Using Eis To Study The Corrosion Failure Behaviors Of Several Single Coating And Composite Coatings In Different Conditions

This thesis focuses on evaluation of three types of epoxy zinc-richprimers and acrylic polyurethane topcoats and zinc-rich epoxy/micaceousferric oxide epoxy/acrylic polyurethane composite coating systems, usingelectrochemical impedance spectroscopy (EIS) to monitor the coating failureprocess. EIS and SEM at different stages and Fourier transform infraredspectras were used to study coatings’ failure mechanism. Some acceleratedcorrosion experiments under different conditions for single coatings andcomposite coatings were compared and each coating’s failure mechanism wasproposed. The order of the coatings’ performance in different failureconditions was obtained. The main contents are as follows:1. The failure processes of three epoxy zinc-rich paints were monitoredby EIS and the obtained EIS data were processed using ZSimpWin software.Detailed failure process was analyzed and compared for these three coatingcombined with scanning electron microscope photographs and fitting out datum. It could be seen the size and content of the Zn powder are keyfactors to the performance of zinc-rich coating, and Zn powder’s cathodicprotection time is not directly proportional to coating’s failure time.2. Three acrylic polyurethane topcoats were respectively arranged in twokinds of corrosion conditions, one was3.5%NaCl solution immersing and UVirradiation, another was the sodium chloride solution immersion. Coatings’failure processes were respectively measured by means of EIS. Threeequivalent circuits by fitting the EIS data of the three coatings on the firstcondition were obtained, and each coating failure mechanism were analysedcombining with their respective infrared spectral changes and SEM, then drewthe order of these three coatings on metal protection effect; Next, one kind ofacrylic polyurethane topcoat was selected and put it under two corrosionconditions, then tested these cooating using EIS. The analysis result showedthat the rise in|Z|0.01Hzof acrylic polyurethane EIS diagram was not due to UVradiation, which might be related to metal corrosion, corrosion blockedcoating porosity. In addition, coating chemical bond didn’t make obviousdegradation on the separate soaking conditions.3. Three composite coatings were respectively tested by EIS under threekinds of corrosion conditions (UV+heat, UV+3.5%NaClsolution,3.5%NaCl solution). Every coatings’ failure process on threecorrosive conditions were analysed and the influence degree of test conditionfor these three kinds of composite coating was compared. At last, the order of three composite coating was obtained by comparing the failure days of thecoating on each condition. The optium set of composite coating with weatherresistance, moisture resistance and salt solution resistance was obtained.4. By comparison of the failure time of three coatings exposed tostrong ultraviolet irradiation and high humidity environment, the topcoat is thekey factor to the composite coating.