海洋环境腐蚀与生物污损重点实验室知识库

对海洋工程材料而言，海洋是复杂而苛刻的腐蚀环境，电偶腐蚀难以避免，但海洋微生物对电偶腐蚀影响的研究报道较少。本论文以船舶用材料EH40钢和B10铜合金为研究对象，主要采用电化学测量方法、表面分析技术等手段探究了假交替单胞菌（Pseudoalteromonas sp.，P.sp.）、硫酸盐还原菌（Sulfate-reducting bacteria，SRB）以及P.sp.与SRB的混合菌对EH40/B10电偶腐蚀的影响机制。主要结果如下：

（1）研究了P.sp.对EH40/B10电偶腐蚀的影响机制。结果发现，P.sp.的存在降低了EH40/B10的电偶腐蚀速率。在无菌体系中，电偶电流密度稳定在12 μA/cm²左右；在P.sp.体系中，电偶电流密度稳定在0.1 μA/cm²左右，比在无菌体系中的电偶电流密度降低约100倍。在P.sp.体系中EH40和B10表面都覆盖了一层生物膜，并且P.sp.体系中的溶解氧含量远低于无菌体系中的溶解氧含量。同时，P.sp.的生命活动使得溶液pH降低，偏酸性。P.sp.对EH40/B10电偶腐蚀的抑制作用与P.sp.的呼吸耗氧及生物膜的形成密切相关。尽管P.sp.的生命活动使得溶液pH降低，但其对腐蚀的促进作用要小于保护性生物膜和呼吸耗氧对腐蚀的抑制作用。

（2）探讨了无氧环境中SRB对EH40/B10电偶腐蚀的影响。结果发现，SRB对EH40/B10电偶腐蚀效应影响微弱，但显著促进了EH40、B10的自腐蚀速率。EH40/B10的电偶电流密度在无菌和SRB体系中都维持在0.8 μA/cm²以下，但相较于无菌体系中EH40和B10表面基本无腐蚀产物形成、R_ct很大，SRB使得EH40、B10表面覆盖腐蚀产物，且去除腐蚀产物后出现点蚀坑，R_ct降低超过2个数量级。并且SRB的存在使得电偶电流密度在第5天和第9天为负值，EH40/B10电偶对极性发生反转，这可能源自SRB对EH40和B10不同腐蚀作用机制的差异。

（3）研究了P.sp.与SRB的混合菌对EH40/B10电偶腐蚀的影响机制。结果发现，P.sp.与SRB的混合菌对EH40/B10电偶腐蚀的影响可以划分为两个阶段，并且与两种菌的协同生长代谢密切相关。浸泡初期，电偶电位迅速负移、电偶电流密度急剧减小，与单独P.sp.体系中电偶电位、电偶电流密度随时间的变化趋势相似，该阶段P.sp.大量繁殖呼吸耗氧。浸泡后期，电偶电位逐渐正移直至稳定，且电偶电流先增大后减小，EH40钢的R_ct一直维持在较低的水平，与单独SRB体系中的相似，该阶段P.sp.衰亡，其创造的缺氧环境有利于厌氧微生物SRB的生长。

Seawater is complex and harsh corrosion environment for marine engineering materials, and galvanic corrosion is difficult to avoid. But few reports have addressed the influence of marine microorganisms on the galvanic corrosion. In this thesis, EH40 steel and B10 copper alloy commonly used on ships were taken as the research objects, and the electrochemical measurement methods and surface analysis technologies were utilized to study the influence mechanism of Pseudoalteromonas sp. (P.sp.), sulfate-reducing bacteria (SRB), and mixed bacteria (P.sp. + SRB) on galvanic corrosion. The main results are as followed:

(1) The influence mechanism of P.sp. on the galvanic corrosion of EH40/B10 was studied. The presence of P.sp. reduced the galvanic corrosion rate of EH40/B10. In the abiotic system, the galvanic current density stablized around 12 μA/cm². In the P.sp. system, the galvanic current density stablized around 0.1 μA/cm², which was about 100 times lower than that in the abiotic system. Biofilms were found on the surface of EH40 and B10 in the P.sp. system, and the dissolved oxygen concentration in the P.sp. system was much lower than that in the abiotic system. Meanwhile, the presence of P.sp. reduced the pH of solution. The galvanic corrosion of EH40/B10 was inhibited by P.sp., which is believed to be closely associated with oxygen depletion and biofilm formation. Although the decrease in pH is harmful for corrosion inhibition, its influence is much smaller than those of oxygen consumption and biofilm protection.

(2) The influence of SRB on EH40/B10 galvanic corrosion in anaerobic environment was discussed. SRB had quite limited effect on EH40/B10 galvanic corrosion, but significantly promoted the self-corrosion rate of EH40 and B10. The galvanic current density of EH40/B10 was maintained below 0.8 μA/cm² in both abiotic and SRB systems. EH40 and B10 basically had no corrosion products on the surface and the R_ct was very large in the abiotic system, but the introduction of SRB led to numerous corrosion products and pitting pits after removing. Furthermore, R_ct decreased by more than 2 orders of magnitude. The galvanic current density was negative on day 5 and day 9 due to the presence of SRB, and the polarity of EH40/B10 was reversed, which may be due to the difference in corrosion mechanisms of SRB on EH40 and B10.

(3) The influence mechanism of the mixture of P.sp. and SRB on EH40/B10 galvanic corrosion was studied. The influence of P.sp. and SRB on EH40/B10 galvanic corrosion could be divided into two stages, which was closely related to the synergistic growth and metabolism of the two bacteria. At the beginning of immersion when P.sp. multiplied and consumed oxygen, the couple potential shifted negatively rapidly and the galvanic current density decreased sharply, which was similar to the case in the P.sp. system. Then, P.sp. declined and created an anoxic environment which facilitated the growth of the anaerobic microorganism SRB. Accordingly, the galvanic potential gradually increased until it stabilized, and the galvanic current density increased firstly and then decreased. Meanwhile, the R_ct of EH40 steel maintained at a low level, similar to that of the SRB system.