磷酸盐对碱性溶液中碳钢小孔腐蚀的影响研究
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 .
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