MECHANISMS OF THE REDUCTION OF ZINC FERRITES IN H2/N2 GAS MIXTURES

The rates of reduction of dense pure zinc ferrite and zinc ferrite containing 1 wt% of CaO, MgO, MnO, and Al₂O₃ in solid solution reduced with H₂/N₂ gas mixtures have been investigated at temperatures between 500 and 1100°C. The rate measurements obtained in these studies were complemented with the structural characterization of the partially reduced zinc ferrite samples. The presence of impurity oxides in ZnFe₂O₄ solid solution influenced the conditions for formation of the porous iron morphology. Where porous iron-type microstructures were formed during the reduction reaction, the pore structure of the reduced samples was found to be dependent on reduction temperature, hydrogen partial pressure, and type of impurity oxide added into the solid solution. The reduction plots of zinc ferrite solid solutions exhibited an initial linear rate followed by a gradual decrease in rate with increased percentage reduction. The changes in growth mechanisms and reduction kinetics that occur with changing reduction conditions are discussed.