Study On Corrosion Behavior Of Marine Metal Material By Vibrio Natriegens And Bacillus

Microbiological influenced corrosion?MIC?is an important part of marine corrosion.After the material is immersed in the ocean,the microorganisms will grow on the surface and gradually form the biofilm.Biofilm can not only affect the adhesion of subsequent large fouling organisms,but also change the physical and chemical properties of the surface,interact with the material,and participate in the corrosion reaction to accelerate or inhibit corrosion.In previous microbial corrosion studies,iron bacteria and sulfur bacteria were mainly studied,which were usually single bacterial corrosion.Marine immersion material is threatened by multiple microorganisms at the same time.Their combined effects on corrosion need further study.Vibrio natriegens and Bacillus are abundant in the ocean,but their corrosion research is relatively less.Marine engineering steel DH36 is selected as experimental material.Compared with the sterile artificial seawater corrosion system,the effects of Vibrio natriegens,Bacillus and mixed bacteria on the corrosion behavior of DH36steel immersed for 7 d were studied by using the electrochemical and modern characterization techniques.The main conclusions obtained are as follows:?1?In the sterile artificial seawater corrosion system,the corrosion rate of the sample was the smallest when immersed for 3 days.At this time,the surface of the sample was covered by a dense iron oxides rust layer,and the diffusion process of Fe²⁺into the solution was inhibited,which enhanced the polarization of the anode to inhibit anode dissolution.After that,the rust layer became loose under the impact of artificial seawater,and gradually became difficult to act as a dissolved oxygen barrier layer.The corrosion rate began to increase.?2?Both Vibrio natriegens and Bacillus could metabolize to produce acidic corrosive products,which deteriorated the corrosive environment.In the first 3 d of immersion,the effect of single bacteria on the corrosion of the sample was similar,both of which accelerated corrosion,and the corrosion rate was higher than that of the sterile artificial seawater corrosion system.?3?After immersion for 3 d,Bacillus showed the effect of inhibiting corrosion because it formed a dense mixed layer of biofilm and rust layer on the surface of the sample,which could not only hinder the diffusion of Fe²⁺into the solution,but also resist the erosion of dissolved oxygen on the sample matrix.The mixed layer increased the corrosion resistance and inhibited the occurrence of corrosion.Corrosion rate was less than that of the sterile artificial seawater system when immersed for 7 days.Vibrio natriegens continued to accelerate corrosion.There were many gaps and cracks in the mixed layer of biofilm and rust layer.The corrosion resistance was weak,and the oxygen concentration battery was easily induced,which kept the corrosion rate at a high level.?4?In the mixed bacteria culture,they competed for nutrients and dissolved oxygen in the medium.Bacillus mostly adhered to the periphery of the rust layer,and the morphology of bacteria was different from that of single Bacillus culture medium.The size of bacteria was smaller,with the spherical shape and poor survival.Biofilm eventually affected the accumulation of rust layer.The adhesion of mixed film layer was very poor.Loose thallus combined with corrosion products between the cracked film layer.The occurrence of local oxygen concentration battery accelerated the corrosion process.The corrosion development of samples was closer to that of Vibrio-natriegens culture medium corrosion system,but the corrosion results were more serious.