An Ellipsometric Study of Chromium Passivation

In situ ellipsometry has been combined with electrochemical measurements to gain insight into the mechanism of passivation of chromium in pH 1.7 K2SO4 solution. At 410 mV vs. NHE a region of active dissolution at an apparently oxide-free surface was observed. With an anodic potential step to 360 mV, passivation occurs with growth of less than 1A of oxide film. This film is thicker at more anodic potentials and probably consists of Cr2O3. The mechanism of passivation most consistent with the experimental observations is that of simultaneous oxide formation and metal dissolution, with passivation resulting from formation of a monolayer of film. © 1971, The Electrochemical Society, Inc. All rights reserved.