Investigation of vaporization behavior of hyper-stoichiometric uranium dioxide by Knudsen effusion mass spectrometry

The determination of partial pressures of UO3(g) and O2(g) over UO2 + x(s) as function of the O/U ratio was attempted at 1473, 1673, 1773 and 1873 K under the condition of the decreasing O/U ratio of the condensed phase by Knudsen effusion mass spectrometry. From these vapor pressures the Gibbs free energy of formation of UO3(g), ΔGf0(UO3,g), was also evaluated. The partial pressures of O2(g) over UO2 + x(s) obtained in this study almost agreed with the experimental data reported in the past as well as the values derived from the empirical equation given by Nakamura and Fujino. Further, it was found that the values of ΔGf0(UO3,g) obtained in this study were in good agreement with the recommended values.