Interlayer growth kinetics of a binary solid-solution based on the thermodynamic extremal principle: Application to the formation of spinel at periclase-corundum contacts

Abstract

A thermodynamic model has been developed for interlayer growth in a binary system between two phases of fixed composition producing an intermediate solid-solution phase. Thereby long-range diffusion, interface migration and generation/ annihilation of vacancies at the reaction interfaces have been considered as potentially rate limiting. The coupling among these processes governs overall growth rate, position of the Kirkendall plane and the compositions of the solid-solution phase at the reaction interfaces. Model calculations illustrating the relations between the corresponding kinetic parameters and system evolution are presented. In particular, the systematics of non-equilibrium element partitioning across moving reaction interfaces is addressed. It is found that the deviation from equilibrium element partitioning at a moving reaction interface is a more sensitive monitor for the departure from local equilibrium than the deviation from parabolic growth behavior. Finally, the model is applied to interlayer growth of magnesio-aluminate spinel.