有机涂层失效过程的电化学阻抗和电位分布响应特征

结合使用电化学阻抗谱(EIS)和扫描Kelvin探针(SKP)技术研究了在质量分数为3.5%的NaCl溶液中的铁基有机涂层劣化过程特征. 结果表明, 根据EIS和SKP的响应特征, 可将涂层劣化过程分为3个主要阶段: (Ⅰ) 涂层渗水阶段. 此时, 涂层渗水阶段的EIS阻抗持续减小, 但保持单容抗弧特征, SKP特征是电位持续降低, 但分布保持均匀; (Ⅱ) 基底金属腐蚀发生阶段. 此时, EIS阻抗快速下降, 并产生第二时间常数; SKP特征为表面电位差增大; (Ⅲ) 基底金属腐蚀发展与涂层失效阶段. 此时, EIS出现扩散尾, SKP电位差保持较大数值. 实验结果表明, 在研究有机涂层劣化过程中, EIS和SKP的结合使用能够互相补充完善, 获得涂层劣化过程中更为准确, 可靠的变化信息.

Studies on Deterioration Process of Organic Coatings Using EIS and SKP

Deterioration process of the organic coatings on carbon steel substrate during exposure to 3.5% NaCl solution was investigated using the electrochemical impedance spectroscopy(EIS) and scanning Kelvin probe(SKP). According to the EIS and SKP responses, the entire deterioration process can be divided into three main stages shown as follows. Stage Ⅰ was the water penetration into coatings. In this stage the EIS plots showed single semi-circel with the impedence of the coatings drops gradually and the Volta potential obtained by SKP keeps decreasing but the potential distribution remaines flat. Stage Ⅱ was the corrosion initiation under coatings. In this stage the EIS plots changed from a single loop to double capacitive loops with the resistance of the coatings decreased sharply, at the same time the surface Volta potential difference of the metal surface increased rapidly. Stage Ⅲ was the corrosion development and extension.The Nyquist plots of the electrochemical impedence showed a capacitive loop in the HF and a oblique line in the LF, with the potential difference remained in the high level. It was confirmed that the novel combination of EIS and SKP can complement and perfect each other to get more exact and credible details in studying the deterioration process of the organic coatings.