Analysis of Passive Films on Stainless Steel by Cyclic Voltammetry and Auger Spectroscopy

Anodic passivation of Type 316L stainless steel in a borate‐boric acid buffer solution was studied using cyclic voltammetry and Auger spectroscopy. Based on a comparison with the results obtained on the metals (iron, chromium, and nickel), the reduction peaks appearing in the voltammograms for the steel were attributed to the reductive dissolution of a ferric oxide and to valence transitions associated with chromium and nickel in the oxide. It is shown that cyclic voltammetry in the buffer solution provides a qualitative and semiquantitative analysis of the passive film growth. Okamoto's model of formation of two types of films, determined by the anodization potential, is found to be applicable; the mechanism of oxide growth is related to selective enrichment of iron or chromium, which is based on solubility relationships predicted by thermodynamic considerations.