Solubility of fluorine in liquid uranium, tungsten, and molybdenum hexafluorides

Abstract

Experimental data on the solubility of fluorine in liquid uranium, tungsten, and molybdenum hexafluorides in the temperature range 66‐90°C and fluorine partial pressure 226‐1066 kPa are presented. Computed values of Henry’s constant for these systems and constants in the equation expressing the linear approximation of the temperature dependence of Henry’s constant are given. Uranium hexafluoride exists as a liquid only at temperature and pressure above the triple point, i.e., 64.05°C and 0.155 MPa. Since it is obtained for commercial purposes by means of the interaction of uranium tetrafluoride with excess fluorine gas [1], liquefaction from commercial gas from fluoridation apparatus can be done only at high pressure and in the process fluorine becomes dissolved in the liquid uranium hexafluoride. For this reason, the solubility of fluorine in liquid uranium hexafluoride affects the choice of the technological arrangement of any facility that is used to liquefy uranium hexafluoride from commercial gases containing fluorine. The objective of the present work is to determine the solubility of gaseous molecular fluorine in liquid metal hexafluorides. The solubility of fluorine in liquid uranium, tungsten, and molybdenum hexafluorides was determined using the apparatus shown schematically in Fig. 1. The nickel vessel 13 with a copper cover 4 had a magnetic mixer 10, placed in plain Teflon bearings 6 and finished on top by a bar made of a ferromagnetic material in aluminum casing 7. The mixer was put into motion by a permanent magnet 3, placed outside and rotated by an electric motor 1 with frequency ranging from 3 to 15 rpm. Three thermocouple pockets 9, made of nickel tubing with 0.2 mm thick wall were uniformly arranged over the height of the vessel. Two couplings with small, nickel, packed gland valves were present on the vessel wall. The initial components were loaded through one of them 5. First, the setup was evacuated, checked for vacuum, and passivated with fluorine gas at 100°C. Metal hexafluorides were loaded by means of condensation into a nickel vessel at liquid-nitrogen temperature. A standard manometer 2 was used to monitor the progress of the loading. The amount of condensed metal hexafluoride permitted the existence of at least 1 cm 3 of vapor above the liquid at the temperature of the experiment. When condensation was completed, fluorine was introduced into the vessel. Next, the vessel 13 with a differential manometer 8 was placed into a water thermostat 14 ,w here the temperature was maintained to within ±0.2°. The total pressure in the vessel was measured with a differential manometer 8. Samples of the liquid metal hexafluoride were extracted every 20 min into the space between the valves 11, whence the liquid sample was completely evaporated into the vessel 12 and delivered in the gas phase to a chromatograph for analysis. Equilibrium was considered to be attained when the solubility with decreasing gas pressure was the same as with increasing gas pressure. Methods for purifying the initial substances and checking their purity as well as the technique for performing chromatographic analysis of extracted samples are described in [2]. The computed error in determining the fluorine concentration did not exceed 0.1%.