The influence of sulfate-reducing bacteria (SRB) on the passivity of a stainless steel, AISI 304, was investigated with X-ray photoelectron spectroscopy (XPS) and electrochemical techniques. Samples were exposed to SRB in growth media for 5 days. Potentiodynamic polarization tests were then conducted in deaerated 0.1 M HCl to determine if prior exposure to SRB compromised the passivity of the steel. The surface chemistry was analyzed with XPS, immediately after the exposure and following subsequent anodic polarization in 0.1 M HCl. Excess biomass generated by SRB could be rinsed from the steel with deaerated deionized water. Therefore, electrochemical and surface analysis were performed on both rinsed and unrinsed samples. Comparisons were made with control samples which were immersed in uninoculated media. The status of a newly polished sample at each stage of the investigation was given as a basis for comparison. It was found that SRB caused a loss of passivity in the 0.1 M HCl solution, due to the formation of sulfides. The following sulfides were observed: FeS, FeS2, NiS, Cr2S3 and possibly Fe1-xSx. The sulfides developed into the sublayer of the substrate during exposure to SRB and remained to hinder repassivation in the test electrolyte.

Subject
Metal surfaces, Iron sulfides, Chromium, Potentiostatic polarization, Anode surfaces, X-ray spectroscopy, Bacteria, Immersion, Sulfides, Anodic polarization, Potentiodynamic polarization, Passivity, Samples
Keywords:
X-ray photoelectron spectroscopy (XPS), potentiodynamic polarization, potentiostatic polarization, sulfate-reducing bacteria (SRB), sulfide, depth dependent information
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1995
Association for Materials Protection and Performance (AMPP)
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