镀锡板钼酸盐-植酸体系电化学钝化膜的制备及性能研究

Preparation of Molybdate-Phytate Passivation Coating on Tin-plating Steel

摘要:

本工作用电化学方法对镀锡板进行钝化处理。采用硫酸铜点滴实验、电化学交流阻抗、Tafel曲线和扫描电子显微镜等方法检验膜层的性能。研究了电流密度、添加物、钝化时间等因素对钝化膜耐腐蚀性的影响，得出钝化膜的耐蚀性随着钝化时间的增大呈现先增大后趋于平稳的趋势，当钝化时间达到40 s时钝化膜的耐蚀性能最佳。优化出了最佳钝化工艺：钼酸钠25 g·L–1；植酸6.5 g·L–1；pH=4.5；钝化时间40 s；Jk=1.5 mA·cm-2。钝化处理后的膜层均匀平整的覆盖了镀锡板表面，膜层的腐蚀电位正移0.108 V，腐蚀电流降低2.3577×10-5 A·cm-2，硫酸铜点滴时间提高了23.3 s，电化学钝化效果接近铬酸盐钝化效果，有效提高了镀锡板的耐蚀性能

Abstract:

Passivation coatings were prepared on tin-plating steel by an electrochemical method. The corrosion resistance of the coatings was tested by CuSO4 drip experiment, electrochemical impedance spectroscopy, Tafel and SEM. Effects of current density, additives and passivation time on the properties of the passivation coatings were studied. It is concluded that the corrosion resistance of passivation films increases first and then becomes steady with the increasing of passivation time. When the passivation time is 40 s, the corrosion resistance of the coating is the best. The technological parameters of the passivation solution are obtained by experiment as following: sodium molybdate 25 g·L–1, phytic acid 6.5 g·L–1, pH=4.5, time 40 s and Jk=1.5 mA·cm-2. The apparent morphologies of the coating are well-proportioned covered on the surface of tin coatings. The results show that the corrosion potential of the tin layer is increased by 0.108 V, the corrosion current decreased by 2.3577×10-5 A·cm-2, and the drip time increased by 23.3 s. The passivation effect of the coatings prepared by the electrochemical method is nearly to that of chromating, and it increases the corrosion resistance of the tin coating effectively