Time of Flight Secondary Ion Mass Spectroscopy, X-Ray Photoelectron Spectroscopy, in situ Photo-Current Spectroscopy and electrochemical analysis were combined to characterize the physicochemical alterations induced by electrochemical passivation of the surface oxide film providing corrosion resistance to 316L stainless steel. The as-prepared surface is covered by a ~2 nm thick, mixed (Cr(III)-Fe(III)) and bi-layered hydroxylated oxide. The inner layer is highly enriched in Cr(III) and the outer layer less so. Molybdenum is concentrated, mostly as Mo(VI), in the outer layer.Nickel is only present at trace level. These inner and outer layers have band gap values of 3.0 and 2.6-2.7 eV, respectively, and the oxide film would behave as an insulator. Electrochemical passivation in sulfuric acid solution causes the preferential dissolution of Fe(III) resulting in the thickness decrease of the outer layer and its increased enrichment in Cr(III) and Mo(IV-VI). The further Cr(III) enrichment of the inner layer causes loss of photoactivity and improved corrosion protection with the anodic shift of the corrosion potential and the increase of the polarization resistance by a factor of ~4.Aging in the passive state promotes the Cr enrichment in the inner barrier layer of the passive film.

Al−Nb containing mixed oxides were grown by anodizing sputter-deposited Al−Nb alloys of different compositions. A photoelectrochemical investigation was carried out in order to estimate the band gap, flat band potential, and conductivity type of these oxides as a function of their composition. The dependence of the band gap on the composition of mixed sp−d metal oxides has been rationalized by using a semiempirical correlation between the difference of electronegativity and band gap of oxides proposed in the literature some years ago and recently tested for regular d−d metal mixed oxides. The band gap increase observed as a function of Al content into the oxides seems mainly depending on the monotonic shift of the conduction band mobility edge, E CBM , derived from 5d orbitals of Nb 5+ in the presence of an almost constant energy location of the valence band mobility edge, E VBM .