硫代硫酸根離子對鎳基690合金於1wt%氯化鈉水溶液中之孔蝕性質影響研究

Effect of Thiosulfate Ion on Pitting Corrosion of Alloy 690 in 1wt% NaCl Solution

本研究主要是以電化學量測方法，探討硫代硫酸根離子(0.001M~0.2M）對鎳基690合金於1wt%氯化鈉水溶液中之孔蝕性質的影響。由實驗結果顯示；鎳基690合金在硫代硫酸鈉水溶液中，並無孔蝕現象發生。但在1wt% NaCl 水溶液中，隨著硫代硫酸根離子的添加，則會降低其孔蝕起始電位值（Enp），但當添加的硫代硫酸鈉濃度超過某一臨界值時，其Enp值有再上升的趨勢；且當硫代硫酸鈉濃度超過0.1M 時，就會有抑制孔蝕的效果發生。此外，經SEM觀察及EDS分析蝕孔得知，硫代硫酸根離子的添加會使得蝕孔平均深度增加，同時在蝕孔內部並發現有硫元素的存在。這顯示硫代硫酸根離子對於孔蝕的成長扮演重要角色。

Effect of S2O32- on pitting corrosion of Alloy 690 in 1wt% NaCl solution was investigated using cyclic potentiodynamic polarization technique. The results showed that no pit was observed on Alloy 690 in the plain S2O32-(0.001~0.1M) solution. The presence of S2O32-(≤0.01M)in 1wt% NaCl solution leaded to a decrease in the pit nucleation potential (Enp)of Alloy 690 as compared with that without S2O32- addition. However, there existed a minimum concentration of S2O32- , beyond which Enp increased with increasing the concentration of S2O32in NaCl solution. Furthermore, pitting corrosion was inhibited as the S2O32- concentration reaching 0.1M. SEM micrographs showed that the pit depth increased with increasing S2O32concentration in 1wt% NaCl solution. EDS analysis also revealed the presence of sulfur within the pits. These results demonstrated that S2O32- played an important role in pitting corrosion growth process of Alloy 690 in 1wt% NaCl solution.