Reduction kinetics and mechanisms of NiFe2O4 with synthesis of nanocrystalline Fe-Ni alloy

Nickel ferrite (NiFe2O4) powder was prepared through the ceramic route by calcination of a stoichiometric mixture of nickel oxide and iron oxide. The produced powders of NiFe2O4 were isothermally reduced in pure hydrogen at 800-1100 degrees C. Based on thermogravimetric analysis. the reduction behavior of nickel ferrite and the kinetics reaction mechanism were studied. The initial ferrite powder and the various reduction products were characterized by XRD, SEM, TEM and reflected light microscope to reveal the effect of hydrogen reduction on composition and microstructure of produced Ferronickel 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 reaction is controlled by the combined gaseous diffusion and interfacial chemical reaction mechanisms at both of the initial and the final reaction stages. Complete reduction of NiFe,04 was almost achieved with 95.5-100% reduction extent at 800-1100 degrees C respectively. The FCC Fe(0.7-0.64)-Ni(0.3-0.36) alloy was synthesized with nanocrystalline size ranged from 24 nm at 800 degrees C to 16.1 nm at 1100 degrees C respectively.