利用极化曲线和阻抗技术,对低碳钢在不同pH值H2S溶液中的腐蚀电化学行为进行了研究.结果表明,在溶液pH值较低时,腐蚀电极主要受阳极酸性溶解过程控制,表面无硫化物沉积,其阻抗谱除高频容抗弧外,低频有一感抗存在;随pH的升高,腐蚀电位明显负移,电流密度减小,表面出现硫化物的不连续沉积,腐蚀因溶液pH值的增加和硫化物的沉积而减小,电极过程主要受硫化物的生长所控制;在pH值为6.2时,由于HS-的阴极去极化,腐蚀电流增加;当Ph大于7后,电极表面因氧化膜的生成而呈现钝化特征,极化电阻显著增加.基于溶液中HS-同OH-的竞争吸附,提出可能的腐蚀历程,据此可解释有关实验事实.
Electrochemical behavior of carbon steel in the simulated solutions containing H2S at different pH values have been investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS). The results indicated that at lower pH value, the electrode process of carbon steel was mainly controlled by anodic dissolution, the Nyquist diagrams were composed of a capacitive loop at high frequency and an inductive loop at the low frequency. With the increase in pH, the corrosion potential of carbon steel became more negative, as well as corrosion current density decreased. These changes could be attributed to the increase in pH and coverage of iron sulfide film, but a higher corrosion current was observed at pH 6.2, which was attributed to the depolarization of HS- in cathodic process. When the pH was higher than 7, the surface of corroding electrodes got into the stage of passivation because of the formation of iron oxide film. Based on the view of competitive adsorption between HS- and OH- on surface electrode, a probable reaction mechanism was suggested.
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