Kinetic modeling of high-temperature oxidation of pure Mg

A variety of experimental tracer diffusivities of Mg and O in magnesium oxide available in the literature were first assessed. Atomic mobilities including bulk and short-circuit diffusion of Mg and O were then obtained by means of the CALPHAD (Calculation of Phase Diagram) approach. Afterwards, the diffusion-controlled kinetic model of oxidation in a gas-MgO-Mg environment was developed based on the moving boundary model and Fick's law, coupling with the modified thermodynamic description of MgO. A mathematical expression for parabolic rate constant kp of the oxide scale was derived for magnesia and correlated with the thermodynamic and diffusion kinetic information. The evaluated kp results were in line with the experimental data. Finally, the oxidation process of pure magnesium at 673 K was model-predicted, and the predicted evolution of the oxide thicknesses agreed very well with the experimental data. It was indicated that the grain boundaries diffusion of magnesium cations predominated the high temperature oxidation process.