Abstract
The initial stages of anodic oxide formation on aluminium in sulphuric, oxalic and phosphoric acid solutions have been studied by Auger electron spectroscopy combined with ion sputter etching. The effects of electron and ion bombardment have been examined. Oxides grown in phosphoric acid are found to be the most unstable during the analysis. Oxygen and aluminium are established to be homogeneously distributed in oxides, but the outer regions are contaminated by acid anions. The kinetics of anion incorporation correlate with a change of oxide growth stages: maximum anion concentration is achieved as the pores are nucleated in the barrier oxide. The data obtained are interpreted in terms of a field-stimulated mechanism of anion incorporation into the oxide that decreases a potential barrier for solvated protons and stimulates oxide dissolution.
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