Abstract
99.99% Al specimens were anodically oxidized in a boric acid-borate solution (pH = 7.4, 20°C) by applying a constant potential of 50 V( vs sce). The oxide films formed were compact and had a thickness of about 76 nm. The distributions of Al(III), O(II), and B(III) ions in the films were determined by X-ray photoelectron spectroscopy and chemical analysis combined with chemical sectioning of the films in a sulfuric acid solution. It was ascertained that the film consists of two parts: the average composition of the outer part is AlO 1.36(OH) 0.28(B 2O 3) 0.07, and that of the inner part is AlO 1.5(B 2O 3) 0.027. The outer part is slightly hydrated, and in sulfuric acid solutions it dissolves more rapidly than the inner part. Borate ions are distributed throughout the films with an average concentration of 5.8 wt% as B 2O 3.
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