Study On Microbiologically Influenced Corrosion Behavior And Mechanism Of Typical Steel And Iron Materials By Halophilic Archaea In High Salinity Environment

With the world's energy exploitation gradually turning to extreme natural environment,such as polar region and deep sea,a large number of archaea inhabiting such environments will inevitably pose a threat to the safe service of metal materials.In addition,some archaea have been used in biogas preparation,bioleaching and wastewater treatment.Therefore,it is of great theoretical value and practical significance to study the microbiologically influenced corrosion(MIC)of archaea for ensuring and improving the safety of energy exploitation and industrial production.In view of the fact that buried pipelines and railway facilities need to cross a large area of alkali soils and salt lakes in the west region of China,this paper focused on the influence of halophilic archaea,which is the main microorganism in alkali soils and salt lakes,on metal corrosion.The corrosion behavior of Q235 carbon steel and 304 stainless steel under the influence of halophilic archaea was studied,and the effects of two key environmental factors,dissolved oxygen concentration and NaCl concentration,on the MIC caused by halophilic archaea were analyzed.Finally,combined with SECM technology,the electron transfer mediator function of catalase was revealed,and the mechanism of MIC caused by halophilic archaea was improved.The main results are as follows:In the immersion experiment,unlike slow uniform corrosion under sterile condition,under the influence of Natronorubrum tibetense,the surfaces of Q235 carbon steels exhibited localized corrosion,and the corrosion pits expanded rapidly with the prolongation of immersion time.After 14 days,the corrosion weight loss reached 0.051g/cm2 in inoculated medium,which was about twice as much as that in sterile medium.The uneven and localized aggregation of N.tibetense biofilm on the surface of carbon steel induced oxygen concentration cell and localized corrosion.At the same time,N.tibetense cells could directly consume metallic iron as an energy source.The coupling effect of iron consumption behavior and oxygen concentration cell promoted the corrosion of carbon steel.After 14 days of immersion in sterile medium,304 stainless steels showed no obvious pitting corrosion.After 14 days of immersion in inoculated medium,the corrosion resistance of passive films of stainless steels decreased significantly,and the surfaces of stainless steels showed serious pitting corrosion.The maximum pitting corrosion depth was 5.0um.In addition to the oxygen concentration cell effect caused by biofilm,the metabolism of N.tibetense had a significant modification effect on the chemical compositions of passive film of stainless steel.Besides,planktonic N.tibetense cells could also consume stainless steel as an energy source.The combination of above three functions accelerated the dissolution and damage of passive film and promoted the pitting corrosion of stainless steel.With the increase of dissolved oxygen concentration(DOC),the uniform corrosion of carbon steel in sterile medium increased gradually,while the localized corrosion of carbon steel in inoculated medium increased and then changed to uniform corrosion.The most serious MIC occurred at 3.0ppm.When DOC was between 0.5ppm?3.0ppm,the increase of DOC promoted the proliferation of N.tibetense cells in inoculated medium,which strengthened the MIC effect of N.tibetense on carbon steel and aggravated localized corrosion.When DOC was 5.0ppm,the amounts of N.tibetense cells continued to expand.Limited energy supply in culture medium forced a large number of cells to adhere to the carbon steel surface to obtain sufficient energy.The relatively uniform distribution of biofilm weakened the effect of oxygen concentration cell.The increased biofilm also strengthened the barrier effect to the diffusion of dissolved oxygen,so the MIC was weakened.With the increase of NaCl concentration,the uniform corrosion of carbon steel in sterile medium was first strengthened and then weakened,and the most serious corrosion occurred when NaCl concentration was 0.1g/mL.In inoculated medium,with the increase of NaCl concentration,the uniform corrosion first appeared on the surface of carbon steel and then turned to localized corrosion,and the MIC gradually increased.Once the NaCl concentration exceeded 0.25g/mL,the localized corrosion began to be weakened.The growth of N.tibetense was difficult under low NaCl concentration(Og/mL and 0.1g/mL),so the influence of MIC was weak.High NaCl concentration promoted the rapid growth and proliferation of N.tibetense,and its MIC effect emerged and dominated,so the localized corrosion appeared and the MIC of carbon steel continued to be promoted.If the NaCl concentration was too high(0.3g/mL),the adsorption of Cl-on the surface of carbon steel repelled the adsorption and reduction reaction of dissolved oxygen on the cathode area of electrochemical process.Hence,the localized corrosion was weakened.The addition of catalase in both sterile and inoculated media could promote MIC of metal matrix,and the promoting effect in inoculated medium was more conspicuous.As a non-energy substance,the coexistence of catalase with metal sample was more conducive to the proliferation of N.tibetense cells.In the MIC process,catalase acted as electron transfer mediator.Through the catalytic cathodic oxygen reduction and disproportionation of catalytic H2O2 decomposition,catalase helped planktonic N.tibetense cells complete the energy uptake process by the combination of its own catalysis effect and the cyclic conversion of O2 and H2O2.