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) |
| |
| Affiliation: | 1. Department of Chemistry, Lobachevsky State University of Nizhny Novgorod, Gagarin Ave. 23, 603950 Nizhny Novgorod, Russia;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;1. Department of Electrical and Biomedical Engineering, University of Nevada, Reno, NV, USA;2. Biomedical Engineering Program, University of Nevada, Reno, NV, USA;3. Department of Chemical and Materials Engineering, University of Nevada, Reno, NV, USA;4. Department of Microbiology and Immunology, University of Nevada, Reno, NV, USA;1. Department of Environmental Science and Analytical Chemistry, Stockholm University, SE10691, Stockholm, Sweden;2. Pharmaceutical Analysis Department, Faculty of Pharmacy, Damanhour University, Damanhour, 22511, Egypt;3. Department of Pharmaceutical Analytical Chemistry, Faculty of Pharmacy, University of Alexandria, Alexandria, 21521, Egypt;4. Department of Respiratory Medicine, Gävle Hospital and Centre for Research at Uppsala University/County Council of Gävleborg, Gävle, Sweden;1. School of Environmental and Chemical Engineering, Shanghai University, No. 99 Shangda Road, Shanghai 200444, China;2. Department of Environmental Science, Zhejiang University, Hangzhou, Zhejiang 310028, China;3. Ministry of Education Key Laboratory of Environmental Remediation and Ecological Health, Zhejiang University, Hangzhou, Zhejiang 310028, China;4. School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia |
| |
| 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, Ср°, 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 Ср° 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 Ср°(Т) 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. |
| |
| Keywords: | Calorimetry Heat capacity Entropy Heat of formation Actinides Uranium Molybdenum Thermodynamic modelling |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
