The Synthesis and Characterization of Nickel and Cobalt Ferrite Nanopowders Obtained by Different Methods

The single-phase NiFe2O4 and CoFe2O4 ferrites were synthesized by four methods: the high-frequency plasma chemical synthesis ("plasma"), sol-gel self-propagating combustion method ("combust"), and co-precipitation technology, combined with the hydrothermal synthesis ("hydrotherm") or spray-drying ("spray"). The specific surface area (SSA), crystallite size, and magnetic properties of the synthesized products have been determined. The synthesized ferrites are nanocrystalline single-phase materials with crystallite size of 5-40 nm. The SSA of nanoparticles synthesized in plasma is 28-30 m2/g, the particle size distribution is in the range of 10-100 nm, with some individual particles up to 200 nm. The SSA of the ferrites obtained by the self-combustion and hydrothermal synthesis is 40 ± 3 and 60 ± 5 m2/g, respectively. The SSA of the samples obtained by the spray-drying method is 80-90 m2/g, and the calculated particle size is 13-15 nm. In this process, pellets up to 10 μm are obtained. After synthesis, CoFe2O4 are characterized by the saturation magnetization Ms of 75 emu/g ("plasma"), 53 emu/g ("combust") and 57 emu/g ("hydrotherm"). The Ms of NiFe2O4 is 44, 29, and 30 emu/g, respectively. The products obtained by the spray-drying method are partially X-ray amorphous and show magnetic properties only after heating above 450°C. These nanopowders were used in sintering studies.