| In this paper, the deterioration processes of single coating and compositecoating were studied comparatively though Electrochemical ImpedanceSpectroscopy (EIS) in3.5%NaCl soaked for8h, dried for16h,2h soaked,4hdried,meanwhile the morphology of metal under the coating surface andcoating substrate surface corrosion reaction point was observed by ScanningElectron Microscope(SEM).The EIS characterization showed that epoxy rust belt and acrylicheat-reflective single coating failure process could be divided into three mainstages under the immersion,8-16h and2-4h: the medium penetration intoorganic coatings, corrosion intiation and corrosion extension underl organiccoatings.Comparing with the immersed, the epoxy rust belt deterioration processwas greatly accelerate in the2-4h and8-16h wet-dry cycles. The acceleratedphases were the phase2and3in2-4h alternating wet and dryenvironment,the accelerated phase was phase2and the delayed phases werephase1and3in8-16h alternating wet and dry environment. The epoxy rust belt coating failure reasons comparing with theimmersion, the8-16h and2-4h wet-dry cycles showed that the coating localbubbling which led to lower the overall impedance of the coating system wascaused by the metal matrix severe localized corrosion underimmersion,besides the coating local bubbling, the rest of the coating also had avery good protection; the oxygen reduction reaction was accelerated due todring for a long time in the8-16h wet-dry cycles,but the rate of coatingstripped was slowed due to the lack of electrolyte solution;the metal substratesperformed equally severe localized corrosion, but the number and area ofcorrosion reaction were larger than full immersionand; the peeling of thecoating was accelerated which was due to the oxygen reducted quickly in thedrying phase in the2-4h wet-dry high frequency cycles, and showed the smallanode and large cathode corrosion reaction characteristics,and the metalsubstrate corrosion was lighter and more uniform. |
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