A calorimetric and thermodynamic investigation of potassium uranyl tungstate K2[(UO2)(W2O8)]

A thermophysical and thermochemical investigation of K2[(UO2)(W2O8)] was undertaken. K2[(UO2)(W2O8)] was synthesized by solid-state reaction of KNO3, WO3 and γ-UO3 and characterized by X-ray powder diffraction and X-ray fluorescence methods. Its low-temperature heat capacity was measured using adiabatic calorimetry from T = (9 to 329) K. Based on these data, the third law entropy, S°, at T = 298.15 K is (423 ± 1) J · K−1 · mol−1. The enthalpy of formation of K2[(UO2)(W2O8)] was determined using HF solution calorimetry giving ΔfH°(298 K, K2[(UO2)(W2O8)], cr) = −(3897 ± 10) kJ · mol−1. From the thermophysical and thermochemical results ΔfG°(298 K, K2[(UO2)(W2O8)], cr) = −(3645 ± 10) kJ · mol−1 is calculated. 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)].

► We determined the low temperature heat capacity of K2[(UO2)(W2O8)] using adiabatic calorimetry.
► We determined enthalpy of formation of K2[(UO2)(W2O8)] by HF solution calorimetry.
► We calculated ΔfG° (298 K) of K2[(UO2)(W2O8)].