扫描电化学显微镜原位表征pH值对核电蒸汽发生器合金腐蚀行为的影响

用扫描电化学显微镜(SECM)和电化学阻抗谱(EIS)原位表征了溶液pH值对核电蒸汽发生器800 合金溶液中的腐蚀行为的影响. 实验结果表明：在酸性氯化钠溶液中，SECM探针渐进曲线为正反馈，表明800合金为活化阳极溶解，腐蚀电位下的EIS 图呈现完整的单容抗弧特征；而在中性或者碱性溶液中，SECM探针渐进曲线为负反馈，表明800 合金为自钝化，不同阳极电位下的EIS 图均呈现不完整的容抗弧特征，但随着阳极极化电位的增加，EIS 谱容抗弧半径减小，表明钝化膜的耐蚀性下降；SECM二维扫描图像结果显示探针电流增加，表明电极表面活性增加，即钝化膜的溶解速度增加. 而在中性或者碱性溶液中的SECM二维图像中均可观察到若干活性点，这可能与晶界或者金属夹杂物等有关.

Characterization of pH Effect on Corrosion Resistance of Nuclear Steam Generator Tubing Alloy by In-situ Scanning Electrochemical Microscopy

The effect of pH on the corrosion resistance of Alloy 800, one of the preferred nuclear steam generator tubing materials, was investigated using in-situ scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). The experimental results show that positive feedback is observed in the probe approach curve (PAC) in acidic chloride solutions, indicating that Alloy 800 is active in acidic solutions; the EIS at the corrosion potential in acidic solutions exhibits an intact capacitance arc. However, negative feedbacks are observed in the PAC in either neutral or basic chloride solutions, showing that Alloy 800 is self-passivated in these two solutions. The EIS plots at different anodic potentials show incomplete capacitance arcs, and the arc radius decreases with increasing potential, indicating that the corrosion resistance of the passive film decreases. The SECM images show that the surface reactivity increases (or the dissolution rate of the passive film increases) as the polarization potential increases from the corrosion potential to the positive direction; this is verified by an increased tip current. Some "active spots" can be seen on the SECM images in neutral or basic chloride solutions, which are possibly related to grain boundaries, triple points, and/or inclusions.