.5
38 % Al-62 % Mg2Sn 4.7 ± 0.5 3.3 ± 0.3 0.75 ± 0.08 5.3 ± 0.5
19 % Al-81 % Mg2Sn 2.0 ± 0.2 3.6 ± 0.4 0.88 ± 0.09 3.9 ± 0.4
28 % Al-72 % Mg2Sn 3.2 ± 0.3 3.5 ± 0.4 0.83 ± 0.08 4.8 ± 0.5
38 % Al-62 % Mg2Sn 3.9 ± 0.4 3.4 ± 0.3 0.79 ± 0.08 5.6 ± 0.6
Table 4: Average room-temperature Vickers hardness and fracture toughness of Mg-Sn-Mg2Sn composites prepared by pressureless infiltration
Tabela 4: Povpre~ne vrednosti trdote po Vickersu in prelomne `ilavosti, izmerjene pri sobni temperaturi na vzorcih Mg-Sn-Mg2Sn-kompozita,
izdelanega s postopkom infiltracije
Composite composition
/%
Retained porosity
/%
Density
/(g/cm3)
Vickers hardness
(GPa)
KIC/
(MPa m1/2)
20 % Mg-80 % Mg2Sn 2.2 ± 0.2 3.3 ± 0.3 0.66 ± 0.07 4.7 ± 0.5
28 % Mg-71 % Mg2Sn 3.5 ± 0.4 3.1 ± 0.3 0.72 ± 0.07 6.5 ± 0.7
41 % Mg-59 % Mg2Sn 4.7 ± 0.5 2.9 ± 0.3 0.77 ± 0.08 7.3 ± 0.7
19 % Mg-81 % Mg2Sn 2.0 ± 0.2 3.4 ± 0.4 0.61 ± 0.06 5.4 ± 0.5
31 % Mg-69 % Mg2Sn 3.2 ± 0.3 3.1 ± 0.4 0.69 ± 0.07 6.6 ± 0.7
38 % Mg-62 % Mg2Sn 3.9 ± 0.4 3.0 ± 0.3 0.71 ± 0.07 7.7 ± 0.8
magnesium solid solution, additionally reinforced with
fine TiC or TiB2 particles, Figures 7a and 8a.
From the X-ray diffraction patterns of the composite
samples, it is evident (Figure 7b and 8b) that besides
Mg2Sn reinforcement and irrespective of the matrix
composition, no secondary phases were detected, which
indicates that the pressureless infiltration of Mg2Sn pre-
forms with molten Mg-Sn-based alloys was not chemi-
cally assisted. A detailed SEM examination of interface
regions of all the samples also confirmed the absence of
chemical reactions between the composite constituents
listed above.
Regarding the mechanical properties of the Mg-
Mg2Sn-TiC and Mg-Mg2Sn-TiB2 composite samples,
which are summarized in Table 6, an increase in the
particulate content (Mg2Sn and TiC or TiB2) was
observed to improve the Vickers hardness, while at the
same time reducing the fracture toughness. In addition,
the Vickers hardness of the Mg-Mg2Sn-TiC and
Mg-Mg2Sn-TiB2 composite samples was found to be
better than in the non-reinforced counterparts, while the
fracture toughness was about 25 % lower.
Compared to the Al-Mg2Sn-TiC or Al-Mg2Sn-TiB2
counterparts, the reduction of Vickers hardness is only
slight. On the other hand, the fracture toughness of the
Mg-Mg2Sn-TiC or Mg-Mg2Sn-TiB2 composites is almost
twice as high as in their Al-Mg2Sn-TiC or Al-Mg2Sn-
TiB2 counterparts, which is due to the lamellar structure
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256 Materiali in tehnologije / Materials and technology 44 (2010) 5, 251–259
Figure6: a) SEM micrograph and b) XRD spectrum of Mg-Sn-
Mg2Sn(p)-TiC(p) with an initial composition of the preform skeleton 
= 70 % Mg2Sn and  = 30 % TiC
Slika6: a) SEM-posnetek in b) XRD-defraktogram vzorca Mg-Sn-
Mg2Sn(p)-TiC(p)-kompozita, izdelanega z infiltracijo predoblike na
osnovi  = 70 % Mg2Sn in  = 30 % TiC
Figure7: a) SEM micrograph and b) XRD spectrum of pressurelessly
sintered Mg2Sn-Sn-TiC(p) composite sample with the initial compo-
sition  = 67 % Mg2Sn,  = 3 % Sn and  = 30 % TiC
Slika7: a) SEM-posnetek in b) XRD-difraktogram Mg2Sn-Sn-TiC(p)
-kompozita, izdelanega s sintranjem vzorcev, sestavljenih iz  = 67 %
Mg2Sn,  = 3 % Sn in  = 30 % TiC
Figure5: a) SEM micrograph and b) XRD spectrum of pressurelessly
infiltrated Al-Sn-Mg2Sn(p)-TiB2(p) composite sample with an initial
composition of the preform skeleton  = 75 % Mg2Sn,  = 25 % TiB2.
Slika 5: a) SEM-posnetek in b) XRD-defraktogram vzorca Al-Sn-
Mg2Sn(p)-TiB2(p) –kompozita, izdelanega iz predoblike na osnovi  =
75 % Mg2Sn in  = 25 % TiB2
consisting of the Mg2Sn "Chinese script" in a matrix of
magnesium.
3.3 Composites made by pressureless sintering
3.3.1 Mg2Sn-Sn-TiC(p) and Mg2Sn-Sn-TiB2(p) composites
made by pressureless sintering
Pressureless sintering of green samples made either
from as-milled Mg2Sn powders of grade A and B, Table 1,
or mixed with various amounts of TiC or TiB2 particles,
resulted in dense composite specimens with a retained
porosity of less than the volume fraction  = 5 %. In
contrast, pressureless sintering of green samples made
either from as-milled Mg2Sn powder of grade C, Table 1,
or mixed with various amounts of TiC or TiB2 particles,
was found to be incomplete, with more than  = 10 % of
retained porosity.
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Table 5: Average room-temperature Vickers hardness and fracture toughness of Al-Sn-Mg2Sn(p)(grade C)-TiC(p) and Al-Sn-Mg2Sn(p)(grade A)-
TiB2(p) composites prepared by pressureless infiltration
Tabela 5: Povpre~ne vrednosti trdote po Vickersu in prelomne `ilavosti, izmerjene pri sobni temperaturi na vzorcih Al-Sn-Mg2Sn(p)(tip C)-TiC(p)
and Al-Sn-Mg2Sn(p)(tip A)-TiB2(p)- kompozitov, izdelanih s postopkom infiltracije
Composite composition
/%
Retained porosity
/%
Density
/(g/cm3)
Vickers hardness
(GPa)
KIC/
(MPa m1/2)
28%Al-48%Mg2Sn-23 %TiC 1.9 ± 0.2 3.6 ± 0.2 1.29 ± 0.13 2.8 ± 0.3
36%Al-46%Mg2Sn-18 %TiC 2.2 ± 0.2 3.5 ± 0.2 1.14 ± 0.11 3.1 ± 0.3
28%Al-49%Mg2Sn-23%TiB2 3.5 ± 0.4 3.6 ± 0.2 1.38 ± 0.14 2.7 ± 0.3
35%Al-46%Mg2Sn-19%TiB2 4.7 ± 0.5 3.5 ± 0.2 1.26 ± 0.13 3.0 ± 0.3
Table 6: Average room-temperature Vickers hardness and fracture toughness of Mg- Mg2Sn(p)-TiC(p) and Mg-Mg2Sn(p)-TiB2(p) composites
prepared by pressureless infiltration
Tabela 6: Povpre~ne vrednosti trdote po Vickersu in prelomne `ilavosti, izmerjene pri sobni temperaturi na vzorcih Al-Sn-Mg2Sn(p)(tip C)-TiC(p)
in Al-Sn-Mg2Sn(p)(tip A)-TiB2(p)-kompozitov, izdelanih s postopkom infiltracije
Composite composition
/%
Retained porosity
/%
Density
/(g/cm3)
Vickers hardness
(GPa)
KIC/
(MPa m1/2)
29% Mg-47%Mg2Sn-1%Al-23 %TiC 1.9±0.2 3.4±0.2 1.16±0.12 4.9±0.5
36%Mg-38%Mg2Sn-7%Al–19%TiC 2.2±0.2 3.5±0.2 1.0±0.19 5.8±0.6
29%Mg-48%Mg2Sn–1%Al-22%TiB2 3.5±0.4 3.3±0.2 1.24±0.12 4.4±0.4
35%Mg-39%Mg2Sn–7%Al-19%TiB2 4.7±0.5 3.3±0.2 1.13±0.11 5.3±0.5
Table 7: Average room-temperature Vickers hardness and fracture toughness of sintered Mg2Sn -Sn-TiC samples.
Tabela 7: Povpre~ne vrednosti trdote po Vickersu in prelomne `ilavosti, izmerjene pri sobni temperaturi na vzorcih, sintranih Mg2Sn
-Sn-TiC-kompozitov
Composite initial composition
/%
Retained porosity
/%
Density
/(g/cm3)
Vickers hardness
(GPa)
KIC/
(MPa m1/2)
97% Mg2Sn (grade A)-3% Sn 4.8 ± 0.5 3.7 ± 0.2 1.0 ± 0.1 1.7 ± 0.2
87% Mg2Sn (grade A)-3% Sn-10% TiC 3.5 ± 0.4 3.8 ± 0.2 1.4 ± 0.1 1.4 ± 0.1
68% Mg2Sn (grade A)-2% Sn-30% TiC 4.3 ± 0.4 4.1 ± 0.4 1.5 ± 0.2 1.0 ± 0.1
49% Mg2Sn (grade A)-1% Sn-50% TiC 4.9 ± 0.5 4.3 ± 0.5 1.8 ± 0.2 0.7 ± 0.1
95% Mg2Sn (grade B)-5% Sn 3.1 ± 0.3 3.8 ± 0.5 0.9 ± 0.1 1.8 ± 0.2
86% Mg2Sn (grade B)-4% Sn-10% TiC 2.7 ± 0.3 3.8 ± 0.3 1.0 ± 0.1 1.4 ± 0.1
66% Mg2Sn (grade B)-3% Sn-30% TiC 3.9 ± 0.4 3.9 ± 0.4 1.3 ± 0.1 1.1 ± 0.1
48% Mg2Sn (grade B)-2% Sn-50% TiC 4.1 ± 0.5 4.1 ± 0.5 1.7 ± 0.2 0.6 ± 0.1
Table 8: Average room-temperature Vickers hardness and fracture toughness of sintered Mg2Sn-Sn-TiB2 composite samples
Tabela 8: Povpre~ne vrednosti trdote po Vickersu in prelomne `ilavosti, izmerjene pri sobni temperatri na vzorcih, sintranih Mg2Sn-Sn-
TiB2-kompozitov
Composite initial composition)
/%
Retained porosity
/%
Density
/(g/cm3)
Vickers hardness
(GPa)
KIC/
(MPa m1/2)
97 % Mg2Sn (grade A)-3 % Sn 4.8 ± 0.5 3.7 ± 0.2 1.0 ± 0.1 1.7 ± 0.2
87 % Mg2Sn (grade A)-3 % Sn-10 % TiB2 3.5 ± 0.4 3.8 ± 0.2 1.5 ± 0.1 1.3 ± 0.1
68 % Mg2Sn (grade A)-2 % Sn-30 % TiB2 4.3 ± 0.4 4.1 ± 0.4 1.7 ± 0.2 0.8 ± 0.1
49 % Mg2Sn (grade A)-1 % Sn-50 % TiB2 4.9 ± 0.5 4.3 ± 0.5 1.9 ± 0.2 0.6 ± 0.1
95 % Mg2Sn (grade B)-5 % Sn 3.1 ± 0.3 3.8 ± 0.5 0.9 ± 0.1 1.8 ± 0.2
86 % Mg2Sn (grade B)-4 % Sn-10 % TiB2 2.7 ± 0.3 3.8 ± 0.3 1.0 ± 0.1 1.4 ± 0.1
66 % Mg2Sn (grade B)-3 % Sn-30 % TiB2 3.9 ± 0.4 3.9 ± 0.4 1.6 ± 0.1 1.0 ± 0.1
48 % Mg2Sn (grade B)-2 % Sn-50 % TiB2 4.1 ± 0.5 4.1 ± 0.5 2.0 ± 0.2 0.5 ± 0.1
The microstructure of the sintered samples reinforced
with ceramic particulates is presented in Figures 7 and
8. The composites obtained consist of a continuous
Mg2Sn matrix and TiC or TiB2 ceramic particulate rein-
forcement dispersed around the sintered Mg2Sn grains
and small Sn inclusions. In contrast, the microstructure
of the dense, non-reinforced samples was uniform, with
fully sintered Mg2Sn grains and Sn inclusions.
The SEM-EDS evaluation of the samples and the
XRD measurements imply that the Mg2Sn-TiC and
Mg2Sn-TiB2 systems are non-reactive, without secondary
phases formed during the sintering, and that the sintering
proceeded via a non-reactive mechanism, assisted by the
liquid Sn phase. The mechanical properties of the sin-
tered samples are listed in Tables 7 and 8.
The Vickers hardness of the pressurelessly sintered
samples was found to be enhanced with an increasing
amount of particulate reinforcement in the Mg2Sn
matrix, Table 2. In addition, the Vickers hardness
measurements also confirmed that the sintering of
samples with the same initial volume fraction of TiC or
TiB2 reinforcement resulted in composites with similar
hardnesses. This is most probably caused by the similar
microstructures of the Mg2Sn-TiC and Mg2Sn-TiB2-com-
posite samples, the same sintering mechanism and
almost the same hardness of the TiC and TiB2 rein-
forcing particulates.
4 CONCLUSIONS
The reactive synthesis of Mg2Sn from the elements
resulted in a high-yield, single-phase product with less
than the mass fraction 0.2 % of impurities (Mg or Sn),
depending on the composition of the initial reactive
mixture.
1. Additional crushing and subsequent milling of the
reaction product (i.e., in a planetary mill) was found
to be an easy operation, enabling the cost-effective
preparation of Mg2Sn powders with an average
particle size of less than 5 μm, suitable for the
production of Mg2Sn-based advanced composites.
2. Depending on the selected synthesis technique of (i)
pressureless infiltration of porous Mg2Sn, Mg2Sn-
TiC and Mg2Sn-TiB2 preforms with molten alumi-
nium and magnesium, or (ii) pressureless sintering
of green Mg2Sn-TiC and Mg2Sn-TiB2 compacts,
Mg2Sn-based composites of different nature, micro-
structure and combination of properties were
successfully prepared, demonstrating the significant
potential of the Mg2Sn phase as a composite matrix
and of the particulate reinforcement.
3. The investigation of the effect of different micro-
structures developed in Mg2Sn-based composites on
their mechanical properties (hardness and toughness)
revealed that Mg2Sn, as the stoichiometric com-
pound, could be useful for tailoring an optimum
combination of these properties.
4. The pressureless infiltration of porous Mg2Sn,
Mg2Sn-TiC and Mg2Sn-TiB2 preforms with molten
magnesium and aluminium resulted in dense (95 %
T.D.) metal matrix composites with a metallic matrix
discontinuously reinforced with Mg2Sn and TiC or
TiB2 particulates. The infiltration proceeded spon-
taneously, without detectable chemical reactions
between the preform skeleton and the molten infil-
trants.
5. The composite samples infiltrated with molten mag-
nesium possessed the characteristic lamellar "Chi-
nese script" eutectic microstructure, while in samples
infiltrated with molten aluminium the appearance of
fine Mg2Sn-Sn precipitates in an Al matrix, mostly in
the vicinity of the initially introduced Mg2Sn parti-
cles, was observed.
6. In preforms with the addition of TiC or TiB2 ceramic
reinforcement, the microstructure development
during the infiltration occurred in the same way as in
their non-reinforced counterparts. Because of the low
temperature of the preform infiltration (750 °C), the
particulate reinforcements remained chemically inert
in contact with molten magnesium or molten alu-
minium, resulting in a final microstructure of infilt-
rated composite samples the same as in the non-rein-
forced counterparts. The only difference was ob-
served inside the Al or Mg phases, which were
completely reinforced with TiC or TiB2 particles.
7. The microstructure of the composite samples ob-
tained by pressureless infiltration could be tailored to
consist of a continuous aluminium or magnesium
matrix, discontinuously reinforced with Mg2Sn of
different morphologies (particulates in samples
infiltrated with aluminium and the characteristic
"Chinese script" eutectic phase in samples infiltrated
with magnesium) and, when added, TiC or TiB2
reinforcements. Such a microstructure design was
projected in order to achieve an optimum combi-
nation of enhanced fracture toughness (particularly
improved by the "Chinese script" phase appearing in
samples infiltrated with magnesium), with tensile
properties and a hardness superior to that of conven-
tional Mg-Sn alloys.
8. The Vickers hardness was found to be better in
samples infiltrated with aluminium than in counter-
parts infiltrated with magnesium. On the other hand,
quite the opposite behaviour was found with regard
to the fracture toughness. Due to their characteristic
lamellar structure consisting of Mg2Sn as the
"Chinese script" in the matrix, composite samples
infiltrated with magnesium possessed an enhanced
fracture toughness almost twice that of the
counterparts infiltrated with aluminium, in which the
Mg2Sn phase appeared as particulates.
9. Within each single group of infiltrated samples (i.e.,
samples with the same qualitative composition), the
Vickers hardness was enhanced, while the fracture
V. KEVORKIJAN, S. D. [KAPIN: PREPARATION AND STUDY OF Mg2Sn-BASED COMPOSITES ...
258 Materiali in tehnologije / Materials and technology 44 (2010) 5, 251–259
toughness decreased with an increasing total amount
of particulate reinforcement.
10. Pressureless sintering of green samples from Mg2Sn
powders with 3–5% of free Sn, or from mixtures of
these powders with various amounts of TiC or TiB2
particles, resulted in dense composite specimens with
a porosity of less than the volume fraction  = 5 %.
In contrast, pressureless sintering of green samples
from Mg2Sn powder without free Sn or a mixture of
the same powder with various amounts of TiC or
TiB2 particles was found to be incomplete, with more
than  = 10 % of porosity.
11. The composites obtained consisted of a continuous
Mg2Sn matrix and TiC or TiB2 ceramic particulate
reinforcement dispersed around the sintered Mg2Sn
grains and small Sn inclusions. In contrast, the
microstructures of the dense, non-reinforced samples
were uniform, with fully sintered Mg2Sn grains and
Sn inclusions.
12. During sintering, the formation of secondary phases
was not observed. Densification of composite sam-
ples proceeded with non-reactive sintering, assisted
by molten tin
13. The Vickers hardness of the sintered samples (inter-
metallic matrix composites with a Mg2Sn matrix
discontinuously reinforced with TiC or TiB2 ceramic
reinforcement) was significantly improved in com-
parison with the metal matrix composites obtained by
infiltration. The exception was the fracture tough-
ness, which in the sintered samples was reduced to
approximately one-third or even one-quarter of the
values measured in the metal matrix composites
obtained by infiltration.
14. With densities higher than the density of aluminium
and magnesium alloys, Mg2Sn-based composites
have a limited potential for the weight reduction of
structural parts. However, some of the Mg2Sn compo-
sites (especially Mg-Mg2Sn metal matrix composites)
could offer a unique combination of properties,
including the ability of the composite microstructure
(lamellar, consisting of the Mg2Sn "Scinese script" in
a magnesium solid solution) to develop a toughening
mechanism in combination with improved tensile
properties and hardness.
Acknowledgement
This work was supported by funding from the Public
Agency for Research and Development of the Republic
of Slovenia, as well as the Impol Aluminium Company
and Bistral, d. o. o. from Slovenska Bistrica, Slovenia,
under contract No. 1000-07-219308.
5 REFERENCES
1 N. Hort, Y. Huang, T. A. Leil, P. Maier, K. U. Kainer, Adv. Eng.
Mat., 8 (2006) 5, 359
2 N. Hort, Y. Huang, K. U. Kainer, F. Moll, K. U. Kainer, Adv. Eng.
Mat., 8 (2006) 4, 235
34 J. Gröbner, A. Janz, A. Kozlov, Dj. Mirkovi}, R. S. Fetzer, JOM, 60
(2009) 12, 32
4 M. Zhang, W. Z. Zhang, G. Z. Zhu, Scrpita Materialia 59 (2008), 866
5 Z. Min, Z. W. Zheng, Z. G. Zhen, Y. Kun, Trans. Nonferrous Met.
China 17 (2007), 1428
6 Z. X. Ping, C. Y. Gui, X. Y. HUa, Trans Nonferrous Met. Soc. China
18 (2008), s299
7 B. H. Kim, J. J. Jeon, K. C. Park, B. G. Park, Y. H. Park, I. M. park,
Archives of Materials Science and Engineering, 30 (2008) 2, 93
8 S. Koch, H. Antrekowitsch, BHM, 153 (2008) 7, 278
9 O. Madelung, U. Rössler, M. Schulz, Non-tetrahedrally bonded
elements and binary compounds I, Springer-Verlag, 1998, 1–3
10 C. Zhang, P. Han, X. Yan, C. Wang, L. Xia, B. Xu, J. Phys. D: Appl.
Phys., 42 (2009), 1. (doi: 125403)
11 W. Y. Feng, D. W. Bo, Z. T. Young, Trans. Nonferrous Met. Soc.
China, 19 (2009), 1196
12 K. Kondoh, H. Oginuma, T. Aizawa, Materials Transactions, 42
(2001), 1293
13 K. Niihara, R. Morena, D. P. Hasselman, J. Mater. Sci. Lett. 1
(1982), 13
14 A. A. Nayeb-Hasemi, J. B. Clark, J. Bull. Alloy Phase Diagrams 63
(1984), 467
V. KEVORKIJAN, S. D. [KAPIN: PREPARATION AND STUDY OF Mg2Sn-BASED COMPOSITES ...
Materiali in tehnologije / Materials and technology 44 (2010) 5, 251–259 259

G. KLAN^NIK et al.: OSSEOINTEGRATION AND REJECTION OF A TITANIUM SCREW
OSSEOINTEGRATION AND REJECTION OF A
TITANIUM SCREW
OSEOINTEGRACIJA IN ZAVRNITEV TITANOVEGA VIJAKA
Grega Klan~nik1, Miro Zdovc2, Uro{ Kov{ca2, Borut Pra~ek3, Janez Kova~3,
Janez Rozman4
1University of Ljubljana, Faculty of Natural Science and Technology, A{ker~eva cesta 12, SI-1000, Ljubljana, Slovenia
2University of Nova Gorica, Material Characterization Graduate Study Programme, Vipavska 13, Ro`na Dolina, 5000 Nova Gorica, Slovenia
3Jo`ef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia
4ITIS, d. o. o., Center for Implantable Technology and Sensors; Lepi pot 11, SI-1000, Ljubljana, Slovenia
grega.klancnik@ntf.uni-lj.si
Prejem rokopisa – received: 2009-12-01; sprejem za objavo – accepted for publication: 2010-04-22
In the present study, a rejected titanium implant, an orthopaedic screw removed from a patient, was investigated. The screw was
implanted into the metacarpal bone for one year and was removed due to irritation. The first signs of irritation were indicated
three months after the implantation. After the removal, the signs of irritation disappeared. AES and EDS analyses showed that
the surface of the screw was significantly different from the bulk material. The high contamination of the surface layer was
found to be caused by the screw-manufacturing process, which is considered to be the main reason for the rejection of the
implant.
Keywords: orthopaedics, titanium implant, titanium screw, contamination, AES, EDS
V predstavljeni {tudiji smo preiskali zavrnjen titanov vijak, ki je bil odstranjen pacientu. Vijak je bil privit v dlan~nico in po
enem letu odstranjen zaradi razdra`enosti okoli{kega tkiva, ki se je pojavila v prvih treh mesecih po implantaciji. Po odstranitvi
razdra`enosti ni bilo ve~. AES analiza in EDS analiza sta pokazali, da se povr{ina mo~no razlikuje od notranjosti vijaka. Odkrita
je bila kontaminacija povr{ine, ki je tehnolo{ke narave in se zato predvideva, da je bil to glavni razlog zavrnitve implantata.
Klju~ne besede: ortopedija, titanov implantat, titanov vijak, kontaminacija, AES, EDS
1 INTRODUCTION
Titanium alloys are commonly used as biomaterials
and, like stainless steels, are used in orthopaedics.
Titanium is a superior orthopaedic material because it
has a high compatibility in contact with bone tissue and
is more corrosion resistant than stainless steels. In
addition, because of its low tension modulus (55–100
GPa), titanium implants tend to be handling-friendly
during the placement. However, one of the most common
problems with titanium alloys is related to the contami-
nation of the implant oxide surface with metal ions,
which can contribute to the rejection of the implant
(Figure 1).
1.1 Osseointegration
The term "osseointegration" describes the process of
having a stable, loaded implant in direct contact with the
bone. Biomaterials with the so-called osseointegrability,
e.g., commercially pure (CP) titanium with a low iron
content, CP tantalum and calcium hydroxyapatite (HA),1
are widely used. Stainless steels are also widely used for
orthopaedic applications. Classical 316L can, for example,
provide a natural surface oxide coating like titanium and
titanium alloys. If we compare titanium (CP) with 316L,
exposed to physiological fluids, no reactions are usually
present. However, stainless-steel implants, after a longer
implantation time, release metal ions, Cr6+, Ni2+, Mo6+
and Fe3+, into the surrounding tissue. A test of cyto-
toxicity performed on rate bone-marrow stromal cells
showed the following order of toxicity: Cr > Mo = Fe >
Co >Ni. All these ions can cause local inflammation by
ion accumulation inside the body.2 Because the surface
of the implant is so important when it is in contact with
the bone, tissue and particular cells, biochemical modi-
fication is used for a better and faster integration.1
1.2 Rejection of the implant
Two of the most common reasons for rejection of the
implant are the mechanical damage that occurs during
the procedures for implantation and the friction between
the two pieces (the plates and the screw).2 Titanium
Materiali in tehnologije / Materials and technology 44 (2010) 5, 261–264 261
UDK 617.3:617.57:669.295:621.9 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 44(5)261(2010)
Figure 1: Titanium screw – rejected implant
Slika 1: Titanov vijak – zavrnjeni implantat
alloys have a high coefficient of friction, which can
cause irritation when an implant rubs with the soft tissue
or when new particles are formed during the placement.
With the loss of fixation at the interface of the bone and
the titanium implant, titanium splinters may be formed
and influence the integration strength.2 Because it is
newly formed, the surface with titanium dioxide is very
reactive with respect to contamination and this is
considered to be an important variable for further storage
until use. Dental titanium implants, however, failed to
osseointegrate when the surface was contaminated with
iron, zinc, tin and lead.1,4
1.3 Formation of calcium phosphate
Calcium phosphate is the name given to a family of
minerals consisting mainly of Ca2+ with PO43– or P2O74–
and hydroxyapatite (Ca10(PO4)6(OH)2), and bone mineral
is one of them. The biology of the interaction with tita-
nium and titanium-based alloys has been studied exten-
sively. The bone formation around the implant derives
from the adjacent bone bed, which grows towards the
implant. The implant surface is a highly attractive
substrate for the bone cells (osteoblasts). Bone tissue is a
mineralized connective tissue; it is composed of cells,
called osteoblasts, that deposit a matrix of type-I colla-
gen and also release calcium, magnesium and phosphate
ions and combine with the collagenous matrix into the
crystalline mineral hydroxyapatite. After a certain time
of exposure of the implant to the internal environment of
the body, the result is a relatively thick surface oxide
layer (the natural oxidation of titanium surfaces inside
the bone or body fluid) augmented with the ions, mainly
calcium and phosphorous.2,5
2 EXPERIMENTAL
The investigation was aimed at the detection of
possible reasons for the rejection of a titanium screw
inserted into the metacarpal bone. After removal, the
screw was investigated with Auger Emission Spectro-
scopy (AES) PHI SAM, model 545A. The first energy
spectrum was recorded from the head surface of the
screw and the last spectrum after ion etching with Ar+.
On a metallographically prepared sample, one AES
spectrum was also recorded to detect the chemical
composition under the surface of the screw. The sputter-
ing rate was determined with a Ni/Cr reference and was
found to be 2 nm/min. For the chemical analyses of
possible phases, an investigation of the microstructure
was made with a JEOL 5610 electron microscope and an
EDS spectrometer. The investigated surface was also
examined with an Olympus CX61 optical microscope
and a DP70 video camera.
3 RESULTS
The AES analysis of the retrieved screw surface after
one year of implantation is shown in Figure 2a, b.
Calcium and phosphorus were both found to be the
electrolyte constituents of the body fluid, and both are
related to the formation of calcium phosphate. The
presence of oxygen, nitrogen, titanium, silicon,
aluminium and iron was also established (Figure 2 a).
However, the last recorded AES spectrum, at the end of
the ion etching inside the oxide layer, did not reveal the
presence of iron (Figure 2 b). A trace of argon was
found, because of the ion etching with Ar+. The presence
of carbon on the screw’s surface is related to the
atmospheric contamination. The AES depth profile in
Figure 3 a shows a high concentration of carbon, which
is a result of backscattering.
The presence of an oxidized surface suggests a strong
affinity for oxygen (Figure 3a). The AES depth profile of
the titanium screw’s surface revealed a surface contami-
nated with iron deep inside the oxide layer (Figure 3 b).
However, the AES spectrum of the bulk material, in
Figure 4, does not show the presence of any iron.
Oxygen is always present in trace amounts. Figure 4
shows that inside the screw, in the titanium, an alpha
structure is also present. The bulk of the screw was
investigated with SEM and EDS (Figure 5).
EDS analysis (Figure 5 a) and AES spectrum of the
bulk material (Figure 4) revealed no aluminium, silicon
or iron in the bulk material. The chemical composition of
G. KLAN^NIK et al.: OSSEOINTEGRATION AND REJECTION OF A TITANIUM SCREW
262 Materiali in tehnologije / Materials and technology 44 (2010) 5, 261–264
Figure 2: AES spectrum of the screw surface: (a) surface before and
(b) after ion sputtering
Slika 2: AES-spekter povr{ine vijaka: (a) povr{ina pred ionskim
jedkanjem in (b) po njem
the titanium screw’s surface strongly differs from the
bulk composition.
The EDS analysis of the precipitates also revealed the
presence of carbon (Figure 5 b). The detection of the
x-ray signal with the EDS system is difficult for carbon
on account of its low atomic number. The results from
the EDS analyses in Figures 5 and 6 hint at the presence
of titanium carbides. The micrograph in Figure 5
revealed a 14-μm-thick layer of titanium with a reduced
presence, or absence, of precipitates. As already discus-
sed, the absence of other elements was established.
G. KLAN^NIK et al.: OSSEOINTEGRATION AND REJECTION OF A TITANIUM SCREW
Materiali in tehnologije / Materials and technology 44 (2010) 5, 261–264 263
Figure 3: AES analysis: (a) depth profile of titanium screw (b) conta-
mination with iron
Slika 3: AES-analiza: (a) profilna analiza titanovega vijaka (b) kon-
taminacija z `elezom
Figure 4: AES spectrum of the bulk material
Slika 4: AES-spekter osnovnega materiala
Figure 7: Macrograph of titanium screw: (a) surface and (b) turning
grooves of the screw
Slika 7: Slika titanovega vijaka: (a) povr{ina in (b) sledi obdeloval-
nega orodja
Figure 6: EDS line analysis: (a) SEM micrograph and (b) EDS line
analysis
Slika 6: EDS-linijska analiza: (a) SEM-posnetek in (b) EDS-linijska
analiza
Figure 5: SEM micrograph and EDS analysis: (a) bulk material and
(b) precipitates
Slika 5: SEM-posnetek in EDS analiza: (a) osnovnega materiala in (b)
precipitatov
The evidence of the machining of the screw is
represented in Figure 7. The shape of the grooves
indicates that the screw was not polished before the
implantation.
4 DISCUSSION
Due to the golden-like colour of the surface of the
screw and the nitrogen found with the AES analysis, it
can be concluded that the surface of the screw was
nitrided (Figure 1, 3 a). This titanium nitride provides a
relatively stable surface (better wear resistance and
hardness). The presence of aluminium and silicon could
be assigned to the technology of the production (blasting
the surface with alumina and silica particles,
contamination with silicon oils, etc.). Furthermore, the
high concentration of silicon on the surface of the screw
could possibly result from an unintentional deposition
during the manufacture. This fact was confirmed by the
corresponding concentration gradient over the sputtering
time. Siliconization increases the resistance of titanium
to oxidation because it dissolves in the TiO2 surface layer
and reduces the diffusion rate of the oxygen atoms
through this layer.6 Nevertheless, silicon increases the
activity of osteoblasts and favours the formation of the
appatite layer.
The presence of aluminium and silicon in the TiO2
coating lowers the friction coefficient of the surface and
becomes more compatible in terms of orthopaedic prac-
tice.7 The presence of aluminium in the oxide layer,
however, confirms the existence of stable Al2O3 oxide.
Aluminium is capable of forming the most stable oxide;
it can also form at room temperature and could form the
piece of necrotic bone that has detached from the sound
bone (the toxic response of the body). From the AES
spectrum of the oxide layer it seems that a relatively high
concentration of aluminium is present. Aluminium par-
ticles on the surface could weaken the stable position of
the implant and cause irritation. It can be concluded from
the AES analysis (Figure 4) that the presence of alumi-
nium on the surface was not correlated with the bulk
material.
The penetration depth of the calcium and phospho-
rous was determined to be over 400 nm and shows the
quality of the osseointegration. From the AES spectrum
in Figure 3 b, the presence of iron was not detected
deeper than 0.4 μm, and iron was not detected in the
basic (inner) material (Figure 4).
5 CONCLUSIONS
From the results of the AES and EDS analyses,
several conclusions can be drawn. The retrieved titanium
implant is unalloyed (alpha) titanium strengthened with
titanium carbides. The presence of calcium and
phosphorous was also established, 0.4 μm deep into the
oxide surface layer, which confirms the quality of the
osseointegration of the bone with the screw, and the bone
as the source of calcium and phosphate ions involved in
the metabolic functions. The nucleation of the growth of
calcium phosphate started from the bone and from the
implant surface. With interconnected pores the osteoblast
cell adhesion, differentiation, proliferation as well as
biomineralization were possible, relatively deep inside
the oxide surface. Aluminium and silicon were found in
higher concentrations and can influence the friction
factor. A lower friction factor can strongly reduce the
possibility of inflammation when an implant is rubbing
against soft tissue. The existence of an ideal friction
coefficient is impossible because it would differ from
patient to patient. The aluminium contamination is
relatively high when we consider that the bulk material is
commercial titanium. Aluminium and iron oxides should
be considered as being in the group of capsule-forming
metal surfaces and the reason for retrieving the implant.
Iron was found deep inside the oxide layer. The screw
surface was examined with a stereo microscope and
machining grooves were observed. The AES depth
profile revealed that the screw surface was contaminated
with iron, which could be the result of using an
iron-containing steel tool. The accumulation of iron as
well as the high contamination with aluminium at the
interface of the implant and soft tissue can cause
inflammation and irritation, which can form splinters at
the implant–bone interface.
6 REFERENCES
1 D. M. Brunette, P. Tengvall, M. Textor, P. Thomsen; Titanium in
medicine; Springer, (2001)
2 J. W. Nicholson; The Chemistry of medical and dental materials;
The Royal society of Chemistry, (2002)
3 M. G. Choi, H. S. Koh, D. Kluess, D. O'Conner, A. Mathur, G. A.
Truskey, Janet Rubin, D. F. Zhou, K. L. P. Sung; PNAS; 102 (2005)
12, 4578–4583
4 G. A. A.Castilho, M. D.Martins, W. A. A. Macedo; Surface characte-
risation of titanium based dental implants; Brazilian journal of
physic; 36 (2006), 1004–1008
5 E. R. Hitzky, K. Ariga, Y. Lvov; Bio-inorganic Hybrid Nanomate-
rials; Willey-Vch Verlag, (2008)
6 D. Vojtìch, T. Kubatik; Siliconizing as a method for improving the
resistance of titanium to oxidation; Mater. Tehnol., 37 (2003),
381–384
7 E. A. Levashov, D. M. Shtansky, N. A. Gloushankova, I. V. Reshe-
tov; Biocompatible multicomponent nanostructured coatings for
medical implants; Avalible from world wide web: http://www.faqs.
org/patents/app/20090050017
G. KLAN^NIK et al.: OSSEOINTEGRATION AND REJECTION OF A TITANIUM SCREW
264 Materiali in tehnologije / Materials and technology 44 (2010) 5, 261–264
M. BAJT LEBAN et al.: CORROSION INVESTIGATION OF THE PRE[EREN MONUMENT IN LJUBLJANA
CORROSION INVESTIGATION OF THE PRE[EREN
MONUMENT IN LJUBLJANA
KOROZIJSKA PREISKAVA PRE[ERNOVEGA SPOMENIKA V
LJUBLJANI
Mirjam Bajt Leban, Viljem Kuhar, Tadeja Kosec, Andra` Legat
Slovenian National Building and Civil Engineering Institute, Dimi~eva 12, 1000 Ljubljana, Slovenia
mirjam.leban@zag.si
Prejem rokopisa – received: 2010-03-30; sprejem za objavo – accepted for publication: 2010-04-13
The investigated monument, erected in honour of the Slovenian poet France Pre{eren, was unveiled in 1905 in Ljubljana, and
restored in 1970. Its appearance differs considerably from the original as a result of corrosion. The strong interaction between
atmospheric pollutants and the bronze alloy in Ljubljana city centre has resulted in the formation of a secondary patina. With the
aim to determine the corrosion state of the Pre{eren monument and to ensure the data for the next restoration procedure, a
chemical and physical examination was performed. The composition of the patina was analysed using energy-dispersive
spectroscopy coupled with scanning electron microscopy and a non-destructive method for determining the alloy composition
was used. The different types of patina were studied.
Key words: Pre{eren monument, bronze, patina, corrosion, urban atmosphere
Spomenik v spomin pesniku Francetu Pre{ernu v Ljubljani je bil odkrit l. 1905, renoviran pa l. 1970. Danes je njegov zunanji
videz zaradi bolezni brona precej druga~en od tistega ob postavitvi. Najve~ji razlog za to je onesna`enje okolja v centru
Ljubljane. Da bi ugotovili korozijsko stanje Pre{ernovega spomenika in pridobili potrebne podatke za predvidene restavratorske
posege, smo izvedli kemijske in fizikalne analize brona spomenika. Sestavo patin smo analizirali z energijsko disperzijsko
spektroskopijo rentgenskih `arkov, kemijsko sestavo brona pa z nedestruktivno metodo.
Klju~ne besede: Pre{ernov spomenik, bron, patina, korozija, mestna atmosfera
1 INTRODUCTION
Artistic sculptures exposed outdoors are subjected to
many environmental pollutants and other influences 1.
Bronze is a copper–tin alloy, sometimes referred to as
phosphor bronze, and may contain other alloying ele-
ments, such as zinc, lead, etc. 2. Copper is a commonly
used material in statuary art, and it is heavily affected by
ageing; however, the rate of ageing depends strongly on
the exposure conditions. Bronze forms a protective oxide
layer, also referred to as natural patina, when exposed to
humid aerated environments. Furthermore, harmful
factors include humidity, oxygen, UV light, biological
pollution, etc., that can change the appearance of
sculptures significantly.
The duration of patina 3–6 formation depends on the
atmosphere. It can last from 20 to 100 years in rural
sites, up to 10 years in urban centres, and up to 1 year in
littoral zones 7. Nowadays, with the aim to achieve the
desired visual effect on bronze surfaces, artificial pati-
nation 7–11 is used. Bronze-brown or green casts patinas
are used on statues exposed to the open air. The desired
colours can be obtained by using various recipes and
concentrations of one or more chemical compounds 12.
In order to ensure the quality of the maintenance and
the long-term protection of outdoor sculptures against
corrosion, various parameters should be taken into
account. The most important parameters are: bronze qua-
lity, type of surface, chemical cleaning and subsequent
treatment, and the type of corrosive atmosphere. In
addition, the chemical composition of different parts of
the bronze sculpture should be determined, as well as the
type and intensity of the corrosion processes should be
evaluated.
1.1 Pre{eren’s monument in Ljubljana
The monument erected in honour of the Slovenian
poet France Pre{eren was unveiled on the 10th of
September 1905. The author of the monument was the
Slovenian sculptor Ivan Zajec and the architecture for the
statue was designed by the architect Maks Fabiani. The
monument consists of a statue of the poet (Pre{eren) and
a statue of his poetic Muse (Muza), in her hand holding a
sprig of laurel (Figure 1). Two reliefs – "Fisherman
(Ribi~)" on the north side (Figure 2) and "^rtomir’s
Farewell to Bogomila (Slovo ^rtomira od Bogomile)" –
on the south side of the pedestal (Figure 3) are also
constituent parts of the monument. The main statues and
both reliefs were cast in bronze in the renowned Vienna
foundry.
The monument was partly restored after 1970. The
old patina was mechanically removed, although not
completely. Once this procedure was finished, the
monument was most likely artificially patinated with
green patina. Subsequently, influenced by the corrosive
environment and rinsing by water, at different locations
on the monument different types of patina were formed
Materiali in tehnologije / Materials and technology 44 (2010) 5, 265–269 265
UDK 620.193:669.35'5'6:730(497.4) ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 44(5)265(2010)
and various colours of green and pale green patinas
developed as secondary corrosion products. The purpose
of our work was to determine the corrosion state of the
Pre{eren monument and to provide the necessary data to
be used in future restoration interventions.
2 EXPERIMENTAL
In order to identify the corrosion processes on the
monument, samples of the corrosion products were
mechanically scrapped off selected sites of the monu-
ment, as well as off both side reliefs. A non-destructive
method of chemical analysis for the bronze was applied
on these areas, using a portable instrument, i.e., a Niton –
Xli/XLp 800 Series Analyser and XDXRF – energy
dispersive x-ray fluorescence. A calibration of the Niton
– Xli/XLp 800 Series Analyser apparatus was made
before and after the analysis, using control etalons of the
qualities C260C (Cartridge brass), C464 (Naval brass);
C443 (Admiralty brass) and C110 (electrolytic copper) –
UNS identification – The Unified Numbering System. In
the laboratory, the corrosion products were examined
with a scanning electron microscope SEM (JEOL JSM –
5500 LV Japan (Japan)) and analyzed with electron-
dispersive spectroscopy (EDX, Oxford Inca, Oxford
Instrument Analytical, UK) at an accelerating voltage of
20 kV.
3 RESULTS
3.1 Results of the chemical analysis of the bronze
The results of the chemical analysis of the bronze
alloy at different parts of the monument are given in
mass fractions (w/%) in Table 1.
In addition to a certain content of elements, such as
Cu, Sn, Pb, Zn, Ni and Fe, which are prescribed for
bronzes, minor quantities of Ag, W, Mn, Cr, V, Ti, Al,
Mo, Nb and Co were detected, also. The presence of Fe,
Al and Mn confirmed the impurity of bronze. The
presence of phosphorus and sulphur is common and
expected in such alloys, but cannot be determined by the
application of the applied method because the detection
of the elements is limited.
3.2 Results of EDS (Energy-Dispersive X-ray Spectro-
scopy) analysis of patinas formed on the monument
Samples of patinas were taken from different sites of
bronze before any renovation on the stone part of the
monument. Powder patina samples from internal and
external layers were analyzed deposed on a carbon
surface. The elemental compositions of the different
corrosion layers are reported in Table 2. The EDS results
of the most representative sites of the monument
analyses are given in mass fractions (w/%).
M. BAJT LEBAN et al.: CORROSION INVESTIGATION OF THE PRE[EREN MONUMENT IN LJUBLJANA
266 Materiali in tehnologije / Materials and technology 44 (2010) 5, 265–269
Figure 2: Relief "Fisherman"
Slika 2: Relief "Ribi~"
Figure 3: Relief "^rtomir’s Farewell to Bogomila"
Slika 3: Relief "Slovo ^rtomira od Bogomile"
Figure 1: Statue of the poet France Pre{eren, with the statue of the
poetry Muse above, holding a sprig of laurel in her hand
Slika 1: Kip pesnika Franceta Pre{erna s kipom pesnikove Muze, ki
dr`i v roki lovorjevo vejico
The corrosion activators (ions that initiate corrosion,
Cl– and S2– in this case) that caused particular patina on
different sites of the sculptures and monuments as well
as the type of bronze patinas that were formed can be
concluded from the composition of the most typical
elements of the corrosion products given in Table 2.
The content of oxygen was higher in the case of the
Pre{eren and Muse statues. These patinas were taken
from sites that are exposed at different angles of
inclination. Moreover, the content of carbon is lower in
the case of corrosion products formed on exposed
surfaces at different angles of inclination. The content of
sulphur is substantially higher in the case of a
multi-angle exposure. The presence of zinc in the
corrosion products is low and it does not vary on the
exposure sites.
4 DISCUSSION
4.1 Visual observations
The visual examination of the monument and the
composition of the bronze and the patina indicate that
secondary patinas were formed on the sites where there
was a non-uniform leaching action of the rain. On the
other hand, at sites where the leaching action of the rain
is weaker (dark, almost black surfaces), the internal layer
of the patina consisted of cuprite (Cu2O). The external
layer consisted mostly of copper sulphates (bronhanite
and antlerite), copper chloride–hydroxide (atacamite)
and other compounds originating from environmental
contamination 13. On some hardly accessible sites (the
Pre{eren and Muse statues), where the leaching action of
the acid rain (pH < 5) was not as strong, the layer of
secondary corrosion products was very thick (up to 0.5
mm).
Only a few corrosion activators accumulated on the
dark (green to black colours) surfaces with the thinner
patina layer (the bronze shine through the layer is clearly
visible). These surfaces are smooth and the bronze is not
deeply etched. The leaching action was observed in
detail and similar observations were made 14. On such
surfaces the presence of copper chlorides was low or
even non-existent, while copper oxides and sulphates
were dominant.
On the surfaces with the green-grey and white
coloured patina substrate, the secondary patina layer
consisted mainly of copper oxides, sulphates, chlorides,
carbonates and plaster. As heavily soluble compounds,
carbonates were not leached by rain. On the other hand,
the secondary layer of corrosion products on the
surfaces, affected by the leaching action of the rain, was
pale green and had a powdery non adhesive texture.
M. BAJT LEBAN et al.: CORROSION INVESTIGATION OF THE PRE[EREN MONUMENT IN LJUBLJANA
Materiali in tehnologije / Materials and technology 44 (2010) 5, 265–269 267
Table 1: Results of the chemical analysis of the bronze (mass fractions, w/%)
Tabela 1: Rezultati kemijske analize brona (masni dele`i, w/%)
Site w/% Cu Sn Pb Zn Ni Fe Rest
Fisherman 87.76 6.37 1.74 3.28 0.18 0.10* 0.57
Farewell 87.25 7.17 1.74 3.07 0.09 0.11 0.57
Pre{eren 88.51 4.78 1.34 4.61 0.12 0.19 0.45
Muse 87.03 6.74 1.64 3.72 0.14 0.21 0.97
C922** 86– 90 5.5–6.5 1–2 3–5 0–1.0 <0.25 –
*** <0.10 0.18 0.04 0.20 0.10 0.04 –
Remarks:
* – below the detection limit of the analyser;
** – regulation for C922 bronze quality (UNS identification);
*** – detection limits of Niton – Xli/XLp 800 Series Analyser.
Table 2: Results of the EDS analysis of the different patinas of the monument and reliefs
Tabela 2: Rezultati EDS-analize razli~nih patin na spomeniku in reliefih
Site of patina
take off
Patina colour, other
properties w/% C O Si S Cl Cu Sn Pb Rest
Farewell white – green 26.80 31.76 1.40 3.30 0.25 34.30 0.27 0.43 1.49
Farewell black – thick layer 4.79 42.58 0.52 6.33 – 42.76 1.16 0.85 1.08
Fisherman bronze red – brown 46.25 31.82 6.29 0.17 0.25 11.82 1.94 0.63 0.83
Fisherman green – white 42.47 34.39 7.07 0.24 0.28 12.30 2.19 0.17 0.89
Fisherman light green – thin layer 6.72 30.26 – 2.03 – 43.68 12.79 2.15 2.37
Fisherman bronze black – thin layer 4.61 30.75 0.23 1.36 – 49.92 7.71 3.16 2.26
Pre{eren black – thin layer 5.26 43.14 0.39 7.76 0.46 40.06 0.32 1.27 1.34
Muse black – thin layer 6.61 32.18 1.91 4.97 0.70 49.05 0.01 0.90 3.67
Pre{eren black brown – thin layer 9.16 50.15 0.39 6.02 – 32.10 0.38 0.81 0.99
Pre{eren light green 4.10 48.37 0.29 6.18 – 38.70 1.89 0.44 0.03
Pre{eren black brown – thin layer 4.77 38.37 0.28 2.88 – 41.73 8.89 1.02 2.06
Muse green-white – thin layer 11.09 34.29 1.11 4.93 0.23 45.62 0.66 0.80 1.27
Flow-off water zones of light green colour were
formed on the sites of the intensive corrosion products.
A minor area on the south side of the monument, known
as Ribi~ relief, has a red-brown bronze surface. The
internal patina layer consists mostly of cuprite, whereas
the secondary layer is very thin. The patina in the
vertical zones is primarily of soluble corrosion products
consisting of copper carbonates.
Since many different patinas were formed over the
entire surface of the monument and different conditions
regulated the water flow-off, it can be assumed that
severe corrosion (e.g., bronze disease) was activated
because of the relatively aggressive atmosphere. The
surface of the reliefs is smoother than the surface of the
monument, which is the main reason for the smaller
corrosion damage.
The depth of the pitting corrosion on particular sites
could not be estimated without a prior patina removal.
The damage is not severe, yet it could have a crucial
influence on the appearance of the monument details –
locally corrosion damage causes an etched appearance of
the surface.
4.2 EDXRF analysis
The results of the bronze chemical analysis suggest
that both sculptures were made from the bronze C922
according to the requirements of the standard UNS 2. As
presented in Table 1, the contents of Sn and Pb in some
analyses deviate from their contents prescribed in the
standards. However, the chemical composition analyzed
on the bronze surface (where the EDXRF analysis was
made) can differ slightly from the bulk composition.
Regardless of this fact, it can be assumed that the bronze
in both sculptures, as well as that in the side reliefs, is
homogeneous. Its purity is comparable to currently valid
regulations. Therefore, it can be concluded that the
casting process of all the component parts of the
monument included in this investigation was under
quality control.
4.3 EDS analysis
The results of the EDS analyses of the different
patinas scraped off different sites of the monument
indicate that the main contributions to the corrosion
processes and to the formation of patinas are effected by
environmental pollution (the pollution in the centre of
Ljubljana is an urban atmosphere), acid rain, salt aerosol
due to winter salting of the roads, dust, soot and bird
excrements. The patina on the bronze statue consists of
an internal, usually thinner, layer and a thicker, external
layer. A schematic presentation is given in Figure 4. The
internal patina layer consists of copper and tin oxides.
The analyses have also proved the presence of copper
carbonate and alloying elements. The thin layers of dark
brown-black, red-brown and green patina corrosion
products do not contain chloride compounds.
In the secondary-external layer of brown-black,
black-green and green-white patina, the following predo-
minant compounds were found: copper oxides, copper
hydroxisulphates, as well as sulphides, chlorides and
carbonates of copper and its alloying elements.
The sites where the water rinsing was not highly
intensive have a relatively stable, predominantly black,
patina. The vertical and horizontal surfaces have been
affected by intensive rinsing. The leaching activity of the
urban rain is therefore stronger and the colour of the
patina is pale green-white.
The presence of Cl, Mg, K and Ca in the corrosion
products is a consequence of the bronze’s contamination
with de-icing salts. Although the content of these
elements is not high, they are in sufficient quantities to
trigger corrosion and "bronze disease". The presence of
chlorides and moisture is the cause for copper disso-
lution. The formation of sulphur compounds of copper
and its alloying elements as well as carbonates in
corrosion products is probably the consequence of acid
rain (carbon and sulphur acid), air pollution (above all
SO2), and moisture. Copper hydroxi-sulphates are
soluble in water – they form green-white lines on the
sides of bronze sculptures. The content of zinc in the
corrosion products is minimal and it can be assumed that
the bronze of the sculptures and reliefs is not sensitive to
dezincification. However, Bernardi and coauthors found
that Cu and Pb in bronze type G85 progressively form
insoluble corrosion compounds, while Zn continuously
dissolves without forming detectable insoluble products
15. They also claim that the absence of dissolved tin is
remarkable.
Pollution with sand powder and soot might be the
reason for the detected presence of Al, Si and C in the
corrosion products.
5 CONCLUSION
Based on a visual examination, a chemical analysis
of the bronze, and an EDS analysis of the patinas formed
on Pre{eren’s monument in Ljubljana, the following
conclusions were drawn:
M. BAJT LEBAN et al.: CORROSION INVESTIGATION OF THE PRE[EREN MONUMENT IN LJUBLJANA
268 Materiali in tehnologije / Materials and technology 44 (2010) 5, 265–269
b
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rn
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a
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Figure 4: Schematic presentation of patina layers on bronze
Slika 4: Shematska predstavitev plasti patin na bronu
• The sculptures of Pre{eren’s monument in Ljubljana
were made from bronze C922. The purity of the
bronze indicates that the casting process of this
monument was strongly controlled.
• Regardless of the corrosion processes and the age of
the bronze monument (approximately 100 years), the
corrosion damage to the bronze alloy is insignificant,
and the patina formation only disturbs the monu-
ment’s visual/aesthetic appearance.
• The variety of patinas formed on the different sites of
the monument under different conditions of wetting/
drying/rinsing shows that the corrosion (bronze
disease) is a consequence of the aggressive urban
atmosphere.
• In order to maintain the bronze statue and to keep the
appearance as long as possible, the protection of the
bronze prepatinated surface is strongly advised.
6 REFERENCES
1 P. A. Schweitzer, Fundamentals of metallic corrosion: Atmospheric
and media corrosion of metals, corrosion engineering handbook,
CRC press, 2nd Ed. 2007
2 P. A. Schweitzer, Metallic materials – physical, mechanical, and
corrosion properties, 1st Ed., Marcel Dekker, New York, 2003
3 C. Chiavari, A. Colledan, A. Frigani, G. Brunoro, Corrosion
evaluation of traditional and new bronzes for artistic castings, Mat.
Chem. Phys., 10 (2005), 252–259
4 F. Gallese, G. Laguzzi, L. Luvidi, V. Ferrari, S. Takacs and G.
Venturi Pagani Cesa, Comparative investigation into the corrosion of
different bronze alloys suitable for outdoor sculptures, Corros. Sci.,
50 (2008) 954–961
5 D. A. Scott, An examination of the patina and corrosion morphology
of some roman bronzes, Journal of the American Institute for
Conservation, 33 (1994), 1–23
6 D. L. Hamilton, Conservation of cuprous metals (Copper, Bronze,
Brass), Conservation Research Laboratory, Texas A&M University,
2000, Available from Word Wide Web: http://nautarch.tamu.edu/crl/
conservationmanual/ConservationManual.pdf
7 Introduction to patinas on brass, bronze and cooper, available from
Word Wide Web: http://www.sciencecompany.com/patinas/patina-
sintro.htm
8 Green patina finishes, Available from Word Wide Web: http/www.
cooper.org/resources/properties/protection/green.html
9 Brown statuary finishes, Available from Word Wide Web: http/www.
cooper.org/resources/properties/protection/brown.html
10 M. Parmenter, Bronze patina basics, 1999, Available from Word
Wide Web: http://www.whiteriverfoundry.com/bronze_patina_
basics.htm
11 Introduction to patinas on brass, bronze and cooper, patina formulas
for brass, bronze and copper, Science Company, Available from
Word Wide Web: http://www.sciencecompany.com/patinas/
patinaformulas.htm
12 R. Huges, M. Rowe, The colouring, bronzing and patination of
metals, Thames and Hudson, London, 1991
13 C. Chiavari, K. Rahmouni, H. Takenouti, S. Joiret, P. Vermaut and L.
Robbiola, Composition and electrochemical properties of natural
patinas of outdoor bronze monuments, Electrochim. Acta, 52 (2007),
7760–7769
14 E. Bernardi, C. Chiavari, B. Lenza, C. Martini, L. Morselli, F.
Ospitali, L. Robbiola, The atmospheric corrosion of quaternary
bronzes: The leaching action of acid rain, Corros. Sci., 51 (2009),
159–170
15 E. Bernardi, C. Chiavari, C. Martini, L. Morselli, The atmospheric
corrosion of quaternary bronzes: An evaluation of the dissolution
rate of the alloying elements Applied Physics A: Materials Science &
Processing, 92 (2008), 83–89
Acknowledgments
The research work presented in this paper was
performed under the auspices and initiative of the
Municipality of Ljubljana (Mestna ob~ina Ljubljana).
M. BAJT LEBAN et al.: CORROSION INVESTIGATION OF THE PRE[EREN MONUMENT IN LJUBLJANA
Materiali in tehnologije / Materials and technology 44 (2010) 5, 265–269 269

F. PLAKOLLI et al.: THE MICROFLORA AND PHYSICO-CHEMICAL PROPERTIES OF LIGNITE ...
THE MICROFLORA AND PHYSICO-CHEMICAL
PROPERTIES OF LIGNITE FROM THE MIRASH MINE,
NEAR KASTRIOT
MIKROFLORA IN FIZIKALNO-KEMIJSKE LASTNOSTI LIGNITA
IZ RUDNIKA MIRASH PRI KASTRIOTU
Fatime Plakollil, Luljeta P. Beqiri2, Agron Millaku3
1Faculty of Education, Rr. Agim Ramadani 10000 Pristine, Kosovo
2University of Pristine, Faculty of Mine and Metallurgy, Mitrovica, Kosovo
3Ministry of Environment and Spatial Planning, Rilindja K3, Kosovo
fatimekoka2008@hotmail.com
Prejem rokopisa – received: 2010-03-08; sprejem za objavo – accepted for publication: 2010-04-29
Coal, as an important source of energy, is very often the subject of study for scientists from the areas of chemistry, physics,
technology, and biology, etc. In Kosovo, large deposits of coal, in the form of lignite, can be found. Lignite is mostly used to
produce electrical energy; however, the interest of the country of Kosovo is to study many of the aspects of lignite.
In this paper an analysis of the microflora of lignite from the mine in the locality of Mirash, near Kastriot, is presented. With
modern microbiological methods, the density, assortment, and some of the morphological and physiological characteristics of
bacteria (heterotrophic, proteolytic, amilolytics, lypolytic and celulolytic) were determined and aerobic bacteria and fungi
(yeasts and moulds) were investigated also. The samples of lignite were analyzed for physic–chemical attributes, for example, a
determination of ash, and of C, O, H, N, S, carbonates, silicates, etc. The biomass of the isolated microflora from lignite was
submitted for a chemical analysis and an astounding number of bacterial microflora and fungal was found. A composition
chemical link between the coal and the microbial biomass was observed: the values of C, O, N, and H were found to be
approximately similar in the coal and the bacterial mass.
Key words: coal, lignite, bacterial and fungal microflora, energy, carbonates, silicates, biomass
Premog kot pomemben vir energije je pogosto predmet {tudija znanstvenikov s podro~ja kemije, fizike, tehnologije, biologije in
drugih ved. Na Kosovu so velike koli~ine premoga v obliki lignita. Najve~ lignita se uporablja za proizvodnjo elektri~ne
energije, zato je razumljiv interes kosovske dru`be in znanosti za njegovo vsestransko preu~evanje. V tem prispevku je
predstavljena analiza mikroflore lignita iz rudnika Mirash pri Kastriotu. Z modernimi mikrobiolo{kimi metodami so bile
dolo~ene gostota, razvrstitev, morfolo{ke in fiziolo{ke zna~ilnosti bakterij (heterotrofnih, proteoliti~nih, aliloliti~nih, lipoliti~nih
in celuliti~nih). Isto~asno so bile preiskane tudi aerobne bakterije in glive (kvasovke in plesni). Vzorci lignita so bili analizirani
in dolo~ene so bile fizikalno-kemi~ne lastnosti, kot so: vsebnost pepela, vsebnosti C, O, H, N, S, karbonatov, silikatov in
podobnega. Biomasa izolirane mikroflore iz lignita je bila kemijsko analizirana. Najdeno je osupljivo veliko {tevilo bakterijske
mikroflore in gliv v lignitu in opa`ena je bila povezava med kemijsko sestavo premoga in biomaso mikrobov. Vsebnosti C, O, N
in H so bile pribli`no enake v premogu in v masi bakterij.
Klju~ne besede: premog, lignit, mikroflora bakterij in gliv, energija, karbonati, silikati, biomasa
1 INTRODUCTION
Coal is considered to be a very important source of
energy, and it has been used since the earliest times
(before the new era). The economic development of
society during the past 1000 years was based on coal as a
source of energy (1). Oil and its derivatives are also an
important source of energy, and by the beginning of the
second half of the 20th Century it had achieved primacy
as a source of energy. Nowadays, an interest in coal has
once again emerged, because 80 % of fossil fuel reserves
are coal as compared to 18 % for oil.
Actually, 45 % of the globally generated energy is
generated with coal, as compared to 30 % from oil and
14 % from natural gas (2). Coal is a fossil fuel; it is an
organic sedimentary rock; and it is formed by the
accumulation of organic matter (plant debris).
This process usually takes place in waterlogged envi-
ronments (water basins, lakes, marshes, swamps) (3).
Coalification covers a number of geological periods,
which can be used to determine the geological history of
the Earth’s crust (4). For this reason, the process of coal
formation took place as a result of a number of different
factors (pressure, humidity, lack of air, microbiological
reactions, physical and chemical reactions, etc.). The
best way to describe this complex process, which took
place over millions of years, is the accumulation of dead
organic (plant) matter that subsequently forms coal. The
composition of coal is very complex; however, it consists
mainly of carbon (between 60 % and 95 %). Thus, it has
a very wide range of uses and a characteristic structure.
Coal contains the following biogenic elements: carbon,
hydrogen, oxygen and sulfur. From the biochemical
point of view coal contains the same elements as did the
tropical plants from which it was formed: oils, resins,
etc. It ranges in color between black and brownish-black.
Its strength is between 0.5 kg/cm2 and 2.5 kg/cm2 and its
specific weight is 1–1.7.
Materiali in tehnologije / Materials and technology 44 (2010) 5, 271–275 271
UDK 622.332/333(497.115) ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 44(5)271(2010)
Coals are divided into humic (formed by the
degradation of land plants) and sapropelic (algae and
fungi) (5) and it is found in the form of sedimentary
rocks. After the fossilization the organic matter was
submitted to degradation and in specific circumstances a
new matter was formed, which served as the skeleton for
the formation of coal. The following can be found in
plant cells: cellulose, hemicellulose, lignin, proteins,
oils, waxes, resins, cutin, etc. Through the interaction of
micro-biological, physical and chemical, as well as
geological factors, the organic matter turns into a mass
called torv (peat), lignite and other kinds of coal. The
coalification process has two phases: humification and
carbonization. During the process of humification,
organic materials, under the influence of the above-
mentioned factors, turn into torv (peat) – humus. The
peat is then degraded by microorganisms. Bacteria are
known to degrade organic matter and cellulose, on which
occasion enzymes and biocatalyzers are produced and
affect the oxidoreduction process, as well. Micro-
organisms affect the inorganic matter by increasing the
mineral solubility (7).
According to several authors (8, 9, 10), upon the
degradation of peat, microorganisms reduce their activity
as a consequence of the formation of antiseptic substan-
ces, such as phenols (8).
During the second phase, torv or sapropel will turn
into anthracite, lignite, coal, etc (9).
In aerobic conditions, 80 % of the organic matter is
lost, whereas in anaerobic conditions only 5 % of the
organic matter is lost (10). During the degradation of the
organic matter proteolytic microorganisms degrade
proteins. Then the degradation of the oils by lipolytic
microorganisms and that of cellulose by cellulolytic
microorganisms follows and afterwards, the degradation
of hemicellulose, lignin, cutin and eventually resins,
occurs.
The influence of physical and chemical factors in the
formation of coal is characterized by increased pressure
and the catalytic influence of minerals and gases together
with water, temperature and pH. From the petrographic
point of view lignite is xylitic. Geological data show that
the Kosovo Coal Basin dates back to the Pliocene
(approximately 2.5 million years ago). This tectonic
basin was formed during the Oligocene (other layers
were sedimented on top of it during the late Tertiary
Period). Its reserves are estimated to 2.2 billion tons and
could be as high as 10 billion tons. According to (11),
the ecoregions in the Kosovo basin during the Pliocene
consisted of wetlands, hills and mountains. Based on the
ecological conditions, in which certain groups of plants
lived, the following wetland vegetation zones existed
(12):
1) Submerged aquatic plants (Myriophyllum)
a) floating plants
b) emergent plants (Graminea and Cyperaceae)
2) Mountain vegetation zone (Taxodiaceae)
3) Shrub zone (Polipodiaceae)
4) Dry forest zone (Sequoia forests) (14)
II. Hilly region
Forest zone: Salix, Alnus, Populus (15)
Deciduous forest zone: Querqus, Fagus, Carpinus, Tilia,
Castanea, Acer, etc.
III. Mountainous region: Pinus, Picea, Abies, Laryx
(16).
From these groups of plants the coal was formed.
According to several references, coal and different
microorganisms co-existed since the time the deposit
was formed, around 2.5 million years ago. They have
survived in a latent or dormant state, which slowed down
their metabolism in order to survive the unfavorable
conditions. The other form is called spores or endo-
spores, and many scientific papers have dealt with coal
and microorganisms.
It was established that certain species of bacteria can
clean coal and improve its quality, e.g., leptospirillum,
ferroxidans and thiobacillus ferroxidans. These species
have been bred to use phenol as their only source of food
(17) and pseudomonas and arthrobacter have degraded
coal molecules by “eating” sulfur and other contami-
nants.
Bacteria increase the intensity of methane degrada-
tion (attested in the labs of the US Energy Department).
The digestive system of the above-mentioned bacteria
eliminates harmful pollutants and helps the production of
clean coal (18). Certain strains (Pseudomonas) can
degrade or ferment, coal derivatives (fenatren) producing
CO2 and H2O: Fenatren – 1 – hydroxyl 2 – naphtoic acid
– salicylic acid – catechol – CO2+H2O (19). The bacteria
digest the carbon in the rocks and produce natural gas for
a period of about 10–1000 years (21) and lock methane
at the bottom of the sea in anaerobic conditions. The aim
of this study was to determine the presence of the
bacterial and fungal microflora in the lignite from the
Mirashi-Kastrioti Coal Mine. The presence of hetero-
trophic, proteolytic, amilolytic, lipolytic, cellulolytic,
aerobic bacteria and fungi was studied in order to get an
idea about the existing microflora at the time when the
lignite was formed.
Furthermore, the aim of this study was to determine
the composition of the ash, biogens and bacterial
biomass in the lignite from the Mirashi Coal Mine. The
authors were motivated by the claim (6) that hopanoids,
the compounds in the membranes of prokaryotic cells (as
well as bacteria), can be found in great abundance here
(as well as by the data on the amount of carbon in the
coal of the Kosova basin). It must be stressed that
hopanoids are the main constituents of coal (90 %).
Scientific data show that the membranes of prokaryotic
cells (bacteria, cyanobacteria) have the most hopanoids.
Since the organic material (in coal) consists largely
of bacteria in the form of kerogen, which is the organic
precursor of petroleum, it becomes obvious that hopa-
F. PLAKOLLI et al.: THE MICROFLORA AND PHYSICO-CHEMICAL PROPERTIES OF LIGNITE ...
272 Materiali in tehnologije / Materials and technology 44 (2010) 5, 271–275
noids or bacteriohopanetetrol are isolated from kerogen.
In order to verify the relation between the accumulation
of kerogens and bacterial activity, the authors (20, 23)
have demonstrated the importance of bacteria in the
formation of fossil fuels and the degradation of organic
matter.
2 MATERIAL AND METHODS
Lignite samples from the Mirashi Coal Mine in the
vicinity of Kastriot were used as study material and
samples of dry and wet coal were examined. For the
physico-chemical analysis of the coal (lignite),
gravimetric, chromatographic and spectrophotometric
methods were used. The following parameters were
determined: moisture, ash, combustible volatile matter,
lower calorific value, fixed carbon, total sulfur, organic
sulfur, inorganic sulfur, SiO2, Al2O3, Fe2O3, CaO,
magnesium oxide and sulfur oxide.
A lump of coal was first examined. Later it was
subjected to grinding and mixed with sterilized tap water
in order to determine the presence of microflora on its
surface and interior. Modern methods were applied to
determine the presence of microflora (Standard Methods
for the Examination of Water and Wastewater, APHA –
last edition). The presence of biogens was determined
using a sophisticated apparatus (VARIO MACRO
CHNS). Initially, wet coal was dried at a temperature of
105 °C for 2 h. A sample of coal with a weight of 75 mg
to 125 mg was used. The minimum weight for a reliable
analysis was 40 mg. First, the content of biogens present
in the lignite, the ratio between C and N, C and H as well
as C and S were determined. Then the presence and the
amount of biogens in the bacterial biomass isolated from
the lignite were determined using the same apparatus.
3 RESULT WITH DISCUSSION
3.1 Microbiological analysis of lignite
The microbiological, physical and chemical results
were obtained in the three-month period of March, April
and May. The results represent the arithmetical average
of three measurements. Wet coal was used due to the fact
that it had a higher density of microorganisms.
F. PLAKOLLI et al.: THE MICROFLORA AND PHYSICO-CHEMICAL PROPERTIES OF LIGNITE ...
Materiali in tehnologije / Materials and technology 44 (2010) 5, 271–275 273
Table 1: Heterotrophic bacteria and physiological groups isolated from lignite
Tabela 1: Heterotrofne bakterije in fiziolo{ke skupine, izolirane iz lignita
Bacterial group Unit Number x/%
Heterotrophic bacteria (saprophytic) mL 28,855,000 100
Proteolytic mL 3,375,000 11.49
Amilolytic mL 4,900,000 16.98
Lipolytic mL 2,380,000 8.24
Cellulolytic mL 3,200,000 11.08
Sporogenic (microaerophilic) mL 15,000,000 51.98
Total 28,855,000 99.97
(The amount of substance fraction, x/%)
Table 2: Fungal microflora isolated from the lignite of the Mirashi Coal Mine.
Tabela 2: Mikroflora gliv, izoliranih iz lignita iz premogovnika Mirashi
Fungi type Unit Number x/%
Mold mL 16,000,000 66.66 %
Yeast mL 8,000,000 33.33 %
Total 24,000,000 99.99
Table 3: Some physical parameters of the lignite from the Mirashi Coal Mine (March, April and May 2008)
Tabela 3: Nekaj fizikalnih parametrov lignita iz premogovnika Mirashi (marec, april in maj 2008)
Month w(M)/% w(A)/% w(Vm)/% Hu/(MJ/kg)
March
41.30 12.84 41.27 8.563
44.64 16.49 38.87 7.809
42.35 18.9 35.94 6.889
April
41.30 19.20 37.35 7.332
42.20 15.1 39.37 7.966
41.25 15.15 38.95 7.834
May
42.40 12.80 39.31 7.947
42.32 17.79 35.67 6.804
42.30 19.60 36.88 7.184
40.28 13.74 36.82 7.165
Average value 42.03 16.16 38.04 7.549
Legend: M – moisture content, A – ash content, Vm – volatile matter, Hu/(MJ/kg) – lower calorific value.
The data show that the sporogenic bacteria (51.98 %)
dominate the microflora, followed by the proteolytic
bacteria (11.49 %) and amilolytic (16.98 %). The results
of the analysis prove that the physiological groups listed
in Table 1 were present in the plant matter from which
the lignite was formed. Based on the results in Table 1
(according to which a single group may contain up to
28,855,000 bacteria), we can conclude that 1 t of lignite
contains about 28.8 · 1012 microorganisms, as was stated
by other authors as well (6).
According to Table 2, just 1 g of lignite with moi-
sture content contains 16 million mold cells (66.6 %).
The remaining 33.33 % are yeast cells.
3.2 Physical and chemical analysis
The above-mentioned lump of coal was used to
determine the content of moisture and ash, combustible
volatile matter as well as the lower calorific value of the
coal (Table 3).
The lower calorific value of lignite present in Table 4
was 8027 MJ.
CaO and SiO2 are the main components in the ash of
the coal from the Mirashi Coal Mine. The large
concentration of CaO shows that it originates from
limestone sedimentary rock. The large presence of SiO2
shows that the lignite originates from silica algae (silica
rich soil) (Table 5).
F. PLAKOLLI et al.: THE MICROFLORA AND PHYSICO-CHEMICAL PROPERTIES OF LIGNITE ...
274 Materiali in tehnologije / Materials and technology 44 (2010) 5, 271–275
Table 6: Content of biogens (C, N, S, H) in lignite from the Mirashi Coal Mine
Tabela 6: Vsebnost biogenov (C, N, S, H) v lignitu iz premogovnika Mirashi
First
measurement
Sample weight Unit Sample m(C)/m(N) ratio Content, w/%
40.4 mg lignite 43.06 w(N) = 1.096 w(C) = 47.19w(S) = 1.268 w(H) = 4.383
Second
measurement 40.0 mg lignite 45.55
w(N) = 1.032 w(C) = 47
w(S) =1.347 w(H) = 4.392
Third
measurement 40.8 mg lignite 49.23
w(N) = 1.055 w(C) = 51.92
w(S) = 1.381 w(H) = 4.405
Average value 45.94 w(N) = 1.061 w(C) = 48.73w(S) = 1.332 w(H) = 4.36
Table 7: Presence of biogens (C, N, S, H) in the microbial biomass isolated from lignite of the Mirashi Coal Mine
Tabela 7: Prisotnost biogenov (C, N, S, H) v biomasi mikrobov, izoliranih iz lignita iz premogovnika Mirashi
Measurement
Sample weight
m/mg
Sample
C/N ratio
w(C)/w(N)
Content, w/%
First measurement 84−95
Microbial biomass
w(C)/w(N) = 2.07
N:
C:
S:
H:
21. 34
44.36
0.77
7.18
Second measurement 84−95 w(C)/w(N) = 2.07
N:
C:
S:
H:
21.53
44.75
0.72
7.31
Third measurement 84−95 w(C)/w(N) = 2.08
N:
C:
S:
H:
21.42
44.68
0.70
7.24
w(AV)/w(N) = 21.43; w(C) = 44.59; w(S) = 0.73; w(H) = 7.24
Table 4: Content of components important for the caloric value of
lignite (Mirashi Coal Mine March, April and May 2008)
Tabela 4: Vsebnost komponent pomembnih za kalori~no vrednost
lignita (premogovnik Mirashi, marec, april in maj 2008)
No Analyzed parameters Content, w/%
1 Coke 34.06
2 Fixed carbon 18
3 Vaporizing matter 20.2
4 Volatile matter 39.64
5 Total sulfur 0.78
6 Other 7.52
Table 5: Chemical composition of ash of lignite from the Mirashi
Coal Mine (March, April and May 2008)
Tabela 5: Kemijska sestava pepela v lignitu iz premogovnika Mirashi
(marec, april in maj 2008)
Components Content, w/%
SiO2 27.48
Al2O3 11.82
Fe2O3 7.46
CaO 37.33
MgO 3.2
SO2 9.6
Other 3.11
3.3 The presence of biogens (C, N, S, H) in the
analyzed coal and in the microbial biomass isolated
from the same
Data in Table 6 show that carbon is the main
component in biogenic coal (48.73). The average value
of m(C)/m(N) ratio is 45.94.
The data in Table 7 confirm, once again, the
domination of carbon in the microbial biomass isolated
from the lignite of the Mirashi Coal Mine. The results
show that there is a resemblance in the constitution of
the biogens in the coal and those in the bacterial
biomass. It has been confirmed that during the Pliocene
the vegetation in the Kosovo basin consisted of 132
different types of plants with numerous sub-types,
grasses, aquatic plants, trees, etc. A number of authors
(11, 12, 13, 14, 15) have reconstructed the vegetation of
that period by comparing the fossil pollen grains and
spores from the Pliocene with those from the present
day. The same plants can nowadays be found in the area
of the Kosovo coal basin.
4 CONCLUSION
Based on the investigations performed, the following
conclusions can be drawn:
• The lignite from the coal mine in Mirash (Kastriot)
has a high density of microorganisms, i.e.,
28,855,000 microorganisms per gram or 28 · 1012
microorganisms per ton.
• Among the isolated microorganisms we have
determined the presence of bacteria, molds and yeasts
(gram positive, negative and variable). The most
common shapes were rods, spheres and spirals.
• Forty pure cultures were isolated (with typical repre-
sentatives).
• Due to it physical and chemical characteristics the
lignite from the Kosovo basin is of a better quality
than that of other basins in the region.
• The presence of biogens (C, N, H, S) in the coal and
the microbial biomass provides evidence of their
functional interaction during the process of coal
formation.
• The number of microorganisms in 1 g of lignite is
evidence that most of the microorganisms are
deposits of hopanoids, respectively carbon.
• The fossil pollen grains and spores found in different
horizontal and vertical layers of the Kosovo coal
basin give us a picture of the vegetation of the area
from which the lignite was formed.
5 REFERENCES
1 M. Berisha: Studij distribucije nekih elemenata u substance Kosov-
skog uglja. Doctor's Thesis. Prirodno matematiqki fakultet. PMF,
Prishtina, 1982, p. 7–9
2 Ll. A, Munro: Chemistry in engineering, Prentice Hall. (Inc), 1964
3 P. Nikoli}, D. Dimitrijevi}: Monografija savremena administracija.
Beograd, (3, 9, 13, 175) 1980
4 A Towle: Modern biology, Rinehard Winston, 1990, 221, 353–354
5 Z. i J. Aljan~i~: Ugalj kao izvoz energije, Nau~na knjiga, Beograd,
1951
6 L. Prescott, J. Harley, D. Klein: Microbiology. Fourth ed. McGraw-
Hill, 1999, 41–42
7 C. L. Brierly: Microbiologycal minig. Science American, 247 (1982)
2, 44–53
8 P. Atlas: Microorganisms and petroleum pollutants. BioScience, 28
(1978) 6, 378–391
9 D. Allen: Coal. Abana (Appalachian Blacksmiths), 2003
10 H. H. Lowny, F. Wily: Chemistry of coal utilization, 1963, 208
11 V. Nikoli}: Prou~avanje spora i polena iz pliocenskog lignita Kosov-
skog basena sa osvrtom na dana{nji izgled vegetacije Kosova.
Prirodnja~ki museum u Beogradu, 1966
12 M. Atanackovi}: Pliocen Kosovskog basena. Geolo{ko paleontolo{ka
studija. Zavod za geolo{ka istra`ivanja C. Gore. Knj. III. Titograd,
1959
13 E. Nagy: Polynoloische Untersuchung der am Fusse des Matra-
Gebirges galagenten ober panonischen, 1952
14 M. Jankovi}: Fitoekologija sa osnovama Fitocenologije i pregledom
tipova vegetacija na Zemlji. Nau~na knjiga, Beograd, 1963
15 I. Horvat: Sistematski odnosi termofilnih hrastova i borovih {uma
jugoisto~ne Evrope. Biolcai glasnik, 12 (1959), 1–2
16 N. Panti}: Paleobotanika, Nau~na knjiga, Beograd, 1960
17 M. Plakolli: Examination of phenolic degrading ability of bacterial
cultures isolated from phenolic waste water of the place drying of the
plant "Kosova" Acta Biol. Med. Exp., 10 (1985), 5–12
18 M. Lin, E. Premuzi~: Coal – purifying bacteria, Brookhaven National
Laboratory, New York, 2001
19 M. Rogoff, I. Wender: Bacterial oxidation of phenanthrene, Bureau
de Mines, U.S Department of Interior Region V Bruceton, Pennsyl-
vania, 1956
20 Ourisson et al: The microbial origin of fossil fuels. Sci. Am. 251
(1984) 2, 44–51
21 A. Martini: Green Car Congress Ecology. University of Massachu-
setts, 2008
22 D. Valentine: Bacteria keep undersea methane out of the atmosphere.
Santa Barbara, California USA, 2007
23 P. Luger et al: The crystal structure of Hop-17 (21)-en-3B-y1 acetate
of Pluchea pteropoda Hemsl. Vietnam. Cryst. Res. Technol. 35
(2002) 3, 355–362
F. PLAKOLLI et al.: THE MICROFLORA AND PHYSICO-CHEMICAL PROPERTIES OF LIGNITE ...
Materiali in tehnologije / Materials and technology 44 (2010) 5, 271–275 275

A. BYTYQI, E. SHERIFI: CADMIUM AND LEAD ACCUMULATION IN ALFALFA (MEDICAGO SATIVA L.) ...
CADMIUM AND LEAD ACCUMULATION IN ALFALFA
(MEDICAGO SATIVA L.) AND THEIR INFLUENCE ON
THE NUMBER OF STOMATA
AKUMULACIJA KADMIJA IN SVINCA V RASTLINI LUCERNA
(MEDICAGO SATIVA L.) IN NJUN VPLIV NA [TEVILO LISTNIH
POR
Arsim Bytyqi1, Enver Sherifi2
1[tore Steel Company, d. o. o. @elezarska cesta 3, [tore, Slovenia
2Department of Biology, Faculty of Natural Sciences, University of Prishtina, Mother Teresa Street, 10000 Pri{tina, Kosovo
arsim.bytyqi@imt.si
Prejem rokopisa – received: 2009-12-09; sprejem za objavo – accepted for publication: 2010-06-08
Accurate measurements of the heavy-metal contents in polluted areas are required to assess the potential ecological risks in
these areas. Chemical and biological indicators are of interest when they provide information about the concentration and
accumulation of heavy metals in the environment. This study was conducted in order to investigate heavy-metal accumulation
and the effect on alfalfa (Medicago sativa L.) at different distances from the road. The total content of heavy metals was
determined using atomic absorption spectrophotometry. The present results showed a variation that indicated that Pb and Cd had
the highest concentration in all the sampling areas near the road. According to the results of the present study, the concentration
of heavy metals has an influence on the number of stomata in both the adaxial and abaxial surfaces of the leaves, particularly in
locations where the concentrations of Pb and Cd were higher. The results showed that the plant demonstrated a physiological
response to the heavy-metal pollution, which suggests that roadside plants are indicators of heavy-metal accumulation and the
effect on the environment.
Key words: concentration of Pb and Cd, Medicago sativa L., adaxial stomata, abaxial stomata
Za oceno ekolo{ke obremenjenosti na obmo~jih, ki so onesna`ena s te`kimi kovinami, moramo izvajati natan~ne in drage
meritve, ~e ho~emo najti kemi~ne in biolo{ke pokazatelje, ki ka`ejo na kopi~enje te`kih kovin v okolju – organizmih. Naredili
smo raziskavo kopi~enja te`kih kovin in njihovih posledic na rastlino lucerna (Medicago sativa L.) na razli~nih oddaljenostih od
ceste. Skupna vsebnost te`kih kovin je bila dolo~ena z atomsko absorpcijsko spektrofotometrijo. Najvi{je koncentracije te`kih
kovin Pb in Cd so bile dose`ene v bli`ini ceste. Prav tako smo ugotovili korelacijo med koncentracijo te`kih kovin v rastlini in
{tevilom por na obeh straneh listov. Vi{ja koncentracija te`kih kovin v rastlini je povezana z ve~jim {tevilom listnih por.
Rezultati so pokazali, da se rastline fiziolo{ko odzovejo na prisotnost te`kih kovin, zato je stanje teh rastlin v okolju lahko
pokazatelj onesna`enja okolja s te`kimi kovinami.
Klju~ne besede: koncentracija Pb in Cd, Medicago sativa L.,, zgornja pora, spodnja pora
1 INTRODUCTION
The contribution of cars and other road transport to
the global emission of atmospheric pollutants is
increasing. In parallel with the rapid growth in
industrialization, environmental pollution is increasing,
with heavy metals like lead and cadmium constituting a
significant part. These elements are released into the
environment as a result of a wide range of industrial
activities. The contamination of heavy metals in the
environment is of major concern because of their toxicity
and the threat to human life and the environment.16
Heavy metals are considered to be the main sources of
pollution in the environment, since they have a
significant effect on its ecological quality. Some heavy
metals at low doses are essential micronutrients for
plants, but in higher doses they may cause metabolic
disorders and growth inhibition for most of the plant
species.12
In monitoring urban pollution there is a need to
consider the materials that cause the occurrence of
pollutants. Among toxic metals, lead and cadmium
appear to be the most dangerous to the environment.11
Lead and cadmium cause toxicity and environmental
impact, although this toxicity is entirely dependent on
the concentration and environmental parameters.
Investigations concerning the concentration of lead
and cadmium in alfalfa (Medicago Sativa L.) at different
distances from the road and their influence on some
morph-anatomic parameters are presented in this study.
2 MATERIAL AND METHODS
Three sites were selected for the collection of 60
plants of Medicago sativa along the Lipjan–Prizren road
(Figure 1).
1. Location I Lipjan
2. Location II Shtime
3. Location III Suharek
The plant samples were cut off at 2 cm or 3 cm above
the soil and stored in plastic bags. In every location the
plants were collected at two different distances from the
Materiali in tehnologije / Materials and technology 44 (2010) 5, 277–282 277
UDK 620.18:546.48:669.4:633.31 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 44(5)277(2010)
road where lead and cadmium were determined in the
tissue extracts of all the specimens.
All the samples were dried in a thermostat at a
temperature of 105 °C for three hours. The digestion of
the plant samples was carried out using an acid solution
with a 20 : 2 : 1 ratio of nitric acid (HNO3), perchloric
acid (HClO4), and sulfuric acid (H2SO4). A portion of 3 g
of each sample was weighed and transferred into a 250
mL beaker. The samples were heated to boiling until the
white color appeared. Then the samples were acid
washed, filtered into the (100 ml) flask, which was added
up to the mark with distilled water. The filtered samples
were then analyzed for heavy-metal concentration in
plant tissues using Atomic Absorption Spectrophoto-
meter.
The stomata number was measured in microscopic
fields of leaf impressions taken from the middle parts of
leaves. Leaf epidermis imprints of the adaxial and
abaxial leaf surfaces were then removed using
transparent sticky tape and placed on a microscopic
slide. The stomata number was expressed as the number
per microscopic field at a magnification of (10X40). Ten
fields were assessed in every specimen and the variable
was analyzed using Excel computer software.
3 RESULTS AND DISCUSSION
In Table 1 the concentrations of heavy metals in
three different localities are presented. Based on the
results related to location 1 (Lipjan), the greatest
quantity of cadmium and lead was established in the
specimens taken near the road where the average content
of cadmium and lead was 1.38 μg/g and 0.814 μg/g,
respectively. Research data revealed that recently this
highway has been an intensive source of pollution with
heavy metals. Heavy-metal accumulation in plant tissues
(leaves, stem) was due to the foliar absorption from the
surroundings (vehicle sources). According to the results,
lead exhibited high levels of contamination closer to the
highway. The smallest content of lead (0.21 μg/g) was
noted in specimens taken at a distance of 10 m from the
highway. The quantity of cadmium in this location was
higher in specimens taken near the highway (1.38 μg/g),
while the smallest concentration of the cadmium was
characteristic for specimens taken at a distance of 10 m
from the highway (0.61 μg/g). The general decrease in
the concentration of metals with distance from the high-
way indicates their relation to traffic. This is attributed
mainly to the aerial deposition of metal particulates from
motor vehicles.14 The results of the investigation show
that the concentration of cadmium in the plant samples
varied between 1.38 μg/g and 0.61 μg/g. The accumu-
lation of the selected metals varied greatly among the
plant species and the uptake of an element by a plant is
primarily dependent on the plant species, its inherent
controls and the soil quality.10
The alfalfa plant has a high potential to uptake toxic
metals like cadmium and lead.9 Alfalfa has the ability to
accumulate concentrations of heavy metals well above
the tolerance levels of other plants, which may be due to
the presence of specialized chemical functional groups
responsible for metal tolerance and accumulation.1
Various studies have shown the heavy contamination of
roadside vegetation with lead. Heavy metals could be
absorbed in investigated samples by clay minerals, Fe
oxides and/or organic matter. They could also be
incorporated into the structures of carbonates.13
Based on the results of locality II (Shtime), it is
evident that the content of metals grows as the distance
between the place of the specimen collection and the
road with heavy traffic decreases. The highest content of
cadmium and lead in this locality was in specimens taken
near the highway (0.29 μg/g, 1.47 μg/g). The concen-
tration of both metals in this location for specimens
taken at a distance of 10 m from the highway varied in
the range (0.24 μg/g to 1.05 μg/g). These high concen-
trations may be due to the aerial deposition of heavy
metals over a long period of time. A significant correla-
tion was noted between the number of passing petrol
vehicles and the lead concentration in the particulate
deposits collected from different designated sites (lead in
deposits 14.4 μg/g, lead in leaves 1.78 μg/g).4
According to the results in location III (Suharek), as
distinguished from the first two locations, the highest
content of cadmium was in the specimens taken at a
distance of 10 m from the highway (2.29 μg/g). The
lowest content of cadmium is observed in specimens
taken near the highway (1.52 μg/g) Table 1. Based on
the results obtained, we can conclude that the quantity of
lead at this location, as in the two other locations, was
greater near the highway (0.79 μg/g), whereas the lowest
quantity was observed in specimens taken at a 10m
distance from the road (0.16 μg/g) (Table 2). Positive
and negative correlations are found in the metal
concentration at different distances from the highway.
Comparatively speaking, almost all the samples collected
A. BYTYQI, E. SHERIFI: CADMIUM AND LEAD ACCUMULATION IN ALFALFA (MEDICAGO SATIVA L.) ...
278 Materiali in tehnologije / Materials and technology 44 (2010) 5, 277–282
Figure 1: Location sketch map of the investigated area.
Slika 1: Lokacijska skica zemljevida podro~ja raziskav
from site A, which was directly at the border of the road,
showed a higher lead concentration than the site-B
samples. The average lead concentration in C. sativa in
the study area was 3.6 mg kg–1, whereas the average
concentration of this metal at the control site was 0.94
mg kg–1.2
3.1 Lead and cadmium affect the number of stomata in
alfalfa (Medicago sativa L.)
A number of stomata were examined on the abaxial
and adaxial leaf surfaces. All the specimens were
gathered at the three localities marked on the map. Based
on the results (related to the effect of these heavy metals
on the number of stomata) it is observed that at location I
in three researched leaves (lower, medium, upper) the
largest number of stomata per 1 mm2 on the surfaces of
the leaves was found in plants examined near the road
(156.5 mm2, 165.7 mm2, 197.8 mm2). The difference
between the specimens in terms of stomata number on
both the abaxial and adaxial surfaces of the leaves was
also significant (Table 3). In all the specimens examined
at different distances from the road the largest number of
stomata per 1 mm2 was on the upper leaf (Table 4). In
the same location the smallest number of stomata was
found in specimens taken at a distance of 10 m from the
road (116.4 mm2, 143.4 mm2, 159.6 mm2). It was
reported that the lead concentration in leaves of Soybean
A. BYTYQI, E. SHERIFI: CADMIUM AND LEAD ACCUMULATION IN ALFALFA (MEDICAGO SATIVA L.) ...
Materiali in tehnologije / Materials and technology 44 (2010) 5, 277–282 279
Table 1: Cadmium accumulation (μg/g) in alfalfa (Medicago sativa L.) at different distances from the road
Tabela 1: Akumulacija Cd (v μg/g) v rastlini lucerna (Medicago sativa L.) pri razli~nih oddaljenostih od ceste
Localities and
individuals
examined
1 2 3 4 5 6 7 8 9 10 X S SX V
Lsd
0.05
Lsd
0.01
P1. 1 m 0.6 0.59 0.28 0.33 0.76 4.52 0.58 2.48 0.47 3.15 1.38 1.47 0.46 1.06 0.16 0.23
P2. 1 m 0.56 0.36 0.29 3.68 0.26 3.05 0.26 3.3 2.69 0.23 1.47 1.49 0.47 1.01 0.36 0.5
P3. 1 m 3.41 0.79 0.26 0.78 0.22 1.14 2.81 0.42 2.94 2.42 1.52 1.23 0.39 0.81 0.21 0.3
P1. 10 m 3.33 0.22 0.39 0.25 0.19 0.26 0.51 0.25 0.35 0.35 0.61 0.9 0.3 1.5 0.16 0.23
P2. 10 m 1.05 0.26 2.83 0.22 0.22 2.69 0.45 0.19 0.51 0.38 2.74 1.1 0.3 1.1 0.36 0.5
P3. 10 m 0.42 0.19 2.87 4.9 2.82 2.74 5.21 0.19 0.29 3.27 2.29 1.9 0.6 0.8 0.21 0.3
Table 2: Lead accumulation (μg/g) in alfalfa (Medicago sativa L.) at different distances from the road
Tabela 2: Akumulacija Pb (v μg/g) v rastlini lucerna (Medicago sativa L.) pri razli~nih oddaljenostih od ceste
Localities and
individuals
examined
1 2 3 4 5 6 7 8 9 10 X S SX V
Lsd
0.05
Lsd
0.01
P1. 1 m 1.05 0.26 0.75 0.25 0.51 1.78 0.73 0.23 0.92 1.61 0.81 0.54 0.17 0.67 0.58 0.08
P2. 1 m 0.28 0.29 0.26 0.09 0.72 0.39 0.23 0.03 0.09 0.49 0.29 0.2 0.06 0.7 0.003 0.004
P3. 1 m 0.66 0.82 0.39 0.84 0.61 0.95 1.02 0.58 1.61 0.43 0.79 0.35 0.11 0.44 0.02 0.03
P1. 10 m 0.32 0.32 0.13 0.19 0.23 0.26 0.03 0.12 0.09 0.45 0.21 0.1 0.04 0.58 0.58 0.08
P2. 10 m 0.45 0.19 0.29 0.41 0.16 0.12 0.13 0.16 0.25 0.22 0.24 0.1 0.03 0.47 0.003 0.004
P3. 10 m 0.22 0.09 0.16 0.43 0.09 0.03 0.06 0.13 0.19 0.23 0.16 0.6 0.03 0.68 0.02 0.03
X- Arithmetic mean, S-Standard deviation, SX- Standard error, V-Coefficient of variability, Lsd- Least Significant Difference
Table 3: Number of stomata in the abaxial and adaxial surfaces per 1 mm2 in alfalfa (Medicago sativa L.) for locality I near the road
Tabela 3: [tevilo por na obeh straneh listov (zgornja in spodnja) na 1 mm2 pri rastlini lucerna (Medicago sativa L.) v bli`ini ceste
Lower leaf Medium leaf Upper leaf
Upper surface Lower surface Upper surface Lower surface Upper surface Lower surface
No. X V X V X V X V X V X V
1 142.8 0.26 111.9 0.25 170.8 0.23 88.3 0.36 218 0.31 139.9 0.24
2 102.5 0.24 86.9 0.32 44.1 0.39 86.9 0.25 145.8 3 122.2 0.25
3 85.4 0.24 78 0.3 86.9 0.36 153 0.2 54.5 0.35 107.5 0.32
4 98.3 0.37 79.5 0.24 112.2 0.3 91.3 0.37 88.7 0.39 82.4 0.33
5 83.9 0.2 91.3 0.26 88.3 0.23 95.7 0.37 76.5 0.27 129.6 0.29
6 79.6 0.45 98.6 0.44 58.92 0.39 98.6 0.28 84.9 0.27 72.1 0.27
7 67.7 0.2 82.4 0.22 63.3 0.29 57.4 0.18 70.7 0.36 66.2 0.18
8 234.2 0.29 98.6 0.33 64.8 0.3 51.5 0.2 252.2 0.26 67.7 0.38
9 109 0.27 94.2 0.43 91.3 0.27 82.4 0.25 69.2 0.52 107.5 0.54
10 200.1 0.31 69.2 0.4 116.3 0.26 98.6 0.29 141.4 0.23 57.4 0.35
X 120.3 89 114.5 90.3 122.2 95.2
Lsd 0.05 183.2 129 17.9 80.3 204.9 43.9
Lsd 0.01 257.1 181.1 25.1 112.8 287.6 61.1
A. BYTYQI, E. SHERIFI: CADMIUM AND LEAD ACCUMULATION IN ALFALFA (MEDICAGO SATIVA L.) ...
280 Materiali in tehnologije / Materials and technology 44 (2010) 5, 277–282
Table 4: Number of stomata in abaxial and adaxial surfaces per 1 mm2 in alfalfa (Medicago sativa L.) for locality I 10 m distance from the road
Tabela 4: [tevilo por na obeh straneh listov (zgornja in spodnja) na 1 mm2 pri rastlini lucerna (Medicago sativa L.) na oddaljenosti 10 m od ceste
Lower leaf Medium leaf Upper leaf
Upper surface Lower surface Upper surface Lower surface Upper surface Lower surface
No. X V X V X V X V X V X V
1 76.5 0.15 82.4 0.42 147.3 0.2 102 0.18 153.1 0.36 79.5 0.42
2 88.3 0.39 107.5 0.35 89.8 0.35 103 0.34 170.8 0.09 103.1 0.27
3 126.6 0.22 98.6 0.29 111.9 0.19 109 0.18 179.7 0.12 131 0.23
4 79.5 0.23 67.7 0.26 178.2 0.27 121 0.39 154.6 0.36 107.5 0.34
5 122.2 0.23 110.4 0.26 181.1 0.14 131 0.31 148.7 0.23 111.9 0.29
6 98.6 0.26 107.5 0.24 162 0.28 119 0.25 188.5 0.17 151.7 0.4
7 172.3 0.27 148.7 0.38 144.3 0.36 118 0.17 107.5 0.32 88.3 0.19
08 86.9 0.28 107.5 0.28 147.3 0.23 121 0.24 100 0.37 75.1 0.35
9 136.9 0.38 73.6 0.24 139.9 0.29 137 0.24 160.5 0.21 119.3 0.28
10 176.7 0.27 178.2 0.14 132.5 0.36 97.4 0.27 232.7 0.37 173.8 0.41
X 116.4 108.2 143.4 115.8 159.6 114.1
Lsd 0.05 183.2 67.7 213.4 22.3 175.4 15.5
Lsd 0.01 257.1 95.1 299.5 31.3 146.2 21.8
X-Arithmetic mean, V-Coefficient of variability, Lsd- Least Significant Difference.
Table 5: Number of stomata in abaxial and adaxial surfaces per 1 mm2 in alfalfa (Medicago sativa L.) for locality II near the road
Tabela 5: [tevilo por na obeh straneh listov (zgornja in spodnja) na 1 mm2 pri rastlini lucerna (Medicago sativa L.) v bli`ini ceste
Lower leaf Medium leaf Upper leaf
Upper surface Lower surface Upper surface Lower surface Upper surface Lower surface
No. X V X V X V X V X V X V
1 190 0.26 100.1 0.31 83.9 0.5 60.3 0.17 136 0.5 117.8 0.42
2 219.4 0.16 145.8 0.29 173.8 0.33 191.4 0.23 307.8 0.1 145.8 0.24
3 109 0.36 89.8 0.29 95.7 0.31 60.3 0.4 331.4 0.1 169.3 0.34
4 60.3 0.38 63.3 0.51 122.2 0.18 95.7 0.44 268 0.25 132.5 0.25
5 166.4 0.37 119.3 0.47 114.8 0.28 54.5 0.22 164.9 0.32 120.7 0.47
6 76.5 0.26 45.6 0.31 132.5 0.2 97.2 0.21 85.4 0.43 85.4 0.46
7 82.4 0.25 89.8 0.28 79.5 0.29 89.8 0.28 136.9 0.27 66.2 0.24
8 101.6 0.3 73.6 0.29 175.2 0.18 85.4 0.35 284.2 0.23 114.8 0.45
9 182.6 0.39 104.5 0.3 184.1 0.12 103.1 0.39 142.8 0.27 106 0.34
10 63.3 0.34 54.5 0.28 89.8 0.33 67.7 0.47 94.2 0.32 88.3 0.38
X 125.1 88.6 125.1 90.5 195.1 114.6
Lsd 0.05 46.5 45.8 27.5 4.6 93.8 35.3
Lsd 0.01 65.2 64.2 38.6 6.45 131.6 49.5
X-Arithmetic mean, V-Coefficient of variability, Lsd- Least Significant Difference.
Table 6: Number of stomata in abaxial and adaxial surfaces per 1 mm2 in alfalfa (Medicago sativa L.) for locality II 10 m distance from the road
Tabela 6: [tevilo por na obeh straneh listov (zgornja in spodnja) na 1 mm2 pri rastlini lucerna (Medicago sativa L.) na oddaljenosti 10 m od ceste
Lower leaf Medium leaf Upper leaf
Upper surface Lower surface Upper surface Lower surface Upper surface Lower surface
No. X V X V X V X V X V X V
1 160.8 0.23 109 0.17 104.5 0.31 73.6 0.33 190 0.27 111.9 0.37
2 73.6 0.24 89.7 0.33 169.3 0.51 45.6 0.42 172.3 0.21 60.3 0.28
3 69.2 0.49 51.5 0.31 150.2 0.4 53 0.35 116.3 0.33 79.5 0.35
4 117.8 0.38 65.4 0.24 97.2 0.4 77.9 0.49 97.2 0.25 67.9 0.22
5 86.9 0.48 60.3 0.4 110.4 0.41 67.7 0.34 182.6 0.35 94.2 0.43
6 113.4 0.21 57.4 0.22 128.1 0.39 54.5 0.27 86.9 0.25 53 0.27
7 72.1 0.31 45.6 0.4 79.5 0.29 50 0.41 119.3 0.6 51.5 0.39
8 67.7 0.21 170.8 0.23 66.2 0.4 57.4 0.42 64.8 0.29 160.5 0.31
9 147.3 0.45 55.9 0.45 88.3 0.36 86.3 0.46 76.5 0.36 53 0.28
10 75.1 0.46 82.4 0.41 151.7 0.3 82.4 0.33 116.3 0.38 60.3 0.33
X 120.3 78.8 89.6 64.8 120.1 79.2
Lsd 0.05 46.5 45.8 27.5 4.6 93.8 35.3
Lsd 0.01 65.2 64.2 38.6 6.45 131.6 49.5
X-Arithmetic mean, V-Coefficient of variability, Lsd- Least Significant Difference.
(Glycine Max) increased the number of stomata per unit
area.5 Metals can be transported via an apoplastic system
and immobilized in the cell walls. Toxic metals become
a real threat to plants, mainly when they reach the
cytosol of the cell. The data clearly indicate that even
very low levels of heavy metals in the soil may have an
influence on plant growth.3
The number of stomata in the leaf epidermis of
Cucumis sativa was increased after cultivation at various
Pb rates (10, 20, 40) mg dm–3 (1297.6 mm2 1714.8 mm2,
1979.5 mm2). After the treatment with lead the cucumber
leaves exhibited a great number of stomata per unit area.6
Positive and negative correlations were noticed among
the metal concentrations and the number of stomata on
the upper and lower surfaces of the leaves. Based on the
results at location II (Table 5, 6) it was observed that
both the adaxial and abaxial surfaces of the leaf had a
significantly lower stomata number in individuals
examined at a distance of 10 m from the road. An
increase in the number of stomata per unit area with a
simultaneous reduction in the size of the guard cells
appeared due to a self-defense system, which is
developed in plants under stress conditions and provided
the support to the plant for their survival in the
contaminated environment.15
The stomata number on the leaf for both the adaxial
and abaxial leaf surfaces is shown in Figure 2 and 3.
With the adaxial leaf surface of all individuals examined
at locality III the largest number of stomata per 1 mm2
was found in the upper leaf surface of the specimens
gathered from near the road, while the smallest number
was in the lower leaf surfaces. A significantly higher
stomata number was found on the upper leaf surfaces
(95.2 mm2) compared with two other leaves (medium
and lower). The experimental data confirmed the
tendency of the increase in the stomata number with
industrial pollution at the site II (213.5 mm2) compared
with the control site (205.4 mm2), and again showed
statistically insignificant differences between the control
plants and those from the site with high traffic.8 From
this it can be concluded that heavy metals at millimolar
concentrations inhibit stomata movements. At higher
concentrations, they interfere with metabolic processes
and inhibit growth, sometimes leading to plant death.7
4 CONCLUSIONS
At three different locations, 60 plant samples of
Medicago sativa were collected at different distances
from the road and the concentration of Pb, Cd and the
number of stomata in the adaxial and abaxial leaf
surfaces were determined.
The analysis of the statistical and comparative
variance of all examined parameters, the LSD and the
coefficient of correlation between the distances from the
road were deduced. The greatest content of heavy metals
(Pb, Cd) in all localities examined was found in the
specimens taken near the road. The lowest quantity of
concentration of these metals was found in specimens at
a distance of 10 m from the road, with the exception of
location III, where the content of Cd was higher at a
distance from the road. The concentration of metals
decreased with increasing distances from the highway
and lead seems to be the most adapted tracer of highway
contamination.
The largest number of stomata per 1 mm2 at locality I
was found in the lower leaf (197.8 mm2). Also at
localities II and III, the number of stomata for the
medium and lower leaf was lower than for the upper leaf.
This study has shown that the street plants are relatively
contaminated with heavy metals. Finally, the results
obtained in this research work are a significant reference
value for future studies of these areas and other regions
as well.
5 REFERENCES
1 A. Sekara, M. Poniedzialek, J. Ciura, E. Jedrsezezyk. Zinc and coper
accumulation and distribution in the tissues of the nine crops:
implication in phytoremediation. Polish Journal of Environmental
Studies 14, (2005) 6, 829–835
A. BYTYQI, E. SHERIFI: CADMIUM AND LEAD ACCUMULATION IN ALFALFA (MEDICAGO SATIVA L.) ...
Materiali in tehnologije / Materials and technology 44 (2010) 5, 277–282 281
Figure 3: Number of stomata in adaxial and abaxial surfaces of leaves
at location III 10 m from the road
Slika 3: [tevilo por na obeh straneh listov (zgornja in spodnja) na
oddaljenosti 10 m od ceste na 1 mm2
Figure 2: Number of stomata in abaxial and adaxial surfaces of leaves
at location III near the road
Slika 2: [tevilo por na obeh straneh listov (zgornja in spodnja) v
bli`ini ceste na 1 mm2
2 Huma Pirzada, Audil Rashid. Multivariate analysis of selected
roadside plants (Dalbergia sissoo, and Canabis sativa) for lead
pollution monitoring. Pak. J. Bot. 41 (2009) 4, 1729–1736
3 Peter Ryser, Wendy R. Sauder. Effects of heavy metal contaminated
soil on growth phenology and boimass turnover of Hieracium
piloselloides. Environmental Pollution. 140 (2006), 1, 52–61
4 Aydinalp, C., Marinova, S. Lead in particulate deposits and in leaves
of roadside plants. Polish Journal of Environmental Studies, 13
(2004) 2, 233–235
5 Elbieta Weryszko-Chmielewska, Miroslava Chwil. Lead-induced
histological and ultrastructural changes in the leaves of soybean
(Glycine Max). Soil Science and Plant Nutrition., 51 (2004) 2,
203–212
6 Miroslawa Chwil. The influence of lead on structure of Cucumis
sativus L. leaves. Folia Horticulturae, 17 (2005) 2, 11–22
7 H. M. Yang, X. Y. Zhang, G. X. Wang. Effects of heavy metals on
stomatal movements in broad bean leaves. Russian journal of plant
physiology. 51 (2004) 4, 464–468
8 Ivanka Dimitrova, Lilyana Yurukova. Bioindication of anthropogenic
pollution with Plantago lanceolata (Plantaginaceae): metal accumu-
lation, morphological and stomatal leaf characteristics. Phytologia
Balcanica 11 (2005) 1, 86–89
9 Anamika Singh, Susan Eapen, M. H. Fulekar. Potential of Medicago
sativa for uptake of cadmium from contaminated environment. Rom.
Biotechnol. Lett., 14 (2009) 1, 4164–4169
10 Riffat Nasem Malik, Syed Zahor, Ishfaq Nazir. Heavy Metal
contamination and accumulation in soil and wild plant species from
industrial area of Islamabad, Pakistan. Pak. J. Bot., 42 (2010) 1,
291–301
11 Shinggu, D. Y., Ogugbuaja, V. O., Barminas, J. T., Toma, I. Analysis
of street dust for heavy metal pollutants in Mubi, Adamawa State,
Nigeria. International Journal of Physical Sciences 2 (2007) 11,
290–293
12 J. R. Peralta, L. Gardea-Torresdey, K. J. Tiemann, Gómez S., Arteaga
E., Rascon, J. G. Parsons. Study of the effects of heavy metals on
seed germination and plant growth on alfalfaplant (Medicago sativa)
grown in solid media. Environmental Science and Engineering. 15
(2000) 4, 135–140
13 Ale{ Plesni~ar, Nina Zupan~i~. Heavy Metal contamination of
roadside soil along Ljubljana-Obre`je highway. Materials and
geoenvironment. 52 (2005) 2, 403–418
14 C. L. Ndiokwere. A study of heavy metal pollution from motor
vehicle emissions and its effect on roadside soil, vegetation and crops
in Nigeria. Environmental pollution. 7 (2003) 1, 35–42
15 Rafia Azmat, Saba Haider, Hajra Nasreen. A Viable Alternative
mechanism in adapting the Plants to heavy metal Environment. Pak.
J. Bot., 41 (2009) 6, 2729–2738
16 Lena Q. Ma., Gade N. Rao. Chemical fractionation of cadmium,
copper, nickel and zinc in contaminated soils. Journal of Environ-
mental Quality. 26 (1997) 1, 259–264
A. BYTYQI, E. SHERIFI: CADMIUM AND LEAD ACCUMULATION IN ALFALFA (MEDICAGO SATIVA L.) ...
282 Materiali in tehnologije / Materials and technology 44 (2010) 5, 277–282
Y. KHARLAMOV et al.: THE SELECTION AND DEVELOPMENT OF TRIBOLOGICAL COATINGS
THE SELECTION AND DEVELOPMENT OF
TRIBOLOGICAL COATINGS
IZBIRA IN RAZVOJ TRIBOLO[KIH PREVLEK
Yuriy Kharlamov1, Vladimir Dal1, Ilija Mamuzi}2, Larysa Lopata3, G. S. Pisarenko3
1East Ukraine National University, Faculty of Applied Mechanics and Material Science, Kvartal Molodesnij, Lugansk 91034, Ukraine
2Metallurgy Faculty of the University of Zagreb, Aleja narodnih heroja 3, 44103 Sisak, Croatia
3Institute for Problems of Strength of the National Academy of Sciences of Ukraine, Kiev, Ukraine
yuriy.kharlamov@gmail.com
Prejem rokopisa – received: 2010-02-01; sprejem za objavo – accepted for publication: 2010-03-10
The main objectives of this study are the strategy and methodology for selecting the optimal surface treatment for a given
tribological application. The classification of the main methods of the coating processes and the surface modification is given
and the scheme of the development of the operation technology of the surface treatment and coating deposition is proposed. The
main initial data are: the structure of tribological system (TrS); the individual properties of the TrS parts; the lubricant
properties; the method of lubrication of the TrS parts; the properties of the surrounding environment; the external influences on
the TrS; the technological limitations on the TrS parts treatment; and the managerial and economic limitations. The selection of
the surface technology method includes the following steps: the preliminary analysis of the TrS part interaction; the
development of models of friction and the wear process of the TrS parts; the choice of rational values of the parameters of the
surface layers of the TrS parts; the choice of the rational composition and the structure parameters of the surface layers of the
TrS parts; the choice of a rational technological route and the methods of the surface treatment of the TrS parts; the
experimental examination of surface-strengthened materials and the TrS and the correction of the surface-treatment technology.
Key words: coatings, friction pair solid surfaces contact, surface engineering, tribological system
Glavni cilj tega ~lanka sta strategija in metodologija optimalne izbire metode za utrditev povr{ine za neko tribolo{ko uporabo.
Dana je razvrstitev glavnih metod in procesov obdelave povr{ine in nanosa prevlek ter predlo`ena je shema razvoja tehnologije
obdelave povr{ine in nanosa prevlek. Najbolj pomembni za~etni podatki: struktura tribolo{kega sistema (TrS); lastnosti
posami~nih delov TrS; lastnosti maziv za TrS; lastnosti okolja; zunanji vplivi na TrS; tehnolo{ke omejitve obdelave TrS-delov;
poslovne in ekonomske omejitve. Metoda izbire povr{inske tehnologije ima naslednje korake: izbira racionalnih parametrov za
povr{inske plasti TrS-delov; izbira racionalnih parametrov sestave in strukture povr{inskih plasti TrS-delov, izbira racionalne
tehnologije za povr{insko obdelavo TrS-delov; eksperimentalna preiskava povr{insko utrjenih plasti TrS-delov in popravki
tehnologije za povr{insko utrditev.
Klju~ne besede: prevleke, torni par kontakta trdih povr{in, utrditev povr{ine, tribolo{ki sistem
1 INTRODUCTION
The use of surface engineering methods in tribolo-
gical applications is growing and will continue to grow,
as evidenced by a literature survey 1–9. A surface
treatment in the form of coatings and films and the
modification of surface layers can offer certain economic
and technical advantages over the use of materials
without the surface-strengthening treatment. Their main
advantage is that the strengthened surface layers allow
the base material of tribological system (TrS) parts to be
optimized for strength purposes, while the surface layer
is optimized for reducing the wear and increasing the
corrosion resistance, promoting film lubrication,
enhancing lubricant effectiveness, the modification of
surface function, etc. Furthermore, replacing the surface
layer by coating deposition during repair may be more
cost effective than the manufacture of a new TrS part.
But the principal disadvantage in using coatings
concerns the possibility of the separation from the base
material of TrS part during use. While the discussions
that follow emphasize the considerations important in the
selection of tribological surface treatment, it should be
noted that other alternatives might exist for any
particular problem. This could involve, for example, use
of a more effective lubricant, or a redesign of the
tribological system’s elements, the use of more effective
methods of lubrication, the development of new or the
use of improved materials, etc.
2 CLASSIFICATION OF
SURFACE-ENGINEERING METHODS
Many technological methods and processes of
surface engineering are available for the modification of
surface characteristics. Tribological surface-treatment
methods are used for different purposes: 1. Replacing
surfaces with coatings and the deposition of films; 2.
Surface modification (surface alloying and/or micro-
structure is altered); and 3. Combination of methods for
coating deposition and surface modification. A wide
variety of surface-modification methods are available for
tribological purposes. The main categories are: 1. Modi-
fication of surface layers in the process of shape
processing; 2. Heat (volume) treatment; 3. Surface heat
treatment; 4. Treatment by surface plastic deformation;
5. Surface thermomechanical treatment; 6. Surface
Materiali in tehnologije / Materials and technology 44 (2010) 5, 283–287 283
UDK 620.179.11:621.794:621.8 ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 44(5)283(2010)
alloying; 7. Chemical and thermochemical treatment,
including microarc oxidization; 8. Ion implantation; 9.
Formation of a surface-layer composite structure by the
introduction of hardening phase particles; 10. Others and
hybrid methods.
Resurfacing essentially replaces the surface layer of a
base material (or previously deposited coating) with
another having more desirable friction and wear proper-
ties. Usually, the new surface is harder than the surface
replaced, but not always. A wide variety of coating
compositions is available. Each of these compositions
can be applied by a variety of processes. The main cate-
gories of the coating-deposition processes are: Electro-
plating; Electrophorus; Electroless plating; Welding;
Thermal spraying; Physical Vapour Deposition;
Chemical Vapor Deposition (CVD); Immersion on melt;
Electro-spark alloying; Electro-magnetic alloying;
Bonding of powder layers; Solid phase plating (bonding
of plates); Painting; and Continuous deposition of films
in process of friction (rotaprint, from environment, etc.).
Some of these application processes are very simple
and inexpensive, such as painting. Others are very com-
plex, either requiring vacuum processing or requiring a
series of treatments and pre-treatment. Some of them can
be applied in the field, while others can only be applied
at particular facilities. There is no shortage of tribolo-
gical coatings and surface layers to try for almost any
need. The primary problem that exists is knowing which
surface treatment to select for any given application. A
related problem is that surface treatment developers
often do not know where their coatings should be used or
what coating or kind of surface modification to develop
to meet a particular need. There is a need for a strategy
or methodology for selecting a surface-layer composition
and structure, and the methods for obtaining a given
tribological application. In this paper such a strategy is
proposed and elements of that strategy are discussed.
3 SOLID SURFACE CHARACTERISTICS
The difficulties of the selection of surface-treatment
methods are connected with a very large number of
parametric variables of solid surface quality, which could
be described by the following ensemble of characteristics
K  Gex  Gin  Sc  Ss  Phc  Phs  Chc  Chs
 Dfc  Dfs  Stc  Sts  Pmpc  Pmps  Ptpc 
Ptps  ...
where Gex is an ensemble of characteristics that are
characterized by the geometry parameters of the
external surface of the strengthened layer and in its turn
could be characterized by the ensemble Gex  Gexw 
Gexm, where Gexw and Gexm are ensembles of the para-
meters of waviness and roughness of the surface,
respectively; Gin is the ensemble of parameters that are
characterized by the geometry parameters of the internal
surface of the strengthened layer (or coating) and in its
turn could be characterized by the ensemble Gix  Gixw
 Gixm; Sc and Ss are the ensembles of the parameters
that are characterized by the geometry configuration
inaccuracy of the surface of the strengthened layer (or
coating) and its interface with main material, respec-
tively; Phc and Phs are the ensembles of parameters that
can be characterized; Chc and Chs are the chemical
compositions; Stc and Sts are the ensembles of
parameters that are characterized by the structure; Dfc
and Dfs are the ensembles of parameters that are
characterized by the deformation; Pmpc and Pmps are
the ensembles of the parameters that are characterized
by the physico-mechanical properties; Ptpc and Ptps are
the ensembles of the parameters that are characterized
by the thermophysical properties; the indices c and s are
for the strengthened layer (or coating) and the structure
of near-surface layer of the main material and/or the
transition zone, respectively.
In searching for the optimal solution of a particular
tribological problem it is necessary to consider the
ensemble of parameters that is characterized by the
assembly and friction surface working conditions
TrS  E  Ce  Le  F  Me  We
where E is the ensemble of the characteristics of the TrS
workpieces; Le is the ensemble of the characteristics of
the linking between workpieces; F is the ensemble of
the kind of friction and its main characteristics; Me is
the ensemble of the mutual shifting of the TrS work-
pieces; We is the ensemble of the wear characteristics of
the TrS.
For dataware of the choice of the surface-treatment
method it is necessary to elaborate the ensemble of the
parametric variables of the solid surface quality that
influences on the wear-resistance at different kinds of
wear and control may affect the wear resistance
QPSSi  Gexi  Gini  Sci  Ssi  Phci  Phsi  Chci
 Chsi  Dfci  Dfsi  Stci  Stsi  Pmpci  Pmpsi 
Ptpci  Ptpsi  ...
where the index mark "i" is given for a certain kind of
wear. Furthermore, it is necessary to elaborate the
ensemble of parametric variables of the solid surface
quality that is possible to control for each method of
surface treatment and to determine the limits of this
control.
QPSSj  Gexj  Ginj  Scj  Ssj  Phcj  Phsj  Chcj
 Chsj  Dfcj  Dfsj  Stcj  Stsj  Pmpcj  Pmpsj 
Ptpcj  Ptpsj  ...
where the index mark "j" is given for a certain kind of
surface treatment.
4 METHODOLOGY FOR THE SELECTION OF
THE SURFACE-ENGINEERING METHODS
Coating deposition and surface modification have
rapidly evolved in recent decades from simple and
traditional methods to extremely sophisticated techno-
284 Materiali in tehnologije / Materials and technology 44 (2010) 5, 283–287
Y. KHARLAMOV et al.: THE SELECTION AND DEVELOPMENT OF TRIBOLOGICAL COATINGS
logies. These developments are part of an effort to
eliminate the limitations imposed by oil-based
lubrication and are changing the general perception of
the limits of wearing contacts 6. Knowledge of the
mechanisms behind these improvements in lubrication
and wear resistance is, in most cases, very limited. The
methods employed in most studies on surface coatings
and modification are empirical and there is relatively
little information available on which surface technology
is the most suitable for a particular application. Prior to
selecting the coating material and the technological
method it is necessary to determine the prime objective
that could be used to reduce the friction or suppress the
wear – or both. During the selection of the most effective
surface material and process to suppress wear in a
particular situation, the prevailing wear mechanism must
first be recognized and assessed.
In the last years, much research is being carried out
in the field of tribological coatings and surface treatment,
and although they are being increasingly used in
practice, little is still known about their properties and
their tribological behaviour, especially for new, advanced
surface technology. Different types of coatings of the
same composition have different mechanical and tribolo-
gical properties, depending mainly on the type of depo-
sition process and the substrate material. Furthermore,
due to the specific test methods and conditions for given
applications or research facilities of an organization, it is
seldom possible to compare the results obtained by
different researches. The selection of a coating-material
and coating-process combination for a specific substrate
can be complex. There are a great number of possible
combinations, not all of which lead to satisfactory
solutions 1,6–9. To overcome these problems, the strategy
and the methodology for the selection of the optimal
tribological coatings and the surface treatment for a
given application are proposed.
The selection of the types of surface-strengthening
treatment include the following stages, shown in Figure 1:
1. study of the initial data, including: composition and
internal relations of the TrS (parts; relations between
them; lubricant; surrounding environment); indivi-
dual properties of the TrS parts, including the
geometry parameters of the parts and the friction
surfaces (macro- and micro-geometry) and the pro-
perties of the main material; the lubricant properties
(volume and surface properties, chemical and physi-
cal, etc.); the aggregate properties of the lubricant
and the TrS parts (the adsorption properties, moist-
ness, etc.); the lubrication manner influencing, at
first, on techniques and the lubrication type; the
properties of the surrounding environment (the
chemical composition, the corroding influence, the
humidity, the temperature, the pressure, etc.);
external influences on the TrS (kinetic – sliding
(rolling) the velocity V, the hydrodynamic velocity;
the dynamic – mechanical force, the pressure P, the
electric field parameters; the thermal – temperature
0, the thermal flow, the thermal gradient); the
technological limitations on the TrS parts treatment
(the shape and the sizes of the parts and surfaces, the
materials, the variability of the properties, the techno-
logical heredity, etc.); the managerial and economic
limitations (the required productivity, the presence of
equipment, the materials, the energy sources and
others, the sanitary, hygienic and ecological de-
mands, the permissible expenses, etc.).
2. the determination of the TrS parts’ interaction during
the static and dynamic conditions (adhesion, adsorp-
tion, chemosorption, oxidation, corrosion, diffusion,
elastic strain, plastic deformation, micro-cutting,
scratching, structure and phase transformation, etc.).
3. the development of the scheme of the TrS action,
including the preliminary determination of the TrS
characteristics for describing the input values X trans-
formation in the output values Y
Y. KHARLAMOV et al.: THE SELECTION AND DEVELOPMENT OF TRIBOLOGICAL COATINGS
Materiali in tehnologije / Materials and technology 44 (2010) 5, 283–287 285
Figure 1: Scheme of the development of the operation technology of
the surface-strengthening treatment
Slika 1: Shema razvoja operacij tehnologije za utrditev povr{ine
{X} = {P,V,0}  {Y} = {Ft,Z,Pt}
where Ft is the friction resistance, Z is the wear and
seizure, Pt is the accompanying processes.
4. the development of the models of friction and the
wear process of the TrS parts (physical, mathema-
tical, imitative, analogue);
5. the determination of the rational values of the para-
meters of the surface layers’ properties by using the
models of friction and wear (by obtaining the permi-
ssible values of Y);
6. the selection of the rational composition and the
structure of the surface layer of the TrS parts (we
must take into account the existing analogues and
also the structure–properties correlations);
7. the determination of the direction of the surface-
strengthening treatment of the friction surface of the
TrS parts: or the surface layers’ modification, or the
coating deposition or their combination;
8. the determination of the list of possible physico-che-
mical methods of surface-strengthening treatment;
9. the preliminary selection of the optimal methods of
surface-strengthening treatment by using elected
criterions of optimisation and the maintenance of the
required technique-economic limitations;
10. the experimental test of the surface-strengthening
treatment in the laboratory or the empirical-industrial
conditions;
11. the preliminary projection of the operating methods
of the surface treatment – equipment, the special
technological rigs, the technological variables, the
technological environment, the facilities of the
mechanisation, the robotisation and the automation,
the methods of management and control, the techno-
economic comparison of the operating variants;
12. the clarification of the relationships between the
operation technology of the surface-strengthening
treatment and the manufacturing procedure of the TrS
parts’ production; the correction of the structure for
both processes for the purpose of their optimisation;
13. the final selection of the surface-strengthening treat-
ment methods, the development of measures for the
reliability of the maintenance of the demanded cha-
racteristics of the technological process; the develop-
ment of a project for the processing system of the
surface treatment.
The selection of the optimal methods of the surface-
strengthening treatment usually realized by employing
technical criteria to secure the required TrS tribo-
technical characteristics according to scheme, shown in
Figure 2. In the case of the presence of some equivalent
surface-treatment variants on the tribotechnical
characteristics for the final selection economic criteria
are used. The system of the selection of the optimal
surface-strengthening treatment includes the scheme of
the TrS action and the database of the multitude of
surface-strengthening treatment classes and the methods’
characteristics. Preliminarily, by using the technological
limitations, other initial data and the database, one could
select a recommended group of parameters of the surface
layers’ quality, which promoted the increasing wear
resistance. The next would be the selection of respective
methods of surface-strengthening treatment, which
allowed a control of the desirable parameters of the
surface-layer quality. Then, with use of the earlier
developed model of friction and wear for the TrS we can
make a more detailed valuation of the selected decision,
including the calculation and the experimental
determination of the tribotechnical characteristics and
the following test of the TrS. The use of different
methods of surface-strengthening treatment opens up
vast possibilities for the control of friction surfaces’
contact interaction, independent of the composition and
the structure of the main materials of the TrS parts.
Depending on the kind of aggregate of the contacting
surface layers of the friction pairs it is possible to divide
286 Materiali in tehnologije / Materials and technology 44 (2010) 5, 283–287
Y. KHARLAMOV et al.: THE SELECTION AND DEVELOPMENT OF TRIBOLOGICAL COATINGS
Figure 2: Scheme of the selection of the optimum methods of
surface-strengthening treatment. Situation: A – the development of a
tribological system not having analogues; B – the selection of a new
friction pair instead of an out-of-date one; C – the selection of a
friction pair for a weak-loaded typical tribological system; D – the
improvement of a typical tribological system; E – the replacement of
friction pair by a new serial one; F – the determination of an
inter-repair cycle. The stages of selection: 0 – the calculation and the
experimental determination of the tribotechnical characteristics; 1 –
the research test at the determined parameter; 2 – the boundary
research test (under extreme conditions); 3 – the model research test; 4
– the defined nature test; and 5 – the exploitation test
Slika 2: Shema za izbiro optimalne metode za utrditev povr{ine.
Situacija: A – razvoj tribolo{kega sistema brez analogov; B – izbira
novega tornega para namesto opu{~enega; C – izbira tornega para za
malo obremenjen tribolo{ki sistem; D – izbolj{anje tipi~nega
tribolo{kega sistema; E – zamenjava tribolo{kega sistema z novim
standardnim; F – dolo~itev vmesnih popravil. Izbira stopnje: 0 –
izra~un in eksperimentalna dolo~itev tribolo{kih zna~ilnosti; 1 –
preizkus pri dolo~enih parametrih; 2 – mejni preizkus (v ekstremnih
razmerah); 3 – preizkus modela; 4 – dolo~itev naravnega preizkusa; 5
– preizkus uporabe
them into three classes: 1) the contact of two one-phase
surface layers; 2) the contact of a one-phase layer and a
composite-structure surface layer; and 3) the contact of
two composite-structure surface layers.
Only in the case of the contact of one-phase surface
layers is the common number of possible variants of the
contacts very high and can be evaluated with the next
equation
Ksum = 2(n
2 + m2 + q2) – 3(n + m + q) + 6 +
+ 2(nm + nq + mq)
where n is the number of simple substances, m is the
number of two- and many-component solid solutions,
and q is the number of two- and many-component che-
mical compounds.
These multiplicity of possible variants of the contact
in the case of only one-phase surface layers is allowed
by the choice of the composition of the surface-layers
materials and their structure to control the quality of the
physical contact of the friction pairs, in particular the
size of real contact area, of the tendency to form
desirable secondary structures in the process of friction,
the properties of a third (intermediate) substance, and the
fatigue-wear resistance, etc.
In reality, the factual variety of the possible contacts
of one-phase layers is considerably more, inasmuch as
the friction processes depend not only on the chemical
composition of the contacted surface layers, but also on
their structure and energetic parameters, including the
size, shape and character of the mutual orientation of the
grains; the structure and strength of the intercrystalline
boundaries; the level of the strain hardening; the type of
the crystal lattice; the mechanical properties; the surface
properties, etc.
The creation on one or both friction surfaces for the
layers with a composite structure leads to an essential
increasing of the possible variants of the friction
surfaces’ contacts and to the appearance of some new
physico-chemical phenomena in the process of friction.
The peculiarities of the contact interaction of such
friction pairs are at first connected with the simultaneous
presence of the contact aggregate between the friction
surfaces. But the description of the friction zone in the
contact of such surface layers demands the use of
complex or special parameters.
5 CONCLUSION
The approach to the development and selection of a
surface-strengthening treatment for tribological purposes
has to involve methods of system analyses. The
tribological system’s workpieces’ and friction surfaces’
functions must be accurately defined in functional,
technological, economic, ecological and other respects.
The proposed strategy has the potential for simplifying
the selection and design of coatings and/or surface layers
and the reduction of the development time for new
tribological systems and/or the improvement of existing
ones. But the subsequent laboratory tests at several levels
must also be completed. The development of computer-
modelling methods for the selection of surface-engi-
neering processes and expert systems for developing the
surface-engineering technology for a particular appli-
cation is necessary. The system approach could also be
useful for the development of new tribological coatings
and surface-modification methods. However, a lot has
still to be done for the development of a methodology for
the selection of optimum methods for surface engi-
neering and their improvement.
6 REFERENCES
1 Holmberg K., Matthews A.: Coatings Tribology. Properties, tech-
niques and applications in surface engineering. – Elsevier Science B.
V., Amsterdam, The Netherlands, 1994
2 Hocking M. G., Vasantasree V., Sidky P. S.: Metallic and ceramic
coatings. production, high temperature properties and applications. –
Longman Group UK Limited, London. 1989
3 Jorn Larsen-Basse: Surface engineering and the new millennium.
Surface Engineering, 14 (1998), 81–83
4 Budinski K.G.: Surface engineering for wear resistance. – New York,
NY, Prentice Hall, 1988
5 Friedrich C., Berg G., Broszeit E., Berger C. Fundamental econo-
mical aspects of functional coatings for tribological applications.
Surface and Coatings Technology, 98 (1998), 816–822
6 Stachowiak G. W., Batchelor A. W.: Engineering tribology. Second
Edition. – Butterworth-Heinemann, 2001
7 Bhushan B, Gupta B. K. Handbook of tribology. Materials, coatings,
and surface treatments. – McGraw-Hill, 1991
8 Schiffmann K., Petrik M., Fetzer H. J., Schwarz S., Gemmler A.,
Griepentrog M., Reiners G. INO-A WWW information system for
innovative coatings and surface technology. Surface and Coatings
Technology, 153 (2002), 217–224
9 Sedlacek M., Podgornik B., Vizintin J. Tribological properties of
DLC coatings and comparison with test results: Development of a
database. Materials Characterization, 59 (2008) 2, 151–161 doi:10.
1016/j.matchar.2006.12.008
Y. KHARLAMOV et al.: THE SELECTION AND DEVELOPMENT OF TRIBOLOGICAL COATINGS
Materiali in tehnologije / Materials and technology 44 (2010) 5, 283–287 287

M. TORKAR et al.: RECYCLING OF STEEL CHIPS
RECYCLING OF STEEL CHIPS
RECIKLIRANJE JEKLENIH OSTRU@KOV
Matja` Torkar, Martin Lamut, Agron Millaku
Institute of Metals and Technology, Lepi pot 11, SI-1000 Ljubljana, Slovenia
matjaz.torkar@imt.si
Prejem rokopisa – received: 2010-05-17; sprejem za objavo – accepted for publication: 2010-06-20
The recycling of waste metallic materials and the use of scrap are important for the economic production of a steelworks. Here,
we investigate the technology of remelting steel chips. It was confirmed that the main problems with using chips in an electric
arc furnace were the chips’ large specific surface and the high losses due to the chips’ oxidation. To overcome both problems the
compaction and remelting of the chips were tested. The investigation revealed that a major problem for the recycling ecology of
steel chips was the safe removal of cutting fluids and oils from the chips’ surface. The chemical analysis of the remelted chips
confirmed that stainless-steel chips can be an acceptable source of the alloying elements chromium, nickel and molybdenum.
Key words: steel chips, magnetic separation, cold compaction, remelting
Recikliranje odpadnih kovinskih materialov in uporaba starega `eleza sta pomembna za ekonomiko `elezarne. Tehnologija
proizvodnje jekla s pretaljevanjem starega `eleza v elektro oblo~ni pe~i je primerna tudi za jeklene ostru`ke. Preizku{ena je bila
tehnologija pretaljevanja jeklenih ostru`kov. Glavni ugotovljeni problemi pri uporabi ostru`kov v elektro oblo~ni pe~i so velika
specifi~na povr{ina in velike talilne izgube zaradi oksidacije ostru`kov. Zato je bilo preizku{eno stiskanje ostru`kov in njihovo
pretaljevanje. Predstavljeni so rezultati teh preizkusov. Ti so pokazali, da je bila glavna te`ava pri ekolo{kem recikliranju
jeklenih ostru`kov odstranitev rezilne teko~ine in olj z njihove povr{ine brez kontaminacije zraka. Kemijska analiza pretaljenih
ostru`kov je potrdila, da so ostru`ki nerjavnega jekla koristen vir legirnih elementov, kot so krom, nikelj in molibden.
Klju~ne besede: jekleni ostru`ki, magnetno lo~evanje, hladno stiskanje, pretaljevanje
1 INTRODUCTION
Wastes that were traditionally discarded from indu-
strial production are nowadays recycled.1 The discarding
of waste materials has a negative environmental impact
and is a waste of time and money for the manufacturer of
steel or machine parts.2 Steel chips are a by-product of
the mechanical working of steel parts in the metal
industry and their quantity is considerable. The quanti-
ties of steel chips recorded by years in Slovenia are
shown in Table 1.
Table 1: Quantity of steel chips in Slovenia
Tabela 1: Koli~ina ostru`kov `eleza v Sloveniji
Year
Leto
Clasification number/Klasifikacijska {tevilka:
120101
Quantitiy of filings and turnings of steel/
Koli~ina opilkov in ostru`kov `eleza (t)
2002 58 120
2003 33 111
2004 48 828
2005 43 991
2006 53 180
2007 93 381
Source: Statistical Office of the Republic of Slovenia
Steel production in the Republic of Slovenia is based
on the remelting of scrap. From the data in Table 1 it is
evident that steel chips could be an important source of
iron and other elements for steel producers.
With the prices of nickel and chromium currently
high, and on the rise in recent years, the production of
steel is becoming increasingly more expensive, and with
the prices rising, the recycling of steel chips is beginning
to look more appealing for steel companies.2,3,4,5 For
better productivity during metal working the cutting
tools are cooled and lubricated with special cooling
liquids consisting of lubrication, cooling and anti-
corrosion agents. However, the chips are contaminated
with these substances and need to be cleaned before any
further processing. It is important to note that discarded
coolants from the manufacturing of steel have a more
harmful impact on the environment than dry chip
processing.4 This means that the coolants have to be
removed in order to obtain more environmentally
friendly waste from the chips generated in the processing
of the steel. The discarding of metallic chips is harmful
to the environment, regardless of whether they are
contaminated or not, and these chips should not end up
in landfills, thereby losing their potential for reuse. In the
near future the recycling of these chips will actually cost
less than disposing of them in a landfill.
The first step during the recycling of chips is usually
the separation of the cooling liquid and the oil with a
centrifuge.3,4 It is also possible to remove the lubricant
by washing them in an organic solvent that dissolves the
organic contaminants from the chips’ surface. The latter
possibility is less acceptable because most organic
solvents are carcinogenic and harmful to the environ-
ment, and their use and removal are regulated by the law.
Materiali in tehnologije / Materials and technology 44 (2010) 5, 289–292 289
UDK 669.1.782 ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 44(5)289(2010)
Vacuum separation2 is also used, by heating the chips
in a vacuum chamber up to 270 °C. The low pressure in
the chamber accelerates the evaporation of volatile
components that are pumped out, cooled in a condenser
at appropriate temperatures and the oils and water are
separated. After regeneration, the oil is reused for
machining.
The best quality of regenerated oil is obtained with a
treatment involving supercritical CO2 gas at a pressure of
100 bar.2 However, when compared to other methods,
this method is too expensive for the cleaning of chips.
After the chips of structural steel are cleaned they are
separated from the chips of stainless steel using magnetic
separation.6
Steel chips have a high specific volume and a low
density that makes the remelting more difficult and with
a low yield. For this reason, compacting with a cold
press or briquetting, which increase the density of the
chips, makes possible a more effective melting process.
The content of chromium in stainless steel is greater
than that of nickel, but the price of nickel makes it more
costly overall than chromium in the production of
stainless steel.
The cost of nickel is so high that the price of stainless
steel is directly related to the price of nickel, which has
increased six fold from 2002 to 2006.3 The price of
ferrochrome has more than doubled in the past four years
(2002 to 2005)3, but the increase in the chromium price
is still lower than the increase in the nickel price. For this
reason, any source of chromium and nickel is cost
attractive for stainless-steel producers.
For the producer of stainless steel in Slovenia an
evaluation of the mixture of chips with respect to the
content of chromium, nickel and molybdenum, as a
possible additional source of alloying elements, was
made.
2 EXPERIMENTAL
Magnetic tests showed the chips, declared as
stainless-steel chips, were in reality a mixture of carbon
steel and stainless steel. After the magnetic separation,
however, only the stainless-steel chips were processed
further.
Two methods of degreasing the chips were tested:
heating in a laboratory furnace up to 400 °C and burning
the volatile gases, and washing the chips in a waste
organic solvent, trichloroethylene. Using both methods,
dry and clean chips were obtained.
The degreased chips were cold pressed into
cylindrical compacts, more suitable for remelting
because of their higher density and lower volume. For
the cold pressing a manually driven screw press was
applied. The chips were charged in a hollow, slightly
conical tool and repeatedly added and pressed until the
tool was full. The pressed chips were then pressed out of
the tool from the opposite site.
The compacts were then melted in a 20-kg
induction-melting furnace using a premelt of known
composition. The compacted chips were added to the
primary melt and after remelting a sample of the melt
was submitted to chemical analysis and the contents of
nickel, chromium and molybdenum in the chips were
calculated. The chemical analysis was performed with
optical emission spectrometry ARL and controlled with
M. TORKAR et al.: RECYCLING OF STEEL CHIPS
290 Materiali in tehnologije / Materials and technology 44 (2010) 5, 289–292
Figure 3: Compacts of stainless steel chips after cold pressing
Slika 3: Stisnjeni ostru`ki nerjavnega jekla po hladnem stiskanju
Figure 2: Separated stainles steel chips and compacted, cold pressed
chips
Slika 2: Lo~eni ostru`ki nerjavnega jekla, hladno stisnjeni ostru`ki
Figure 1: Mixture of steel chips
Slika 1: Me{anica jeklenih ostru`kov
wet chemical analysis. The quantity and composition of
the slag were not taken into account.
3 RESULTS AND DISCUSSION
The magnetic separation revealed that the investi-
gated sample consisted of a mixture of 1/3 of stainless
steel and 2/3 of carbon steels, but for further processing
only the chips of stainless steel were used.
Two methods for removal of the cooling fluid were
tested. First, degreasing in trichloroethylene, which is an
effective solvent for greases and a variety of organic
materials. Its use is harmful because it is carcinogenic
and it is suitable only for applications in laboratory-
controlled conditions, whereas it is not suitable for
industrial processing.
The second method was heating the chips to 400 °C
in an electric furnace, when the water and oil evaporated,
and clean and dry chips were obtained. The heating
smoke was burned to CO2 and H2O by introducing it into
a flame.
On an industrial level, it is also possible to charge
oil-contaminated chips with scrap directly. In this case
the organic impurities would be burned out at high
temperatures and the formed gases would escape through
the filters for furnace exhaust gases. In the case of a too
low temperature, the evaporation of oils and their
collection in filters may reduce the filters’ efficiency.
3.1 Compacting the chips
The direct melting of the chips in the 20-kg induction
furnace was not possible. Because of the low density, the
chips in the furnace would only be heated to a tempe-
rature below the melting point. For the melting it was
necessary to prepare chips in a compacted form and for
this reason, the chips were cold pressed into a cylindrical
form with a pressure of 1765.8 kPa. For comparison the
pressing of contaminated and degreased chips was
tested. In both cases the product was compacted into a
round, cylindrical form with a diameter of 55 mm and
length of 120 mm, and with a density of between
3 kg/dm3 and 4 kg/dm3. The pressed forms were of round
section and had a diameter of 55 mm and a length of 120
mm. The size of the forms was limited by the dimensions
and the height of the pressing-tool cavity.
3.2 Remelting the chips
An induction-melting furnace requires a minimal
density of charge, and the density of the compacts was
still too low for direct melting in an induction furnace.
The compacts were only heated and their temperature
did not reach the melting point. To master the melting a
primary melt with known composition was prepared and
then the compacts were charged into the molten steel.
First, 7 kg of mild steel was melted in the 20-kg
induction furnace and its chemical composition was
determined. The mass of the molten steel was reduced by
765 g to 6 235 g, 13 000 g of compacts added and a total
melt mass of 19 235 g was achieved. The slag was
M. TORKAR et al.: RECYCLING OF STEEL CHIPS
Materiali in tehnologije / Materials and technology 44 (2010) 5, 289–292 291
Figure 5: Casting of sample for chemical analysis
Slika 5: Ulivanje vzorca za kemijsko analizo
Figure 6: Ingots composed of basic steel and added compacts
Slika 6: Ingota, sestavljena iz osnovnega jekla in dodanih stisnjencev
Figure 4: Charging of compact into melt
Slika 4: Dodajanje stisnjencev v talino
removed from the melt and a sample for chemical
analysis was taken. The rest of the melt was cast into
ingots with a square cross-section. The weight of the
as-cast sample for the chemical analysis and ingots
together was 18 150 g. The difference between 1 085 g
and 19 235 g is the material loss (slag, drops, remains in
the melting furnace).
3.3 Determination of the composition of the chips
The basis for the calculation of the content of
elements in the stainless-steel chips was the total mass of
19 235 g. This represents 13 000 g of chips of unknown
composition diluted within 6 235 g of mild steel with
known composition. A programme was prepared in
Excel for the calculation of the chemical composition of
the premelt, of the ingots and of the content of the
individual elements in the chips. From the chemical
composition of the premelt and of the composition of the
ingot the content of elements in the chips in Table 2 was
calculated.
4 CONCLUSIONS
The recycling of steel chips with remelting in an
induction-melting furnace was investigated. Based on the
experimental results, the following conclusions can be
drawn:
Tests with magnets revealed that the investigated
chips were a mixture of 1/3 of non-magnetic fraction
(stainless steel) and 2/3 of magnetic fraction (structural
steel). Both fractions of chips were successfully sepa-
rated with magnetic separation and the following com-
position of the investigated chips was obtained: 13.01 %
Cr, 6.34 % Ni, 0.86 % Mo and 0.45 % Cu.
The higher carbon content and the lower chromium
content in the chips are probably due to the inaccuracy of
magnetic separation method or the incomplete elimi-
nation during the burning of the oil contamination.
The investigations confirmed that the compaction of
the chips is necessary for a better yield of material in the
melting process and that stainless steel is a valuable
source of alloying elements.
5 REFERENCES
1 D. Janke, L. Savov, H.-J. Weddige, E. Schulz, Scrap-based steel
production and recycling of steel, Materiali in tehnologije 34, (2000)
6, 387–399
2 J. Bongardt, Technical Note: Reduction of waste from fabrication
processes. The Journal of The South African Institute of Mining and
Metallurgy, March/April 1997, pp 63–67
3 Sean Dyer, Bao Ngo, Kurt Wivagg, Chip Recycling: Recycling of
chips from BZZ conditioning processes, Worcester Polytechnic
Institute, A Major Qualifying Project for Degree of Bachelor of
Science, www.wpi.edu/Pubs/E-project/Availabel/E-project-04267-
151242/unrestricted/YR_SGMQP_05.pdf
4 V. A. Kurdyukov, A. A. Sergeev and A. A. Reznyakov, Efficient
methods of processing metal chips, Metallurgist, 41 (1997) 9–11,
331–335
5 S. I. Stepanov, Some laws on the hot and cold compression of steel
chips, Powder Metallurgy and Metal ceramics, 5 (1966) 2, 99–102
6 William J. Bronkala, Magnetic separation, Wiley-VCH Verlag
GmbH & Co. KGaA., DOI:10.1002/14356007.b02_19, June 15,
2000
M. TORKAR et al.: RECYCLING OF STEEL CHIPS
292 Materiali in tehnologije / Materials and technology 44 (2010) 5, 289–292
Table 2: Chemical composition of primary melt, after the addition of chips and calculated composition of chips. All in mass fractions, w/%
Tabela 2: Kemijska sestava primarne taline, po dodatku ostru`kov in izra~unana sestava ostru`kov. Vse v mas. dele`ih, w/%
Chemical composition C Si Mn Ni Cr Mo Cu Fe
Primary melt w/% 0.14 0.25 0.19 0.04 0.03 0.05 0.11 99.30
Weight (g) 6235 8.73 15.59 11.85 2.49 1.87 3.12 6.86 6191.36
Mixture w/% 0.24 0.35 0.89 4.30 8.80 0.60 0.34 84.82
Weight (g) 19235 46.16 67.32 171.19 827.11 1692.68 115.41 65.40 16315.13
Chips w/% 0.29 0.40 1.23 6.34 13.01 0.86 0.45 77.88
Weight (g) 13000 37.44 51.74 159.35 824.61 1690.81 112.29 58.54 10065.23