The solubility in triple water-salt systems containing NdCl3, PrCl3, YCl3, TbCl3 chlorides, and water-soluble fullerenol C60(OH)24 at 25 °C was studied by isothermal saturation in ampoules. The analysis for the content of rare earth elements was carried out by atomic absorption spectroscopy, for the content of fullerenol—by electronic spectrophotometry. The solubility diagrams in all four ternary systems are simple eutonic, both consisting of two branches, corresponding to the crystallization of fullerenol crystal-hydrate and rare earth chloride crystal-hydrates, and containing one nonvariant point corresponding to the saturation of both solid phases. On the long branches of C60(OH)24*18H2O crystallization, a C60(OH)24 decreases by more than 2 orders of magnitude compared to the solubility of fullerenol in pure water (salting-out effect). On very short branches of crystallization of NdCl3*6H2O, PrCl3*7H2O, YCl3*6H2O, and TbCl3*6H2O, the salting-in effect is clearly observed, and the solubility of all four chlorides increases markedly. The four diagrams cannot be correctly approximated by the simple one-term Sechenov equation (SE-1), and very accurately approximated by the three-term modified Sechenov equation (SEM-3). Both equations for the calculation of nonelectrolyte solubility in electrolyte solutions (SE-1 and SEM-3 models) are obtained, using Pitzer model of virial decomposition of excess Gibbs energy of electrolyte solution. It is shown, that semi-empirical equations of SE-1 and SEM-3 models may be extended to the systems with crystallization of crystal-solvates.
In the article the General classification of all nonvariant points in the arbitrary types diagrams of phase equilibria with arbitrary number of components is carried out. The topological features of the arrangement of such nonvariant points relative to the figurative points of equilibrium phases are considered. Stability of monovariant equilibria (curves on phase diagrams) in the nearest neighborhood of nonvariant points is also considered. Recurrent equations are given for calculating the number of topological elements of phase diagrams (points, curves, surfaces, volumes, etc.) of phase coexistence from the data on the number of similar elements in less component subsystems. All the obtained regularities are confirmed by examples of specific phase diagrams of solubility, fusibility, liquid-vapor, delamination, etc.
Solubility diagram was investigated by the method of saturation in ampules at 25 ± 0.02 • C for 4 hours. The solubility diagram of the PrCl 3-C 60 (OH) 24-H 2 O ternary system at 25 • C occurs as simple eutonics, consisting of two branches, corresponding to the crystallization of crystalhydrates: PrCl 3 • 7H 2 O and C 60 (OH) 24 • 18H 2 O. The diagram contains one non-variant point each-eutonics, which corresponds to saturation with pair of crystal-hydrates simultaneously. The diagram also contains very short branch of PrCl 3 • 7H 2 O crystallization, and long branch of C 60 (OH) 24 • 18H 2 O, where the effect of fullerenol salt-out is distinctly observed.
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