The kinetics and mechanism of formation of compounds of the spinel type

Abstract

This thesis describes a study of the kinetics of formation of compounds of the spinel structure from the corresponding oxides, with particular reference to the spinel zinc ferrite (ZnFe2O4). The solid state reaction between zinc oxide and α-ferric oxide to form zinc ferrite has been studied by investigating the effect of particle size, temperature, and initial concentrations of reactants on the rate, A simple method of X-ray diffraction analysis has been developed for following the reaction. From a consideration of the structures of the reactant oxides and the product spinel, a diffusion model for the reaction has been proposed. The experimental data have been compared with several theoretical diffusion equations based on Fick's Law. The rate constants obtained for a range of temperatures have been tabulated and the enthalpy of activation calculated for the reaction of powder samples is 70 Kcals./gm.mole while that for pellets is 120 Kcals./gm.mole. The corresponding entropies of activation are +0.2 to +3.5 cals./deg./mole and -48 to -49 cals./deg./mole respectively, for the temperature ranges considered.