采用电化学技术(动电位极化曲线, 自腐蚀电位, EIS, Mott-Schottcky(MS)曲线及循环伏安曲线)和表面分析方法(SEM和原位Raman 光谱)研究了空冷20SiMn钢在pH值均为10.64的3种浓度的碳酸盐缓冲液和浓度恒定为0.437×10^-3 mol/L的NaOH溶液中的腐蚀行为. 结果表明, 20SiMn钢在NaOH溶液中发生了均匀腐蚀, 经Fe(OH)₂转变为最终产物a-Fe₂O₃和g-FeOOH; 在低浓度碳酸盐缓冲液中发生了局部腐蚀, 经绿锈GRs得到最终腐蚀产物a-Fe₂O₃和b-FeOOH; 在高浓度碳酸盐缓冲液中发生了钝化, 并且受可溶性离子Fe(CO₃)₂^2-的影响, 钝化膜的耐蚀性随碳酸盐总浓度的升高存在极值.

The aggressive ions, such as Cl^- and SO₄^2-, as well as the carbonation caused by CO₂ from the air are two main reasons for the depassivation of steel rebar in reinforcement concrete. Under normal conditions, the pH value of concrete pore solution is taken as the criterion for determining whether the corrosion of steel occurs or not. However, carbonation process results not only in the decrease of the pH value of concrete pore solution, but also in the accession of HCO₃^- and CO₃^2-. It is demonstrated that these two ions are able to influence the corrosion behaviors of steel rebar. Additionally, the failure of reinforcement concrete is a time consuming process, so the corrosion evolution laws of steel at the presence of HCO₃^- and CO₃^2- is necessary to study systemically. Nevertheless, little relative work has been done so far. In this work, the electrochemical behavior of 20SiMn steel in three different content carbonate buffer solutions (0.01, 0.05 and 0.5 mol/L) was studied using electrochemical techniques (polarization curves, free corrosion potential measurements, EIS, Mott-Schottcky (MS) curves and cycle voltage curves) and surface analysis techniques (SEM and in situ Raman spectroscopy), compared with that in NaOH solution (0.437×10^-3 mol/L ). These four solutions are of the same pH value 10.64. The results indicated that 20SiMn steel was in active corrosion state in NaOH solution and low content carbonate solution, while it was in passive state in high content carbonate solutions. In NaOH solution, 20SiMn steel was destroyed by uniform corrosion and the corrosion products were a-Fe₂O₃ and g-FeOOH, transformed from Fe(OH)₂. In 0.01 mol/L carbonate solution, 20SiMn steel was destroyed by localized corrosion, and the final products were a-Fe₂O₃ and b-FeOOH, developed from the intermediate products GRs (green rusts). The passive film formed on 20SiMn steel was more resistive in 0.05 mol/L carbonate solution than that in 0.5 mol/L due to the formation of soluble complex anion Fe(CO₃)₂^2- in latter solution. There was a maximum corrosion resistance of the passive film with the increase of carbonate content.