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采用浸泡实验,电化学测试和表面分析技术研究了硫酸根离子浓度对铁在稀碳酸氢钠溶液中开路状态和阳极极化行为的影响.在无硫酸根离子及含有少量硫酸根离子的碳酸氢钠溶液中,铁的开路电位约为(-0.225±0.005)V,并呈现钝化状态,其电化学阻抗很大,腐蚀速率较低.在含有较高浓度硫酸根离子的碳酸氢钠溶液中,铁的开路电位为(-0.790±0.010)V并呈现活性溶解状态,其电化学阻抗较小,腐蚀速率较高,同时阳极极化曲线上能观察到活化-钝化转变现象.由于铁在含有较高浓度硫酸根离子的碳酸氢钠溶液中处于活化状态,阳极极化曲线上存在数个电流峰.足够高的硫酸根离子浓度会导致铁表面预先形成或转变而成的氧化膜失效.相比于自然曝氧状态,在除氧条件下较低的硫酸根离子浓度即可引起铁在碳酸氢钠溶液中由钝态向活性溶解态的转变.
The effects of sulfate ion concentration on the open-circuit state and anodic polarization of iron in dilute sodium bicarbonate solution were investigated by immersion test, electrochemical test and surface analysis technique. In the presence of sulfate-free ions and hydrogen sulphate-free bicarbonate In sodium solution, the open circuit potential of iron is about (-0.225 ± 0.005) V, which shows a passivated state with large electrochemical impedance and low corrosion rate.In the sodium bicarbonate solution containing higher concentration of sulfate ion , The open circuit potential of iron is (-0.790 ± 0.010) V and shows an active dissolution state, and its electrochemical impedance is smaller and the corrosion rate is higher. At the same time, the activation-deactivation transition can be observed on the anodic polarization curve. The sodium bicarbonate solution containing higher concentration of sulfate ions is in an activated state and there are several current peaks in the anodic polarization curve, and a sufficiently high sulfate ion concentration can lead to failure of the oxide film formed or transformed on the iron surface in advance. In contrast to the natural aeration, the lower sulfate ion concentration under deoxygenation conditions causes the transition of iron from the passive state to the active dissolved state in sodium bicarbonate solution.