The influence of dichromate ions on aluminum dissolution kinetics in artificial crevice electrode cells

Dissolution kinetics for pits and crevices in aluminum and the effect of dichromate ions on the dissolution kinetics were investigated by using artificial crevice electrodes. The aluminum artificial crevice electrodes were potentiostatically polarized over a range of potential in 0.1 M NaCl solution with and without dichromate ions. The anodic dissolution charge; and cathodic charges for the hydrogen and dichromate reduction reactions, were measured. The addition of dichromate ions did not suppress the active dissolution. This indicates that the mechanism of localized corrosion inhibition by dichromates is something other than anodic inhibition of Al dissolution in the pit or crevice environment. The relative amount of local cathodic reactions on Al was increased by the addition of dichromate because of the dichromate reduction. The initial dissolution of aluminum in a crevice was ohmic controlled. From the change in the dissolution current with time, the conductivity of the crevice and potential at the bottom of crevice were estimated. The conductivity and the bottom potential decreased with the ratio of cathodic charge of hydrogen evolution to anodic dissolution charge. The conductivity in the crevice and thus the dissolution current seem to be controlled by hydrogen evolution and only indirectly by dichromate concentration. (C) 1999 The Electrochemical Society. S0013-4651(99)04-015-X. All rights reserved.