Anodization of Aluminum in Phosphate and Carbonate Solutions

Growth of anodic oxide on Al has been studied for porous and nonporous films using the galvanostatic technique. Measurements have been made in 0.1M solutions of H₃PO₄, Na₂HPO₄, Na₃PO₄, and Na₂CO₃. The high field approximation holds for all results. Evidence is given in support of the Verwey model. The parameters of oxide growth at high fields are nearly equal for the two types of oxide, which indicates a similar mechanism of oxide growth. The effective activation distance lies between 3.6 and 4.6 Å for all four electrolytes. While the pH of solution affects the partial solubility of oxide at high fields and the porosity of the film at low fields, the nature of anions determines the thickness and potential to which the film may grow before breakdown.