2008 Volume 49 Issue 4 Pages 860-868
Nickel cobalt ferrite (Ni0.5Co0.5Fe2O4) powder was prepared through the ceramic route by calcination of a stoichiometric mixture of nickel oxide, cobalt oxide and iron oxide at 1100 and 1200°C. The produced powders of Ni0.5Co0.5Fe2O4 were isothermally reduced in pure hydrogen at 800–1100°C. Based on thermogravimetric analysis, the reduction behavior of nickel cobalt ferrite and the kinetics reaction mechanism were studied. The initial ferrite powder and the various reduction products were characterized by XRD, pore size, SEM, VSM and reflected light microscope to reveal the effect of hydrogen reduction on composition, microstructure and magnetic properties of produced Fe-Ni-Co alloy. Microstructure of partially and completely reduced samples was studied and the activation energy values were calculated from Arrhenius equation. The approved mathematical formulations for the gas solid reaction were applied and it was found that the initial reaction stages are controlled by the combined gaseous diffusion and interfacial chemical reaction mechanisms with high contribution to gas diffusion while the final reaction stages is controlled by chemical reaction mechanism. Complete reduction of Ni0.5Co0.5Fe2O4 was achieved with synthesis of nanocrystalline (18–20 nm) Fe-Ni-Co alloy.