A SURFACE SPECTROSCOPY STUDY OF THE OXIDATION PROPERTIES OF UNI2 AND UNI5

Ultraviolet photoelectron, X-ray photoelectron and X-ray induced Auger electron spectroscopies (UPS, XPS and XAES, respectively) were used to study the surface oxidation of UNi2 and UNi5. O2 adsorption results in a preferential oxidation of U to sub- and hyper-stoichiometric UO2 depending on the exposure and temperature. Ni stays metallic but disappears from the surface. The influence of temperature and exposure on the Ni surface concentration was established. UNi5 was shown to be more resistant towards decomposition than UNi2. The binding energy of the Ni 3d electrons changes during surface oxidation, which may be explained by a change in the surface concentration of U metal.