Study On Corrosion Behavior Of Nitrate Reducing Bacteria To Carbon Steel Under Polarization

Generally microbiological influenced corrosion(MIC)can occur to varying degrees in any environment,such as water or wet air,which is conducive to the growth and reproduction of microorganisms,such as oil extraction,storage or transportation systems,and aircraft fuel storage tanks.For a long time,the research on MIC has focused on Sulfate-reducing Bacteria,but the classification of microorganisms in nature is complex,and the mechanisms of metal corrosion are different.At present,there are few reports on the corrosion of metals by Nitrate-reducing Bacteria.Moreover some studies have pointed out that bacillus are the dominant flora in the process of metal corrosion.Therefore,this paper chose Bacillus subtilis as the research object,and investigated its corrosion behavior under different polarizations.First,the growth curves of Bacillus subtilis at different polarization potentials were measured by spectrophotometry,and the adhesion of microorganisms on the electrode surface was observed with fluorescence staining technology.Consequently,the influence of cathodic polarization and anodic polarization on the adhesion of Bacillus subtilis can be concluded.In order to obtain the law of microorganisms on the corrosion of carbon steel under polarization,different values of cathodic polarization potential and AC potential were applied to the electrodes.During the experiment,in order to determine the corrosion rate and tendency of the X80,the electrochemical parameters of metal electrodes were measured by the electrochemical method.Subsequently,the change of the corrosion potential / current density distribution of the metal surface was measured by using the WBE technology to determine the integrity of the metal surface film and the type of corrosion.The results show:(1)When using fluorescent staining technology,it was found that when the cathodic polarization potential was applied,the amount of bacteria attached on the electrode surface gradually decreased with the continuous negative shift of the applied potential;when the anodic polarization potential was applied,the more positive the potential,the lower the number of live bacteria on the electrode surface,namely the more inactivated bacteria can be observed at the same time.This shows that cathodic polarization can only inhibit the attachment of microorganisms and fail to cause inactivation of microorganisms;while anodic polarization can not only affect the activity and growth of microorganisms,but also may change the attachment and structure of microbial film.When the potential reached a critical value,it can even kill them.(2)Using electrochemical methodes,it was found that when the cathodic polarization potential was applied,if the polarization potential was low,metal corrosion was mainly controlled by Bacillus subtilis;then with the negative shift of polarization potential,the electrochemical reaction gradually dominated the metal corrosion process.When mixed polarization was applied,due to the existence of the electric double layer capacitor,the electrode was less corroded under a weak potential;as the potential gradually increased,the protective film on the electrode surface became a loose and porous structure,so that the localized corrosion of the metal was intensified.(3)Using WBE technology,it was found that when the cathodic polarization potential was applied,as the polarization potential continued to move negatively,the potential difference between the electrodes first increased and then decreased.The increase represented the process of falling off the biofilm,and the decrease represented the formation of the corrosion product film.When mixed polarization was applied,as the potential gradually moved forward,X80 progressed from uniform corrosion to the localized.