目的 研究聚丙烯涂层的失效机制。方法 利用电化学阻抗谱技术，对某聚丙烯涂层在3.5%NaCl溶液中的失效机制及水在该涂层中的传输行为进行了研究，使用等效电路图对电化学阻抗谱数据进行了拟合，评价了涂层在不同浸泡时间后的腐蚀保护性能，并计算了水在涂层中的扩散速率。结果 聚丙烯涂层浸泡在3.5%NaCl溶液后，其腐蚀防护性能会快速下降，当浸泡到第6天时，涂层阻值从初始5.33×10⁹ Ω.cm²快速下降至1.08×10⁹ Ω.cm²，随后开始稳定。通过对在10 kHz下涂层电容值随浸泡时间的变化关系获知，在浸泡初期，水在涂层中的渗透是均匀的，其传输行为符合Fick第二定律，属于复杂的非稳态过程，其扩散系数为3.12×10^–11 cm²/s。水在涂层中的均匀传输时间与涂层阻值下降并达到稳定的时间基本相符，大约为144 h，此时涂层吸水率为8.25%。结论 聚丙烯树脂涂层在NaCl溶液中浸泡时，水的浸入及向金属基体方向传输是导致涂层失效的主要原因。在浸泡初期，水在涂层中的传输符合Fick第二定律，当水在涂层中传输不再符合Fick第二定律，水在涂层中到达饱和，此时涂层的保护性能大幅下降，腐蚀反应已经开始在界面发生。电化学阻抗谱技术可以很好地检测水在涂层中的传输行为，并给出量化数据，这可以用于评价涂层防护性能、预测涂层使用寿命和分析涂层失效机制。

The failure mechanism and the transportation behavior of water of a polypropylene coating in 3.5wt.%NaCl solution was investigated by electrochemical impedance spectroscopy (EIS). The EIS data were fitted by equivalent circuits, the corrosion protection performance in different immersing time was obtained, and the diffusion rate of water in the coating was calculated. The results indicated that the corrosion protection performance of the polypropylene coating was rapidly weakened after immersed in the 3.5wt.% NaCl solution. The resistance of the coating dramatically dropped from 5.33×109 Ω.cm2 to 1.08×109 Ω.cm2 after immersed for 6 days, and then became stable. Based on the relation between the capacitance of coating and immersing time under 10 kHz, the water had uniform penetration in the coating at the early stage, and its transportation behavior followed the second Fick’s law, which was a complex unsteady process. The diffusion coefficient was 3.12×10–11 cm2/s. The time of homogeneous diffusion of water in the coating is about 144 h, consistent with the time for the resistance of coating dropped down to a stable value. At this time, the water absorptivity of the coating was 8.25wt.%. When the polypropylene resin coating was immersed in NaCl solution, the infiltration of water and its transportation to the metal substrate was the main reason to lead the failure of the polypropylene coating. When the water transportation did not follow the the second Fick’s law, the water in the coating reached saturation. At that time, the protection performance of the coating was hugely declined, and the corrosion reaction has begun to occur at the interface. It could be known from this study that the EIS could be well used in detecting the diffision of water through coating quantitatively. This could be used in evalating the protection performance of coating, preticting the service life and analysing failure mechanism.