Investigation of oxidation of a U-2.5 wt% Nb alloy in air at low temperatures: kinetic study and oxide characterization

Alloying uranium with niobium can greatly enhance the corrosion resistance of metallic uranium. In the present article, the oxidation behavior of a U-2.5 wt% Nb alloy in air over the temperature range 333 to 573 K was investigated. XPS technique was employed to characterize the oxide products. The results of oxidation-rate curves show that at temperatures below 353 K the oxidation of U-2.5 wt% Nb alloy follows a parabolic-rate law, and in the temperature range of 373 - 423 K paralinear rate laws seem to apply, however, above 473 K linear laws are observed. The oxidation-rate dependence of temperature is obtained, and the activation energies for different oxidation stages are determined. The XPS analysis indicates that under experimental conditions the predominant oxide formed on the outer surface is stoichiometric UO2.0 intermixed with Nb2O5, and below the outmost thin layer, an inner oxide layer consisting of UO2, NbO is presented. Copyright (c) 2008 John Wiley & Sons, Ltd.