Thermodynamics of the dimerization of gaseous UF/sub 5/

Journal Article · Sun Jul 01 00:00:00 EDT 1979 · J. Chem. Phys.; (United States)

OSTI ID:5989062

Kleinschmidt, P D; Hildenbrand, D L

The gaseous dimerization equilibrium 2 UF/sub 5/=U/sub 2/F/sub 10/ was studied by high temperature mass spectrometry over the range 600 to 870 K. Gaseous UF/sub 5/ monomer and dimer were generated by the reaction of UF/sub 6/(g) with a solid phase that was initially UF/sub 4/(s), and the abundances of the two species were monitored with both the parent and major fragment ions. Measurements of the U/sub 2/F/sub 10//UF/sub 5/ ratio as a function of pressure established that gaseous equilibrium was achieved. The average of several second-law determinations yielded a value of -39.0 +- 1.0 kcal/mole for the enthalpy of dimerization of UF/sub 5/ at 750 K corrected to -40.0 +- 1.0 kcal/mole at 298 K. From an absolute pressure calibration, the equilibrium constant was evaluated, leading to an entropy of dimerization of -40.0 cal/mole deg at 750 K. The results indicate that previously reported transpiration studies on UF/sub 5/(s) should be interpreted in terms of vapor transport by U/sub 2/F/sub 10/ (g) rather than UF/sub 5/ (g). The enthalpies of sublimation of UF/sub 5/ (g) and U/sub 2/F/sub 10/ (g) from UF/sub 5/ (s) at 298 K are calculated to be 39.0 and 38.5 kcal/mole, respectively, from the corrected transpiration vapor pressure data and the UF/sub 5/ dimerization data reported here. The electron impact mass spectra of UF/sub 6/ and UF/sub 5/ at several ionizing energies are reported. A weak U/sub 2/F/sup +//sub 11/ signal was observed at high UF/sub 6/ flow rates, apparently the product of the secondary ion source reaction of UF/sup +//sub 5/ and UF/sub 6/.

• Research Organization: SRI International, Menlo Park, California 94025
• OSTI ID: 5989062
• Journal Information: J. Chem. Phys.; (United States), Vol. 71:1
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
URANIUM PENTAFLUORIDE
DIMERIZATION
THERMODYNAMIC PROPERTIES
DIMERS
HIGH TEMPERATURE
MASS SPECTROSCOPY
ACTINIDE COMPOUNDS
CHEMICAL REACTIONS
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
PHYSICAL PROPERTIES
POLYMERIZATION
SPECTROSCOPY
URANIUM COMPOUNDS
URANIUM FLUORIDES
640302* - Atomic
Molecular & Chemical Physics- Atomic & Molecular Properties & Theory