Effect of hydrogen reduction temperature on the microstructure and magnetic properties of Fe-Ni powders

Abstract

The effect of hydrogen reduction temperature on the properties of Fe-Ni powders was described. The mixed powders of Fe-oxide and NiO were prepared by chemical solution mixing of nitrates powders and calcination at 350 A degrees C for 2 h in air. The calcined powders formed small agglomeration with an average particle size of 100 nm. The microstructure and magnetic properties were investigated by using X-ray diffractometry, thermogravimetry, differential thermal analyzer, and vibrating sample magnetometer. Microstructure and thermal analysis revealed that the Fe-oxide and NiO phase were changed to FeNi(3) phase in the temperature range of 245-310 A degrees C, and by heat-up to 690 A degrees C the FeNi(3) phase was transformed to gamma-FeNi phase. The reduced powder at 350 A degrees C showed saturation magnetization of 76.3 emu/g and coercivity of 205.5 Oe, while the reduced powders at 690 A degrees C exhibited saturation magnetization of 84.0 emu/g and coercivity of 14.0 Oe. The change of magnetic properties was discussed by the observed microstructural features.