Study of the initial oxidation characteristics of uranium with pure oxygen below 100 degrees C by spectroscopic ellipsometry

In this work, the initial oxidation characteristics of uranium with pure oxygen was studied by spectroscopic ellipsometry. The samples used in experiments were depleted uranium, which were finely polished before experiments. In the study the surface of the uranium was sputtered to clean in vacuum by Ar+ gun firstly, and then n and k values of pure metallic uranium were measured within wavelength range 350-1000 nm. The series experiments were done by introducing oxygen into vacuum chamber to a pressure of 5000 Pa while the samples were under various temperatures (45, 65, 85, and 95 degrees C, and the thickness of the surface oxidation film with time was obtained by spectroscopic ellipsometry under these conditions in situ. The results show that the oxidation process obeys the parabolic kinetics, which indicates that the reaction is controlled by oxygen diffusion. The reaction constants at these temperatures (45, 65, 85, and 95 degrees C) under 5000 Pa were calculated from experimental results, which depended obviously on temperature. From calculation, the activation energy is 73.7 kJ mol(-1) for uranium below 100 degrees C at oxygen pressure 5000 Pa. Our study showed that spectroscopic ellipsometry is suitable for studying uranium oxidation at initial stage. Copyright (C) 2008 John Wiley & Sons, Ltd.