The structure of barrier anodic films formed on aluminum covered with a layer of hydrous oxide

Abstract

Barrier anodic film formation on aluminum covered with a layer of hydrous oxide has been investigated by transmission electron microscopy of ultramicrotomed sections. Hydrous oxide film formed on aluminum by 5min reaction with boiling distilled water was found to consist of an inner dense layer of relatively uniform thickness, about 1100 Å, and an outer fibrillar laver of varying thickness. During anodic oxidation, the inner dense layer of hydrous oxide film was found to be incorporated into the barrier oxide layer growing beneath the hydrous oxide film. Presence of γ’- crystalline layer containing voids and cracks was revealed clearly in the barrier oxide layer. The mode of the growth of γ’-crystalline layer within the barrier oxide was found to be consistent with the mechanism of the barrier anodic film formation on aluminum in the presence of hydrous oxide layer proposed by Alwitt. © 1985, The Japan Institute of Light Metals. All rights reserved.