690合金钝化膜半导体性能与腐蚀电化学行为研究

发布时间：2018-06-13 04:47

本文选题：690合金 + 腐蚀电化学　；参考：《山东大学》2017年硕士论文

【摘要】：蒸汽发生器(SG)传热管对压水堆(PWR)型核电站的安全运行起着非常重要的作用,作为连接一、二回路的枢纽,其服役环境十分严苛。镍基合金690因其具有较好的力学性能和优良的耐高温高压腐蚀性能,广泛应用于压水堆核电站蒸汽发生器建设。镍基合金之所以在高温侵蚀性溶液中具有优异的耐腐蚀性能,是由于其表面会自发形成一层厚度为几纳米到几百纳米稳定的钝化膜。这层钝化膜阻止了基体与腐蚀介质的进一步接触,有效防止了合金或金属腐蚀现象的发生。研究表明,金属及合金表面形成的钝化膜具有半导体结构,其半导体电子特性与钝化膜的耐蚀性密切相关。在实际的工作环境中,在蒸汽发生器内积累起来的不同杂质离子(如SO42-和Cl-)以及局部不同的酸碱环境对于镍基合金钝化膜影响的也不同。因此研究钝化膜在侵蚀性环境下的半导体性质及耐蚀性变化有着重要的理论意义和应用价值。本论文以690合金作为研究材料,以Cl-和SO42-作为侵蚀性离子,采用动电位极化曲线、电化学阻抗谱(EIS)和Mott-Schottky法等传统电化学方法,研究离子浓度、浸泡时间、极化电位和溶液pH值等因素对合金腐蚀电化学行为和钝化膜半导体特性的影响。并结合局部电化学测量技术-扫描电化学显微镜(Scanning Electrochemical Microscopy,SECM),利用反馈模式(feed-back mode),通过面扫描和逼近曲线(probe approve curves)研究合金表面局部区域电化学活性变化及腐蚀特征。通过研究690合金表面微观电化学活性与钝化膜组成、结构等因素之间的联系,以深入探讨其腐蚀机理。本论文的主要工作如下:1、传统电化学研究(1)在中性NaCl、Na2SO4溶液中,对690合金进行动电位极化曲线、电化学阻抗谱(EIS)以及Mott-Schottky曲线测试,探讨浓度、浸泡时间和极化电位对材料腐蚀电位、腐蚀电流、钝化电流以及点蚀电位等腐蚀电化学特征的影响规律。并通过对获得的数据进行进一步分析拟合,解释不同条件下形成的钝化膜的电化学行为和半导体性能。(2)采用动电位极化曲线、电化学阻抗谱和Mott-Schottky曲线等电化学测试方法,研究了 0.5 MNaCl溶液中pH值变化对690合金腐蚀电化学行为的影响。比较不同pH溶液中钝化膜耐蚀性和表面活性。2、原位电化学研究(1)采用循环伏安方法对Pt探针性能进行测试。通过极限扩散电流计算出氧化还原中介体二茂铁甲醇(FcMeOH)在溶液中的扩散系数为7.37×10-6cm2/s。(2)利用扫描电化学显微镜(SECM)的反馈模式(feed-backmode)以二茂铁甲醇(FcMeOH作为氧化还原中介体,研究了在0.5 M NaCl、Na2SO4溶液中浸泡时间、极化电位对690合金试样表面Faraday电流的影响。将局部电化学活性分布与金属/溶液界面的微区电化学反应联系起来,表征合金表面的腐蚀规律变化。并通过逼近曲线探究合金表面钝化膜性质变化规律,探究钝化膜的形成过程及致密程度变化。(3)研究酸性、中性、碱性0.5 MNaCl溶液中合金表面电活性随浸泡时间的变化规律,并探究极化条件对合金耐蚀性的影响。
[Abstract]:Steam generator (SG) heat transfer tube plays a very important role in the safe operation of PWR (PWR) nuclear power plant. As the junction of connecting one and two loops, its service environment is very harsh. Nickel Base Alloy 690 is widely used in the steam generator of PWR nuclear power plant because of its good mechanical properties and excellent high temperature and high corrosion resistance. Construction. The excellent corrosion resistance of nickel based alloy in high temperature erosive solution is due to the spontaneous formation of a passivating film with a thickness of several nanoscale to several hundred nanometers on its surface. This passivation film prevents the further contact between the matrix and the corrosive medium, and effectively prevents the occurrence of corrosion of alloy or metal. It is shown that the passivation film formed on the surface of metal and alloy has a semiconductor structure, and its semiconductor electronic properties are closely related to the corrosion resistance of the passivation film. In the actual working environment, the different impurity ions (such as SO42- and Cl-) accumulated in the steam generator and the local different acid and alkali environment have influence on the passivation film of the nickel base alloy Therefore, it is of great theoretical and practical value to study the semiconductor properties and corrosion resistance changes of the passivating film in erosive environment. In this paper, 690 alloys are used as research materials, Cl- and SO42- are used as erosive ions, and the electrodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and Mott-Schottky methods are used in the traditional electrochemical methods. The effects of ion concentration, soaking time, polarization potential and pH value on the electrochemical behavior of alloy corrosion and the characteristics of passivating film semiconductor are studied. Combined with the local electrochemical measurement technology, Scanning Electrochemical Microscopy (SECM), the use of feedback mode (feed-back mode), through surface scanning and approximation Probe approve curves was used to study the electrochemical activity changes and corrosion characteristics of the local area of the alloy surface. By studying the relationship between the microstructure of the 690 alloy surface and the composition of passivation film, structure and other factors, the corrosion mechanism was discussed. The main work of this paper was as follows: 1, the traditional electrochemical study (1) was in neutral NaCl, Na2S In O4 solution, the action potential polarization curve, electrochemical impedance spectroscopy (EIS) and Mott-Schottky curve were tested on 690 alloy. The effects of concentration, immersion time and polarization potential on corrosion potential, corrosion current, passivation current and pitting potential were investigated. The electrochemical behavior and semiconductor properties of the passivation film formed under different conditions were analyzed. (2) the effects of the change of pH value on the corrosion electrochemistry behavior of 690 alloy in the 0.5 MNaCl solution were studied by electrodynamic polarization curve, electrochemical impedance spectroscopy and Mott-Schottky curve. The resistance of passivation film in different pH solutions was compared. Corrosion and surface active.2, in situ electrochemical study (1) the performance of Pt probe was tested by cyclic voltammetry. The diffusion coefficient of redox intermediator two metallocenyl alcohol (FcMeOH) in the solution was calculated by the limit diffusion current, and the diffusion coefficient of FcMeOH in the solution was 7.37 * 10-6cm2/s. (2) using the feedback mode of scanning electrochemical microscopy (SECM). Two metallocenyl alcohol (FcMeOH as an oxidation-reduction agent, studied the effect of immersion time in 0.5 M NaCl, Na2SO4 solution, and the effect of polarization potential on the Faraday current on the surface of 690 alloy. The local electrochemical activity was associated with the micro electrochemical reaction of the metal / solution interface to characterize the corrosion regularity of the surface of the alloy. The properties of the passivation film on the alloy surface were investigated by the approximation curve, and the formation process and the density change of the passivation film were investigated. (3) the changes of the surface electrical activity of the alloy in the acid, neutral, alkaline 0.5 MNaCl solution with the immersion time were studied, and the effect of polarization conditions on the corrosion resistance of the alloy was investigated.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.4

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