Superconductivity of Beta-Uranium

Adsorption behavior of O2 on U-Nb surface: a first-principles study

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.

A Review of Irradiation Damage and Effects in α-Uranium

Understanding irradiation damage and effects in α-uranium (α-U) is critical to modeling the behavior of U-based metallic fuels. The aim of this review is to address the renewed interest in U-based metallic fuels by examining the state-of-the-art knowledge associated with the effect of irradiation on the microstructure, dimensional changes, and properties of α-U. We critically review the research progress on irradiation-induced growth and swelling, the enhancement of plastic flow and superplasticity by irradiation, and the effect of irradiation on thermal and electrical properties of α-U. Finally, we outline the research directions that require advancements, specifically the need to carry out fundamental research on several of the less understood mechanisms of irradiation damage and effects in α-U.

Superconductivity of Alpha-Uranium and the Role of 5 f Electrons

A much sharper and lower superconducting transition has been found for alpha-uranium than any reported previously. A model that explains the unusual volume dependence of alpha-uranium below 43 degrees K and the unusual pressure dependence of its superconducting transition temperature is presented.