环氧富锌-石墨烯涂层在中性盐雾和高低温循环浸泡中的失效研究

Failure Behavior of Graphene Modified Zinc-Rich Epoxy Coating in Neutral Salt Spray and Cyclic Temperature Immersion Tests

目的研究20#钢表面环氧富锌-石墨烯涂层在中性盐雾和高低温循环浸泡(3.5%NaCl溶液,45℃12 h+RT 12 h)试验中的失效过程与行为。方法采用电化学交流阻抗(EIS)测试、开路电位(OCP)监测、扫描电镜观察与分析(SEM/EDS)以及红外光谱(FTIR)等方法研究涂层在两种试验环境中的失效特征和对20#钢的保护作用,并探讨涂层失效的低频阻抗评价标准。结果涂层试样分别在中性盐雾79 d和高低温循环浸泡160 d后,表面开始出现锈点,失去对基体的保护作用,此时低频阻抗(|Z|0.01 Hz)值降至7×104Ω·cm2左右。除了屏蔽作用以外,环氧富锌-石墨烯涂层还可为钢基体提供一定的阴极保护作用,其中高低温浸泡环境中的阴极保护作用时间略长。在两种加速试验环境中,涂层后期的失光率均处于“明显失光”,色差值达到或接近“较大变色”。红外光谱显示,涂层中的特征官能团未发生明显的变化。结论通常利用低频阻抗(|Z|0.01 Hz)低于1×10^(6)Ω·cm^(2)来衡量有机涂层(不含导电颗粒)失效的判据,不适用于评价碳钢表面的环氧富锌-石墨烯涂层体系,对于该体系的失效评价可能需要再降低近2个数量级,约为7×10^(4)Ω·cm^(2)左右。

This paper aims to study the failure process and behavior of the epoxy zinc-rich graphene coating on the surface of 20#steel in neutral salt spray and high and low temperature cyclic immersion(3.5%NaCl solution,45℃12 h+RT 12 h)tests.Electrochemical impedance spectroscopy(EIS),open circuit potential(OCP),scanning electron microscopy(SEM/EDS)and infrared spectroscopy(FTIR)methods were used to study the failure behavior of graphene modified zinc-rich epoxy coating and the protection of 20#steel in neutral salt spray and cyclic temperature immersion tests(3.5wt%NaCl solution,45℃12 h+RT 12 h).And explore the low-frequency impedance evaluation standard of coating failure.The results showed that after coating samples were immersed in neutral salt spray for 79 d and high and low temperature cycles for 160 d,rust spots began to appear on the surface and lost the protective effect on the substrate.At this time,the low-frequency impedance(|Z|0.01 Hz)value dropped to 7×10^(4)W×cm^(2).Except for the shielding property,the graphene modified zinc-rich epoxy coating can also provide the cathodic protection for the steel substrate,meanwhile,the cathodic protection in the high and low temperature immersion environment has a slightly longer duration of action.In the two accelerated test environments,the gloss loss rate of the coating was“signifi-cant loss of light”,the color difference reached or approached“large discoloration”,and the characteristic functional groups in the coating presented did not change significantly.Low frequency impedance(|Z|0.01 Hz)usually is lower than 1×10^(6)W×cm^(2) to measure the failure criterion of organic coating(without conductive particles),which is not suitable for evaluating epoxy zinc-rich graphene on carbon steel surface for the coating system,the failure evaluation of the system may need to be reduced by about 2 orders of magnitude,which is about 7×10^(4)Ω·cm^(2).