The influence of oxygen on the cathodic behaviour of manganese dioxide was studied qualitatively by galvanostatic reduction of MnO2 deposited electrochemically onto stainless steel (SS), under aerated and deaerated conditions. The results indicate that the reduction takes place primarily at the interface MnO2/SS-substrate and leads to detachment of the deposit.
Oxygen may parlicipate in the reduction reaction being reduced itself and retarding the detachment process. This effect is diminished at higher current densities due to diffusion limitation of oxygen. It is concluded that the wide possible range of surface coverage by MnO2 that cart be produced by microorganisms may result in a cathodic behaviour that is between almost potentiostatic and strong current limitation. This behaviour is discussed with respect to pitting of SS. It is concluded that
microscopic surface coverage of MnO2 on SS causing ennoblement may promote repassivating pitting rather than stable pit growth due to cathodic current limitation. Under certain conditions this could lead to an improvement in the resistance against pitting attack for a given surface of SS undergoing such a process. Keywords: microbiologically influenced corrosion (MIC), manganese oxidizing microorganisms, manganese dioxide
ennoblement, stainless steel, pitting corrosion