【作者】 常雪婷；

【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， 2010， 博士

【摘要】 Fe和Al是海洋中应用最为广泛的金属材料,对这两种材料的研发和设计可能会成为实现海洋材料工程化与功能化改革的关键,在理论和实验研究中都具有重要的意义。然而单纯的Fe合金和Al合金已经远远不能满足当今快速发展的海洋科技的需求：钢材的力学性能较好,但是耐蚀性很差,不能达到高强轻质海洋材料的要求；Al合金密度较小,在海洋环境中的耐蚀性较其它金属材料优秀,但是其机械强度不高,不能广泛应用于海洋工程建筑。同时,目前发展的海洋材料腐蚀研究方法只是从腐蚀形态表征或腐蚀机理讨论,对具有代表性的好氧菌微生物膜形成机理,以及微生物膜/材料之间界面动力学的认识还很不够。本文将Fe3Al金属间化合物及其复合材料引入海洋领域,研究其表面优势附着菌种种类及其生长特性。探索Fe3Al金属间化合物在不同优势附着菌种生长环境下表面微生物膜的生长机制,建立优势菌种附着机制模型。深入研究微生物膜附着与Fe3Al金属间化合物界面状态、物理性质和化学性质之间的关联。综合使用胶体化学理论、流体力学理论、第一密度泛函方法以及计算机分子模拟技术,对微生物膜在Fe3Al表面附着动力学加以研究,并最终为Fe3Al金属间化合物及其复合材料适合用于海洋菌类附着环境提供理论依据。通过实海挂片取得Fe3Al材料表面优势附着菌种,经过16S rDNA等微生物生化检测方法,准确判断出三种优势附着菌种分别为芽孢杆菌Bacillus baekryungensis、氯酚节杆菌Arthrobacter chlorophenolicus和耐盐黄色链霉菌Streptomyces flavus。这三类菌种都是好氧革兰氏阳性菌。Bacillus ba,的新陈代谢作用会迅速消耗环境中的游离氧,并降低周围pH值；在有Fe3+存在的条件下,A. chlorophenolicus的新陈代谢产物会与Fe3+形成络合物；Streptomyces flavus是一种硝酸盐还原菌,释放的亚硝酸盐有一定缓蚀作用,且细胞外生长菌丝,易于在材料表面附着。论文通过研究微生物膜在Fe3Al材料表面附着生长的形态及膜内成分,揭示了三种优势菌种在Fe3Al材料表面成膜的一般规律：Bacillus ba在Fe3Al材料表面附着形成的微生物膜经历疏松多孔-致密增厚-破裂脱离的三个过程,浸泡一段时间后Fe3Al材料表面孔蚀严重；A.chlorophenolicus菌种附着则首先在Fe3Al材料表面生成特征性纳米级氧化铝薄膜,再依靠新陈代谢产物羟基喹啉同Fe3Al材料中释放的Fe3+生成络合产物,有效填补氧化铝破裂造成的表面钝化膜不完整；Streptomyces flavus在Fe3Al表面形成的微生物膜从初期“玫瑰花瓣”状A1203组织转变为均匀的“蜂窝”状组织,引起溶液中NO2-的吸附,在一定程度上减轻了酸性环境对Fe3Al的腐蚀作用。基于对微生物膜附着Fe3Al材料物理性质和电化学性质的一系列测试,验证了各菌种在Fe3Al材料成膜的形成机制和对表面性能的影响；在此基础上通过胶体化学理论和牛顿流体力学方法进一步建立了菌种在Fe3Al表面形成微生物膜界面动力学模型,并最终确定了三种优势菌种在Fe3Al材料表面可逆附着阶段及发展增长阶段的动力学方程。设计了测定微生物膜与Fe3Al试样界面结合力实验模型,推导出优势附着菌种在Fe3Al表面附着的界面结合力计算方程。文中还确定了微生物膜与Fe3Al材料界面之间的界面结合力随浸泡时间变化规律,为进一步探索Fe3Al在微生物膜附着条件下的应用性能奠定了坚实的基础。通过深入原子和分子层次了解优势附着菌种细胞组织(以磷壁酸为主)与Fe3Al材料表面(以氧化铝薄膜为主)相互作用的键合方式、附着参数以及电子结构特征,找到磷壁酸单分子的能量最低状态。根据原子电荷密度负性推测,认为磷壁酸分子在材料表面的吸附由磷脂基主要完成,并证实磷壁酸单体分子在A1203基体上结合主要依靠氧原子向表面的附着能力。磷壁酸单体分子与A1203基体之间的界面结合能较大,也由此解释革兰氏阳性菌成为Fe3Al材料表面优势附着菌种的根源。论文最后制备了不同组分比例的Fe3Al/ZrO2复合材料,并考察其在无菌环境以及Bacillus ba.附着生长环境中的电化学参数变化趋势,结合Bacillus ba.生长过程中培养基中pH值变化规律,揭示不同成分Fe3Al/ZrO2复合材料的抗腐蚀性能。实验结果表明,ZrO2含量为80%的Fe3Al/ZrO2复合材料由于ZrO2含量较高,并且有适量Fe3Al参与形成钝化膜,两者互相配合,共同抵制酸性附着产物的腐蚀作用,在Bacillus ba,附着生长条件下表现优秀的耐腐蚀性能。更多还原

【Abstract】 Iron and aluminum are the most widely-accepted materials for the construction of offshore structures and marine hulls. The investigation and design on iron and aluminum may probably be crucial to achieve the combination of industrial applications and functionalizing of ocean materials, and are also theoretically and experimentally of great significance. However, single iron and aluminum alloys are far from meeting the requirement of the rapid development of ocean technology. For example, iron alloys exhibit good mechanical properties but with bad corrosion resistance and high density. Relatively, aluminum alloys exhibit lower density, and improved corrosion resistance due to the passive films, but possess lower mechanical strength, making them unsuitable candidates for marine engineering structures.Simultaneously, the present ongoing researches about the corrosion of marine materials are limited to the characterization of corrosion morphology or mechanisms. Little effort has been done on the formation mechanisms of the representative aerobic biofilm and the interface dynamics between biofilms and substrate. In addition, examinations about anti-MIC (microbiologically influenced corrosion) performance of new kinds of marine materials are still inadequate and need further explored.Based on the above discussions, Fe3Al intermetallic compounds and its composites were brought into marine area in this dissertation. The species of dominantly-adhered bacteria on the surface of Fe3Al, their growth characteristics, the adhesion mechanism and models of biofilms and the interface features between biofilms and Fe3Al were investigated. Colloid chemistry theory, fluid mechanics theory, first density functional theory (DFT) and molecular simulation methods were alos synthetically used to characterize the interface dynamics, which provide valuable theoretical basis for the potential applications of Fe3Al metallic compounds and its composites in the ocean.The dominantly-adhered bacteria on Fe3Al surfaces were obtained by hanging samples in seawater. Through a variety of analysis methods such as 16 S rDNA, the three dominantly-adhered bacteria were confirmed to be Bacillus baekyungensis, Arthrobacter chlorophenolicus and Streptomyces flavus, respectively. These bacteria are all aerobic gram-positive bacteria. Bacillus ba. could consume oxygen rapidly and reduce the pH value of the environmental through metabolization; with the presence of Fe3+, complex would be formed by the reaction between the metabolic products of A. chlorophenolicus and Fe3+; Streptomyces flavus, which is a kind of nitrate-reducing bacteria, could easily adhere to the material surface because of its hyphae.The general formation mechanisms of biofilms associated with the three dominant bacteria were revealed by investigating the morphology and composition of different biofilms on the Fe3Al surfaces. The attached biofilms formed by Bacillus ba. were loose and porous at first, then became thick and dense, and finally fractured and peeled off from Fe3Al. Serious pitting could be found on the Fe3Al surface after the samples have been immersed in seawater for about 10 days. In the case of A. chlorophenolicus, the characteristic nanostructured Al2O3 films were firstly formed due to the attached biofilms; then, metabolic products of A. chlorophenolicus, Oxine (HQ), reacted with Fe3+ to form complex, which could effectively help repairing the fracture of Al2O3 films. Biofilms caused by Streptomyces flavus underwent morphological evolutions from the roselike oxide film to homogeneous honeycomb-like structure, which led to the adsorption of NO2- and correspondingly mitigated to some extent the acid-induced corrosion of Fe3Al.According to a set of measurements of physical and electrochemical properties of Fe3Al, the formation mechanisms of biofilms corresponding to different dominant bacteria and their effects on the surface characteristics of Fe3Al were verified. On this basis, interface dynamic models of biofilms caused by the three dominant bacteria were further established through colloid chemistry theory and Newtonian fluid dynamics methods. Referring to the reversible adhesion theory and the exponential growth model of biofilms, the maximum adhesion amount and the total adhesion coefficient during the reversible adhesion stage were confirmed by analyzing the variation of the adhesion amount of the three dominant bacteria on the Fe3Al surfaces as a function of time and their growth index during the initial growth stage. Finally, dynamic models of the three dominant bacteria on the Fe3Al surfaces during both reversible adhesion stage and developing stage were established. The variation of critical bonding strength between the three dominantly-adhered biofilms and Fe3Al as a function of immersion time was also fixed. This part provides a solid foundation for further exploring the unique physical and chemical properties of Fe3Al-based materials and their potential applications.The lowest energy state of a single teichoic acid molecule was determined through in-depth understanding the bonding pattern, adhesion parameters and electronic structure features of mutual interaction between dominantly-adhered microbial cells. According to the speculation of atomic charge density, it can be identified that the phosphatide contributed largely to the adsorption of teichoic acid molecule on the surfaces. It can also be proved that the binding of single teichoic acid molecule to the Al2O3 substrate depend mainly on the adhesion ability of oxygen atoms on the surface, strong binding energy between single teichoic acid molecule and the Al2O3 substrate occurred, evidencing that gram positive bacteria is the source of the dominantly-adhered microbe on the Fe3Al surfaces.At the end of this dissertation, we devoted our attention to the preparation of Fe3Al/ZrO2 composites with different Fe3Al-to-ZrO2 ratio and their anti-corrosion performance under both sterile environment and Bacillus ba. existing environment. The results showed that Fe3Al/ZrO2 composites with 80 vol.% ZrO2 exhibited superior anti-corrosion behavior under the Bacillus ba.-adhered condition, which may be due to the mutual cooperation of high content of ZrO2 and the passivation films formed by a small amount of Fe3Al.更多还原