Thermodynamics of the sublimation and disproportionation of uranium trifluoride

A mass-spectrometric investigation of the thermodynamics of sublimation and of the disproportionation of uranium trifluoride was carried out. The work was performed in an MS1301 magnetic mass-spectrometer designed for studying the vaporiation processes of difficulty volatile substances. The substance to be tested was evaporated from a molybdenum effusion cell with a graphite lining. Uranium trifluoride was obtained from the tetrafluoride by reduction with aluminum, after first distilling the tetrafluoride in high vacuum. The reduction reaction was carried out in an effusion cell placed in the evaporation unit of the mass spectrometer, and this enabled the course of the reaction to be followed. The ionization potentials of the UF4 and UF2 molecules were found in a separate experiment, was used to calibrate the electron energy scale. Silver evaporated from the effusion cell simultaneously with UF4 was used as the standard in measuring the ionization potential of UF4. In all cases except that of UF2 the extrapolated difference method was used in the treatment of the ionization efficiency curves; in the case of UF2, because of the low intensity of the UF2 ion current, the ionization potential was determined by the linear extrapolation method. In two experiments, 25 measurements of UF+3 and 23 measurements of UF+4 were made over the range 1252-14680K. At the end of the evaporated process in these experiments, a rapid and simultaneous fall of the UF+3 and UF+4 intensities occurred, which characterised the pressure of a pure UF3(c) phase