X-ray photoelectron spectroscopic studies of the oxidation of aluminium byliquid water monitored in an anaerobic cell

The oxidation of clean polycrystalline aluminium foil was performed in a pr eviously described anaerobic cell and studied by core level and valence ban d X-ray photoelectron spectroscopy. Oxide free sample surfaces were exposed under inert atmosphere at room temperature to increasingly oxidative envir onments of water vapor and liquid water beginning with an oxide free metal foil each time. Minor oxidative environments were found to produce a film o f boehmite with a thinner outer film of gibbsite. Harsher oxidation in liqu id water resulted in an oxide film much thicker than that found on the as r eceived sample which contained an inner composition of gamma alumina with a n outer film of gibbsite. As expected, the oxide film observed for ultra hi gh purity polycrystalline aluminium foil in the as received state was gibbs ite. The valence band of the cleaned metal is discussed in terms of residua l surface species. The evaluation and determination of these residual surfa ce species is evaluated following an analysis of two different band structu re calculations which use different d orbital exponents. It is found that w hile the density of states is almost unaltered by changes in the d exponent , the predicted spectrum is substantially changed. The work makes extensive use of valence band X-ray photoelectron spectroscopy.