Surface characterization of oxidative corrosion of U-Nb alloys

We have studied the relative rates of oxidative corrosion of U-Nb alloys containing 2-8 wt. % Nb, using x-ray photoelectron spectroscopy and depth profiling by sputtered neutrals mass spectroscopy. The alloys have been characterized after exposure to dry and humidified air (up to 50% relative humidity) at temperatures from 25 to 125 deg. C, and after exposure to electrochemical solutions. Oxidation of the U-Nb alloys in a tube furnace results in oxide layers comprised of UO2 and Nb2O5 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 h treatment at 75 deg. C and 50% relative humidity results in an oxide layer on U-2% Nb that is approximately 1.5 times as thick as that on U-8% Nb. Electrochemical oxidation of U-Nb alloys facilely generated UO3(·nH2O) and Nb2O5 layers ∼1000 Aa thick, qualitatively similar to thermal oxidation results. U-Nb alloys electrochemically oxidized at low pH exhibit oxide layers with near-surface regions (50 Aa) enhanced in Nb content, as compared to the bulk material. Surface UO3(·nH2O) was not readily reduced upon exposure to molecular D2; however, D atoms facilely reduced UO3(·nH2O) to UO2