The influence of inhibitor ions on dissolution kinetics of Al and Mg using the artificial crevice technique

The effect of four anions on dissolution kinetics of Al and Mg in chloride-containing solution was investigated using the artificial crevice technique. Polarization curves for At and Mg artificial crevice electrodes were obtained by first dissolving the artificial crevice electrode to a fixed depth at a high potential and then scanning the potential downward to the repassivation potential. Potential components were obtained by fitting the polarization curve to an equation describing activation overpotential and ohmic potential drops. Of chromate, dichromate. molybdate, and nitrate. only nitrate was found to inhibit the dissolution kinetics of At artificial crevice electrodes. In contrast, all anions inhibited the dissolution kinetics of Mg artificial crevice electrodes. The results indicate that the mechanism of localized corrosion inhibition of Al alloys by chromate must be something other than inhibition of anodic dissolution in an active pit or crevice. (C) 2001 The Electrochemical Society.