An Investigation of Composite Aluminum Oxide Films by Radiotracer and Gravimetric Methods

Abstract

Composite oxide films on aluminum were produced by reaction with boiling water followed by anodic oxidation in a phosphate electrolyte tagged with P32 tracer. The amount of phosphorus remaining in the film was followed during stepwise dissolution. It was found that the phosphorus concentration in the barrier portion of this film was two orders of magnitude lower than in a conventional anodic oxide. The amounts of hydrous oxide and barrier oxide in the composite film were determined using a combination of film stripping and metal dissolution procedures. The weight of barrier oxide was only 75% of the weight of a conventional anodic oxide, while the dielectric constants of the two films were about the same. Some important properties of the hydrous oxide were inferred from the behavior observed in these experiments.