Experimental Study on Phase Equilibria in Na₂B₄O₇–Na₂SO₄–H₂O and Li₂B₄O₇–Na₂B₄O₇–H₂O Aqueous Ternary Systems at 273 K

The solubility data for ternary systems Na₂SO₄–Na₂B₄O₇–H₂O and Li₂B₄O₇–Na₂B₄O₇–H₂O at 273 K were obtained experimentally by the isothermal solution equilibrium method, and the solid phases were analyzed by X-ray diffraction. On the base of the experimental results, the stable phase equilibrium diagrams for these two systems were constructed at 273 K. The stable phase equilibrium diagrams indicate that both phase diagrams show an invariant point, two univariant solubility curves and two solid phase crystalline regions. The two solid phases corresponding to the invariant point of ternary system Na₂SO₄–Na₂B₄O₇–H₂O are Na₂B₄O₇ · 10H₂O and Na₂SO₄ · 10H₂O, and the two crystallization regions of the ternary system Li₂B₄O₇–Na₂B₄O₇–H₂O are Na₂B₄O₇ · 10H₂O and Li₂B₄O₇ · 3H₂O, respectively. Thus, the two ternary systems belong to simple co-saturated type without complex salt or solid solution.