Effect And Mechanism Of Several Typical Fungi On Corrosion Of Carbon Steel

The ocean contains abundant resources and is a huge treasure pot in nature.Therefore,China has put forward the major strategic layout of " maritime power".However,in the process of developing and utilizing these marine resources,people have to face the bad marine environment.The corrosion of a lot of infrastructure in marine environment not only brings great economic loss to people,but also causes many serious safety accidents.There,it is of great significance to understand the corrosion mechanism of metal materials in the marine environment,reduce the loss of metal materials and strengthen the control of metal corrosion,and avoid the premature damage of equipment in the marine environment.Metal materials are mainly corroded by microorganisms and non-microorganisms in the ocean,and the loss caused by microbial corrosion accounts for about 20% of the total corrosion loss.At present,the research on bacteria in microbial corrosion is very extensive and systematic,but the research on typical fungi is less,which seriously restricts people’s in-depth understanding and treatment of microbial corrosion.In this paper,three typical mangrove fungi were selected as experimental strains to explore the effects of these three typical marine fungi on the corrosion of X70 carbon steel in artificial seawater environment.The experimental results show that:1.The effect of Trichoderma elongata(T.elongata)on the corrosion of X70 carbon steel in artificial seawater was studied.By fluorescence microscope(FM),it was observed that T.elongata could adhere to the surface of carbon steel well and form stable biofilms.Through scanning microscope(SEM),it can be observed that the biofilm formed by T.elongata on the surface of carbon steel is very loose,and can not effectively inhibit the entry of corrosive ions and oxygen in seawater.The p H test results showed that T.elongata produced acidic substances during the process of metabolism,which accelerated the corrosion of carbon steel.The results of water contact angle(CA)showed that the biofilm formed by T.elongata on the surface of carbon steel had good hydrophilicity,which was beneficial to the wetting of seawater and the entry of corrosive ions,forming a corrosive liquid film and accelerating the corrosion of carbon steel.Meanwhile,the results of electrochemical impedance spectroscopy and Tafel polarization showed that T.elongata could promote the corrosion of carbon steel.In addition,it was found that the extracellular polymer of T.elongata had a certain sustained release effect on carbon steel in artificial seawater solution.2.The corrosion effect of Trichoderma viride(T.viride)on X70 carbon steel in artificial seawater was studied.Through FM,it can be observed that T.viride can adhere well on the surface of carbon steel and generate stable biofilms.We can observe by SEM at 15 d,T.viride on carbon steel surface to form a layer of dense mesh structure,on the hypha and hyphae and a large amount of nanoparticles can be observed,the nanoparticles reduced the gap between the mesh structure,to some extent inhibited the seawater corrosive ions and oxygen to enter.The characterization results of FTIR,Mapping,XPS and XRD showed that the interaction between T.viride and carbon steel produced a composite material,which could effectively inhibit the corrosion of carbon steel.The results of CA showed that the biofilm formed by T.viride on the surface of carbon steel was stable,with large contact angle,good hydrophobicity and good protection effect on carbon steel.The results of electrochemical impedance spectroscopy and Tafel polarization showed that T.viride had sustained release effect on carbon steel.In addition,it was found that the extracellular polymer of T.viride had sustained release effect on carbon steel in artificial seawater solution.When the temperature was between 10℃ and 40℃ and the concentration was between 0.0520 mg/L and 0.2080 mg/L,T.viride extracellular polymer had the best sustained release effect on carbon steel at 20℃ and0.1040 mg/L.3.The corrosion effect of Paecilomyces lilacinus(P.lilacinus)on X70 carbon steel in artificial seawater was studied.Through FM,it could be observed that P.lilacinus could attach well on the surface of carbon steel and generated stable biofilms.It was observed by SEM that P.lilacinus formed a dense biologicalized film on the surface of carbon steel at 15 d.The dense biomineralization film could inhibit the entry of corrosive ions and oxygen in seawater to a certain extent.The characterization results of FTIR,XPS and EDS showed that P.lilacinus could interact with carbon steel to form a biologicalized film,which could exist stably in seawater and effectively inhibit the corrosion of carbon steel.The results of CA showed that the biofilm formed by P.lilacinus on the surface of carbon steel was stable,with large contact angle,good hydrophobicity and good protective effect on carbon steel.In addition,it was also found that P.lilacinus extracellular polymer had a certain slow-release effect on X70 carbon steel in artificial seawater solution.In conclusion,the effects of the three strains of fungi on X70 carbon steel were different.T.elongata accelerated the corrosion of carbon steel.The interaction between T.viride and carbon steel produced a large number of nanoparticles,which filled the biofilm gap formed by T.viride and effectively inhibited the corrosion of carbon steel.P.lilacinus would form a dense biomineralized film on the surface of carbon steel,thus inhibiting the corrosion of carbon steel.However,the extracellular polymers of the three fungi all had a certain anti-corrosion effect on carbon steel,among which,the extracellular polymer of T.viride had the best anti-corrosion effect.