Study On Microbiologically Influenced Corrosion Behaviors And Extracellular Electron Transfer Mechanism Of Typical Steels By Marine Methanogenic Archaea

In the marine environment,microbiological influenced corrosion(MIC)is one of the most important factors which leads to the failure of marine engineering equipment,causing huge economic losses,endangering the safety of personnel and bringing about environmental damage.In recent years,many studies have proved that methanogenic archaea is one of the main culprit of MIC in anaerobic environments.However,there is still relatively little work on the MIC caused by methanogenic archaea and corrosion mechanisms of methanogenic archaea is also unclear.Therefore,it is necessary to study the mechanism of steel materials corrosion caused by methanogenic archaea,which is of great theoretical value and practical significance for the in-depth understanding of marine corrosion mechanisms and the enrichment of marine corrosion protection theory.In this paper,Methanococcus maripaludis(M.maripaludis),a typical methanogenic archaea strain in marine environment,was selected as the object of study.First,the growth and metabolic behaviour of M.maripaludis and its effect on the corrosion of 316L stainless steel were investigated by controlling the concentrarion of organic carbon source in the culture media.Then,the electron transfer mediators were added to the culture medium to investigate ththe effect of M.maripaludis on the corrosion behaviour of EH40 steel in sea water.And according to the experimental results,the MIC mechanism of M maripaludis was discussed.The main conclusions of this study are as follows.(1)In organic carbon source(acetate)deficient environment,M.maripaludis can utilize 316L SS as an alternative electron donor to maintain the growth metabolism.The extracellular electron transfer from 316L SS relies on redox-active substances secreted by M.maripaludis.Corrosion of 3 16L SS is promoted along with decrease of acetate concentration.M.maripaludis causes severe pitting corrosion of 316L SS in the absence of acetate due to that more redoxactive substances are secreted,which has little relationship with the M.maripaludis biofilm.(2)With the addition of natural electron transfer mediators,the MIC ability of M.maripaludis is enhanced,which promotes the pitting corrosion of EH40 steel,and this promoting tends to slow down as the concentration of riboflavin increases.The results of growth metabolism and electrochemical tests indicates that the presence of electron transfer mediators does not stimulate the growth ofM maripaludis,but rather enhances the extracellular electron transfer capacity of M.maripaludis by reducing the charge transfer resistance between the steel and M maripaludis,thereby promoting the anodic reaction of steel corrosion.(3)As well as riboflavin,M.maripaludis can also utilize artificial electron transfer mediators to acquire electrons from EH40 steel,which promotes the pitting corrosion of EH40 steel.At the same molar concentration,the artificial electron transfer mediator is less effective than riboflavin in promoting the corrosion ability of M.maripaludis.In addition,the promotion effect of different electron mediators on the corrosion of EH40 steel caused by M.maripaludis also varied.The promotion effect is AQC>Neutral red>Thionin.The results of electrochemical tests indicate that this difference is related to the charge transfer capacity of the electron transfer mediator itself.