Study of surface modification of uranium and UFe2 by various surface analysis techniques

The surface modification of U, UFe2 by exposition in air at room temperature and at 63°C was studied by secondary ion mass spectroscopy (SIMS), time of flight-secondary ion mass spectroscopy (ToF-SIMS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) with variable detection angle. For the two systems, a first layer of carbon contamination, followed by complex oxide layer constitutes the surface. For U, the oxide layer is composed of a mixture of UO2 and UO2+x with x maximal at the surface. In UFe2, the oxide layer is composed of a mixture of UO2 and UO2+x, oxidised iron in Fe2+ and Fe3+ chemical states (more probably FeO), a few percent of a ternary oxide UFeO4, and less than 1% of uranium carbide. A surface segregation of uranium is shown in UFe2.