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铀钼合金在贮存、运输等过程中, 易受到小分子的表面腐蚀作用, 其中影响最大的是氢蚀和氧化作用. 为进一步探究该反应机理, 基于密度泛函理论和过渡态计算程序, 本文开展了H2分子在Mo原子掺杂和Mo涂层γ-U (100)的解离吸附, H和O原子在上述表面的表面扩散、体相扩散的第一性原理研究. 主要计算了H2分子在上述表面解离的最小能量路径; 开展了H和O原子在最稳定吸附位点间扩散的过渡态研究; 分析了H和O原子体相扩散中吸附能与吸附高度的联系. 研究结果表明, 当H2分子在顶位平行吸附后, 需跨越能量势垒, 诱发H—H键断裂, 之后体系能量降低, 两个氢原子与近邻原子成键, 稳定吸附在表面的桥位, 同时H2在Mo涂层表面解离所需能垒高于Mo原子掺杂表面; O原子在Mo-U表面扩散所需的能垒较低, 能够在铀钼合金表面迅速吸附、解离、扩散, 进而在表面形成氧化膜; H原子和O原子向体相内扩散首先均需要跨越能垒, 进而与体相原子形成化学键, 最后稳定吸附于体相中. 本文利用理论模拟方法, 较为全面地分析了铀钼合金氢蚀和氧化初始阶段的相关机理, 完备了小分子在铀钼合金表面吸附的研究. 研究结果为从理论上探究铀钼合金表面腐蚀机理奠定基础, 为探究铀钼合金腐蚀老化、预估极端环境和特殊环境下铀钼合金的材料性能提供理论支持, 并为进一步指导铀合金的抗腐蚀研究提供参考和帮助.As an important uranium alloy, U-Mo alloy has excellent mechanical properties, structural stability and thermal conductivity, which is an important nuclear reactor fuel and tank armor. However, there exists a serious of fundamental problems of U-Mo alloy which need solving for practical applications. U-Mo alloy is easily subjected to surface corrosion of small molecules including the H2, O2, H2O, and CO2. The hydrogen corrosion and oxidation will have significant influence on it. In order to further investigate the reaction mechanism, based on the density functional theory and the transition state algorithm, the first principles calculation of γ-U (100) with Mo atom doping and Mo coating is carried out.Firstly, the minimum energy path of H2 molecule is calculated for the dissociation adsorption on Mo-U and 4Mo-U surface. Secondly, the transition states of H and O atoms are studied during surface diffusing between adjacent most stable adsorption sites. Thirdly, the bulk phase diffusion of H and O atoms are investigated and the relationship is analyzed between adsorption energy and adsorption height in the bulk phase diffusion.The results show that when H2 molecule is adsorbed at the configuration of top horizontal position, the H atom needs to overcome a barrier to triggering off the H—H bond-broken and then is adsorbed on surface bridge site by the neighboring atoms. The energy barrier for H2 dissociation on 4Mo-U is higher than that of Mo-U. Meanwhile, the lower energy barrier is required for O atom to diffuse in Mo-U, so that it can be adsorbed, dissociated and diffused quickly, and then forming an oxidation film on the surface. Furthermore, both H and O atoms need to cross the energy barrier to diffuse into the body phase, forming chemical bonds with the atoms and staying in the body phase stably finally.In this paper, we comprehensively analyze the dissociation and diffusion of the initial stage for hydrogen corrosion and oxidation on uranium-molybdenum alloy by theoretical studies. The results lay a foundation for theoretically exploring the surface corrosion mechanism of U-Mo alloy. Meanwhile, They provide theoretical support for investigating burn-in and corrosion of uranium-molybdenum alloy, predicting material properties under extreme and special environment, and providing a reference for further research on corrosion resistance of uranium-molybdenum alloy.
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Keywords:
- uranium-molybdenum alloy /
- surface corrosion /
- transient state /
- dissociation and adsorption
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中国物理学会期刊
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