Effect of crystal orientation on anodic oxide film growth of Al

Abstract

During galvanostatic anodisation of a high purity aluminium sheet of randomly orientated single crystals, the formation of the barrier-type oxide film is accompanied by a bluish white luminescence, whose intensity is different on each crystal grain. The oxide film morphology and film growth kinetics were studied by electron microscopic observation. It was found that the surface of the oxide film with intense luminescent pattern was remarkably rugged, while that with weak luminescent pattern was entirely uniform. The film thickness at each crystal plane was nearly the same (330 nm) at forming voltage ( V f ) of 250 V, except that the surface with intense luminescent film had a random fluctuation by ca 20 nm. The oxide film formed on an Al polycrystal grew uniformly and the film thickness increased linearly with the forming voltage up to the final breakdown voltage; then the film grew scarcely, with accompanying surface irregularities. The film breakdown voltage was influenced by the crystal orientation.