316NG不锈钢在硼-锂溶液中的电化学腐蚀行为研究

Studies on Electrochemical Corrosion Behaviors and 316NG Stainless Steel in Boron-Lithium Solutions

利用电化学方法获得316NG不锈钢(316NG)在300℃、pH=5～8硼-锂溶液中的极化曲线和交流阻抗(EIS),并绘制相应水化学条件下的电位-pH图。结果表明:碱性条件下钝化区尤其是二次钝化区极化电流急剧减小,pH=7～8时阳极极化表现出3次钝化现象,偏碱性条件极化阻抗显著高于偏酸性和近中性条件,说明碱性条件下316NG表面钝化膜保护效果更佳。pH=5时电化学极化后样品表面主要生成Cr2O3和Fe2O3;碱性条件下(pH=6～8)样品表面氧化膜为分层结构:最外层为Fe3O4,随深度增加开始出现NiFe2O4,内层成分主要为FeCr2O4。随着电导率升高,溶液电阻、电荷传递电阻和钝化膜电阻均显著降低。依据极化曲线绘制的电位-pH图与文献结果相吻合。

The electrochemical behaviors of 316 NG stainless steel in the boron-lithium solutions（pH=5～8） at 300℃ were studied by using electrochemical polarization curves and the electrochemical impedance spectroscopy（EIS）, and the experimental E-pH diagram at the same environment was graphed. The results indicated that the polarization current in the passivation region decreased sharply, especially in the region close to the secondary transpassivation point, and there were three passivation domains when pH was 7～8, The polarization resistance of 316 NG stainless steel in the alkaline solution was apparently higher than that in the acidic solution or in the neutral solution, which was found by using electrochemical impedance spectroscopy, showing the oxide film at alkaline environment had a better protective effect. The oxide film was consisted of Cr2 O3 and Fe2 O3 in the acidic solution; When pH=6～8, a multilayered oxide film occurred： the outer Fe-rich layer consisted of Fe3 O4 while NiFe2 O4 occurred as the depth of layer increased, and the inner Cr-rich layer was composed of FeCr2 O4. Rsol and the polarization resistance significantly decreased as the conductivity of the solution increased. The E-pH diagram based on the polarization curves was consistent with the inference.