Valence and core photoemission of the films formed electrochemically on aluminium in nitric acid

The chemical composition of the oxide films formed on aluminium after electrochemical oxidation in nitric acid solution has been examined by valence and core phtoemission. Angle-resolved X-ray photoemission in the valence band indicated that the films in 0.5 mol dm–3 nitric acid consisted of a mixed composition at less positive potentials consisting of a gibbsite [Al(OH)3] surface with an inner layer of γ-Al2O3. At more positive potentials the film consisted entirely of γ-Al2O3. In more concentrated acid (5 mol dm–3), especially for longer (60 min) exposure time, the films were essentially γ-Al2O3.