AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS-MoP

Paper SS-MoP3
Gas Phase Oxidation of Uranium-Niobium Alloys by O@sub 2@ and H@sub 2@O

Monday, November 2, 1998, 5:30 pm, Room Hall A

Session: Surface Science Division Poster Session
Presenter: W.L. Manner, Los Alamos National Laboratory
Authors: W.L. Manner, Los Alamos National Laboratory
M.T. Paffett, Los Alamos National Laboratory
R.J. Hanrahan, Los Alamos National Laboratory
Correspondent: Click to Email
Secondary concentrations of certain transition metals (e.g. niobium, titanium, and chromium) alloyed with uranium are known to improve numerous physical and mechanical properties. One such property is the enhancement of corrosion resistance exhibited by the uranium alloy with six weight percent niobium (denoted as U6Nb) relative to the unalloyed uranium. Despite a tremendous knowledge base concerning the bulk metallurgical properties of this material, very little is known concerning the surface chemistry of U6Nb toward corrosion by O@sub 2@ or H@sub 2@O. Specifically, we seek to understand the role of niobium toward oxidation resistance of this alloy. We have initiated a series of studies using surface-sensitive techniques that include X-ray photoelectron spectroscopy (XPS), thermal desorption-mass spectroscopy (TDMS), and secondary-ion mass spectroscopy (SIMS) in order to better understand the chemistry between this alloy and O@sub 2@ or H@sub 2@O. XPS studies of the oxidation of clean U6Nb by O@sub 2@ at 300 K produces a thin oxide overlayer of stoichiometric UO@sub 2.0@ intermixed with Nb@sub 2@O@sub 5@. While the same stoichiometry is exhibited for uranium when the oxide is prepared at 500 K with O@sub 2@, niobium is much less oxidized showing a mixture of NbO and Nb. Depth profiling studies reveal that oxidation by O@sub 2@ is much greater than that exhibited by H@sub 2@O. Only the first layer or two is oxidized using H@sub 2@O as an oxidant at 300 K (the oxidation by O@sub 2@ is approximately an order of magnitude higher). Formation of a critical density of Nb@sub 2@O@sub 5@ is suggested to be responsible for the enhanced corrosion resistance by preventing diffusion of O@super -@ (O@super 2-@) or OH@super -@ into the oxide/metal interface region.