A Comparative Study Of Microbiologically Influenced Corrosion Of Two Kinds Of Copper Alloy

In this study, microbiological technology, surface analysis technique, and Electrochemical Impedance Spectroscopy (EIS) were used. The microbial and growth characteristics of Sulfate Reducing Bacteria (SRB) isolated from deposition in the bottom of the cooling tower of a power plant were investigated. The structure of biofilms formed by cultures of SRB on surfaces of copper alloy (HSn70-1A and BFe30-1-1) was studied. The electrochemical data was also used to elucidate the role of biofilms in the microbiologically influenced corrosion of copper alloy.It was found that SRB isolated from deposition in the bottom of the cooling tower consist mainly of Desulfovibrio. A few Desulfotomaculum was also observed. The SRB grows best at pH values between 7 and 8. Sulfate cannot be reduced by SRB when pH value is lower than 6, while the activity of SRB was inhibited when pH value is 9 or higher. Moreover, the higher the value of c(COD)/c(SO₄^2-), the higher the reduction ratio of SRB.Surface with biofilms present and removed were examined by Atomic Force Microscopy (AFM). The study revealed that biofilms formed on the surfaces of HSn70-1 A and BFe30-1-1 were quite different. A homogeneous biofilm was formed on the surface of HSn70-1A with surface roughness of 71.3±7.8 nm, while the biofilm formed on the surface of BFe30-1-1 was much rougher, whose roughness average was 284.0±28.2nm. Following the removal of biofilms, the surfaces of copper alloy were estimated by AFM to determine the degree of deterioration. Values of surface roughness of exposed copper alloy of HSn70-1A and BFe30-1-1 were 22.0±9.3nm and 16.2±4.3nm, respectively. Exposure of copper alloy to SRB inoculated culture resulted a significant increase in the surface roughness of the specimens compared to polished specimens. Corrosion pits on the surface of BFe30-1-1 were observed, while no pits were found on the surface of HSn70-1A.The study also showed that biofilm formed on the surface of HSn70-1A initially played a role of protection. However, the oxidation film beneath the biofilm was destroyed by the bioprocess and non-biological process, which accelerated the corrosion ratio of material. Biofilm formed on the surface of BFe30-1-1, which was much sensitive to SRB, cannot prevent metal from corrosion.