【作者】 刘华剑；

【导师】 王佳；

【作者基本信息】 中国海洋大学 ， 海洋化学工程与技术， 2011， 硕士

【摘要】 大型海洋工程(如海上石油钻井平台、跨海大桥、船舶等)的机械结构系统中通常会采用不同的材料,这些材料在海水或潮湿的海洋大气中会引起不同程度的电偶腐蚀。金属材料在实际应用中常采用防腐涂层进行保护,但现有金属材料的室内和实海暴露试验多采用裸样,与实际工况环境相差甚远,不能完全反映实际环境下的腐蚀规律。有机涂层的防护性能在实际体系的电偶腐蚀过程中起着重要的作用。涂层物理屏蔽能力降低,界面腐蚀电化学反应以及涂层的剥离都影响着涂层下偶对体系的电偶腐蚀进程。本论文的主要研究工作包括:应用电化学阻抗谱技术,结合线性极化技术,电偶电位和电偶电流测量,对比研究了涂层/钢-裸钢体系的电偶腐蚀过程。根据阻抗谱响应建立与涂层失效各个阶段相对应的等效电路模型,分析浸泡过程中涂层失效与电偶腐蚀电化学参数的相关性。研究发现,当涂层的物理屏蔽能力很强即涂层渗水阶段,体系的电偶电流密度几乎为零,裸钢处于自腐蚀状态;当基底金属腐蚀反应发生后,体系的电偶电流密度迅速增大,裸钢腐蚀速率增大;裸钢对涂层体系起保护作用时,涂层阻抗在试验周期内不再下降,体系的电偶电流密度趋于稳定。结合阻抗谱技术和阵列电极技术,分别研究裸钢和涂层下阵列电极的偶合电流、电位和阻抗分布特征及其与涂层失效过程的相关性。研究表明由于钢丝的空间位置不同,在电偶腐蚀中存着阴阳极分布的不均匀性。对于裸钢体系,由于阴阳极极化作用,使得电偶腐蚀驱动力减小,偶合电流密度逐渐减小,并且随着浸泡的进行,阳极区会发生转移。对于涂层体系,阳极电流出现在涂层的缺陷处,阴极电流被整个涂层平分。随着腐蚀过程的发展,自腐蚀电位较负的一侧出现阳极电流,虽然早期缺陷区仍表现为阳极区,但电流密度已经减小,阴极电流逐渐向缺陷处附近涂层扩展,这说明在浸泡后期,自腐蚀电位较负的一侧会对较正的一侧产生保护作用。阻抗谱测试结果表明,涂层下阵列电极阻抗响应主要反映了缺陷区电极过程特征,直至涂层完好区也出现剥离和鼓泡的失效现象。而阴极区涂层性能和涂层下金属腐蚀反应信息被“掩盖”。但是通过检测电极表面的电流密度分布,能够监测涂层和涂层下的局部电化学过程。更多还原

【Abstract】 Various materials are be used in the mechanical structure of great coastal engineering projects (e.g., offshore oil rig, sea-crossing bridge, ships, etc). Under the action of corroding medium, such as wet air and seawater, these materials will emerge varied galvanic corrosion. Organic coatings have been used extensively for corrosion protection of metal. However, most outdoor exposure and indoor accelerated corrosion tests were performed using bare metal, which are fare away from the real working condition, and can’t reflect the discipline of the real environment completely.The protective function of the organic coating plays an importantly role during the galvanic corrosion in real system. The galvanic corrosion of the coupled system was mainly influenced by the loss of adhesion between coating and metal , electrochemical reactions at interface, and the stripping of coating from surface of metal, etc. Consequently, the main researches in this article are listed as following:(1) The galvanic corrosion process of coating/steel-steel system was studied by EIS, LPR, galvanic potential and galvanic current. According to the EIS responses at every stage, the equivalent circuit models were established. Meanwhile, the relevance between electrochemical parameters and degradation of the organic coating was analyzed. Within this context, several appearances have been found: the current density of galvanic nearly reached zero, when resistance of the coating was very large, and meanwhile the bare steel was under free-corrosion state; when electrochemical reactions happened under the coating, the current density of galvanic increased quickly and the corrosion rate of the steel was accelerated; at the beginning of bare steel to protect the coating system, the resistance of the coating changed slowly and never decreased during the experiment period, until the current density of galvanic became steady. (2) For coating steel and bare steel, by using EIS and WBE technology, the relevance between coating degradation and distribution of current and potential was also researched. It was studied that some otherness existed during the galvanic corrosion because of the space difference of the steel wire. For the bare system, the driving force of the couple and the galvanic current density were decreased by the polarization. The zone of the anode and the cathode changed during the immersion. For the coating system, the current distribution results of the WBE show that the high anode current existed at the defect of the coating, the cathodic current dispersed over the coating. The anode current was found in the region of negative Ecorr with the development of the corrosion. Although the early defect region was still anode area, the current density diminished, and the cathode current expanded to the area near the defect. It showed that in the late immersion, the negative part would protect the positive part. During the entire coating deterioration process, the EIS diagrams were dominated by the substrate corrosion process of the defect, the coatings and the underlying electrochemical process were“averaged”out. However, through detecting the current distribution information on the metal surface, the local electrochemical process occurring in the coatings and the underlying could be monitored.更多还原