Isothermal reduction kinetics at 900-1100°C of NiFe2O4 sintered at 1000-1200°

Nickel ferrite is one of very important material, which is suitable for using in computer peripherals, telecommunications equipments, permanent magnets, electronic and microwave devices. Thus, the study of the behavior of NiFe,04 in reducing atmosphere is very important. NiFe2O4 is prepared by mixing chemically pure powders of Fe2O3 and NiO in stoichiometric ratios then pressed at 250 kg/cm(2) into cylindrical form of compacts before being fired at 1000, 1100 and 1200 degrees C for 10 h. The characteristic of the prepared nickel ferrite have been studied using X-ray diffraction analysis technique, reflected light microscope and porosity measurements. The behavior of nickel ferrite in hydrogen atmosphere at 900-1100 degrees C has been studied using thermogravimetric techniques. The reduction of NiFe2O4 is not found to proceed to completion at any firing or reduction temperature. The reduction proceeds via a topochemical mode. At firing temperatures 1000 and 1100 degrees C, the rate is controlled initially by the combined gaseous diffusion interfacial chemical reaction mechanism while at the final stages, the interfacial chemical reaction is predominantly the rate-control ling mechanism. At 1200 degrees C, initially the rate controlling is the interfacial chemical reaction mechanism while the solid-state diffusion is rate-controlling mechanisms at the final stages. (c) 2005 Elsevier B.V. All rights reserved.