Microbiologically Induced Corrosion of 70Cu-30Ni Alloy in Anaerobic Seawater

The corrosion of 70Cu-30Ni alloy induced by sulfate-reducing bacteria (SRB) in seawater was investigated by microscopic and electrochemical methods. Under anaerobic conditions, the SRB attached on the alloy surface formed blotchy biofilms, as observed by confocal laser scanning microscopy. Intergranular corrosion of the alloy occurred after immersion in SRB-containing seawater for 7 days, as observed by atomic force and scanning electron microscopy. Compared to the control experiment in the absence of SRB, a 330 mV shift of open-circuit potential resulted in the active direction and the polarization resistance decreased by a factor of 10. Electrochemical impedance spectroscopy data revealed that the impedance had remarkable capacitive characteristics. The response of the impedance was determined by two time constants for both the media with and without SRB. Analyses of concentrations of bacteria, metabolites, Cu, and Ni showed that the variation of concentrations of metabolites coincided with the growth of bacteria, and copper and nickel precipitated due to the production of metal sulfide. The effect of bacteria growth was the precipitation of cuprous sulfide to lower the potential of the anodic reaction and the reduction of hydrogen sulfide as the possible cathodic reaction.