Study On The Degradation Process Of Organic Coating By EIS Under Wet-dry Cycle Enviroment

The degradation process of organic coating was investigated usingelectrochemical impedance spectroscopy （EIS）. The water absorption ratesand micro pores rates were discussed based on the EIS results with equivalentcircuit model. Combining FT IR and SEM analysis, the failure mechanism oforganic coating was presented. Furthermore the changes of EIS spectrum indrying period of wet dry cycle were studied using double electrode cell, andthe affects of wet dry cycle on the degradation process was discussed.1The degradation process of the thick epoxy primer coating under cyclicwet dry and immersion condition was investigated by EIS, FT IR and SEMrespectively. Based on the EIS spectrum results the|Z|_0.01Hz-time curve ofthe thick epoxy primer coating could be divided into three stages.Furthermore the degradation of coatings under the two conditions wereattributed to hydrolysis of epoxy groups. As the supplying of oxygen duringdrying period and physical process in the wet dry cycle, the degradationprocess of coatings under cyclic wet dry was faster evidently than that underimmersion condition. 2The changes of EIS spectrum results of the thick epoxy primercoating in drying period of wet dry cycle were investigated using doubleelectrode system. The difference between double electrode system and threeelectrode system in immersion period of wet dry cycle was compared. Theresults indicated that EIS spectrum results of the double electrode system wasconsistent with the three electrode system’s. The|Z|_0.01Hz-time curve of thethick epoxy primer coating also could be divided into three stages in thedrying period.3The degradation process of the polyurethane heat reflection top coatand epoxy antirust coating HB under cyclic wet dry and immersion conditionwere investigated by EIS, FT IR and SEM respectively. The fitted EISspectrum results indicated that both water absorption rate and micro pore ratewere increased with time. As FT IR and SEM result showing, thedegradation of coatings under the two conditions were mainly due tohydrolysis of epoxy groups. Moreover the degradation process of coatingsunder cyclic wet dry was faster than that under immersion condition.4Compared with single primer coating and top coating, the degradationprocess of the composite coating was investigated. The results indicated thatthe degradation degree of the top coating of composite coating was moresevere than that single top coating, and the miero pore penetrated though thetop coating of composite coating.5The effects of wet dry cycle on the degradation process of the polyurethane heat reflection top coat and epoxy antirust coating HB werediscusssd. The results indicated that the degradation of the coating was fasterwith the immersion time increased in single wet dry cycle.