Solid–Liquid Phase Equilibria of the Aqueous Ternary System (CaCl₂+CaB₆O₁₀+H₂O) at 308.15, 323.15 K and 0.1 MPa

Abstract

Solubilities and physicochemical properties including refractive index, density, and pH of the ternary system (CaCl₂+CaB₆O₁₀+H₂O) at 308.15, 323.15 K and 0.1 MPa were determined experimentally with the method of isothermal dissolution equilibrium. Based on the experimental data, the phase diagrams and the diagrams of physicochemical properties versus the composition of CaCl₂ in the system at 308.15 and 323.15 K were plotted. The phase diagrams of the ternary system at two temperatures are all consisted with one invariant co-saturation point, two univariant curves and two crystallization regions corresponding to calcium chloride tetrahydrate (CaCl₂·4H₂O) and gowerite (CaB₆O₁₀·5H₂O) at 308.15 K and siniarite (CaCl₂·2H₂O) and gowerite (CaB₆O₁₀·5H₂O) at 323.15 K, respectively. The hydrates in this system at both temperatures belong to a hydrate type I, and neither double salts nor solid solution were formed. A comparison of the phase diagrams at both temperatures shows that the areas of the crystallized regions of calcium chloride and calcium borate are decreased obviously, and those results indicate the solubilities of calcium chloride and calcium borate increased with the increasing of temperature correspondingly. The physicochemical properties (density, refractive index and pH) in the ternary system at both temperatures changed regularly with the mass fraction of calcium chloride in the solution. With the increasing of calcium chloride composition, the density and refractive index are increased significantly to reach the maximum values at the invariant points, and then decreased obviously. On the contrary, pH values in the system at two temperatures are similarly decreased firstly, and then increased, and gain the minimum values at the invariant points.