地下水环境中典型金属材料腐蚀行为的研究

发布时间：2018-11-05 07:52

【摘要】：采用地下深埋是处置高放废物最安全、可行和实用的方法。金属包装容器作为防止高放废物泄漏的第一道人工屏障,在长期地质处置过程中,可能会受到地下水的侵蚀而发生失效。甘肃省北山地区是我国地质处置库候选场址之一,在此环境中选用何种金属作为包装容器材料是我国高放废物地质处置工程急需解决的问题之一。本文利用长期浸泡和电化学方法,同时借助扫描电子显微镜(SEM)、X射线能谱(EDS)、X射线衍射(XRD)、拉曼光谱和表面轮廓仪等分析手段,研究了环境因素和合金元素对典型金属材料在模拟北山地下水溶液中缝隙腐蚀的影响。首先,研究了碳钢(Q235)、低合金钢(16Mn、SPHC、Corten A和CortenB)、铸铁、铝合金(2024、7B04)、纯铜、纯钛、镍基合金(C22)和不锈钢(SUS 304、SUS430、316L)等多种材料在不同腐蚀时间、不同温度、不同氧条件下地下水模拟溶液中的缝隙腐蚀行为。经过1年浸泡,碳钢、低合金钢和铸铁在常温有氧时均未观察到缝隙腐蚀,这可能与其孕育期较长有关；常温无氧时,Corten钢出现了缝隙腐蚀：高温时,碳钢和低合金钢均表现出较严重的缝隙腐蚀。铝合金在常温时就发生了较严重的点蚀和缝隙腐蚀。纯铜在常温时的缝隙腐蚀较轻微,高温时较严重,表现出“反缝隙腐蚀”现象。纯钛、镍基合金和不锈钢均没有表现出缝隙腐蚀。其次,重点研究了地下水溶液中Cl-、SO42和CO32-对碳钢和铜的均匀腐蚀速率和缝隙腐蚀深度的影响。在单一阴离子溶液中,碳钢和铜的缝隙腐蚀均对SO42-最为敏感,而在复杂的地下水模拟溶液中,Cl-对碳钢和铜的缝隙腐蚀过程起控制作用。再次,研究了低合金钢在地下水溶液中朝上面比朝下面腐蚀严重的机理。电化学的测试结果表明,由于试样上下表面氧浓度的差异,朝上面的电位比朝下面更负。在浸泡过程中,朝上面为阳极,阳极反应生成的FeOOH会抑制CaCO3的沉积,因此朝上面腐蚀产物膜主要由疏松的FeOOH和Fe304组成;朝下面为阴极,阴极有利于CaCO3的沉积,所以朝下面的腐蚀产物膜主要是由致密的CaCO3和Fe3O4组成。腐蚀产物膜成分结构的差异导致了浸泡过程中试样上表面的腐蚀程度高于下表面。最后,研究了合金元素Cr和Cu对低合金钢缝隙腐蚀的影响,证明了合金元素Cr和Cu在缝隙腐蚀过程中具有协同作用。当钢中含Cr时,缝隙内部会出现点蚀状腐蚀坑,而Cu的添加会加速点蚀坑的发展。金相分析表明,Cu促进Cr在珠光体组织富集,从而导致缝内点蚀在珠光体组织处发生。本文通过对典型金属材料在地下水模拟溶液中腐蚀行为的研究,初步弄清了不同类型材料在我国甘肃北山地区地质处置环境中缝隙腐蚀的行为和机制,为金属包装容器材料的选择提供了理论和实验依据。
[Abstract]:It is the safest, feasible and practical method to dispose high-level radioactive waste by deep underground burying. As the first artificial barrier to prevent the leakage of high-level radioactive waste, the metal packaging container may be damaged by groundwater erosion during the long term geological disposal. Beishan area of Gansu Province is one of the candidate sites for geological disposal repository in China. It is one of the urgent problems for geological disposal engineering of high-level radioactive waste in China to choose what metal as packaging container material in this environment. In this paper, long term immersion and electrochemical methods were used, and scanning electron microscope (SEM), (SEM), X ray spectrum, (EDS), X ray diffraction, (XRD), Raman spectroscopy and surface profilometer were used to analyze the results. The effects of environmental factors and alloying elements on gap corrosion of typical metal materials in simulated underground aqueous solution of Beishan were studied. First of all, the corrosion time of carbon steel (Q235), low alloy steel (16MnSSPHC-Corten A and CortenB), cast iron), aluminum alloy (20247B04), pure copper, pure titanium, nickel-base alloy (C22) and stainless steel (SUS 304SUS430316L) were studied. The crevice corrosion behavior of groundwater is simulated under different temperature and oxygen conditions. After one year immersion, no crevice corrosion was observed in carbon steel, low alloy steel and cast iron at room temperature, which may be related to the longer incubation period. Crack corrosion occurs in Corten steel at room temperature and oxygen free, and serious crevice corrosion occurs in carbon steel and low alloy steel at high temperature. Serious pitting and crevice corrosion occurred in aluminum alloy at room temperature. The crevice corrosion of pure copper is mild at room temperature and serious at high temperature, showing the phenomenon of "reverse crevice corrosion". Pure titanium, nickel base alloy and stainless steel did not show crevice corrosion. Secondly, the effects of Cl-,SO42 and CO32- on the uniform corrosion rate and crevice corrosion depth of carbon steel and copper in underground aqueous solution were studied. In a single anionic solution, the crevice corrosion of carbon steel and copper is the most sensitive to SO42-, while in the complex groundwater simulation solution, Cl- plays a controlling role in the crevice corrosion process of carbon steel and copper. Thirdly, the corrosion mechanism of low alloy steel in underground aqueous solution is studied. The results of electrochemical measurements show that due to the difference of oxygen concentration in the upper and lower surfaces of the sample, the potential toward the top is more negative than that towards the bottom. During soaking, the anode is toward the top, and the FeOOH produced by anodic reaction can inhibit the deposition of CaCO3, so the corrosion product film is mainly composed of loose FeOOH and Fe304. The cathode is the cathode which is favorable to the deposition of CaCO3, so the corrosion product film is mainly composed of dense CaCO3 and Fe3O4. The difference of composition and structure of corrosion products resulted in higher corrosion degree on the upper surface of the sample than on the lower surface during soaking. Finally, the effect of alloying elements Cr and Cu on crevice corrosion of low alloy steel was studied. It was proved that the alloy elements Cr and Cu had synergistic effect in the process of crevice corrosion. When the steel contains Cr, the pitting corrosion pits will appear in the cracks, and the addition of Cu will accelerate the development of the pitting pits. Metallographic analysis shows that Cu promotes the enrichment of Cr in pearlite, which leads to pitting in the pearlite. Based on the study of corrosion behavior of typical metal materials in groundwater simulated solution, the behavior and mechanism of gap corrosion of different kinds of materials in geological disposal environment of Beishan area, Gansu Province, are preliminarily clarified in this paper. It provides theoretical and experimental basis for material selection of metal packaging container.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG172

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