Calphad-informed thermodynamic non-equilibrium simulation of non-isothermal solid-state reactions of magnesium aluminate spinel based on the thermodynamic extremal principle

The understanding of solid-state reactions and interphase formation at elevated temperatures and also under non-isothermal conditions, e.g., of the interphase formation of magnesium aluminate spinel at the periclase corundum contact system is of high interest. In this work, a computational framework which allows the simulation of interlayer formation under non-isothermal conditions is developed. Therefore, Gibbs energies of the CALPHAD database have been directly coupled with kinetic evolution equations derived from the thermodynamic extremal principle, which itself is extended in this work for considering besides internal phenomena like diffusion, interface migration and vacancy generation and annihilation also externally applied thermal rates in terms of cooling and heating. With the developed framework the magnesium aluminate spinel formation is studied under different isothermal states and non-isothermal conditions, where special focus is put on the thermal rate dependent asymmetric interface movements during interlayer growth.