Solid–Liquid Phase Equilibrium in the Ternary Systems (Li₂B₄O₇ + MgB₄O₇ + H₂O) and (Na₂B₄O₇ + MgB₄O₇ + H₂O) at 298.15 K

Abstract

Solid–liquid phase equilibria of the two ternary systems (Li2B4O7 + MgB4O7 + H2O) and (Na2B4O7 + MgB4O7 + H2O) at T = 298.15 K and p = 0.1 MPa were studied with the isothermal dissolution equilibrium method. Solubilities, densities, pH values, and refractive indices were measured experimentally. In the ternary system (Li2B4O7 + MgB4O7 + H2O) at 298.15 K, there are one invariant point corresponding to (Li2B4O7·3H2O + MgB4O7·9H2O), two isothermal dissolution curves, and two crystallization regions. The crystallized area of MgB4O7·9H2O is increased obviously with the increase of temperature, while that of Li2B4O7·3H2O is decreased slightly. In the ternary system (Na2B4O7 + MgB4O7 + H2O) at 298.15 K, there are one invariant point (Na2B4O7·10H2O + MgB4O7·9H2O), two isothermal dissolution curves, and two crystallization regions. The crystallized area of MgB4O7·9H2O is increased with the increase of temperature, while that of Na2B4O7·10H2O is decreased obviously. Both of the systems belong to a simple eutectic type, and neither double salts nor solid solutions formed.