Enrichment of chromium-content in passive layers on stainless steel coated with polyaniline

Enrichment of chromium-content in passive layers on a 304 stainless steel (SS) by coating polyaniline (PANI) has been confirmed by means of electrochemical and X-ray photoelectron spectroscope (XPS) techniques and thus prepared oxide films demonstrated to be highly stable in aggressive environment. PANI films are deposited on SS from a sulfuric acid solution with aniline monomer. The PANI-coated SS is found to maintain the passive state in a deaerated 1 M H2SO4 at 45 °C for several weeks. The passive state of SS remains in the same solution for several days even after the PANI films were completely removed. The passive layers underlying the PANI are certified to have higher chromium-content compared with the air-formed and anodically-formed oxide films on SS. It is suggested that PANI films enhance the passivation of SS by increasing the Cr2O3 content in the passive layer and by preventing the chromic oxide from directly interacting with aggressive solution.