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 di chromate ions on the dissolution kinetics were investigated by using artifi cial crevice electrodes. The aluminum artificial crevice electrodes were po tentiostatically polarized over a range of potential in 0.1 M NaCl solution with and without dichromate ions. The anodic dissolution charge; and catho dic charges for the hydrogen and dichromate reduction reactions, were measu red. The addition of dichromate ions did not suppress the active dissolutio n. This indicates that the mechanism of localized corrosion inhibition by d ichromates is something other than anodic inhibition of Al dissolution in t he pit or crevice environment. The relative amount of local cathodic reacti ons on Al was increased by the addition of dichromate because of the dichro mate reduction. The initial dissolution of aluminum in a crevice was ohmic controlled. From the change in the dissolution current with time, the condu ctivity of the crevice and potential at the bottom of crevice were estimate d. The conductivity and the bottom potential decreased with the ratio of ca thodic charge of hydrogen evolution to anodic dissolution charge. The condu ctivity in the crevice and thus the dissolution current seem to be controll ed by hydrogen evolution and only indirectly by dichromate concentration. ( C) 1999 The Electrochemical Society. S0013-4651(99)04-015-X. All rights res erved.