Sinteza in karakterizacija magnetnih nanodelcev za mikrovalovne absorberje elektromagnetnega valovanja : doktorska disertacija

slovenian

doktorska dela

2012

Univerza v Mariboru, Fakulteta za kemijo in kemijsko tehnologijo

Nano-crystalline strontium hexaferrite (SrFe12O19) powder was synthesized using the classical co-precipitation and microemulsion methods. The precursors were obtained by precipitating Sr2+ and Fe2+ ions using tetramethylammonium hydroxide and calcinating at different temperatures ranging from 400 °C to 1000 °C in air. The influence of the Sr2+ / Fe3+ mol ratio and the calcination temperature on the product formation and their magnetic properties were studied. The formation of nanosized particles of SrFe12O19 with a relatively high saturation magnetization ?s = 64 Am2/kg, remanent magnetization of ?r = 39 Am2/kg and a coercitivity of Hc = 430 kA/m was achieved at a Sr2+ / Fe3+ mol ratio of 1 : 8 calcined at 900 °C. The formation of the SrFe12O19 was inspected using X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), differential thermal analysis (DTA), transmission electron microscopy (TEM), dynamic light scattering analysis (DLS) and specific surface area measurements (BET). The magnetic properties were inspected using magneto-susceptometer DSM-10. Furthermore, we have investigated nanocomposites designed for absorption of electromagnetic waves based on magnetic filler, composed of phases within the SrO - Fe2O3 system, embedded in a polymer matrix based on polyphenylene sulfide (PPS) with a concentration ratio of 80 : 20 by weight. The formation of the nanosized particles of SrFe12O19 and Fe3O4, as the principal magnetic phases, was achieved via the classical co-precipitation of Sr2+ / Fe3+ ions using different molar ratios. The various precursors obtained were calcined between600 °C and 900 °C in air atmosfere. The electromagnetic parameters of the nanocomposites were measured with a vector network analyzer in frequency range from 400 MHz to 32 GHz. The results show that with a nancomposite composed of a complex magnetic filler comprising the nanoparticles of two magnetically diverse phases, i.e., a spinel phase as the electromagnetic wave absorber in the lower GHz range and a hexagonal phase operating at a higher GHz range, above 32 GHz, a microwave absorber with an broad absorption range can be prepared.

07.08.2023