Carbon Impurities On The Corrosion Behavior Of Uranium Hydride

Carbon impurity effects on the uranium-hydrogen reaction were studied by the density function theory and hot stage microscope system.The adsorptions of molecule hydrogen and atomic hydrogen on theγ-U surface were studied by the density function theory(DFT). The most favourable adsorption sites,the dissociation barriers and the diffusion barriers were got. Then different carbons were introduced to the surface and the influences of these carbons were calculated. The results showed that the adsorption carbon had very small influence, and the interstitial carbon lowered the adsorption energy, and substitunet carbon slightly increased the adsorption energy. The adsorptions of hydrogen on the UC surface were smaller and the adsorptions of hydrogen in the UC interstitial sites were larger than the adsorption energy onγ-U. Then UC obviously delayed the uranium-hydrogen reaction.The influence of different carbon contents was studied by using different uranium samples by hot stage microscope system. Then different forms of carbon were introduced to the uranium surface by evaporation or passivation. And the influence of different carbon forms was studied by these samples. The differences of the uranium-hydrogen reaction were charactered by the induction and nucleation. The induction times,nucleation densities and nucleation velocities for different samples were measured. The result showed that the carbon impurity sites were the initial nucleation sites on the uranium surface, and the corrision turned from site-corrision to surface-corrision by the increasing of carbon content. The amorphism carbon that introduced by evaporation had no obvious influence for uranium-hydrogen reaction. There was a layer of uranium carbide on the uranium surface after passivated by CO, and this layer obviously delayed the hydrogen corrision.So the influence of carbon on uranium-hydrogen reaction was it made the changes of the uranium surface. For the carbon impurities on the uranium, they made the discontinues of the oxide layers and there were cracks and stress in these sites, these defects were the initial nucleation sites. For the UC layer formed after passivated by the CO, its effect like the oxide layer on the uranium surface, the continuous UC layers could impede the hydrogen corrision and the discontinue sites were the precedence nucleation sites.