Mechanisms Of Iron Reducing Bacteria Halomonas Titanicae On Corrosion Of Typical Metal Materials In Seawater Environment

Microbiologically influenced corrosion（MIC）is one of the factors that affect the safety of marine engineering metal materials such as steels during the service period.Damages to the equipment induced by bacterial cause huge economic losses,personal threats and environmental pressures.Iron-reducing bacteria（IRB）can reduce solid Fe（Ⅲ）to dissoluble Fe（Ⅱ）,which plays an important role in the iron cycle.However,summarizing the existing research results,the influence of IRB on corrosion of metal materials is controversial,and there are many factors to be responsible for the conflict in corrosion affected by IRB.From the perspective of microbial metabolism,it may be related to the choice of electron acceptors.At the same time,alloying is one of the important means to improve the antibacterial property of metallic materials,but the effects of alloying elements on IRB are rarely reported.In this paper,focusing on the utilization of electron acceptor,a facultative anaerobic IRB（Halomonas titanicae,H.titanicae）,isolated from Huiquan Bay,was selected to explore the effect on corrosion of typical metal materials in the marine environment including alloy steels and stainless steels in base of different choices of electron acceptors in different dissolved oxygen environments.And according to the experimental results,the different corrosion mechanisms were explained.In the meantime,the effect of alloying elements Cu and Ni in inhibiting the corrosion of metal materials caused by H.titanicae was explored and compared,and the mechanisms of H.titanicae on corrosion of different metal materials was discussed.The specific research contents are as follows:（1）The electron acceptor dependence of H.titanicae on corrosion of EH40 steel was revealed.The effects of H.titanicae on corrosion of EH40 steel under different dissolved oxygen concentrations was studied,and it was found that the influences of H.titanicae is different under aerobic and anaerobic environments.In the aerobic system,H.titanicae selected O₂ as electron acceptor resulting in the decreased dissolved oxygen concentration,which inhibited corrosion of EH40 steel via weakening cathodic oxygen reduction reaction.But in the anaerobic system,H.titanicae utilized Fe（Ⅲ）as electron acceptor,so that solid Fe（Ⅲ）was converted to ionic Fe²⁺,exposing more fresh surface.And the conversion of the loose Fe（Ⅲ）corrosion product films to the dense Fe₃O₄ film reduced.Hence,the protective properties of the product films were destroyed,providing more active sites.At the same time,H.titanicae under the biofilm might use H₂ as the electron donor to cause corrosion,thereby promoting the corrosion of EH40steel.（2）The inhibitory effect of Cu and Ni alloying elements on corrosion of alloy steel caused by H.titanicae with Fe（Ⅲ）as the electron acceptor was explored.The tempered sorbite alloy steels with different contents of Cu and Ni were selected,and the corrosion behaviors under the action of H.titanicae using Fe（Ⅲ）in the anaerobic environment was studied.It was found that the Cu addition and high-content of Ni both have inhibitory effect on corrosion caused by H.titanicae,and the inhibitory effect of 1.3%Cu was stronger than that of increasing the content of Ni from 4.8%to 7.2%.The corrosion inhibitions by adding Cu and increasing content of Ni were due to the reduction of bacterial cells in the biofilm,thereby reducing the dissimilatory reduction of H.titanicae from Fe（Ⅲ）to Fe（II）,but the mechanisms were different from each other.1.3Cu3.3Ni-HSLA had a certain sterilization effect on H.titanicae by releasing copper ions and reduced the number of attached bacteria;while 7.2Ni-HSLA steel had no obvious sterilization effect on attached bacteria,and it inhibited the attachment of bacteria through formatting more Ni-containing compounds such as Ni Fe₂O₄.（3）The electron acceptor dependence of H.titanicae on corrosion of passive metallic stainless steel was studied.The 2205 DSS was selected to explore its corrosion behaviour in different dissolved oxygen environments.The results showed that the different choices of electron acceptors of H.titanicae in different dissolved oxygen concentrations all accelerated the corrosion of 2205 DSS,which was different from EH40 steel.In the aerobic environment,H.titanicae selected O₂ as electron acceptor,which leaded to a decrease in dissolved oxygen concentration.On the one hand,corrosive ions in seawater such as Cl^-triggered pitting corrosion of 2205 DSS,destroying the passivation film.It could not be repaired timely in the case of low O₂concentration,resulting in further deepening of pitting corrosion.On the other hand,the attachment of H.titanicae on the sample surface formed a local oxygen concentration cell,which caused local corrosion under the biofilm and promoted the development of pitting corrosion.In the anaerobic environment,H.titanicae used Fe（Ⅲ）as electron acceptor,which destroyed the protectivity of the passivation film.Due to the lack of O₂,the damaged passivation film could not be repaired,causing corrosive ions such as Cl^-to deepen to a point.Thus,it enhanced the development of pitting corrosion.（4）The resistance to H.titanicae of Cu-bearing 2205 DSS was explored utilized one kind of 2205Cu DSS（2.27%Cu content）.The inhibitory effects on corrosion of2205Cu DSS induced by H.titanicae in different dissolved oxygen environments were studied.Under the aerobic condition,the addition of Cu reduced the corrosion resistance of 2205 DSS in a sterile/biotic system.The presence of O₂ made the Cu atoms in 2205Cu DSS underwent an anodic dissolution reaction and dissolved into the system.Hence,the passive film on the surface of the stainless steel was destroyed,and the metabolic process of H.titanicae using O₂ as the electron acceptor consumed O₂and reduced the dissolved oxygen concentration,which adversely affected the repair of the passive film,resulting in deeper pitting of 2205Cu DSS.Under the anaerobic condition,the release of Cu ions from 2205Cu DSS had a certain bactericidal effect,reducing the metabolic activity of H.titanicae using Fe（Ⅲ）as the electron acceptor.Therefore,it reduced the damage to the passivation film,inhibiting the depth of pitting corrosion of 2205Cu DSS.This paper answered the controversial reasons for the corrosion mechanism of IRB from the perspective of the electron acceptor and its correlation with the surface characteristics of the material.It revealed the dependence of the electron acceptor of H.titanicae on the corrosion of metal materials in aerobic/anaerobic environments.At the same time,the effects of Cu and Ni alloying elements in inhibiting the corrosion of metal materials under the action of H.titanicae were studied and compared for the first time,and the corrosion inhibition mechanisms were discussed respectively.Therefore,the work in this article had a certain theoretical guiding significance for the improvement of the marine environment MIC theory and the research of antibacterial materials.