Role of Transient Iron Sulfide Films in Microbial Corrosion of Steel

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Abstract
To simulate the role of sulfurized iron generated by sulfate-reducing bacteria (SRB) in the biocorrosion of steel, ultrathin (50-nm to 200-nm-thick) iron sulfide layers were prepared by metal organic chemical vapor deposition (MOCVD), sulfurization of iron oxides, and spray pyrolysis. After analyzing the morphology of the layers, they were exposed to sulfide-oxidizing bacteria (Thiobacillus ferrooxidans) to investigate their corrosion activities for two different iron sulfides (pyrite and marcasite). The corrosion patterns generated by bacterial cells and the morphological changes that the cells underwent during leaching were studied in-situ with high-resolution video-optical microscopy. The role of structural defects in the sulfide layers and the influence of an anionic surfactant on sulfide corrosion also were evaluated. TEM observations revealed the Thiobacillus ferrooxidans cells used an excreted organic film in which sulfide-sulfur was collected from iron disulfide (FeS2) in the form of tiny particles acting as temporary energy storage sites. The energy cycle responsible for microbial corrosion of steel and the symbiosis (collective corrosion) between SRB and aerobic iron sulfide-oxidizing bacteria were discussed based upon the investigated systems.

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