Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

Thermodynamic investigation of Na2U2O7 using Knudsen effusion mass spectrometry and high temperature X-ray diffraction

Smith, A. L., Colle, J.-Y., Raison, P. E., Benes, O., Konings, R. J. M.
J. Chem. Thermodyn. 2015, 90, 199-208
ABSTRACT
The vaporization behavior and decomposition mechanism of NaUO3 were studied using Knudsen effusion mass spectrometry. The temperature dependence of the sodium partial pressure over the ternary phase field NaUO3 Na2U2O7 UO2 was measured for the first time: logoPNa=PaP 1/4 10:98o 0:04P 14; 999o 50P=oT=KP. The enthalpy of formation of a-Na2U2O7 was moreover derived from second law analysis of the data at DfHo moa-Na2U2O7; cr; T 1/4 298:15 KP = (3208.4 +- 5.5) kJ mol 1, in very good agreement with the value reported in the literature from solution calorimetry. The existence of three polymorphs for Na2U2O7 (a, b, and c) was confirmed using high temperature X-ray diffraction. The two phase transitions occur above about T = 600 K, and around T = 1323 K, respectively. Our results were finally assessed with respect to similar vaporization studies carried out in neighboring ternary phase fields of the Na-U-O phase diagram.
Compounds
# Formula Name
1 Na sodium
2 U uranium
3 O2 oxygen
4 O2U uranium dioxide
5 NaO3U sodium uranate (NaUO3)
6 Na2O7U2 sodium uranate (Na2U2O7)
Datasets
The table above is generated from the ThermoML associated json file (link above). POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied; the numbers refer to the table of compounds on the left.
Type Compound-# Property Variable Constraint Phase Method #Points
  • POMD
  • 6
  • Mass density, kg/m3 ; Crystal 3
  • Temperature, K; Crystal 3
  • Pressure, kPa; Crystal 3
  • Crystal 3
  • X-ray diffraction
  • 4
  • POMD
  • 6
  • Mass density, kg/m3 ; Crystal 2
  • Temperature, K; Crystal 2
  • Pressure, kPa; Crystal 2
  • Crystal 2
  • X-ray diffraction
  • 6
  • POMD
  • 6
  • Mass density, kg/m3 ; Crystal 1
  • Temperature, K; Crystal 1
  • Pressure, kPa; Crystal 1
  • Crystal 1
  • X-ray diffraction
  • 1
  • RXND
  • 4
  • 1
  • 5
  • 6
  • Thermodynamic equilibrium constant
  • Dynamic equilibration
  • 32
  • RXND
  • 1
  • 2
  • 6
  • 3
  • Molar enthalpy of reaction, kJ/mol
  • Derived from knudsen effusion method
  • 1
  • RXND
  • 1
  • 2
  • 6
  • 3
  • Molar Gibbs energy of reaction, kJ/mol
  • derived from knudsen effusion method
  • 20