【作者】 程莎；

【导师】 尹衍升；

【作者基本信息】 中国海洋大学 ， 海洋化学工程与技术， 2009， 博士

【摘要】 在海洋环境中，环境因素对金属材料的腐蚀速率有重要影响，其中，微生物的附着通常会使材料腐蚀加速，并成为导致金属局部腐蚀的一个重要因素。材料浸入海水数小时内表面就会形成一层细菌膜，并进一步形成生物膜，以有利于后来海洋宏观生物的附着。由于防腐保护措施很难在整个浸泡过程中起到良好的保护作用，材料在海水中的腐蚀特别是浸泡初期的腐蚀对后续腐蚀程度的加深显得尤为重要。因此，研究海洋环境中，材料浸泡初期表面形成的细菌膜对材料腐蚀所产生的影响、对细菌膜中起主要作用的细菌进行鉴定、研究该细菌对金属腐蚀所产生的影响及作用机理具有重要意义。本文通过静态挂片法获得碳钢、不锈钢及铜在青岛天然海水中浸泡不同时间后表面的优势菌种，经过生物方法——聚合酶链反应（Polymerase ChainReaction，PCR）鉴定获悉，优势菌种为Vibrio natriegens（以下简称V．natriegens）。采用比浊法测定细菌的生长曲线，明确了该细菌在培养条件下的生长规律。通过天然海水和无菌海水两种环境中不同金属的电化学测试，研究优势菌种生物膜对金属表面性质的影响。结果表明，浸泡初期碳钢表面的氧化膜即使在无菌海水中也很容易被破坏，因此，碳钢的自身腐蚀在整个腐蚀过程中占主导地位，而优势菌膜对碳钢腐蚀过程影响可以忽略；不锈钢和铜表面存在钝化、致密的氧化膜，在无菌环境下能对基体起到良好的保护作用，而表面附着了细菌的试样，由于细菌活跃的代谢活动极大地影响到金属腐蚀电位，并且从所得腐蚀速率上可以得出，在细菌作用下，不锈钢和铜的腐蚀速率呈上升趋势。使用原子力显微镜观测了不锈钢在V．natriegens培养基中浸泡不同时间后表面的生物膜，总结了该菌在不锈钢表面附着、发展过程的规律。该微生物膜在其表面的附着不是一成不变的，而是随着时间的延长，处于吸附、脱附的动态变化中。通过腐蚀电位的测试，发现V．natriegens的附着改变了不锈钢表面的电化学性质，细菌的繁殖致使已钝化的表面再活化，不锈钢进入了活化状态的腐蚀。交流阻抗测试结果表明，随着浸泡时间的延长，阻抗值在不断降低，抗腐蚀能力逐渐减弱。对阻抗谱进行拟合得出，不锈钢表面的钝化膜已经不再完整，开始发生点蚀。从极化曲线可以看出，致钝电流密度增大，钝化层变薄，不锈钢的耐蚀性降低。阳极极化曲线斜率变化较大，随浸泡时间延长而减小，阳极极化阻力减小，阳极溶解过程加速。从腐蚀产物电镜分析可以看出，不锈钢表面形成的生物膜和腐蚀产物膜多孔疏松，在腐蚀产物的能谱图中发现了细菌代谢产生的生物源S、P。去除腐蚀产物后的不锈钢表面形貌证明了点蚀的发生，验证了电化学测试中的推论。利用原子力显微镜观察了铜表面V．natriegens生物膜的形成过程。通过腐蚀电位的测试，发现附着的V．natriegens的繁殖致使铜表面原有的氧化膜逐渐受到破坏，开始了活化状态的腐蚀。交流阻抗的测定得到，随着浸泡时间的推移，阻抗值在不断降低，抗腐蚀能力逐渐减弱。对阻抗谱进行拟合，结果显示，铜表面的氧化膜遭到V．natriegens的破坏已经不再完整，并有点蚀发生。从动电位极化曲线可以看出，随浸泡时间延长，铜阳极溶解过程加速。从腐蚀产物电镜分析可以看出，铜表面形成的生物膜、腐蚀产物膜多孔疏松，在细菌新陈代谢作用下，逐渐解离成颗粒，然后不均匀地脱落。在腐蚀产物的能谱图中也发现了细菌代谢产生的生物源S、P。为证实V．natriegens的固氮作用对不锈钢和铜的腐蚀有影响，本论文设计了四种不同介质。将不锈钢、铜试样在不同介质中浸泡7天后用电化学方法测试腐蚀情况，并用表面测试手段对金属腐蚀后的表面进行了表征。结果发现，V．natriegens的存在破坏了不锈钢表面原本生成的保护性钝化膜的致密性，且固氮作用对不锈钢的腐蚀有显著的促进作用，但此影响并非来自固氮作用的产物NH₃，而是固氮过程本身。生物膜对基体元素Ni的捕捉破坏了钝化膜的修复功能。铜试样的试验结果也显示，V．natriegens的固氮过程能加速铜的腐蚀过程，且推测在固氮过程中分泌产生了一些腐蚀性的物质，从而使得最终腐蚀要比产物NH₃单独引起的腐蚀更加严重。点蚀是碳钢及低合金钢最主要的一种局部腐蚀形式。在点蚀环境下，pH值低，Cl^-浓度高，而1mol／LHCl是最常用的模拟该环境的实验介质。本文将滴pH引起的碳钢点蚀环境扩大化，研究壳聚糖衍生物——羧甲基壳聚糖（CMCT）在1mol／L HCl中对碳钢的缓蚀作用，来评价CMCT作为缓解点蚀涂料添加剂的可行性。并且测试其抑菌性，通过失重、电化学实验确定CMCT在酸性溶液中的缓蚀机理。结果显示，CMCT能有效抑制表面附着细菌的生长繁殖。缓蚀数据表明，随着CMCT浓度的增大，缓蚀效率提高，在200mg／L的浓度下达到最高，且CMCT在碳钢表面的吸附遵循Langmuir规律，并获得吸附过程的各个热力学参数，确立了吸附模型。对CMCT结构的量子化计算、分子构型优化在理论上证明了吸附模型的正确性。低浓度的CMCT中添加Cu²⁺能改善缓蚀效率，并在20mg／L CMCT+10^-4 mol／L Cu²⁺下，缓蚀效率最高，其缓蚀机理是Cu²⁺和CMCT相互作用后在电极表面形成吸附层，增大电极电荷迁移电阻和减小双电层电容，抑制电化学腐蚀过程的发生。更多还原

【Abstract】 Environmental factors play a significant role in influencing the corrosion rate of metal materials in marine environment. The adsorption of microbes always enhances corrosion and is vital for metallic local corrosion. A layer of bacterial film could be formed in several hours on material surfaces after the immersion in sea water, and then the formation of biofilm occurs which favors the subsequent attachment of macroscopical marine organisms. The loss of material even for short-term exposures is important in part because protective measures are not always wholly effective. Consequently, it is very meaningful to research the effect of bacterial film formed on the material surfaces after the early period of immersion, and the identification of the preponderant bacterium, and the influencing behaviours and mechanisms of this bacterium on metal corrosion.In present work, the preponderant bacterium was obtained from the surfaces of mild steel, stainless steel and copper which were staticly hung in natural sea water from Qingdao for different times. The preponderant bacterium was identified as Vibrio natriegens （V. natriegens） through biological method namely PCR. The survival habit and growth curve were studied using nephelometery.Through the comparatively electrochemical experiments of different metals in natural and sterile sea water, the effect of the preponderant bacterial film on the changes of metallic surface properties was studied. The results showed that the influence of this bacterium on mild steel corrosion could be neglectable and that the biologic activites of bacteria greatly influenced the open potential (E_corr) of metals and induced the increasing corrosion rates of two metals.The growth process of V. natriegens biofilm covering on stainless steel surface was observed by atomic force microscopy （AFM） after different immersion in bacteria culture medium and these AFM images confirmed that biofilms were dynamic structural entities in which cell attachment and growth, the formation of micro-colonies, and subsequent detachment took place. Through the E_corr test, it could be found that the attachment of V. natriegens could change the electrochemical properties of stainless steel surface and that the proliferation of the bacteria could induce the reactivation of the passive surface and the occurrence of active corrosion. The results from electrochemical impedance spectra （EIS） showed that the impedance value decreased with immersion time and the anticorrosion abilities of stainless steel were weakened. Utilizing the equivalent circuit models to interpret the EIS data, it could be obtained that the passive film on stainless steel was not intact and pitting corrosion took place. The corrosion behaviours were also inspected using dynamic polarization curve. The passive current density increased and the passive film was thinned, resulting in the anticorrosion ability was weakened. The changes of anodic polarization curve slope were more significant and decreased with immersion time which demonstrated that the resistance of anodic polarization decreased and the anodic dissolution was accelerated. The corrosion product was analyzed by SEM, revealing the porous biofilm and corrosion product layer. The EDS analysis of the corrosion product proved the existence of biologic S、P from bacterial metabolite. The pitting on the stainless steel after the removal of corrosion product validated the conclusions obtained from electrochemical experiments.The growth process of V. natriegens biofilm covering on copper surface was observed by AFM after different immersion in bacteria culture medium. The results from E_corr test showed that the proliferation of these bacteria on copper surface induced the break of the protective oxide film formed previously and the start of active corrosion. The EIS data showed that the impedance value decreased with immersion time and the anticorrosion abilities were weakened. Utilizing the equivalent circuit models to interpret the EIS data, it could be obtained that the oxide film on copper surface was not intact and pitting corrosion took place. The dissolution of copper was accelerated with immersion time which was obtained from dynamic polarization curve test. The SEM images revealed that the corrosion product layer was loose and that the surface consisted of small copper particles and fell off unevenly with the bacterial metabolism. From the EDS analysis, biologic elements S、P were found in the corrosion product.In order to confirm whether the N2-fixation influenced the corrosion of stainless steel and copper, four kinds of media were designed in this work. The corrosion degree of stainless steel and copper coupons immersion in different media for 7 days was tested using electrochemical experiments and the corrosion morphology was characterized by surface analysis. The results showed that the existence of V. natriegens destroyed the protective passive film formed on stainless steel. N₂-fixation had significantly acceleration on corrosion, and the real cause was N₂- fixation not NH3 produced in this process. Element Ni from the matrix was extracted by the bioflim formed on the surface which destroyed the restoration of passive film on stainless steel. These results from copper coupons also demonstrated that N₂-fixation could enhance the corrosion. It was conferred that some aggressive materials were secreted in this process and the final corrosion was more serious than the corrosion induced by NH₃.Pitting corrosion is the most familiar way of local corrosion for mild steel. And 1mol/L HCl is the most commonly used mimic medium for the environment in pit, due to low value of pH and high concentration of Cl^-. In this work, we tried to find the effective additive in coating to inhibit the pitting corrosion. In order to evaluate the feasibility of adding Carboxymethylchitosan （CMCT） into coating as the additive, the pit environment was broadened and 1mol/L HCl was treated as the experiment medium to test the inhibitive effect of CMCT on mild steel. The inhibition of bacterial growth was tested by the epifluorescence microscopy observation. Through weight loss experiment and electrochemical tests, the inhibition of CMCT was determined. The results showed that the inhibiting efficiency increased with the rise of CMCT concentration and reached the maxium at 200mg/L. The adsorption of CMCT on mild steel obeyed Langmuir rule, some thermodynamic parameters were obtained and the adsorption model was established. The correctness of the model was proved by quantum chemical calculation and optimization of molecular structure. The proper addition of Cu²⁺ could improve inhibiting efficiency and reached the maxium at 20mg/L CMCT +10^-4 mol/L Cu²⁺. The mechanism was determined as that Cu²⁺ and CMCT could interact to form a protective layer on mild steel, increasing the charge transfer resistance and decreasing the double layer capacitance, and inhibit the electrochemical corrosion.更多还原