Reduction mechanisms and behaviour of zinc ferrite—Part 2: ZnFe 2 O 4 solid solutions

The behaviour of dense zinc ferrite samples containing 1–6 wt% CaO, MgO, MnO or Al₂O₃ in solid solution has been investigated during reduction with CO–N₂ and CO–CO₂ gas mixtures at temperatures between 800 and 1100°C. The iron product microstructures, i.e. porous or dense iron, that were formed on the completion of reduction could be correlated with the shape of the reduction curves. The presence of impurity oxides in ZnFe₂O₄ solid solution was found to affect the conditions for formation of the porous iron morphology. The additions of CaO and MgO to ZnFe₂O₄ increased the region for porous iron growth, whereas Al₂O₃ and MnO restricted the range of reduction conditions over which porous iron was formed. The pore structure of the reduced samples was found to be dependent on reduction temperature, partial pressure of CO and amount of impurity oxide added into the solid solution as well as the species. The changes in growth mechanisms and reduction kinetics that occur with changing reduction conditions are discussed.