钼酸钠对热镀锌钢板表面磷化膜电化学行为的影响

Effect of Sodium Molybdate on Electrochemical Behavior of Phosphating Coatings on Hot-Dip Galvanized Steel Sheet

在磷化液中添加钼酸钠可改善和提高热镀锌钢板表面磷化膜的质量。运用极化和电化学阻抗的测试方法,研究了磷化液中加入钼酸钠对热镀锌钢板表面磷化膜在5%NaCl溶液中的电化学行为的影响。结果表明,在磷化液中加入钼酸钠可促进磷化膜生长,大大降低电化学体系的腐蚀电流密度,提高其极化电阻和电化学阻抗,改善膜层的耐蚀性能。最佳的钼酸钠用量为1.0g/L,膜层呈暗灰色,膜重为1.6g/m2,耐硫酸铜点蚀时间大于65s。当钼酸钠用量为2.0g/L时,膜层的各项性能指标均下降。

Sodium molybdate was added in phosphating solution to improve the performance of phosphating coatings on hot-dip galvanized (HDG) steel sheet. The polarization curves and electrochemical impedance spectroscopy (EIS) of the phosphating coatings in 5% NaCl solution were measured so as to investigate the effect of the sodium molybdate added in phosphating solution on the electrochemical behavior of the coatings. It was found that the introduction of sodium molybdate in the phosphating solution contributed to promoting the growth of the phosphating coatings, greatly decreasing the corrosion current of the electrochemical systems, and increasing the polarization resistance and electrochemical impedance of the coatings. Subsequently the corrosion resistance of the phosphating coatings was significantly increased. The optimum concentration of the sodium molybdate was suggested as 1.0 g/L, at which the corresponding phosphating coatings appeared to be dark gray and weighed to be 1.6 g/m 2 , with the endurance to pitting of aqueous copper sulfate to be over 65 s. However, when the concentration of sodium molybdate in the phosphating liquid rose to 2.0 g/L, the performance of the corresponding phosphating coatings would be worsened.