Influence of incorporated Mo and Nb on the Mott–Schottky behaviour of anodic films formed on AISI 304L

The effect of incorporated Mo and Nb on the electronic properties of oxide films formed on AISI 304L was investigated by Mott–Schottky analysis. The films show a bi-layer structure and behave as n-type and p-type semiconductors at potentials above and below the flat band potential. The inner p-type layer is Cr-enriched, while the outer n-type layer shows a slight increase in Fe-content close to the outer surface, where NbO3+-oxalate or MoO42− incorporation occurred. The observed enhancement of pitting corrosion resistance of anodized steels is most probably related to compositional changes and thickness increase of the film after the surface treatments.