环氧涂层在低温、紫外环境下的失效行为对比研究

Failure Behavior of Epoxy Coatings in Low Temperature and Ultraviolet Environment

目的研究环氧富锌涂层(EP-Zinc)、环氧耐磨快干涂层(EP-WR)在紫外和低温2种环境下的失效行为和机理。方法以Q235钢为金属基底,分别用喷枪喷涂涂层在基体表面,将喷涂好的上述2种涂层材料放入干燥箱(60℃)中保持1 d,然后将涂层放在室温条件下6 d,以确保涂层内部的有机溶剂完全挥发。在紫外线(UV)辐射和低温2种实验环境下,通过电化学阻抗测试、红外光谱测试、表面表征(扫描电镜)、附着力测试等方法研究环氧涂层的失效行为及机理。结果2种涂层在紫外和低温环境下的防护功能均有所下降。在紫外环境下,EP-Zinc和EP-WR涂层的|Z|0.01 Hz分别降至10^(6)Ω·cm^(2)和10^(7)Ω·cm^(2)。在低温环境下,2种涂层的|Z|0.01 Hz均剧烈降至10^(6)Ω·cm^(2)和10^(5)Ω·cm^(2)。在低温环境下,环氧涂层主要因其热膨胀系数与金属基体存在较大差异,导致涂层与基体的体积变化出现差异,产生应力,从而失效。紫外环境改变了涂层表面的化学结构,导致涂层表面出现孔洞、裂纹等微观缺陷。结论在低温环境下,主要因物理因素的变化导致涂层失效。强紫外线环境破坏了涂层的交联结构,使得涂层的韧性下降、脆性上升,涂层表面产生了数量众多的微缺陷,并加速了涂层的失效。相较于低温环境,紫外辐照对基体与涂层界面结合强度的损害更明显,附着力明显降低。

The failure behavior and mechanism of epoxy zinc-rich coatings(EP-Zinc)and epoxy wear-resistant fast drying coatings(EP-WR)in ultraviolet(UV)and low temperature environments were studied in this work.The Q235 steel was used as the base material,and the coating was sprayed on the substrate surface with an airbrush.The two coating systems were put into a drying oven and kept at 60℃for 1 day,and then were placed at the room temperature for 6 days to ensure that the organic solvent inside the coating was completely volatilized.The failure behavior and mechanism of epoxy coatings were studied by means of ultraviolet radiation and low temperature exposure,open circuit potential test,electrochemical impedance test,infrared spectrum test,surface characterization(SEM),and adhesion test.The results showed that the failure of the epoxy coating failed in the low temperature environment was mainly due to the large difference between the thermal expansion coefficient and the metal substrate,which resulted in the stress caused by the difference in volume between the coating and the metal substrate.The EP-WR coating produced tiny holes on the coating surface,resulting in the unsmooth coating surface.The ultraviolet(UV)environment changed the chemical structure of the coating surface,leading to the formation of the holes,cracks,and other microscopic defects within the coating.The electrochemical test results showed that the protection ability of the two coatings decreased in the ultraviolet(UV)and low temperature environment.The open circuit potential of the two coatings decreased and fluctuated with the extension of aging time,indicating that the electrochemical activity of the system increased,and the protection performance decreased.In the ultraviolet(UV)environment,the modulus values of the EP-Zinc and EP-WR coating decreased to 10^(6)Ω·cm^(2)and 10^(7)Ω·cm^(2),respectively.In the low temperature environment,the modulus values of the two coatings decreased to 10^(6)Ω·cm^(2)and 10^(5)Ω·cm^(2).In addition,adhesion played an important role in the failure behavior analysis of coatings.In the low temperature environment,the adhesion of the EP-Zinc coating decreased from 5.92 MPa to 4.97 MPa,and that of the EP-WR coating decreased from 6.51 MPa to 4.94 MPa.This indicated that the damage to the interfacial bonding strength between the coating and the substrate was relatively small in the low temperature environment.In the ultraviolet(UV)environment,the adhesion of EP-Zinc and EP-WR coatings had similar changes,and both of them showed a large decrease with the extension of ultraviolet irradiation time,among which the EP-Zinc coating adhesion decreased from 5.92 MPa to 2.02 MPa and the EP-WR coating adhesion decreased from 6.51 MPa to 3.44 MPa.FT-IR results showed that both EP-Zinc and EP-WR epoxy coatings produced similar characteristic peaks in 1708-1736 cm–1 in the UV environment,which was the stretching vibration peak of carbonyl group in saturated aldehydes,ketones and acids,indicating that aging occurred.However,no new bond was formed in the low temperature environment.The failure of coatings in low temperature environment is mainly caused by the change of physical factors,and the failure of coatings in ultraviolet environment is mainly due to the change of chemical factors.