Phase Equilibrium CsBr-CeBr3-HBr(12.52 wt %)—H2O at 298 ± 0.1 K and a New Solid Phase Compound

Abstract

The equilibrium solubility of the quaternary system CsBr-CeBr3-HBr(12.52 wt %)—H2O was determined at 298K and the corresponding equilibrium diagram was constructed. The quaternary system is complicated by three equilibrium solid phases: CsBr, Cs5Ce2Br11 · 22H2O (5: 2 type), and CeBr3 · 7H2O, of which the new compound Cs5Ce2Br11 · 22H2O was found to be incongruently soluble in the system. The new compound obtained was identified and characterized by the method of X-ray diffraction and the thermal analysis methods of thermogravimetry-differential thermogravimetry (TG-DTG), and it loses its crystal water in two steps from 325 to 511 K. The standard molar enthalpy of solution of Cs5Ce2Br11 · 22H2O in deionized water was measured to be (129.105 ± 0.150) kJ mol−1 with a heat conduction microcalorimeter. The standard molar enthalpy of formation was calculated as (−10438.215 ± 0.150) kJ mol−1.