PO_4^(3-)对304不锈钢在氯离子水溶液中小孔腐蚀形核过程的影响

Effects of PO_4^(3-) on Pitting Nucleation of 304 Stainless Steel in Chloride Solutions

利用动电位循环扫描的方法研究了PO_4^(3-)对304不锈钢亚稳态孔蚀及稳定孔蚀形核与生长阶段的影响。随着PO_4^(3-)浓度的增大,亚稳态孔蚀电位E_m和稳定孔蚀电位E_b值均增大,即PO_4^(3-)浓度的增大,抑制了亚稳态孔蚀和稳定孔蚀的形核。PO_4^(3-)增加导致亚稳态孔蚀的平均生长速度和电流峰值降低,从而增大了亚稳态孔蚀转化为稳定孔蚀的难度,抑制了稳定孔蚀形核。但PO_4^(3-)增加导致孔蚀再钝化电位E_p降低,使充分发展的稳定蚀孔更难于再钝化,其原因可能是磷酸盐膜在小孔孔口的沉淀会促进蚀孔生长的稳定性。

The effects of PO43- on nucleation and growth of metastable and stable pitting were investigated by cycling potentiodynamic polarization. Both metastable pitting potential Em and stable pitting potential Eb increase with the increasing of PO43- concentration. Higher PO43- concentration results in lower average growth rate and peak current of metastable pitting, hence inhibits the nucleation of stable pitting. However, as PO43- concentration increases, the repassivation potential of stable pitting Ep decreases, indicating that the repassivation of the pit is retarded. The reason is explained by the deposition of phosphate film around the pit mouth, which may promote the growth stability of the pit.