Mass-spectrometric investigation of UO3(g)

Vaporization behavior of UO3(g) over UO2+x(s) coloaded with MgO(s) was investigated by means of a quadrupole mass spectrometer equipped with a Knudsen-cell up to 1923 K. The ion current behavior of UO3+ and X-ray diffraction analysis of the UO2+x(s) sample after the vapor pressure measurement suggested that magnesium negligibly dissolved into UO2+x(s). The partial pressures of UO3(g) and Mg(g) were determined in a modified integral method. The partial pressure of O2(g) was obtained indirectly from the partial pressures of UO3(g) and Mg(g). The Gibbs free energy of formation of UO3(g) was calculated from the partial pressures of UO3(g) and O2(g) in the temperature range of 1723–1923 K. It was found that the Gibbs energy of formation of UO3(g) obtained in this study was a little higher than the recommended values recently reported.