VALENCE BAND SPECTRA OF ALUMINUM-OXIDES, HYDROXIDES, AND OXYHYDROXIDES INTERPRETED BY X-ALPHA-CALCULATIONS

The oxides, hydroxides, and oxyhydroxides of aluminium cannot be distinguished by their core X-ray photoelectron (XPS) regions, but have significantly different valence band regions. The differences observed experimentally can be explained by Xalpha calculations. By combining the valence band XPS data to identify surface composition, with bulk purity identified by x-ray powder diffraction, and the expected spectra from the calculations, we conclude that while the oxides and hydroxides are unchanged on the surface, the oxyhydroxides are only seen as hydroxide (bayerite or nordstrandite) on their surfaces. The surface oxide on the "as received" metal is found to be in the form of gibbsite. The ability of valence band XPS to distinguish these compounds will aid in their identification in corrosion and catalytic situations.