Cathodic Degradation of Passive Films on Ti in High-Level Radioactive Waste Disposal Environments

高放射性废物处置环境中钛钝化膜的阴极降解

基本信息

批准号：
10450266
负责人：
HARA Nobuyoshi
金额：
$ 9.02万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

项目摘要

In order to better understand the corrosion behavior of Ti over-packs used for the underground disposal of high-level radioactive wastes, the degradation processes of surface oxide films on Ti and the stress corrosion cracking (SCC) behavior of the metal have been examined.The principal findings of this study are summarized as follows :1. The immersion corrosion tests of Ti were performed for about 3 years in water in contact with bentonite containing 0-0.5M NaCl at 50 and 95℃. Changes in the corrosion potential and properties of surface oxide films were examined as a function of immersion time. It was found that the corrosion potential stays approximately constant and was almost independent of the concentration of NaCl. There was no significant change in the thickness of the oxide films, while the composition of the films changes with time : the ratio of OH bonds in the films increased with increasing immersion time up to 1.5 years, and then became constant as the immersion time was increased further.2. The changes in the thickness, optical constants and chemical composition of surface oxide films on Ti were analyzed under electrochemical cathodic polarization in water in contact with bentonite. There was little or no change in the properties of the films in the potential range between the corrosion potential and -0.8V.At potentials lower than -0.8V, the changes in film properties became evident : the thickness decreased, the refractive index decreased, and the extinction coefficient increased with decreasing potential.3. The results of SCC tests in water in contact with bentonite showed that hydrogen embrittlement-induced cracking initiated in the potential region where hydrogen evolution takes place, while no cracking occurred in the potential region corresponding to the waste disposal environments.

为了更好地理解用于高级放射性废物的基础处置的Ti过包的腐蚀行为，已经检查了TI表面氧化物膜的降解过程以及金属的应力腐蚀裂纹（SCC）行为。 Ti的浸入腐蚀试验在与含有0-05m NaCl的膨润土接触的水中进行了约3年，在50和95℃时进行。检查表面氧化物膜的腐蚀潜力和性能的变化是浸入时间的函数。发现腐蚀电位保持大致恒定，几乎与NaCl的浓度无关。氧化物膜的厚度没有显着变化，而膜的组成随时间变化：膜中OH键的比率随浸入时间增加1.5年而增加，然后随着浸入时间的增加而变得恒定。2。在与膨润土接触的水中分析了Ti表面氧化物膜在Ti上的厚度，光学常数和化学成分的变化。在腐蚀电势和-0.8V.AT电位低于-0.8V之间的电势范围内，膜的性质几乎没有变化，膜性能的变化变成了证据：厚度下降，折射率下降，延伸系数降低，随着电势的降低而增加。3。与膨润土接触的水中SCC测试的结果表明，在发生氢进化的潜在区域启动了氢拥材引起的开裂，而在与废物处理环境相对应的潜在区域中没有裂纹。