Equilibria of the ternary systems CsBr–LnBr3 (Ln = Gd, Dy)–H2O and the quaternary system CsBr–GdBr3–HBr (∼12.1 mass %)–H2O at T = 298.15 K and standard molar enthalpies of formation for new compounds

Abstract

As part of a series of studies, this paper reports experimental phase equilibrium data for CsBr–GdBr3–H2O, CsBr–DyBr3–H2O and CsBr–GdBr3–HBr (∼12.1 mass %)–H2O systems at T = 298.15 K. The phase diagrams were constructed based on the measured data. In the phase diagrams of the ternary system CsBr–GdBr3–H2O and the quaternary system CsBr–GdBr3–HBr (∼12.1 mass %)–H2O,there are all two invariant points, and three crystallization regions corresponding to CsBr, Cs3GdBr6·10H2O, and GdBr3·6H2O, respectively.There are two invariant points and three crystallization regions corresponding to CsBr, Cs3Dy2Br9·16H2O and DyBr3·6H2Oin the system CsBr–DyBr3–H2O.The experimental solubility values of gadolinium bromide and dysprosium bromide at 298.15 K were 65.42 mass % and 65.94 mass %. The compounds Cs3GdBr6·10H2O and Cs3Dy2Br9·16H2O are incongruently soluble in water or a medium of ∼ 12.1 mass % HBr, and were characterized by XRD and TG-DTG techniques. The standard molar enthalpies of solution for Cs3GdBr6·10H2O, Cs3Dy2Br9·16H2O, GdBr3·nH2O (n = 6.00) and DyBr3·nH2O (n = 5.99) were obtainedby means of microcalorimetric measurement, the values found for standard molar enthalpies of formation of Cs3GdBr6·10H2O, Cs3Dy2Br9·16H2O, GdBr3·nH2O (n = 6.00) and DyBr3·nH2O (n = 5.99) were – (5104.8 ± 3.2) kJ·mol−1, – (7827.3 ± 3.6) kJ·mol−1, – (2726.0 ± 2.7) kJ·mol−1 and – (2734.5 ± 3.3) kJ·mol−1, respectively.