Solubilities, Densities, and Refractive Indices of Ternary Systems (LiB5O8 + RbB5O8 + H2O) and (NaB5O8 + RbB5O8 + H2O) at 308.15 K and 0.1 MPa

Solid-liquid phase equilibria of the two ternary systems (LiB5O8 + RbB5O8 + H2O) and (NaB5O8 + RbB5O8 + H2O) were investigated at T = 308.15 K and p = 0.1 MPa by the isothermal solution equilibrium method. The experimental results show that the phase diagrams of the systems (LiB5O8 + RbB5O8 + H2O) and (NaB5O8 + RbB5O8 + H2O) at 308.15 K contain one invariant point, two univariant curves and two crystallization regions. The area of the crystallization region of RbB5O8·4H2O is much larger than that of LiB5O8·5H2O in the former system and that of NaB5O8·5H2O in the latter system. Owing to the different solubilities of the salts in the aqueous systems, the solubility of RbB5O8 in the solution decreased obviously with the increasing concentration of LiB5O8 or NaB5O8 in either ternary system, indicating that both have a relatively strong effect on the solubility of RbB5O8. It was found that both systems belong to the simple eutectic type, and neither double salts nor solid solutions were formed.