Uranium Oxidation Kinetics: An X-Ray Photoelectron Spectroscopy Study

The initial oxidation behavior of uranium surfaces,in the ultra-high vacuum(UHV) chamber of ESCALAB 250 at an oxygen partial pressure of 5×10^-6 Pa and a temperature below 413 K,was investigated in-situ with X-ray photoelectron spectroscopy,which is capable of semi-quantitatively evaluating in real-time the thickness growth of uranium oxide because of the penetration characteristic of the excitation electron. The results show that the thickness of uranium oxides depended parabolically on the oxidation time,indicating that the oxygen diffusion through uranium oxide layer significantly affected the oxidation rate of uranium. As expected,the oxidation rate increased with an increase of temperature.In addition,the oxidation activation energy was calculated to be 23.9 kJ/mol.