Low temperature isothermal reduction kinetics of Fe2O 3/NiO mixed oxides and comparative synthesis of Fei 1-xNix alloys

Abstract

Two Molar ratios 1 : 1 and 1 : 2 of AR grade nickel oxide and iron oxide powder was mixed and compacted. The fired compacts were isothermally reduced in pure hydrogen at 500, 550, 600 and 650°C. Based on thermogravimetric analysis, the reduction behavior and kinetics reaction mechanism were studied comparatively for the different mixed oxides ratios. The initial fired 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. Synthesis of nanocrystalline Fe1-xNix alloy with 33 and 20at% Ni for reduction of 1 : 1 and 1 : 2 NiO/Fe2O3 ratios was detected respectively. The activation energy values were calculated from Arrhenius equation and the approved mathematical formulations for the gas solid reaction were applied. It was found that for NiO/Fe2O3 of both 1 : 1 and 1 : 2 ratios, the initial reduction stages is controlled by the combined gaseous diffusion and interfacial chemical reaction mechanisms while at the final reduction stages the reaction is controlled by the interfacial chemical reaction mechanism. © 2008 The Japan Institute of Metals.