Role of H2O2 in microbially influenced ennoblement of open circuit potentials for type 316L stainless steel in seawater

Type 316L stainless steel specimens were exposed to natural seawater during several seasons. The concentration of H2O2 in native biofilms formed on the specimens was detected after the exposures, and open circuit potentials (OCP) for the specimens were also measured. During the summer season, the concentration of H2O2 was higher than 10 ppm and OCP were nobler than +0.6 V vs. SHE. On the other hand, during the winter season, the H2O2 concentration was lower than 2 ppm and OCP were less noble than +0.3 V vs. SHE. The specimens were exposed to synthetic seawater, to which catalase or peroxidase was added, and H2O2 in native biofilms was found to be decomposed. The ennoblement of OCP was offset by the decomposing H2O2. The value of OCP for type 316L with H2O2-free biofilms was as less noble as that with no biofilm growth. (C) 2003 Elsevier Ltd. All rights reserved.