Electrochemical and Photoelectrochemical Characterization of the Passive Film Formed on AISI 254SMO Super-Austenitic Stainless Steel

Abstract

The structure and composition of the passive film formed on the super-austenitic AISI 254SMO stainless steel in borate solution were studied using photocurrent spectroscopy coupled with electrochemical measurements. Charge passed calculations suggested that the Cr(VI) phase formed in the transpassive region is insoluble. Evidence for the presence of Ni in the passive film was also found. Photocurrent spectroscopy revealed that an n-type Fe(III) oxide phase dominated at more positive potentials, where Cr(VI) was expected. However, once the Cr(III) phase started to form in the reverse potential scan both Fe(III) and Cr(III) phases appeared together in the passive region between 200 and -300 mV, with both showing n-type behavior. At more negative potentials, cathodic photocurrents were observed, most likely due to the reduction of the Fe2 O3 to p-type FeO. The magnitude of the bandgaps of the oxides were found to be independent of the values of the applied potential. © 2006 The Electrochemical Society.