不同浓度比的硫酸根和氯离子溶液中钝化膜的半导体特性转变机制研究

800合金作为核电站蒸汽发生器的一种关键材料，服役环境下其表面钝化膜的特性一直是人们研究的热点. 本文用Mott-Schottky方法研究了800合金在不同硫酸根离子和氯离子浓度比的溶液中钝化膜的半导体特性，并结合电化学阻抗谱（EIS）、扫描电镜（SEM）、扫描电化学显微镜（SECM）研究了钝化膜的耐蚀性和表面活性. Mott-Schottky结果表明，800合金表面钝化膜的半导体特性与溶液中硫酸根、氯离子的浓度比有关，随硫酸根与氯离子浓度比的降低，半导体特性发生转变. 当硫酸根与氯离子的浓度比较高时，钝化膜为p型半导体；而当硫酸根与氯离子的浓度比较低时，钝化膜为n型半导体. EIS、SECM、SEM结果表明，随浓度比的降低钝化膜由过钝化溶解转为明显的点蚀特征，钝化膜表面活性增加. 钝化膜特性的改变与其半导体类型的转变密切相关，而半导体特性的转变由氯离子、硫酸根离子在800合金钝化膜表面的竞争吸附所致，其在表面的竞争吸附直接影响钝化膜表面发生的化学反应，改变电极/溶液界面电势差，使钝化膜中的空位类型改变，最终决定半导体类型.

AMechanistic Study on Semiconductivity Conversion of Passive Films under Varying Sulfate to Chloride Concentration Ratios

Alloy 800 is an important steamgenerator material used in nuclear power plants, and so there is significant interest in the properties of passive films of this alloy under service conditions. In this work, the semiconductivity of Alloy 800 in sulfate and chloride solutions was investigated using Mott-Schottky analysis, electrochemistry impedance spectroscopy (EIS), scanning electron microscopy (SEM), and scanning electrochemical microscopy (SECM). The Mott-Schottky results show that the semiconductivity is affected by the sulfate to chloride concentration ratio; p-type semiconductivity is exhibited at high concentration ratios but transitions to n-type when the concentration ratio is low. EIS, SEM, and SECM results indicate that the degradation formof the passive filmchanges fromtranspassive dissolution to pitting as the concentration ratio decreases while the film's surface reactivity increases, an effect that is related to the semiconductivity conversion. The observed variation in semiconductivity results fromthe competitive adsorption of sulfate and chloride, a process that modifies the potential drop at the film/solution interface, changes the vacancy types and ultimately determines the semiconductivity.