Pit propagation in carbon steel exposed to a phosphate-containing electrolyte required either stagnant conditions or microbial colonisation of anodic regions. A scanning vibrating electrode (SVE) was used to resolve formation and inactivation of anodic and cathodic sites on carbon steel. In a sterile continuously aerated medium, pits initiated and repassivated. However, in a medium that was not aerated, pits initiated and propagated. Pit propagation was also observed in a continuously aerated medium when a heterotrophic bacterium, originally isolated from a corrosion tubercle was inoculated into the medium. Autoradiography in combination with SVE analysis demonstrated that the sites of anodic activity coincided with sites of bacterial activity and that the bacteria were attached preferentially to the corrosion products over the anodic sites. Attraction to the anodic sites did not depend on the viability of the bacteria and was not specific for iron as a substratum.
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