Solubility, Density, and Refractive Index of the Ternary System Na2B4O7 + Mg2B6O11 + H2O at 308.15 K

Experimental studies on the solubility, density and refractive index in the ternary system (Na2B4O7 + Mg2B6O11 + H2O) at 308.15 K were determined with the method of isothermal dissolution equilibrium. Based on the experimental results, the phase diagram and its corresponding physicochemical properties versus composition diagram in the system were plotted. In the phase diagram of the ternary system at 308.15 K, there are one eutectic point and two crystallization regions corresponding to the large area of inderite (Mg2B6O11 · 15H2O) and the relative small area of borax (Na2B4O7 · 10H2O), respectively. Neither double salt nor solid solution was found in this system. The physicochemical properties (density and refractive index) of the ternary system at 308.15 K changes regularly with the increasing of sodium borate concentration. The calculated values of density and refractive index using empirical equations of the ternary system are in good agreement with the experimental values.