Formation mechanism of zinc ferrite in high-temperature roasting of zinc oxide and ferric oxide

Abstract

The formation mechanism of zinc ferrite during the heat treatment of zinc oxide and ferric oxide was investigated. It is revealed in the kinetic study that the formation of zinc ferrite is an endothermic reaction with an apparent activation energy Ea that increases from 9.76 kJ mol−1 to 290.70 kJ mol−1. This variation of Ea indicates that the reaction between ZnO and Fe2O3 is a multistep reaction, which could be described by the D3 (3D Jander Equation) - An (n-dimension Avrami-Erofeev Equation) model. The first step is the diffusion of the reactant, corresponding to the stage when the Ea is low. As the reaction proceeds, the rate-determining process switches to the crystallization of zinc ferrite, which is reflected by a simultaneous increase in the XRD peak height and Ea. The results of first-princeples calculations show that zinc oxide preferentially diffuses to the iron oxide matrix, and the inverse process causes an increase in the system energy. These results provide great insight into the kinetic basis for understanding the formation of spinel ferrites via a high-temperature solid-state reaction.