Dissolution of the Native Oxide Film on Polycrystalline and Single-Crystal Aluminum in NaCl Solutions

The rate of dissolution, of the native film on electrochemically polished, single-crystal [(100), (110), and (111) orientations] and polycrystalline Al electrodes is reported. Measurements were made in solutions containing between 0 and 75 mM NaCl. is determined by analysis of voltammetric curves recorded during film growth, 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. is observed to be dependent upon the surface orientation in the order: polycrystalline Small enhancements in both the rate of ion transport within the oxide film and at polycrystalline Al are attributed to lowering of activation barriers at grain boundaries. is also shown to increase with increasing concentration, reaching a limiting value at ∼40 mM, regardless of electrode crystallinity or orientation. The dependence of on concentration is consistent with adsorption of at the oxide/electrolyte interface, followed by desorption of an complex.