XPS analysis of the passive film formed on austenitic stainless steel coated with conductive polymer

Improvement of the passivation behavior of Type 304 austenitic stainless steel (SS) by coating with conductive polymers (CPs), like polyaniline (PANI) and poly(o-phenylenediamine) (PoPD), followed by exposure in an acid solution has been demonstrated. The passive films formed on SSs (after peeling off the polymer layer) are compared with those formed during anodic polarization under the same exposure condition. The passive films beneath the CPs are thicker and less hydrated than those formed on uncoated stainless steel. The polymer layer enhances the enrichment of chromium and nickel in the entire passive oxide, forming a more protective film than that formed during anodic polarization. The elemental distribution within the passive film is different in the two modes of passivation. The type of the polymer influences on the composition of the passive film. The best passivation is obtained by PoPD, with the passive film resulting in significant resistance of the SS to pitting corrosion in the 3% NaCl solution. The oxide film of this steel is characterized, in its inner and outer layers, by the highest ratio of Cr(OH)₃/Cr₂O₃ and the lowest content of iron species.