Simultaneous ellipsometric and chronoamperometric study of barrier aluminium oxide growth and dissolution in acetate buffer

In situ ellipsometric and chronoamperometic measurements were applied simultaneously to monitor barrier oxide growth and dissolution on aluminium. The steady-state thickness prior to each potential step was determined by electrochemical impedance spectroscopy (EIS) for calibration of the transient data. The growth of the barrier oxide, following a positive potential step, was consistent with the Cabrera-Mott inverse square logarithmic growth law. About 20 % of the measured current resulted in barrier oxide growth. The oxide dissolution rate, following a negative potential step, was controlled by diffusion of aluminium ions into the test solution. The obtained dissolution rate was thus much smaller than the corresponding oxide growth rates. Oxide solubilities calculated from Fick’s second law, by using literature data for the diffusion coefficient of Al 3+ , were about two orders of magnitude larger than that obtainable from thermodynamic considerations. The methodology developed provides the kinetic and solubility data needed for improving the existing know-how about the growth and dissolution kinetics of the barrier oxide layer in aqueous solution.