The interaction of uranium metal with nitrogen oxides: The formation of an oxynitride surface layer

The interaction of nitric oxide, nitrogen dioxide and nitrous oxide with a polycrystalline uranium surface has been investigated at 298 K. The surface composition and electronic structure of the developing oxide films were studied using X-ray and ultraviolet photoelectron spectroscopy. Nitrous oxide adsorbs dissociatively leaving only oxygen adsorbed on the uranium surface. Nitric oxide and nitrogen dioxide also adsorb dissociatively but in these cases both oxygen and nitrogen remain on the surface. We propose the formation of uranium oxynitride (UOxNy). For exposures >350 L the rate of reaction of NO with the oxynitride surface decreases significantly. In contrast, NO2 continues to react with the surface and a further increase in surface oxygen concentration is observed.