Thermodynamic properties and behaviour of A(2) (UO2)(MoO4)(2) compounds with A = Li, Na, K, Rb, and Cs

Lelet, Maxim I., Suleimanov, Evgeny V., Golubev, Aleksey V., Geiger, Charles A., Depmeier, Wulf, Bosbach, Dirk and Alekseev, Evgeny V. (2014) Thermodynamic properties and behaviour of A(2) (UO2)(MoO4)(2) compounds with A = Li, Na, K, Rb, and Cs Journal of Chemical Thermodynamics, 79 . pp. 205-214.

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Abstract

A thermodynamic investigation of five alkali-metal uranyl molybdates of the general formula A(2)[(UO2)(MoO4)(2)], where A = Li, Na, K, Rb, and Cs, was undertaken. The various phases were synthesized by solid-state reaction of ANO(3), with A = Li, Na, K, Rb, or Cs, MoO3 and gamma-UO3. The synthetic products were characterized by X-ray powder diffraction and X-ray fluorescence methods. The low-temperature heat capacity, C-p degrees, was measured using adiabatic calorimetry from T = (6 to 335) K. Based on these data, the third law entropy at T = 298.15 K, S degrees, is (345 +/- 1) J . K (1) . mol (1) for LiA(2)[(UO2)(MoO4)(2)], (373 +/- 1) J . 1 mol (1) for NaA(2)[(UO2)(MoO4)(2)], (390 +/- 1) J . K (1) . mol (1) for KA(2)[(UO2)(MoO4)(2)], (377 +/- 1) J . K (1) . mol (1) for RbA(2)[(UO2)(MoO4)(2)] and (394 +/- 1) J . K (1) . mol (1) for CsA(2)[(UO2)(MoO4)(2)]. The enthalpy of formation of LiA(2)[(UO2)(MoO4)(2)] was determined using HF solution calorimetry giving DfH +/-(T = 298 K, Li2[(UO2)( MoO4) 2], cr) = -(3456 +/- 9) kJ . mol (1). Using these new experimental results, together with literature data, the Gibbs free energy of formation of each compound was calculated, giving: Delta(f)G degrees (T = 298 K, LiA(2)[(UO2)(MoO4)(2)], cr) =-(3204 +/- 9) kJ.mol (1), Delta(f)G degrees (T = 298 K, Na2[(UO2)(MoO4) 2], cr) =-(3243 +/- 2) kJ . mol (1), Delta(f)G degrees (T = 298 K, KA(2)[(UO2)(MoO4)(2)], cr) =-(3269 +/- 3) kJ . mol (1), Delta(f)G degrees (T = 298 K, RbA(2)[(UO2)(MoO4)(2)], cr) = -(3262 +/- 3) kJ . mol (1), and Delta(f)G degrees (T = 298 K, CsA(2)[(UO2)(MoO4)(2)], cr) = -(3259 +/- 3) kJ . mol(1). Smoothed C-p degrees (T) values between T = (0 and 320) K are presented along with values for S - and the functions [H degrees(T)-H degrees(0)] and [G degrees(T)-H degrees(0)]. Delta S-f, Delta H-f, and Delta(f)G behaviour at T = 298 K of the A(2)[(UO2)(MoO4)(2)] group is analysed as a function of the molar volumes of the different phases. The phase relations of KA(2)[(UO2)(MoO4)(2)] in aqueous solution, in the presence and absent of carbon dioxide at T = 298 K, were studied by thermodynamic model calculations. (C) 2014 Elsevier Ltd. All rights reserved.

Document Type: Article
Additional Information: Times Cited: 0 0
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence
Kiel University
Refereed: Yes
ISSN: 0021-9614
Projects: Future Ocean
Date Deposited: 30 Mar 2015 12:31
Last Modified: 28 Mar 2018 10:28
URI: http://eprints.uni-kiel.de/id/eprint/27803

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