Influence of sulfide on the passivation behavior and surface chemistry of 2507 super duplex stainless steel in acidified artificial seawater

In the present work, influence of sulfide on the passivation behavior and film chemistry of 2507 super duplex stainless steel (SDSS) in deaerated and acidified artificial seawater was investigated by electrochemical analysis and X-ray photoelectron spectroscopy characterization. Sulfide ion accelerates the film degradation process of 2507 SDSS as indicated by the increased anodic dissolution current. There exists a critical sulfide concentration above which the adsorbed sulfur-assisted corrosion strongly facilitates the film dissolution. Below this threshold value, the field strength and point defect diffusivity inside the passive film are increased. Addition of sulfide results in the depletion of oxides and Fe2+ compounds in the passive film but no sulfur-containing constituent is detected. The n-type semiconductor of the passive film is not altered but the donor density decreases with addition of sulfide, attributed to the blocking of oxygen vacancies and the consumption of Fe2+ interstitials by sulfur.