The Phase and Physicochemical Properties Diagrams of Systems Rb⁺(Mg²⁺)//Cl^– and Borate–H₂O at 323 K

Abstract

The phase and physicochemical properties diagrams at 323 K of systems Rb⁺//Cl^–, borate–H₂O, and Mg²⁺//Cl^–, borate–H₂O were plotted using the solubilities, densities, and refractive indices of the systems. The Schreinemakers’ wet residue method and the X-ray diffraction method were used for the determination of the compositions of solid phase. Results show that these two systems belong to the hydrate I type, without solid solution or double salt formation. The phase diagrams of both systems consist of one invariant point, two monovariant curves, and two crystallization zones. The borates formed in the studied systems are RbB₅O₆(OH)₄ · 2H₂O, and MgB₄O₅(OH)₄ · 7H₂O. The comparison between the stable phase diagrams of the system Rb⁺//Cl^–, borate–H₂O at 323 and 348 K shows that no matter at which temperature point, the crystallization form of salts are not changed and the crystallization zones have slightly changed.