AVS 49th International Symposium
    Surface Science Monday Sessions
       Session SS2-MoM

Paper SS2-MoM6
Surface Chemistry of Calcined UO@sub 2@ Powders

Monday, November 4, 2002, 10:00 am, Room C-112C

Session: Oxide Structure and Surface Chemistry
Presenter: A.J. Nelson, Lawrence Livermore National Laboratory
Authors: A.J. Nelson, Lawrence Livermore National Laboratory
T.C. Meier, Lawrence Livermore National Laboratory
C.K. Saw, Lawrence Livermore National Laboratory
L.V. Griffith, Lawrence Livermore National Laboratory
Correspondent: Click to Email
High resolution X-ray photoemission spectroscopy (XPS) was used to examine the surface composition and chemical bonding of calcined UO@sub 2@ powders as a function of process parameters. It is believed that the surface composition of the powder grains ult imately affects packing density. XPS quantitative analysis revealed O/U ratios indicative of mixed uranium valences. In addition, high resolution U 4f@sub 7/2,5/2@ core-level spectra revealed reoxidation of U@super 4+@ to U@super 6+@ for the lower temperatures, and a reduction of U@super 6+@ to U@super 4+@ for the higher temperatures using 4% H@sub 2@/Ar. Reoxidation can also be affected by the presence of water or OH, and the powder samples calcined at the lower temperatures have the highest OH@super ?@/O@super 2?@ peak area ratio. Also, electrons in the 6d, 5f, and 7s orbitals near the valence band maximum can participate in bond formation so long as adjacent atoms are capable of donating their electrons to these unfilled orbitals. The valence band electronic structure for the higher temperature calcinations clearly shows a stronger 5f emission peak near the Fermi edge, a feature that is indicative of a highly localized state. Results were correlated with bulk structural analysis using x-ray diffraction. This work was performed under the auspices of the U.S. Dept. of Energy by the University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.