Electron Microscopic Study of Anodic Oxide Films Formed on Aluminum with Thermal Oxidation

The effects of thermal oxidation on the formation of barrier-type oxide films on aluminum were investigated by electron microscopy, gravimetry, and chemical analysis. Highly pure aluminum specimens were heated in air at 773-873 K for 1-24 hr, and then anodized in a neutral borate solution at 353 K with a constant current density of 50 A/m 2 . Thermal oxide films were found to have a terminal thickness of ca. 30 nm after long heating periods, and to have a crystalline structure of γ-alumina