AVS 47th International Symposium
    Surface Science Thursday Sessions
       Session SS1+MC-ThM

Paper SS1+MC-ThM9
Surface Characterization of Oxidative Corrosion of U-Nb Alloys

Thursday, October 5, 2000, 11:00 am, Room 208

Session: Oxide Applications and Oxidation
Presenter: D. Kelly, Los Alamos National Laboratory
Authors: D. Kelly, Los Alamos National Laboratory
W.L. Manner, Union Carbide Corporation
J.A. Lillard, Los Alamos National Laboratory
R.J. Hanrahan, Jr., Los Alamos National Laboratory
M.T. Paffett, Los Alamos National Laboratory
Correspondent: Click to Email
We have studied the relative rates of oxidative corrosion of U-Nb alloys containing 2 to 8 wt. % Nb, using X-ray photoelectron spectroscopy (XPS) and depth profiling by sputtered neutrals mass spectroscopy (SNMS), The alloys have been characterized after exposure to dry and humidified air (up to 50% relative humidity) at temperatures from 25 to 125 @super o@C, and exposure to electrochemical solutions. XPS studies of U-6 wt. % Nb following oxidation at 300 K with oxygen indicate formation of a thin overlayer of stoichiometric UO@sub 2@ intermixed with Nb@sub 2@O@sub 5@. This same stoichiometry is exhibited upon oxygen treatment at 500 K, however, niobium is much less oxidized, forming a mixture of NbO and Nb. SNMS depth profiling indicates that oxides formed using oxygen are thicker than those obtained using water. The formation of a critical density of Nb@sub 2@O@sub 5@ is suggested to enhance corrosion resistance by preventing diffusion of oxygen and/or hydroxyl species into the oxide/metal interface region. Tube furnace oxidation of the U-Nb alloys produces oxide layers comprised of UO@sub 2@ and Nb@sub 2@O@sub 5@ under all experimental conditions used. The thickness of the oxides increased with treatment time and temperature, but decreased with increasing Nb alloy content. For example, a 48 hour treatment at 75 @super o@C and 50% relative humidity results in oxide thickness on U-2%Nb that are three times that on U-8%Nb. Electrochemical oxidation of U-Nb alloys facilely generated UO@sub 3@ and Nb@sub 2@O@sub 5@ oxide layers with thicknesses qualitatively similar to thermal oxidation results. U-Nb alloys electrochemically oxidized at low pH exhibit oxide layers with near-surface regions (50 ???) enhanced in Nb content, as compared to the bulk material. Surface UO@sub 3@ was not readily reduced upon exposure to molecular D@sub 2@; however, D atoms facilely reduced UO@sub 3@ to UO@sub 2@.