PASSIVE FILM CHEMISTRY on 316L STAINLESS STEEL ENNOBLED BY BIOMINERALIZED MANGANESE

摘要

The effect of ennoblement on chemistry of passive films on 316L stainless steel (SS) was quantified using surface-sensitive analytical techniques. Under well-defined laboratory conditions, SS coupons were ennobled to approx +350mV_(SCE) by biofilms of manganese-oxidizing bacterium Leptothrix discophora SP-6. Ennobled coupons were analyzed by x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TofSIMS). From the XPS depth profiles of Fe, Cr, O, Ni, C and Mn, we evaluated thickness of the passive layers before and after ennoblement, while the TofSIMS depth profiles were used to evaluate spatial distribution of Mn, Cr, Fe and Ni on the surface. Because the ennobled coupons were covered with biomineralized deposits, sputtering was used to remove these deposits under ultrahigh vacuum (UHV) conditions before probing the chemistry of the underlying passive layers. The main conclusion of the paper is that oxide layers on the ennobled coupons are significantly thinner than those on the pre-ennobled coupons, which may, hypothetically, contribute to their susceptibility to localized corrosion.