Combination of Different Electrochemical Techniques to Characterize the Anodic Behaviour of Chromium

Abstract

A literature survey on the active dissolution and passive state of pure chromium in acidic solutions revealed that there is considerable discrepancy concerning the properties of the anodic passive film on Cr. The conclusions concerning especially the type of conductivity of the anodic film at different potentials were contradictory. This work was undertaken to clarify the anodic behaviour of Cr using a combination of several experimental techniques, including in situ dc resistance measurements with the contact electric resistance (CER) technique. Rotating ring disk electrode measurements in the active dissolution region showed that release of soluble Cr species proceeds in solutions with a pH of 5, in contradiction with earlier reports which had indicated that active dissolution occurs only at pH 0.7 V, i.e. at potentials approaching the transpassive region. Photocurrent measurements pointed to an almost opposite behaviour as a function of potential, and the change in the sign of the photocurrent was dependent on the initial oxidation potential. Measurements performed using the CER technique indicated that irreversible changes in the film properties take place at high potentials in the passive region. This lead us to suggest that different layers of the film determine the photoresponse and the capacitive behaviour of the electrode.