Investigation of the pore formation in anodic aluminium oxide

The mechanism accounting for the self-organization of nanoscale pores during anodic oxidation of aluminium is studied. Microstructural studies support the equifield strength model, which can be used to explain the formation of the hemispherical electrolyte/oxide and oxide/metal interfaces, uniform thickness of the oxide layer, as well as self-adjustment of the pore size and pore ordering. The fundamentals of the model are the electric field enhanced oxide dissolution rate and oxygen anion migration rate. The most important factor for determining the porosity of anodic alumina films with both ordered and disordered pores is the relative dissociation rate of water. The relationships between the porosity and anodization conditions, such as voltage, current density, and electric field strength, are also estimated.