Al2O3 film dissolution in aqueous chloride solutions

The dissolution rate of the Al2O3 passive film in near neutral (similar topH 6.7) 50 mM H3BO3/0.3 mM Na(2)B4O(7).10 H2O solutions containing between 0 and 150 mM NaCl is reported. Dissolution rates are determined by analysis of the voltammetric anodic growth curves, using a model in which oxide growth is governed by high-field transport of ions within the film, while oxide dissolution at the oxide/electrolyte interface occurs by a potential-independent mechanism. Oxide dissolution rates increase from 3.5 x 10(-14) mol/cm(2) s in the absence of Cl- to 1.6 x 10(-12) mol/cm(2) s in solutions containing 150 mM Cl-. No enhancement in dissolution rate is observed in NaBr solutions. The dependence of dissolution rate on Cl- concentration is modeled assuming equilibrium adsorption of Cl- at the oxide/electrolyte interface, followed by desorption of an AlClx complex. The results indicate that the oxide dissolution rate has a second-order dependence on the surface concentration of Cl-. (C) 2003 The Electrochemical Society.