Electrochemistry of passive metals modified by manganse oxides deposited by leptothrix discophora: two-step model verified by tof-sims

Abstract

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.