The interaction of oxygen with the γ-U (001) and (110) surfaces: An ab initio study

Abstract

The reactions of the γ-U (001) and (110) surfaces in contact with O2 were investigated by density functional theory (DFT), ab initio thermodynamic methods and ab initio molecular dynamics simulations (AIMD). The adsorption of the O atom and O2 molecule on the (001) and (110) surfaces and subsurface are first studied, which provides insights into the adsorption, dissociation, and diffusion of O2 on the surfaces. Furthermore, the effects of coverages on surface adsorption are considered to help us further understand surface oxidation corrosion. Based on the above research, we can speculate on the initial process of surface corrosion: 1. O2 molecules in the atmosphere first approach the U surface in the form of physical adsorption; 2. O2 molecules dissociate into O atoms on the surface; 3. O atoms diffuse on the surface after overcoming a small energy barrier and eventually occupy hollow (H) sites; 4. O atoms penetrate from the H sites to the subsurface; 5. The diffusion of O atoms inside the metal is more likely to be carried out by octahedral interstitial sites. Moreover, the adsorption phase diagrams indicate that O2 will readily react with U even under ultra-high vacuum conditions, which is consistent with the experimental results.