Growth of Anodic Aluminum Oxide Films Without pH-Buffer

The anodic behavior of abraded pure Al in un-buffered solutions has been addressed using the cyclic voltammetry and the numerical modeling. In buffer solutions such as borate and phosphate, the Al oxidation current increases rapidly at first and then reaches a plateau region, which can be explained in terms of the high field conduction model and oxide dissolution. However, the anodic current in un-buffered solutions such as sulfate solution continues to increase with potential, which necessitates modification to the conventional high field conduction model. The behavior in un-buffered solutions has been ascribed to the increases in acidity at oxide/electrolyte interface as the anodization proceeds. By assuming that the oxide formation efficiency is diminishing with the degree of surface acidity, features of the anodic behavior in un-buffered solutions, absent in buffered solutions, were simulated.