کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
215341 | 1426234 | 2014 | 10 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Thermodynamic properties and behaviour of A2[(UO2)(MoO4)2] compounds with A = Li, Na, K, Rb, and Cs Thermodynamic properties and behaviour of A2[(UO2)(MoO4)2] compounds with A = Li, Na, K, Rb, and Cs](/preview/png/215341.png)
• Low temperature heat capacity of A2[(UO2)(MoO4)2] (A = Li, Na, K, Rb, and Cs) series was determined.
• Enthalpy of formation of Li2[(UO2)(MoO4)2] was determined by HF solution calorimetry.
• ΔfG° (T = 298 K) of all phases from studied series were calculated.
A thermodynamic investigation of five alkali-metal uranyl molybdates of the general formula A2[(UO2)(MoO4)2], where A = Li, Na, K, Rb, and Cs, was undertaken. The various phases were synthesized by solid-state reaction of ANO3, with A = Li, Na, K, Rb, or Cs, MoO3 and γ-UO3. The synthetic products were characterized by X-ray powder diffraction and X-ray fluorescence methods. The low-temperature heat capacity, Ср°, 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°, is (345 ± 1) J · K−1 · mol−1 for Li2[(UO2)(MoO4)2], (373 ± 1) J · K−1 · mol−1 for Na2[(UO2)(MoO4)2], (390 ± 1) J · K−1 · mol−1 for K2[(UO2)(MoO4)2], (377 ± 1) J · K−1 · mol−1 for Rb2[(UO2)(MoO4)2] and (394 ± 1) J · K−1 · mol−1 for Cs2[(UO2)(MoO4)2]. The enthalpy of formation of Li2[(UO2)(MoO4)2] was determined using HF solution calorimetry giving ΔfH°(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: ΔfG°(T = 298 K, Li2[(UO2)(MoO4)2], cr) = −(3204 ± 9) kJ · mol−1, ΔfG°(T = 298 K, Na2[(UO2)(MoO4)2], cr) = −(3243 ± 2) kJ · mol−1, ΔfG°(T = 298 K, K2[(UO2)(MoO4)2], cr) = −(3269 ± 3) kJ · mol−1, ΔfG°(T = 298 K, Rb2[(UO2)(MoO4)2], cr) = −(3262 ± 3) kJ · mol−1, and ΔfG°(T = 298 K, Cs2[(UO2)(MoO4)2], cr) = −(3259 ± 3) kJ · mol−1. Smoothed Ср°(Т) values between T = (0 and 320) K are presented along with values for S° and the functions [H°(T) − H°(0)] and [G°(T) − H°(0)]. ΔfS, ΔfH, and ΔfG behaviour at T = 298 K of the A2[(UO2)(MoO4)2] group is analysed as a function of the molar volumes of the different phases. The phase relations of K2[(UO2)(MoO4)2 in aqueous solution, in the presence and absent of carbon dioxide at T = 298 K, were studied by thermodynamic model calculations.
Journal: The Journal of Chemical Thermodynamics - Volume 79, December 2014, Pages 205–214