Electrochemistry of passive metals modified by manganse oxides deposited by leptothrix discophora: two-step model verified by tof-sims
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We have applied time-of-flight secondary ion mass spectroscopy (ToF-SIMS) to study microbially induced ennoblement of 316L stainless steel and Ti-A1-4V surfaces exposed to manganese-oxidizing bacteria Leptothrix discophora SP-6. Our observations indicate that manganese biomineralization occurs in two steps: first, the divalent manganese (Mn2+) is oxidized to manganese dioxide, MnO2. Both reactions contribute to an increase in the open circuit potential and hence to the ennoblement of the material. Manganese cycling at a surface of passive metals produces renewable cathodic reactants, manganese oxyhydroxide and manganese dioxide, and endangers the material integrity.
Shi, X., R. Avci, and Z. Lewandowksi, "Electrochemistry of passive metals modified by manganse oxides deposited by leptothrix discophora: two-step model verified by tof-sims," Corrosion Science, 44:1027-1045 (2002).