碳钢和不锈钢在不同模拟混凝土孔隙液中的耐蚀性研究

发布时间：2018-05-09 09:14

本文选题：Q235碳钢 + 304不锈钢　；参考：《北京化工大学》2015年硕士论文

【摘要】：由于混凝土的碳化作用和环境中氯离子的侵蚀均能导致钢筋锈蚀,采用不锈钢代替碳素钢可以有效延长混凝土结构的使用期限。因此研究和对比不同钢筋在混凝土孔隙液中的耐蚀性能对钢筋混凝土结构的应用有着十分重要的意义。本文通过动电位极化,恒电位极化,Mott-Schottky曲线,EIS等电化学技术以及XPS、扫描电镜观察等方法对Q235碳钢和304不锈钢(304 SS)两种材料在五种不同的模拟孔隙液中的耐蚀性进行了对比研究；对两种碳化混凝土模拟孔隙液中Cl-对碳钢亚稳态孔蚀的特征参数的影响进行了深入的分析;并对碳钢表面亚稳态孔蚀向稳态孔蚀的转化进行了探讨。所得到的主要结论如下：(1)对五种不同pH值的模拟孔隙液中无氯以及有氯离子两种情况下Q235碳钢和304 SS的耐腐蚀性能进行对比。无氯条件下,两种钢材在五种pH值的孔隙液中均能保持很好的钝化状态,耐蚀性能无明显差别;加入0.05 mol/L Cl-后304 SS的耐蚀性仍然没有变化,而Q235碳钢仅在pH 13.3的孔隙液中能维持很好的钝化性能,但在轻微碳化(pH 11.5)和碳化(pH 10.3和9.7)的模拟孔隙液中耐蚀性能显著下降,极化曲线上产生明显的亚稳态电流波动并发生了小孔腐蚀。Mott-Schottky曲线测试结果显示,304 SS表面钝化膜中的掺杂浓度随着溶液pH值的降低略有上升,有氯和无氯条件下相差不大;Q235碳钢在无氯条件下钝化膜的掺杂浓度随pH值的变化不明显,有氯时钝化膜掺杂浓度随溶液pH值的降低有较大提升,导致耐蚀性下降。XPS结果表明：无氯离子条件下Q235碳钢表面膜层中Fe3+/Fe2+随pH值下降无明显变化,而在有氯离子的孔隙液中Fe3+/Fe2+随pH值下降明显降低,表明钝化膜的稳定性下降；不同pH的模拟孔隙液中304SS的钝化膜成分变化不明显,因而其耐蚀性也无明显变化。(2)两种碳化模拟孔隙液(pH 10.3和9.7)中随着Cl-浓度的增大,Q235碳钢的亚稳态孔蚀电位Em和稳定孔蚀电位Eb值均负移,其中Eb与ln[Cl-]成线性关系：Em和Eb均随着溶液中ln[Cl-]/[OH]和1nCagg/Cinh(侵蚀性离子与缓蚀性离子之比,[Cl*]/[OH-][HCO3][CO32-])的增加而下降,也呈良好的线性关系。Cl-浓度增加,碳钢表面钝化膜中的施主浓度Nd和平带电位Efb均增大,膜中的空位增多,钝化膜电阻下降,电容升高,膜层的致密性下降,碳钢的孔蚀敏感性增加。(3)随着Cl-浓度的增大,Q235碳钢的亚稳态小孔形核数目增加、形核率最大值对应电位负移、小孔平均寿命增加、理论亚稳孔半径增大,因此Cl-对亚稳态孔蚀的形核和生长均起到促进作用。亚稳态小孔半径的最大值出现的电位与亚稳孔形核率最大值出现的电位相一致,该电位略低于稳定孔蚀电位Eb,说明亚稳小孔半径越大、小孔数量越多,转化为稳定孔的几率越大,大量的小孔集中爆发后会很快转入稳定孔蚀阶段。(4)Q235碳钢在略高于Em的电位进行恒电位极化,形成的亚稳态小孔的孔径较小(小于1μm),孔口多呈开放状态。极化电位升高到钝化区中段(高于Em,但远低于Eb),形成的亚稳态小孔的尺寸增大(1μm左右);多个亚稳态小孔有聚集形核、生长的趋势,蚀孔底部可以观察到有小孔向下生长的痕迹；部分孔口尚存未完全破裂的钝化膜,由电流波动峰积分计算证实亚稳态小孔在膜下继续深挖发展。极化电位接近Eb时,碳钢表面发生几百微米的稳定蚀孔群,蚀孔群由许多集中生长的小孔组成,许多小孔较深,表面多有腐蚀产物覆盖；腐蚀产物膜中有氯离子富集,与基体接触诱发大量孔蚀形核,即亚稳态孔蚀主要在稳定孔的周围形核与生长,导致了稳定蚀孔在试样表面的横向生长。
[Abstract]:As the carbonization of concrete and the erosion of chloride ions in the environment can cause corrosion of steel, the use of stainless steel instead of carbon steel can effectively prolong the use period of concrete structures. Therefore, it is of great significance to study and compare the corrosion resistance of different reinforcing bars in the pore fluid of concrete. In this paper, the corrosion resistance of two kinds of Q235 carbon steel and 304 stainless steel (304 SS) materials in five different simulated pore fluids were studied by means of dynamic potential polarization, constant potential polarization, Mott-Schottky curve, EIS and other electrochemical techniques, XPS and scanning electron microscopy, and Cl- to carbon steel in two carbonated concrete pore fluid. The influence of the characteristic parameters of steady-state pore erosion was deeply analyzed, and the transformation of metastable pore erosion to steady-state pore erosion of carbon steel surface was discussed. The main conclusions are as follows: (1) the comparison of corrosion resistance of Q235 carbon steel and 304 SS under two different pH values of simulated pore fluid and two kinds of chloride ions Under the condition of chlorine free, two kinds of steel can keep a very good passivation state in the five pH value pores, and there is no obvious difference in corrosion resistance. The corrosion resistance of 304 SS after adding 0.05 mol/L Cl- remains unchanged, and Q235 carbon steel can maintain very good passivation properties in the pore solution of pH 13.3, but in mild carbonization (pH 11.5) and carbonization (pH 10.3, and 10.3) 9.7) the corrosion resistance in the simulated pore fluid decreased significantly. The apparent metastable current fluctuation on the polarization curve and the small hole corrosion.Mott-Schottky curve showed that the doping concentration in the passivation film on the 304 SS surface slightly increased with the decrease of the pH value of the solution, and the difference between the chlorine and the chlorine free conditions was not significant; Q235 carbon steel was no chlorine. The doping concentration of passivating film is not obvious with the change of pH value. The doping concentration of passivating film increases with the decrease of pH value, which leads to the decrease of corrosion resistance.XPS. The result shows that the Fe3+/Fe2+ in the surface film layer of Q235 carbon steel film decreases with the decrease of pH value under the condition of chlorine free ion, and Fe3+/Fe2+ in the pore solution with chlorine ion is followed by Fe3+/Fe2+ The decrease of pH value indicates a decrease in the stability of the passivation film, and there is no obvious change in the passivation film composition of the 304SS in the simulated pore fluid of different pH. (2) the metastable potential Em of Q235 carbon steel and the stable orifice potential Eb in the two simulated pore fluid (pH 10.3 and 9.7) with the increase of Cl- concentration Both Eb and ln[Cl-] have a linear relationship. Both Em and Eb decrease with the increase of ln[Cl-]/[OH] and 1nCagg/Cinh in the solution (the ratio of erosive ions to corrosion ions, [Cl*]/[OH-][HCO3][CO32-]), and a good linear relationship between the concentration of.Cl- and the increase of the concentration Nd and potential Efb in the passivation film on the surface of carbon steel. The number of vacancies in the film increases, the resistance of the passivation film decreases, the capacitance increases, the density of the film decreases, and the porosity of carbon steel increases. (3) as the concentration of Cl- increases, the number of metastable small pores in the Q235 carbon steel increases, the maximum value of the nucleation rate corresponds to the negative shift of the potential, the average life span of the pores increases, and the radius of the theoretical metastable hole increases, thus Cl- is substable to metastable metastabilities. The nucleation and growth of the orifice are all promoted. The potential of the maximum value of the metastable pore radius coincides with the potential of the maximum value of the metastable pore nucleation rate. The potential is slightly lower than the stable orifice potential Eb. It shows that the larger the radius of the metastable pore is, the more the number of small pores is, the greater the probability of transforming into a stable hole, and a large number of small holes concentrated. It will soon turn into the stable pore erosion stage. (4) the Q235 carbon steel has a constant potential polarization of slightly higher than the potential of Em, the pore size of the metastable small hole is smaller (less than 1 m), and the pore opening is more open. The polarization potential rises to the middle part of the passivation region (higher than Em, but far below Eb), and the size of the metastable small hole is increased (about 1 mu m), and a number of metastable metastabilities. At the bottom of the orifice, there is a trace of downward growth of small holes, and there is a passivating film that has not been completely broken at the bottom of the orifice. It is confirmed that the metastable small hole continues to develop under the membrane by the current wave peak integral calculation. The stable etch group of several hundred microns on the surface of carbon steel occurs when the polarization potential is close to Eb. The orifice group is composed of many small pores which are concentrated. Many small holes are deep and the surface is covered with corrosion products. The chloride ion is enriched in the corrosion product membrane, and a large number of orifice nucleation is induced by contact with the matrix. That is, the metastable pore erosion mainly nucleates and grows around the stable hole, leading to the lateral growth of the stable etch on the surface of the specimen.

【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU528

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