General growth pattern of anodic aluminum oxides

Abstract

One of the effective methods for the formation of coatings with required functional properties on the aluminum surface is the anodization. Usually anodic aluminum oxides are divided into dense (barrier) and porous. This work shows that such the division is very conditional. In any electrolyte, the alumina film origin and growth is defined by two factors. These are the rate of Al→Al2O3 transformation at the aluminum/alumina interface (V0) and the rate of the alumina dissolution at the alumina/electrolyte interface (Vd). In all cases V0>> Vd. When Vd→0, a preferential growth of dense alumina takes place. However, Vd is never equal to zero, even in water. It depends on the electrolyte composition, concentration and temperature and ion current density (Ji). With specified electrolyte, temperature and anodization voltage, only the anodization time defines either dense or porous alumina will be formed.