Details

Autor(en) / Beteiligte

• Smith, A.L.
• Colle, J.-Y.
• Beneš, O.
• Konings, R.J.M.
• Sundman, B.
• Guéneau, C.

Titel

Thermodynamic assessment of the neptunium–oxygen system: Mass spectrometric studies and thermodynamic modelling

Ist Teil von

• The Journal of chemical thermodynamics, 2016-12, Vol.103, p.257-275

Ort / Verlag

Elsevier Ltd

Erscheinungsjahr

2016

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• •The enthalpy of sublimation of NpO2(cr) has been re-assessed as (606.8±1.9)kJ·mol−1 using Knudsen effusion mass spectrometry.•The enthalpy of formation of NpO2(g) has been re-assessed as −(471.7±3.3)kJ·mol−1 using Knudsen effusion mass spectrometry.•The composition of neptunia at congruent vapourization has been estimated as O/Np=(1.92±0.01) at 2260K.•A CALPHAD model is reported for the Np–O system, which reproduces well the main experimental features.•The enthalpy of formation of NpO(g) has been re-assessed as −(9.8±7.8)kJ·mol−1 based on literature data. Knudsen effusion mass spectrometry measurements on neptunium dioxide are reported in this work, which have allowed to improve the understanding of its vapourization behaviour and solved discrepancies noticed in the literature: the enthalpy of formation of NpO2(g) has been re-assessed and the composition of neptunia at congruent vapourization has been determined at 2262K. In addition, a thermodynamic model for the neptunium-oxygen system has been developed using the CALPHAD method. The non stoichiometric NpO2−x phase is described herein using the compound energy formalism with ionic constituents (Np3+,Np4+)1(O2-,Va)2, while the liquid phase is represented with the ionic two-sublattice model (Np4+)P(O2-,VaQ-,O)Q. The reliability and consistency of all optimized Gibbs energies have been verified by calculating the phase equilibria, thermodynamic data, oxygen chemical potential and equilibrium partial pressures. Finally, a number of ill-defined data in the Np–O system have been identified after critical review of the literature and comparison with the present experimental results and CALPHAD model.