目的研究环氧涂层下碳钢与铜合金在海水中的电偶腐蚀行为及涂层整体和局部区域的劣化过程。方法使用丝束电极(WBE)技术和电化学阻抗谱(EIS)技术研究丝束电极表面的电流密度分布和涂层阻抗谱演化,同时对比分析碳钢区域与铜合金区域涂层的阻抗谱特征。结果阳极电流峰首先出现在碳钢局部区域,而电流密度较大的阴极电流峰主要集中出现在铜合金区域的边缘。当浸泡至122 h时,铜合金区域的涂层阻抗明显低于碳钢区域的涂层阻抗,且EIS响应出现了Warburg扩散阻抗特征。在浸泡456 h后,单根钢电极发生由阴极向阳极的极性转换。结论涂层下碳钢与铜合金在海水中发生电偶腐蚀时,铜合金作为阴极被保护,但铜合金区域的涂层在阴极剥离的作用下加速劣化。在涂层劣化过程中,碳钢区域的涂层缺陷处成为腐蚀反应的阳极区,而主要的阴极区位于铜合金的边缘区域,这与溶解氧的“竞争效应”有关。由于涂层发生阴极剥离现象使得基底金属被腐蚀,从而导致涂层下单根钢电极的电流发生由阴极向阳极的极性转换。
The work aims to study the galvanic corrosion behaviors of carbon steel/copper alloy couple under epoxy coating and the degradation process of the whole and local area of the coating exposed to seawater. The current density distributions of the WBE and the EIS evolution of the coating on WBE surface were studied by WBE and EIS techniques. Meanwhile, the EIS characteristics of the coating on carbon steel and copper alloy surface were also compared and analyzed. It showed that the anodic current peak first appeared at the local area of carbon steel, while the cathodic current peaks with larger current densities appeared at the edge of the copper alloy area. After 122 h of immersion, the impendence value of the coating on copper alloy surface was obviously lower than that of the coating on carbon steel surface, and the Warburg impedance behavior could be observed in the EIS of the coating on copper alloy surface. The current of the single steel electrode changed from cathodic to anodic when the WBE was immersed for 456 h. In conclusion, when the carbon steel and copper alloy under epoxy coating were electrically coupled in seawater, the copper alloy was protected by carbon steel from corrosion but the degradation processes of the coating on copper alloy surface was accelerated by cathodic delamination. During the degradation processes of the epoxy coating, the local defect area of the coating on carbon steel surface became the anodic area and the main cathodic area was concentrated at the edge of copper alloy area, which was related to the “competition effect” for dissolved oxygen. The reason of the polarity reversals from cathodic to anodic of the single carbon steel electrode may be that the metal was corroded because of cathodic delamination.
wire beam electrode
electrochemical impedance spectroscopy