Stability of the Metal-Oxide Interface during Anodization of Aluminum

The growth behavior of the metal-oxide interface during anodization of aluminum was analyzed by considering the contributions of interfacial diffusion and electric field-driven migration of the interface. The analysis of linear stability showed that the electric field enhances the growth of interfacial perturbations and leads to interfacial instability, while the interfacial diffusion suppresses the instability. The instability is long-wave with the critical spatial frequency being determined by the competition between the interfacial diffusion and the electric field-driven migration of the metal-oxide interface. For an interfacial perturbation of given spatial frequency, the critical electrical voltage was obtained, which increases with the spatial frequency.