关键词: 有机涂层, 干湿循环, EIS

Abstract: 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.

Key words: organic coatings, wet-dry cycles, electrochemical impedance spectroscopy