Model for porous alumina template formation: constant voltage anodization

In spite of the extensive experimental investigations reported in the literature on porous alumina templates, the theoretical mechanisms, and their dependence on process parameters such as potential difference, current density and electrolytes, are not well understood. A theoretical model developed and published for porous structure formation under constant current electrochemical anodization of aluminum is adopted for constant voltage anodization. The model is based on the rate equation approach in which both the alumina formation and etching are considered. The model employs a minimal number of parameters and yet captures the essence of the experimental observations. The model yields an analytical solution relating the model parameters, process parameters and thickness of the film, which is easy to interpret and use. The results of normalized current versus time obtained from the model are in good agreement with the experimental results reported for a range of voltages, 20-40 V. It is also observed that the thickness of the Al2O3 pore follows V-1/2 behavior for anytime during the anodization.