A new perspective on the mechanism of swift corrosion perforation of copper in solutions containing sulfate-reducing bacteria

Due to the higher electrode potential of copper compared to hydrogen, the conventional pitting corrosion theory applicable to materials like steel, known as occluded self-catalytic batteries, cannot elucidate the swift corrosion perforation observed in copper tubes in heat exchangers of air conditioning and other equipment. This study uncovers a novel mechanism contributing to the rapid corrosion perforation of copper by investigating the impact of copper ion addition on the corrosion behavior induced by sulfate-reducing bacteria (SRB). The findings reveal that the introduction of Cu2+ results in a distinct "passivation-like zone" on the anode polarization curve. Additionally, the extracellular polymeric substances (EPS) produced by SRB exhibit a considerable increase, and the presence of sulfide ions in the solution greatly reduces the electrode potential of copper, indicating the formation of an intact composite biofilm (organic and inorganic Cu2S) on the surface of Cu. The biofilm effectively retards the corrosion rate by SRB. On the other hand, in the absence of Cu, the film formed on the surface is primarily composed of cuprous sulfide. This brittle film, exhibiting piezoelectric properties, cracks under potential fluctuations. Consequently, the exposed metal corrodes under the influence of hydrogen and sulfur ions, leading to the regeneration of a cuprous sulfide film. This cyclic process results in the rapid formation of corroding pits. If residual dissolved oxygen is present in the solution, the local corrosion rate will be further accelerated. This has important reference value for solving the high-energy consumption operation and environmental pollution problems caused by coolant leakage caused by SRB corrosion in practical engineering.