Kinetics and Mechanism of the Reaction Between Zinc Oxide and Aluminum Oxide

TLDR: In this article, the diffusion of zinc ions through the spinel layer is the rate controlling mechanism for spinel formation and the activation energy for the process is 54,200 cal/mole.

Abstract: Quantitative X-ray diffraction methods were used to define the kinetics of spinel formation. Diffusion controlled reaction rate constants were calculated on the basis of the reaction models of Jander, Dunwald-Wagner, Valensi, Zhuravlev et al., Ginstling-Brounshte'n, and Kroger-Ziegler. The model proposed by Valensi is valid for describing solid-solid reaction rates in the later stages of the reaction. Inert markers indicated that diffusion of zinc ions through the spinel layer is the rate controlling mechanism. The activation energy for the process is 54,200 cal/mole. In the early stages of the reaction there is a second-order phase boundary kinetic process with an activation energy of 28,700 cal/ mole. The rate of chemical combination at the zinc-oxide-spinel phase boundary is believed to be rate controlling.