Published November 2015 | Version v1
Journal article Metadata-only

A calorimetric and thermodynamic investigation of A2[(UO2)2(MoO4)O2] compounds with A = K and Rb and calculated phase relations in the system (K2MoO4 + UO3 + H2O)

Creators

  • 1. Department of Chemistry, Lobachevsky State University of Nizhny Novgorod, Gagarin Ave. 23, 603950 Nizhny Novgorod (Russian Federation)
  • 2. Department of Materials Science and Physics, Section Mineralogy, University of Salzburg, A-5020 Salzburg (Austria)
  • 3. Institute of Energy and Climate Research (IEK-6), Forschungszentrum Jülich, D-52428 Jülich (Germany)
  • 4. Institut für Kristallographie, RWTH Aachen University, D-52056 Aachen (Germany)

Description

Highlights: • We determined the low temperature heat capacity of A2[(UO2)2(MoO4)O2] compounds with A = K and Rb. • We determined enthalpy of formation of K2[(UO2)2(MoO4)O2] by HF solution calorimetry. • We calculated ΔfG° (T = 298 K) of all phases from studied series. • Using obtained data we performed a thermodynamic modelling in the system (K2MoO4 + UO3 + H2O). - Abstract: A calorimetric and thermodynamic investigation of two alkali-metal uranyl molybdates with general composition A2[(UO2)2(MoO4)O2], where A = K and Rb, was performed. Both phases were synthesized by solid-state sintering of a mixture of potassium or rubidium nitrate, molybdenum (VI) oxide and gamma-uranium (VI) oxide at high temperatures. The synthetic products were characterised by X-ray powder diffraction and X-ray fluorescence methods. The enthalpy of formation of K2[(UO2)2(MoO4)O2] was determined using HF-solution calorimetry giving ΔfH° (T = 298 K, K2[(UO2)2(MoO4)O2], cr) = −(4018 ± 8) kJ · mol−1. The low-temperature heat capacity, Cp°, was measured using adiabatic calorimetry from T = (7 to 335) K for K2[(UO2)2(MoO4)O2] and from T = (7 to 326) K for Rb2[(UO2)2(MoO4)O2]. Using these Cp° values, the third law entropy at T = 298.15 K, S°, is calculated as (374 ± 1) J · K−1 · mol−1 for K2[(UO2)2(MoO4)O2] and (390 ± 1) J · K−1 · mol−1 for Rb2[(UO2)2(MoO4)O2]. These new experimental results, together with literature data, are used to calculate the Gibbs energy of formation, ΔfG°, for both phases giving: ΔfG° (T = 298 K, K2[(UO2)2(MoO4)O2], cr) = (−3747 ± 8) kJ · mol−1 and ΔfG° (T = 298 K, Rb2[(UO2)2(MoO4)], cr) = −3736 ± 5 kJ · mol−1. Smoothed Cp°(T) values between 0 K and 320 K are presented, along with values for S° and the functions [H°(T) − H°(0)] and [G°(T) − H°(0)], for both phases. The stability behaviour of various solid phases and solution complexes in the (K2MoO4 + UO3 + H2O) system with and without CO2 at T = 298 K was investigated by thermodynamic model calculations using the Gibbs energy minimisation approach

Availability note (English)

Available from http://dx.doi.org/10.1016/j.jct.2015.06.028

Additional details

Identifiers

DOI
10.1016/j.jct.2015.06.028;
PII
S0021-9614(15)00204-9;

Publishing Information

Journal Title
Journal of Chemical Thermodynamics
Journal Volume
90
Journal Page Range
p. 270-276
ISSN
0021-9614
CODEN
JCTDAF

INIS

Country of Publication
United Kingdom
Country of Input or Organization
International Atomic Energy Agency (IAEA)
INIS RN
47043244
Subject category
S37: INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY;
Descriptors DEI
CALORIMETRY; CARBON DIOXIDE; ENTROPY; FLUORESCENCE; FORMATION HEAT; HYDROFLUORIC ACID; MOLYBDATES; MOLYBDENUM; POTASSIUM; RUBIDIUM NITRATES; SOLUTIONS; SPECIFIC HEAT; TEMPERATURE DEPENDENCE; URANIUM; URANIUM DIOXIDE; URANIUM TRIOXIDE; X-RAY DIFFRACTION
Descriptors DEC
ACTINIDE COMPOUNDS; ACTINIDES; ALKALI METAL COMPOUNDS; ALKALI METALS; CARBON COMPOUNDS; CARBON OXIDES; CHALCOGENIDES; COHERENT SCATTERING; DIFFRACTION; DISPERSIONS; ELEMENTS; EMISSION; ENTHALPY; FLUORINE COMPOUNDS; HALOGEN COMPOUNDS; HOMOGENEOUS MIXTURES; HYDROGEN COMPOUNDS; INORGANIC ACIDS; INORGANIC COMPOUNDS; LUMINESCENCE; METALS; MIXTURES; MOLYBDENUM COMPOUNDS; NITRATES; NITROGEN COMPOUNDS; OXIDES; OXYGEN COMPOUNDS; PHOTON EMISSION; PHYSICAL PROPERTIES; REACTION HEAT; REFRACTORY METAL COMPOUNDS; REFRACTORY METALS; RUBIDIUM COMPOUNDS; SCATTERING; THERMODYNAMIC PROPERTIES; TRANSITION ELEMENT COMPOUNDS; TRANSITION ELEMENTS; URANIUM COMPOUNDS; URANIUM OXIDES

Optional Information

Copyright
Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.