SO_4^(2-)对模拟孔隙液中Q235B钢筋腐蚀行为的影响

Influence of SO_4^(2-) on the Corrosion Behavior of Q235B Steel Bar in Simulated Pore Solution

通过阳极极化曲线、EIS、Mott-Schottky (M-S)以及恒电位极化测量研究了不同pH值模拟混凝土孔隙溶液中SO_4^(2-)对Q235B钢筋钝化和腐蚀行为的影响。极化曲线测量结果表明,在pH值高于11的模拟孔隙液中,SO_4^(2-)对Q235B钢的钝化膜没有破坏作用,而在pH值为10的模拟孔隙液中,少量SO_4^(2-)的存在就会造成Q235B钢表面钝化膜的破裂,从而导致点蚀的萌发。EIS和M-S测量结果表明,碳钢表面的钝化膜在低pH值的模拟孔隙液中稳定性较差并具有更高的缺陷浓度,从而促进了SO_4^(2-)对碳钢的侵蚀性。结合恒电位极化测试和SEM观测进一步研究了SO_4^(2-)对碳钢钝化膜的破坏作用。在高pH值的模拟孔隙液中,SO_4^(2-)在钝化膜的形成阶段能够抑制钝化膜的生长,造成亚稳态点蚀的出现,而在低pH值的模拟孔隙液中,SO_4^(2-)可以聚集在钝化膜的缺陷处,造成钝化膜的破损和稳态点蚀的发展。

Cl-and SO4^2- are most common aggressive ions containing in the seawater which may cause the localized corrosion of reinforcement structures. It is found that a protective passive film will form on the steel surface in the concrete pore solution. The localized breakdown of the passive film caused by the aggressive ions and the carbonation are the main reason for the localized corrosion initiation of reinforcements. In the previous studies, it is found that the performances of the SO4^2- on the rebar corrosion were quite different in different pH value conditions and the test results did not unify. Therefore,the influence of pH value and the SO4^2- on the corrosion behavior of Q235B carbon steel in the simulated pore solution was studied using anodic polarization, electrochemical impedance spectra(EIS), MottSchottky(M-S) and potentiostatic polarization methods. The anodic polarization curves indicate that when the pH value of the simulated pore solution was higher than 11, SO4^2- had no damage to the passive film. However, once the pH value of the simulated pore solution decreased to 10, a small amount of SO42- can lead to the breakdown of the passive film and induce pitting initiation. EIS and M-S measurement results suggest that the stability of the passive film would decrease with the decreasing of the solution p H. The concentration of the defect would increase in the passive film due to the pH decrease. The stability reduction and the increase of defect concentration both can lead to the passive film become fragile and more easily to be destroyed by SO4^2-. Through the potentiostatic polarization test in conjunction with SEM observation, it is found that SO4^2- can inhibit the growth of the passive film during the initial film formation period and lead to the appearance of metastable pitting corrosion under high pH value conditions. In the low p H value conditions, SO4^2- could accumulate at the defect of the passive film and lead to stable pitting propagate on the steel surface.