THE ELECTRODE-KINETICS OF PIT INITIATION ON ALUMINUM

An electrode kinetic model for pit initiation has been described in terms of the charge on the oxide surface and the pH of zero charge parameter. The model takes into account adsorption of chloride ions on the oxide surface, penetration of chloride ions through the oxide him via vacancy transport, and localized dissolution of aluminum at the metal/oxide interface in three consecutive single electron transfer steps. Mathematical expressions are derived which agree with the experimentally determined variation in pitting potential with chloride ion concentration al constant pH and with the variation in pitting potential with pH at constant chloride ion concentration.