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摘 要 钢筋混凝土结构作为用量最大的工程材料，广泛应用于建筑、海洋平台、高速公路等结构中，碳钢价格低廉，在钢筋混凝土中容易发生点蚀，危害严重。然而人们对碳钢的点蚀研究不够充分，主要集中在不锈钢点蚀方面。磷酸盐系缓蚀剂作为一种新型缓蚀剂，一方面不像亚硝酸盐具有致癌性，另一方面能有效提高碳钢耐蚀性，因此受到了学者们的关注。本文利用动电位扫描极化曲线、恒电位极化、交流阻抗、Mott-Schottky 曲线等方法研究了 Q235 碳钢在模拟混凝土孔隙液中亚稳态小孔腐蚀的行为及特征，探讨了三聚磷酸铝浓度对 Q235 碳钢小孔腐蚀的影响，并分析了与亚稳态小孔有关的一些电化学参数的关系，得出了以下结论： (1) 随着三聚磷酸铝浓度的增加，阻抗膜半径逐渐增大，阻抗膜值也增大，等效电路中膜层电阻Rc、电极表面反应电阻 Rct均降低，膜层电容 Qc、电极表面双电层电容Qdl均升高，这些均表明随着缓蚀剂浓度增加，碳钢耐蚀性越好； (2) 对Mott-Schottky曲线进行分析，随着缓蚀剂浓度增高，钝化膜中氧空位浓度降低，平带电位也明显负移，碳钢表面双电层电容厚度显著增加，这与交流阻抗拟合相一致，表明缓蚀剂浓度越高，碳钢发生点蚀的几率越低； (3) 慢扫描极化曲线表明，缓蚀剂浓度越高，亚稳态孔蚀电位 Em、孔蚀电位Eb越高，恒电位极化曲线表明，缓蚀剂浓度增加，会降低亚稳孔的形核速率、生长速率、再钝化速率，这表明缓蚀剂能减少亚稳孔的萌生及生长，从而抑制点蚀的发生； (4) 利用概率统计研究峰值电流的极值分布，结果表明缓蚀剂浓度越高，亚稳孔转变为稳定点蚀的概率越小。此外，交流阻抗、Mott-Schottky 曲线及恒电位极化曲线均表明，缓蚀剂浓度较低（0.1g/L 左右）时，缓蚀剂的加入会使碳钢耐蚀性大幅提升，当缓蚀剂浓度较大(0.25g/L左右)时，再提高缓蚀剂浓度，缓蚀效果提高缓慢。因此，有待研究缓蚀效果趋于饱和所对应的三聚磷酸铝浓度。 58196
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毕业论文关键词：Q235碳钢；小孔腐蚀；亚稳态孔蚀；磷酸盐系缓蚀剂
Abstract As the largest amount of engineering materials, reinforced concrete structure has been widely used in building construction, offshore platforms, highways, etc. However, low carbon steel was prone to pitting corrosion in reinforced concrete, which was seriously harmful. Compared with stainless steel ,the study of pitting corrosion of carbon steel was insufficient.As an environment-friendly inhibitor, phosphate corrosion inhibitor can effectively improve the corrosion resistance of steel. The methods of dynamic potential scanning polarization curve, constant potential polarization, EIS, Mott Schottky curve were used to study the metastable pitting corrosion behavior and characteristics of Q235 steel in simulated concrete pore solution. We discussesed the effect of aluminum triphosphate concentration on the metastable pitting corrosion of Q235 carbon steel. And the relationship between some electrochemical parameters related to the metastable pitting corrosion has been analyzed. The main conclusions were set as follows: (1) With the increase of the concentration of aluminum tripolyphosphate, the radius of resistance film and the value of resistance film increased; the film equivalent circuit resistance Rc and the electrode surface reaction resistance Rct decresed. But the layer capacitance Qc and electrode surface single-layer capacitance Qdl increased. All of these showed that with the increase of inhibitor concentration, the better of the corrosion resistance of carbon steel; (2)As can be seen in the Mott-Schottky curve , with increase of inhibitor concentration, the value of oxygen vacancy concentration in the passivation film and the flat band potential decreased significantly, the thickness of a single-layer capacitance in the carbon steel surface increased, which is supported by the EIS fitting parameters . (3) The slow scan polarization curves showed that the higher the concentration of inhibitor, metastable pitting potential Em, pitting potential Eb higher. Potentiostatic polarization curves showed that inhibitor reduced the rate of metastable pits nucleation, growth rate and the rate of re-passivation peak current, which indicates the corrosion inhibitors can reduce the initiation and growh of metastable pitting corrosion, thereby suppressed the occurrence of pitting corrosion. (4) The distribution of the current extreme value has been researched with the help of Probability Statistic, and the results showed that the higher the concentration of inhibitor was, the lower possibility of metastable pitting changing into stable pitting was. Besides, EIS, Mott-Schottky curve and potentiostatic polarization curves showed that when in a low condition (0.1g / L or so), the increase of inhibitor significantly improved corrosion resistance, however when in the high condition (about 0.25g / L or so), the further increase of inhibitor concentration improved corrosion resistance slightly. Therefore, further studies were looking forward to work out the value of aluminum triphosphate concentrations when inhibition effect becomes saturated .