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.

为了更好地了解高放废物地下处置用钛外包装的腐蚀行为，对钛表面氧化膜的降解过程和金属的应力腐蚀开裂（SCC）行为进行了研究。本研究的主要结果总结如下： 1．钛在50℃和95℃下与含有0-0.5M NaCl的膨润土接触的水中进行了约3年的浸泡腐蚀试验。研究了腐蚀电位和表面氧化膜的性能随浸泡时间的变化，结果发现腐蚀电位几乎保持恒定，并且几乎与氯化钠的浓度无关，氧化膜的厚度没有显着变化。而薄膜的组成随时间的变化：薄膜中OH键的比例随着浸泡时间的增加而增加，直至1.5年，然后随着浸泡时间的进一步增加而变得恒定。2．厚度、光学常数的变化。和化学成分在与膨润土接触的水中，在电化学阴极极化下分析了钛表面氧化膜的性能，在腐蚀电位和-0.8V之间的电位范围内，膜的性能几乎没有变化。在电位低于-0.8时。 V、随着电位的降低，薄膜性能的变化变得明显：厚度减小，折射率减小，消光系数增大。 3．水中与膨润土接触的SCC测试结果表明，氢脆引起。在发生析氢的潜在区域中开始出现裂纹，而在废物处理环境对应的潜在区域中没有发生裂纹。