Abstract: The anodic polarization curves of mild steel were measured potentiodynamically in sodium carbonate solution containing different concentrations of sodium bicarbonate, and the surface products of steel were analyzed with XPS. The potentiodynamical studies showed two anodic peaks and two passive zones present in all the polarization curves. Compared to those obtained in NaHCO₃ solutions, the first passive zones of the polarization curves in Na₂CO₃-NaHCO₃ solutions became wider and clearer. Both of the potentials at two peaks shifted to positive direction after adding bicarbonate in carbonate solution, which meaned bicarbonate ions could weaken the passivation of iron in carbonate solutions. A good linear relationship was found between the potential at the second peak and the logarithm of the concentration of bicarbonate ions. According to the electrochemical thermodynamics of iron in Na₂CO₃-NaHCO₃ solution, the following reaction might take place at the second peak:3FeCO₃+4H₂O---Fe₃O₄+3HCO^-₃+5H⁺+2e.The results with XPS showed that the iron surface consisted mainly of ferrous and ferric oxides, which further supported the above reaction.

摘要： 使用动电位极化技术研究了碳钢在Na₂CO₃-NaHCO₃溶液中的阳极极化行为，测试结果表明，阳极极化曲线上存在着两个电流峰和两个钝化区.与在NaHCO3溶液中相比，碳钢在Na₂CO₃-NaHCO₃溶液中的极化曲线上的第一个钝化区变得更宽.当增加NaHCO₃浓度后，两个峰值电位均往正方向移动，表明碳钢的钝化能力降低.研究发现，第二个电流峰对应的电位与NaHCO₃浓度的对数呈良好的线性关系.根据铁在Na₂CO₃-NaHCO₃溶液中的腐蚀热力学，推测该峰处发生的反应可能是：3FeCO₃+4H₂O---Fe₃O₄+3HCO^-₃+5H⁺+2e.XPS分析表明铁电极表面主要由二价铁和三价铁的氧化物组成，进一步支持了以上反应.