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The NiFe₂O₄ and CoFe₂O₄ ferrites were synthesized by two methods – chemical sol-gel self-combustion method and the high frequency plasma chemical synthesis and magnetic properties, crystallite size, specific surface area of synthesized products are characterized. Nanopowders synthesized in the high frequency plasma are with specific surface area in the range of (28 – 30) m²/g (the average particle size (38 – 40) nm, crystallite size ~40 nm). The ferrite nanopowders obtained by sol-gel self-combustion method have the specific surface area of (37 – 43) m²/g (average particle size
(26 – 31) nm, crystallite size (10 – 20) nm). All synthesized nanopowders were sintered via pressure-less sintering method and magnetic properties of compacted materials were studied, as well.

DOI: http://dx.doi.org/10.5755/j01.ms.18.1.1332

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The single-phase NiFe 2 O 4 and CoFe 2 O 4 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 m 2 /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 m 2 /g, respectively. The SSA of the samples obtained by the spray-drying method is 80-90 m 2 /g, and the calculated particle size is 13-15 nm. In this process, pellets up to 10 μm are obtained. After synthesis, CoFe 2 O 4 are characterized by the saturation magnetization M s of 75 emu/g ("plasma"), 53 emu/g ("combust") and 57 emu/g ("hydrotherm"). The M s 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.

Nickel oxide nanoparticles were prepared via molten salts and microwave assisted synthesis from nickel nitrate and the parameters of obtained nanopowders were compared. NiO nanoparticles with crystallite size in the range of 6-8 nm have been prepared by combining microwave assisted treatment of Ni (NO3)2 and urea solution with calcination at 300-320 °C. Molten salts (NaNO2-NaCl) ensured direct formation of NiO from Ni (NO3)2.6H2O and salts mixture at 350 °C but crystallite size of the particles reached 51-69 nm.