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

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.

SMITH Anna;  COLLE Jean-Yves;  RAISON Philippe;  BENES Ondrej;  KONINGS Rudy; 

2016-01-04

ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD

JRC91051

0021-9614,   

http://www.sciencedirect.com/science/article/pii/S0021961415002025,    https://publications.jrc.ec.europa.eu/repository/handle/JRC91051,   

10.1016/j.jct.2015.06.026,