PROCESSING AND CHARACTERIZATION OF MAGNETIC FERRITES

Abstract

Nanosized magnetic nickel ferrite powders have been prepared via both hydrothermal and microemulsion processing routes. In the former method, nickel ferrite powders were produced by heating a pressurized mixture of Ni(NO3)2, Fe(NO3)3 and aqueous ammonia solutions at a temperature of 200°C for 10 hours. In the second technique, the ferrite powders were prepared using bicontinuous and inverse microemulsion processes. These microemulsion systems consisted of Ni(NO3)2 and Fe(NO3)3 solutions as the aqueous phase, cyclohexane as the oil phase and poly(oxyethylene)5 nonyl phenol ether (NP5) and poly(oxyethylene)9 nonyl phenol ether (NP9) as the non-ionic surfactants. The hydroxide precursors were obtained by carrying out the precipitation reaction between the nickel and ferric nitrates, and aqueous ammonium hydroxide (NH4OH) solution in the microemulsion. The desired nickel ferrite powders were then formed by the subsequent calcination or the hydroxide precursors al different temperatures. Thermal analysis was performed on the hydroxide precursors. The nickel ferrite powders obtained from both methods were characterized using X-ray diffractometer, BET specific surface area analyzer, light scattering particle size analyzer, transmission electron microscope, scanning electron microscope and vibrating sample magnetometer. It was found that a molar ratio of 1:2 for Ni:Fe is needed to produce NiFe2O4 when hydrothermal synthesis is utilized, while a ratio of 1: 1 has to be used in the microemulsion processing. The ferrite particles obtained by both approaches have a relatively narrow size distribution that increases with increasing processing temperature. In any case, the nickel ferrite powders exhibit a saturation magnetization ranging from 35 to 48 emu/g. This magnetic property is very satisfactory.