AN INVESTIGATION OF THE PASSIVATION AND BREAKDOWN OF PASSIVITY OF CHROMIUM BY CYCLIC VOLTAMMETRY AND ELLIPSOMETRY

The passivation phenomena of pure chromium have been investigated using a combination of cyclic voltammetry and ellipsometry. It was observed that the current only reaches its maximum in the active-passive transition region during a potential scan when the electrode is already partially covered with an oxide/hydroxide layer. A change in optical parameters, Δ and Ψ, in the transpassive region of an anodic scan, is explained in terms of internal reorganization of the film preceding transpassive dissolution. In the cathodic scan the reduction of Cr ions, which are formed in the transpassive region, gives rise to a maximum. It is suggested that repassivation during the cathodic scan is due to more than one reduction process. © 1990.