环氧厚涂底漆在干湿交替环境条件下的劣化过程

Degradation Process of an Impasto Epoxy Primer Coating under Cyclic Wet-dry and Immersion Condition

采用电化学阻抗谱(EIS)和傅里叶变换红外光谱(FTIR)等方法研究了干湿交替环境和全浸环境试验条件下,环氧厚涂底漆在3.5%NaCl溶液中的劣化过程和机制。在干湿交替和全浸两种条件下,涂层的劣化主要是由于涂层中环氧基团在电解质溶液中的水解。涂层中孔洞等缺陷及环氧基团水解生成的亲水性-OH,-NH_2等基团,促进了电解液的渗透,加速了涂层的劣化进程。在干湿交替环境中,涂层劣化明显快于全浸环境。这是由于干湿交替环境中,涂层水解程度较全浸环境中更高,且干燥过程中氧的补充加速了阴极区的反应,促进了金属基体的腐蚀,使得涂层附着力变差。另外,在干湿交替循环作用下,由于涂层与基体涨缩不一致引起的内应力也加速了涂层的劣化过程。

The degradation process and mechanism of a thick epoxy primer coating was investigated in 3. 5% NaCl solution under cyclic wet-dry and immersion condition by electrochemical impedance spectroscopy （EIS） and fourier transform infrared spectroscopy （FTIR）. The degradation of the coating under the two conditions was mainly due to the hydrolysis of epoxy groups in electrolyte solution. The defects of coating such as micro-pores and the hydrophilic groups such as --OH and --NH2, which came from hydrolysis of epoxy groups, promoted the electrolyte solution penetration and accelerated the degradation process. But the degradation process of the coating under cyclic wet-dry condition was faster evidently than that under immersion condition. The main reasons were as follows. The hydrolysis degree of the coating under cyclic wet-dry condition exceeded that under immersion condition. During drying period, oxygen accelerated the reaction on the cathode, resulting in a relatively quick corrosion of metal matrix and a decrease of the coating adhesion. Besides, the inner stress, which resulted from the incongruity of shrinking and swelling between coating and substrate, accelerated the degradation process of the coating.