Title: Low temperature heat capacity of α-Na2NpO4
Citation: THERMOCHIMICA ACTA vol. 617 p. 129 - 135
Publication Year: 2015
JRC N°: JRC95202
ISSN: 0040-6031
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC95202
DOI: 10.1016/j.tca.2015.08.029
Type: Articles in periodicals and books
Abstract: The heat capacity of α-Na2NpO4 has been measured for the first time in the temperature range 2.1 to 301 K using a PPMS instrument (Physical Properties Measurement System, Quantum Design). The heat capacity and entropy values at 298.15 K have been derived at C0p,m(α-Na2NpO4, cr,298.15K) = (151.9±4.6) J.K-1.mol-1 and S0m( α-Na2NpO4, cr,298.15K) = (178.2±5.3) J.K-1.mol-1, respectively. The standard entropy of this sodium neptunate material matches very well the trend followed by its isostructural compound α-Na2UO4 and alkaline earth uranatesMgUO4, SrUO4, BaUO4, and Cs2UO4. When combined with the enthalpy of formation tabulated in the literature, these data yield a standard entropy of formation at 298.15 K at ΔS0f (α-Na2NpO4, cr,298.15K) =-(385.1±5.3) J.K-1.mol-1 and a standard Gibbs energy of formation at 298.15 K at ΔG0f (α-Na2NpO4, cr,298.15K )= -(1649.0 ±5.9) kJ.mol-1.
JRC Directorate:Nuclear Safety and Security

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