The Role of Vapour Phase Transport and the Effect of Reaction Conditions on the Formation of Spinels

Abstract

Previous work on the formation of complex oxides (spinels) by solid-state reaction between two simple oxides is reviewed and discussed with reference to possible mechanisms and kinetic models and the effect of reaction conditions on the relative importance of the various reaction processes. The kinetics of reaction between un-compacted ZnO and Fe2O3 powders have been investigated and compared to those of compacted powders. A quantitative analysis method has been developed using Mossbauer spectra. Comparison of the kinetic results obtained by this method with those of an x-ray method have enabled the diffusion rate of the iron ions to be investigated. The importance of vapour phase transport in spinel formation has been established and the volatility of the ZnO has been examined by measuring its rate of evaporation and equilibrium oxygen pressures as a function of temperature. A detailed reaction model is advanced and related to the reaction conditions.