RESUMO
CONTEXT: Oxygen is a chemically active gas. Metal uranium will be rapidly oxidized when exposed to oxygen directly, forming a complex and uncompacted oxide layer on the surface. The U-O2 reaction system is a very complex metal oxidation system. The surface oxidation reaction of uranium-niobium alloy is more complex, and it is also the main corrosion form of uranium-niobium alloy. Exploring the microscopic mechanism of surface oxidation corrosion of uranium-niobium alloy is of great significance for understanding the surface corrosion phenomenon in practical applications. The adsorption of O2 on U-Nb (5at.%) surface was investigated by first-principles calculation using a periodic slab model within the density functional theory (DFT). The effect of different levels of Nb doping on O adsorption was investigated, and the stability of O-U and O-Nb adsorption was studied in conjunction with the Bader charge distribution, differential charge density map, electron density of states, and surface work function. The results showed that physical adsorption happens when O2 is vertically adsorbed at the top site of Nb atom, whereas dissociative adsorption happened in all other configurations considered here. The interaction between adsorbed O2 and U-Nb surface was essentially the hybridization between the O/2p orbital electrons and the U/6d, U/5f, Nb/4p, Nb/5s, and Nb/4d orbital electrons to form a relatively stable ionic bond. When Nb was doped into the second layer of the surface, the most stable O2 adsorption configuration was top-site horizontal adsorption. The adsorption energy was - 22.38 eV, which was more negative than the adsorption energy of - 21.38 eV for the first doped layer horizontal adsorption at hollow-site. The interaction was essentially the hybridization between O/2p orbital electrons and U/6d and U/5f electrons and between O/2s orbital electrons and U/6p orbital electrons to form a relatively stable ionic bond. METHOD: In this paper, the adsorption and dissociation of oxygen molecules on the surface of U-Nb system were systematically studied by first-principles calculations, in order to explore the surface oxidation corrosion mechanism of uranium-niobium alloy from the micro level. The VASP program uses PAW pseudopotential, which belongs to the density functional method, and uses DSP.
