Corrosion Effect And Mecchanism Study Of Microbial EPS On Carb On Steel And Copper Coupon

Metal corrosion will cause economic losses,waste of resources,potential safety hazards and other issues,which has attracted the attention of all walks of life.Therefore,research on metal corrosion protection methods has very positive practical significance.The method of protective layer is a relatively common method.However,the commonly used anti-corrosion coatings pose a potential safety hazard to human health and environment due to its toxicity.Therefore,the research and application of environmentally friendly coatings is an inevitable trend in the future of anti-corrosion research.Microbial anti-corrosion is a green and environmentally friendly method,It has been reported that the extracellular polymeric substance secreted by microorganisms can inhibit metal corrosion.However,there are few studies on its anti-corrosion mechanism and further research is needed.In this study,the EPS secreted by three bacteria,L.reuteri,P.fluorescens,and E.coli,was selected as the study object.The UV spectrop Hotometer,LC-MS mass spectrometer,infrared spectrometer,electrochemical workstation,and inductive coupled plasma emission spectrometer,atomic force microscopes and other test methods were used.Starting from the comparative analysis of the properties of the three bacterial EPS,we explored the effect and mechanism of EPS on the corrosion of carbon steel and copper coupon.The main conclusions are as follows:Polysaccharide is the main component of L.reuteri EPS,while protein is the main component of P.fluorescens EPS and E.coli EPS;and the EPSs of the three bacteria were all negatively charged and was positively related to the protein/polysaccharide content ratio（PN/PS）.Infrared and protein structure tests showed that the carboxyl groups contained L.reuteri EPS was more than P.fluorescens EPS and E.coli EPS.L.reuteri EPS,P.fluorescens EPS,and E.coli EPS all had inhibitory effects on the corrosion of carbon steel,and the inhibitory degrees were 28.25%,23.87%,and 21.72%,respectively,and all had a promoting effect on copper coupon corrosion.The promotion rates were 20%,13.33%,and 11.85%,respectively.The order of the maximum adsorption and removal rates of EPSs on Fe³⁺,Fe²⁺,Cu2+and Zn2+ was L.reuteri EPS> P.fluorescens EPS> E.coli EPS.And the adsorption process of the three EPS on the surface of carbon steel and copper coupon is a spontaneous monolayer adsorption process mainly based on physical adsorption.However,the adsorption with Fe³⁺ and Fe²⁺ of the three kinds of EPS forms a dense protective layer at the interface of carbon steel and blocks the invasion of corrosive ions.Therefore,the carbon steel is inhibited,and the formation time of the protective layer needs at least 8h,16 h and 16 h respectively.The membrane thickness of L.reuteri EPS,P.fluorescens EPS and E.coli EPS formed on the surface of carbon steel were 14.33 nm,4.83 nm,and 4.56 nm,respectively;the order of uniformity was L.reuteri EPS> P.fluorescens EPS>E.coli EPS;Compared to the original carbon steel,the three types of EPS after dip coated showed a roughness Ra decrease of 69.73%,53.67%,and 48.46%,respectively,and the percent reduction in adhesion was 63.23% and 61.65%,56.60% respectively;After dip coated the with the three kinds of EPS on the surface of carbon steel,the adhesion of L.reuteri,P.fluorescens and E.coli was inhibited.On the copper coupon surface,EPS is not easy to form a dense and uniform protective layer on the copper coupon surface,the membrane thickness of L.reuteri EPS,P.fluorescens EPS,and E.coli EPS formed on the surface of copper coupon are almost the same,all around 10 nm;the order of homogeneity is L.reuteri EPS< P.fluorescens EPS<E.coli EPS;Compared to the original copper coupon,the roughness Ra dip coated with the three kinds of EPS increased by 54.69%,26.79%,3.03%,respectively,the increase in adhesion force is 2.81 times,2.60 times,1.17 times respectively;The dip coated copper coupon surface with the three kinds of EPS promoted the adhesion of L.reuteri,P.fluorescens,and E.coli.The results show that PN/PS and carboxyl groups are the main factors affecting the adsorption capacity of EPS on metal ions and the nature of EPS coating on metal surfaces,which in turn makes the three EPSs have different effects on the corrosion of carbon steel and copper coupon.