Investigation Of Severe Microbiologically Influenced Corrosion Of Stainless Steels By Acid Producing Bacterium Acidithiobacillus Caldus SM-1

The development of human civilization and social progress are closely related to metal materials,and the application of new metal materials is a significant progress of era.Nowadays,various kinds of metal materials are not only the important material basis of human social development,but also play an important role in our daily production and life.However,the problem of material maintenance has been a hot topic during the process of continuous application of new materials,wherein corrosion problem of metal materials is one of the most serious problem.Traditional corrosions mainly include local corrosions and uniform corrosions,and therein pitting corrosion caused by microbiologically influenced corrosion(MIC)is an extremely severe problem among local corrosion in addition to intergranular corrosion,crevice corrosion and corrosion fatigue and so on.Today,researches in the field of microbial corrosion are still incomprehensive and incipient.The variety of microorganism species and their complex ways to accelerate the corrosion are the main reasons that block further development of MIC contriol,so we need more researchers to do comprehensive and detailed researches on these issues.Study of corrosion behavior and mechanism of 316L/316L-Cu stainless steels and S32654 super austenitic stainless steel(S32654 SASS)by a new bacterium Acidithiobacillus caldus SM-1(A.caldus SM-1)has been explored in this thesis,devoting to fill the blank in the field of microbial corrosion about this bacterium,and understanding the specific microbial corrosion mechanism,fundamentally to prevent and availably control the corrosion of metal materials in presence of A.caldus SM-1.In this thesis,the MIC characteristics of 316L/316L-Cu stainless steels which is used as the material for bioreactor containing this type of bacteria,and S32654 super austenitic stainless steel(S32654 SASS),an excellent corrosion resistance material,caused by the acid producing bacterium(APB)Acidithiobacillus caldus SM-1(A.caldus SM-1),were investigated by using electrochemical methods and surface analysis techniques,and analysis of the corrosion products by XPS to deduce the potential corrosion mechanism of A.caldus SM-1 on the surface of metal materials finally.Experimental results showed that coupons immersed in the A.caldus SM-1 medium were obviously highly corroded.However,the copper in the 316L-Cu SS samples resisted with the affect of A.caldus SM-1,thus 316L-Cu SS samples in the A.caldus SM-1 medium were immuned to MIC.Meanwhile,according to the results of XPS analysis,molybdenum sulfide was found in the corrosion products.As we all known,molybdenum plays a very important role in the passive film,so precipitation of molybdenum element from stainless steel is deemed to be the key point of MIC mechanism.