有机涂层在浸泡和干湿循环条件下劣化过程的EIS对比研究

Comparative Studies on the Deterioration Process of Organic Coatings under Immersed and Cyclic Wet-Dry Conditions by EIS

应用电化学阻抗谱(EIS)技术以对比法研究了浸泡在3.5%NaCl溶液中的铁基有机涂层在浸泡和干湿循环条件下的劣化过程.干湿循环实验步骤为12h浸泡和12h干燥(298 K、50%RH).结果表明,根据EIS响应特征,浸泡和干湿循环下的涂层劣化过程均可分为3个主要阶段:涂层渗水阶段,基底金属腐蚀发生阶段和基底金属腐蚀发展与涂层失效阶段.与单一浸泡过程相比,干湿循环明显加速了腐蚀反应的发生,但减缓了其渗水、腐蚀发展以及涂层失效劣化过程.根据实验结果,深入讨论了干湿循环加速涂层劣化和涂层下基底金属的腐蚀机理.

Under the immersed and wet-dry cyclic conditions,the deterioration processes of the organic coatings on carbon steel surface have been comparatively studied by using electrochemical techniques.The wet-dry cycles were carried out in the alternating conditions of 12 h by immersing in a 3.5% sodium chloride solution and drying at 25 ℃ and 50% RH.Coating resistance,Rf,coating capacitance,Cf,and double layer capacitance,Cd,were monitored continuously and separately under above two conditions.The percentages of the intenfacial active area,Aw,were estimated from the obtained double layer capacitance,Cd.According to the EIS characteristics,the entire deterioration processes under above two mentioned conditions can be divided into three main stages,consisting of the medium penetration into coatings,corrosion initiation and corrosion extension underlying coatings.Comparing with the immersed,the cyclic wet-dry greatly accelerated the corrosion initiation stage,but decelerated the medium penetration and corrosion extension underlying coatings stages.The acceleration mechanism of the coatings and underlying metal corrosion under wet-dry cycles was discussed based on above results.