| Due to the complexity of marine environment,the protection of steel structure coating is seriously challenged,and the cases of structural damage failure occur one after another before the service life of the coating.The coating has a great influence on the protective effect of the substrate and the common failure forms of the coating include loss of light,surface powdering,defects,lose of adhesion and so on.A lot of studies have been done on the aging behavior of polyurea coatings,but the surface phenomena and chemical composition are not enough to analyze the failure mechanism.In order to further study the failure behavior mechanism of polyurea coating,the hydrogen bond behavior and phase separation structure of polyurea coating in natural exposure environment and Xenon arc lamp accelerated environment were studied by FTIR,AFM,XPS et al,and the aging mechanism was analyzed.Based on the above experiments,the experimental conclusions were as follows:1.After 150 days of natural exposure to marine atmosphere,the macroscopic properties of polyurea coating changed obviously: gloss and contact angle decreased by 41.95% and 51.28%,respectively.The mechanical properties of the coating,such as tensile strength,tear strength and elongation at break,decreased by about 7.43%,18.38% and 26.4%,respectively.From the microscopic point of view,SEM showed that a large number of micropores and microcracks appeared on the surface of the coating during exposure,and the defect area of the coating was positively correlated with the aging time,and the calculated results showed that there is a negative correlation between the defect area and the contact angle of the coating.From the point of view of chemical composition,FTIR analysis showed that the bonds such as C=O,C-H and other bonds were broken in varying degrees after 150 days of exposure to the sun.The hydrogen bond length of the amino region of the coating remained stable,but the content of ordered hydrogen bond and total hydrogen bond decreased after aging in the carbonyl region,which proved the decrease of the intermolecular force.AFM and XPS analysis showed that the relative content of soft segment and hard segment of the coating changed after 150 days of exposure,and the surface of the coating was uneven and the roughness of the coating was improved due to the etch of the soft segment of the coating after aging.2.After 1000 h irradiation with Xenon arc lamp,the macroscopic properties of polyurea coating decreased: gloss and contact angle decreased by 15.64% and 22.19%,tensile strength,tear strength and elongation at break decreased by about 20.9%,12.57% and 22.46%,respectively.From the microscopic point of view,SEM shows holes and microcracks on the surface of the coating irradiated by Xenon lamp.FTIR analysis showed that the bond length of amino region remained stable and the content of ordered hydrogen bond and total hydrogen bond decreased after irradiation for 1000 h,which proved the decrease of intermolecular force.AFM and XPS analysis showed that the relative content of soft segment and hard segment changes after 1000 h irradiation,and the roughness of the coating improved after aging when the soft segment of the coating was etched.3.When immersion time reached 60 days,the tensile strength,tear strength and elongation at break of single chlorine immersion polyurea coating decreased by 8.3%,3.6% and 9.6%,respectively,while those under the double factor decreased by 13.3%,4.9% and 11.7%,respectively.The contact angle change rates of the two environments are-12.5% and-20.1%,respectively.FTIR showed that the chemical properties of the coatings under the action of chlorine salt and chlorine salt dynamic water environment are basically stable,the degree of molecular bond fracture was low,and the main reason for the decrease of macroscopical properties was physical factors.The adhesion of the coating decreased with the increase of soaking time,and the dynamic water adhesion of chlorine salt and chlorine salt decreased by 22.8% and 40.7%,respectively.EIS experiment showed that the dynamic water effect greatly accelerates the diffusion of corrosion medium to the interface of coating substrate,which led to the accumulation of a large number of corrosion products at the interface of coating substrate and made the coating enter the middle stage of corrosion ahead of time,which was also an important reason for the decrease of adhesion of coating.4.When the coating was immersed in 10% hydrochloric acid and sodium hydroxide solution,the gloss of the coating decreased by 12.6% and 13.8%,respectively,and the tensile strength,tear strength and elongation at break of the coating decreased by 14.8%,8.0% and 16.5%,respectively,under the action of 10% hydrochloric acid and sodium hydroxide solution,and the tensile strength,tear strength and elongation at break of the coating decreased by 12.6% and 13.8%,respectively.However,under the action of 10% sodium hydroxide,it decreased by 15.7%,17.6% and 18.4%,respectively.FTIR showed that the corrosion degree of the coating in sodium hydroxide solution was higher than that in hydrochloric acid solution.The strength of C = O and C-O-C bands of the coating after soaking in sodium hydroxide solution was obviously weakened,while the chemical properties of the coating were stable and a small amount of bond breaking occurs after soaking in hydrochloric acid solution.In conclusion,the surface properties of polyurea coatings changed obviously after natural exposure to marine atmosphere and Xenon arc lamp irradiation,and the mechanical and thermodynamic properties decreased to a certain extent,but the strength of polyurea coatings remained high.After aging,there were different degrees of bond breaking and obvious microphase separation,and the aging behavior was basically the same,which indicated that it was feasible to simulate natural exposure to marine atmosphere by Xenon lamp aging.The corrosion results of chlorine salt,moving water and acid-base action on the coating in simulated marine environment showed that the marine dynamic water factor had a greater damage effect on the coating,and the corrosion rate of the coating in sodium hydroxide was higher than that in hydrochloric acid. |
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