Thermodynamics of ultra-thin oxide overgrowths on Al-Mg alloys: Role of interface energy

A thermodynamic model is developed to predict the ultra-thin crystalline oxide overgrowth due to dry, thermal oxidation of single crystalline 〈AlMg〉 alloy substrate with respect to various parameters. Along with the bulk Gibbs free energies, this model also took the alloy/oxide interface energies and oxide surface energies into consideration. The developed model was then compared with the amorphous oxide overgrowths on this alloy substrate. For all cases, stability of a particular oxide at lower oxide-film thicknesses is found to be due to its lower interface and surface energies. The model predictions are found to be at par with the experimental observations.