Microbiologically Influenced Corrosion Behavior And Mechanism Of Corrosion Resistant Metallic Materials In Marine Environment

Microbiologically influenced corrosion(MIC)is a big threat to the reliability of marine engineering materials,causing severe economic losses and unpredictable safety hazards.Therefore,it is important to study the MIC behavior and mechanism of different metallic materials in marine environment using common marine microorganisms.MIC inhibition could be achieved by using different corrosion protection techniques and the development of corrosion resistant materials.In the present study,different corrosion-resistant metallic materials TC4 titanium alloy,2205 duplex stainless steel(DSS)and 316L stainless steel(SS)which are commonly used in marine environment were selected.Electrochemical tests,surface analytical techniques and corrosion product analysis were performed to study their MIC behavior and mechanism in the presence of acid-producing bacteria A.aceti,P.aeruginosa and S.algae,respectively.Copper-containing antibacterial materials were adopted to study the antibacterial property and corrosion resistance of the materials.(1)The corrosion potential of TC4 titanium alloy was more negative in P.aeruginosa broth than that in the sterile medium,indicating a greater corrosion tendency.Moreover,the corrosion rate of TC4 titanium alloy in biotic medium increased.The endogenous electron carrier PCN might promoted electron transfer,accelerating the reduction of TiO2.The nonstable sub-oxides(Ti2O3)encouraged the occurrence of pitting corrosion on TC4 surface.The corrosion type is extracellular electron transfer-MIC(EET-MIC).(2)S.algae caused severe corrosion to 2205 DSS.Electrochemical results showed that the corrosion potential of 2205 DSS is negatively shifted in the presence of S.algae,and corrosion rate is significantly increased.The electron carrier riboflavin which was secreted by S.algae promoted electron transfer between 2205 DSS and bacteria,accelerating the corrosion of 2205 DSS.Corrosion type caused by S.algae belongs to EET-MIC.(3)Electrochemical techniques were used to study the corrosion behavior of 2205 DSS in the presence of marine bacterium A.aceti.It was found that 2205 DSS having lower corrosion potential and higher corrosion rate in the presence of A.aceti.A.aceti secretes corrosive acetic acid,which destroyed the passive film on the surface of 2205 DSS,causing pitting corrosion.Cr2O3,CrO3 and iron oxides were detected during the analysis of corrosion products using XPS.The corrosion of 2205 DSS caused by A.aceti belongs to MetaboliteMIC(M-MIC).(4)Corrosion behavior of 316L stainless steel was studied in the presence of A.aceti by using electrochemical test.The results showed decrease in the corrosion potential of 316L SS in the A.aceti broth compared to that in the abiotic medium.Corrosion rate of 316L SS studied by linear polarization resistance,electrochemical impedance spectroscopy and polarization curve increased significantly in the biotic broth.Oxides of Cr and Fe were the main components of corrosion products.The pitting corrosion was attributed to dissolution of soluble CrO3.(5)Antibacterial effect of 2205-Cu DSS against S.algae was remarkable.MIC caused by S.algae was effectively inhibited by 2205-Cu DSS.Results of electrochemical test showed that the corrosion rate of 2205-Cu DSS was very low compared to the 2205 DSS.In addition,the pit depth detected on the surface of 2205-Cu DSS was less than 2205 DSS.AAS result showed the distribution of certain amount of copper ions in the solution,which resulted from the dissolution of copper from the material matrix.The analysis of biofilm morphology showed high number of dead bacterial cells on the material surface,demonstrating the inhibition of S.algae biofilm on the surface of 2205-Cu DSS.It was confirmed from this study that 2205-Cu DSS possesses excellent antibacterial properties.Cu2+released from 2205-Cu DSS matrix inhibited the biofilm formation on the metal surface,thus leading to effective mitigation of MIC caused by S.algae.(6)The antibacterial properties of 2205-Cu DSS against acid-producing bacteria A.aceti were investigated by means of scanning electron microscopy and laser confocal microscopy.The corrosion resistance of 2205-Cu DSS was studied using electrochemical test.The results showed decrease in the number of bacteria and biofilms on the surface of 2205-Cu DSS.The number of dead bacterial cells was increased significantly,showing good antibacterial properties of 2205-Cu DSS;results of electrochemical test showed that corrosion rate of 2205-Cu DSS decreased significantly compared to 2205 DSS.The pit depth detected on 2205-Cu DSS surface was smaller than 2205 DSS.The good antibacterial properties of 2205Cu DSS was attributed to the dispersion of copper in the matrix of the material,thus inhibiting the corrosion caused by A.aceti.(7)The antibacterial properties and microbial corrosion resistance of 316L-Cu SS against MIC caused by A.aceti were investigated by surface analytical techniques and electrochemical tests.The results showed that 316L-Cu SS inhibited the growth and activity of A.aceti which decreased the corrosion rate of 316L-Cu SS compared to 316L SS.Corrosion of 316L-Cu SS caused by A.aceti was inhibited effectively.