Low temperature heat capacity of Na4UO5 and Na4NpO5. (December 2015)

• Record Type: Journal Article
• Authors: Smith, A.L.; Griveau, J.-C.; Colineau, E.; Raison, P.E.; Wallez, G.; Konings, R.J.M.
• Is Part Of: Journal of chemical thermodynamics. Volume 91(2015:Dec.)
• Page Start: 245
• Page End: 255
• Publication Date: 2015-12
• Subjects: Heat capacity -- Entropy -- Calorimetry -- Sodium uranates -- Sodium neptunates; Thermodynamics -- Periodicals; Thermochemistry -- Periodicals; Thermodynamique -- Périodiques; Thermochimie -- Périodiques; Thermochemistry; Thermodynamics; Periodicals; 541.369
• DOI: 10.1016/j.jct.2015.08.003
• Languages: English
• ISSNs: 0021-9614

Abstract

Highlights: The heat capacities of Na4 MO5 (M = U, Np) have been measured in the range T = (2 to 292) K. The standard molar entropies and Gibbs energies have been determined at T = 298.15 K. Na4 NpO5 shows a Schottky anomaly around T = 7 K. Abstract: The low temperature heat capacities of Na4 UO5 and Na4 NpO5 have been measured for the first time in the temperature range (1.9 to 292) K using a Quantum Design PPMS (Physical Property Measurement System) calorimeter. The experimental data have been fitted to theoretical functions below 20 K, and to a combination of Debye and Einstein functions above this temperature. The heat capacity and entropy values at T = 298.15 K have been derived as C p, m o ( Na 4 UO 5, cr, 298.15 K ) = ( 220.6 ± 6.7 ) J · K −1 · mol −1, S m o ( Na 4 UO 5, cr, 298.15 K ) = ( 247.5 ± 6.2 ) J · K −1 · mol −1, C p, m o ( Na 4 NpO 5, cr, 298.15 K ) = ( 219.0 ± 6.6 ) J · K −1 · mol −1, and S m o ( Na 4 NpO 5, cr, 298.15 K ) = ( 247.5 ± 6.2 ) J · K −1 · mol −1 . When combined with the enthalpies of formation reported in the literature, these data yield standard entropies and Gibbs energies of formation as Δ f S m o ( Na 4 UO 5, cr, 298.15 K ) = - ( 520.8 ± 6.3 ) J · K −1 · mol −1, Δ f S m o ( Na 4 NpO 5, cr, 298.15 K ) = - ( 521.0 ± 6.3 ) J · K −1 · mol −1, Δ f G m o ( Na 4 UO 5, cr, 298.15 K ) = - ( 2301.7 ± 2.9 ) kJ · mol −1 and Δ f G m o ( Na 4 NpO 5, cr, 298.15 K ) = - ( 2159.7 ± 6.0 ) kJ · mol −1 .