Title: Thermodynamic investigation of Na2U2O7 using Knudsen effusion mass spectrometry and high temperature X-ray diffraction
Authors: SMITH ANNACOLLE Jean-YvesRAISON PhilippeBENES ONDREJKONINGS Rudy
Citation: JOURNAL OF CHEMICAL THERMODYNAMICS vol. 90 p. 199 - 208
Publisher: ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
Publication Year: 2015
JRC N°: JRC91051
ISSN: 0021-9614
URI: http://www.sciencedirect.com/science/article/pii/S0021961415002025
http://publications.jrc.ec.europa.eu/repository/handle/JRC91051
DOI: 10.1016/j.jct.2015.06.026
Type: Articles in periodicals and books
Abstract: The vaporization mechanism of NaUO3 was studied using Knudsen effusion cell mass spectrometry. The temperature dependence of the sodium partial pressure over the ternary phase field NaUO3-Na2U2O7-UO2 was measured for the first time: logPNa=Pa = 10.92-14999/T. The enthalpy of formation of α-Na2U2O7 was derived from second law analysis of the data at ΔfH(α-Na2U2O7) = (-3208.4 ± 5.5) kJ.mol-1, in very good agreement with the value reported in the literature from solution calorimetry. High temperature X-ray diffraction measurements have also confirmed the existence of three polymorphs of Na2U2O7 (α, β, and γ), the two phase transitions occurring above about 600 K and around 1323 K respectively. X-ray diffraction patterns for the β and γ forms of the compound are reported for the first time. Our results are finally assessed with respect to similar vaporization studies carried out in neighboring ternary phase fields of the Na-U-O phase diagram.
JRC Directorate:Nuclear Safety and Security

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