Passivity breakdown of Al 2024-T3 alloy in chloride solutions: a test of the point defect model

Cyclic voltammograms of Al 2024-T3 alloy samples, in deaerated aqueous chloride solutions of various concentrations, have been recorded and analysed. A linear dependence between the breakdown potential, E-b, and the square root of the scan rate, v(1/2), was found for all chloride concentrations and also for synthetic seawater leading to alpha values between 0.41 and 0.38. The breakdown potential at zero scan rate, E-b (v = 0), showed also a good linear dependence on the logarithm of the activity of the chloride anions. From the slope of the straight line a value of 3.29 was obtained for the ratio (xi/J(m)) from which a xi value less than or equal to 3 x 10(15) cation vacancies cm(-2) was calculated. Average critical concentration of cation vacancies on Al and gamma-Al2O3 computed from geometric arguments has showed excellent agreement with those computed from experimental data and analytical equations derived from the Point defect model (PDM). (C) 2002 Published by Elsevier Science B.V.