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

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 (similar to 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 (similar to 12.1 mass %)-H2O, there are all two invariant points, and three crystallization regions corresponding to CsBr, Cs3GdBr6 center dot 10H(2)O, and GdBr3 center dot 6H(2)O, respectively. There are two invariant points and three crystallization regions corresponding to CsBr, Cs3Dy2Br9 center dot 16H(2)O and DyBr3 center dot 6H(2)O in 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 center dot 10H(2)O and Cs3Dy2Br9 center dot 16H(2)O are incongruently soluble in water or a medium of similar to 12.1 mass % HBr, and were characterized by XRD and TG-DTG techniques. The standard molar enthalpies of solution for Cs3GdBr6 center dot 10H(2)O, Cs3Dy2Br9 center dot 16H(2)O, GdBr3 center dot nH(2)O (n = 6.00) and DyBr3 center dot nH(2)O (n = 5.99) were obtained by means of microcalorimetric measurement, the values found for standard molar enthalpies of formation of Cs3GdBr6 center dot 10H(2)O, Cs3Dy2Br9 center dot 16H(2)O, GdBr3 center dot nH(2)O (n = 6.00) and DyBr3 center dot nH(2)O (n = 5.99) were - (5104.8 +/- 3.2) kJ center dot mol(-1), - (7827.3 +/- 3.6) kJ center dot mol(-1), - (2726.0 +/- 2.7) kJ center dot mol(-1) and - (2734.5 +/- 3.3) kJ center dot mol(-1), respectively.