Metastable phase equilibria in the systems K2SO4 + K2B4O7 + H2O and KCl + K2B4O7 + H2O at 308.15 K

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Experimental studies on the metastable solubilities and physicochemical properties (density and refractive index) in the ternary systems K2SO4 + K2B4O7 + H2O and KCl + K2B4O7 + H2O at 308.15 K were determined with the method of isothermal evaporation. According to the experimental results, the phase diagrams of the two ternary systems were plotted. In the phase diagrams, there are both two isotherm evaporation curves, one eutectic point corresponding to K2SO4 + K2B4O7 · 4H2O, and KCl + K2B4O7 · 4H2O, respectively. Both of the ternary systems belong to a simple eutectic type, and neither double salts nor solid solutions formed in the ternary systems. A comparison of the stable and metastable phase diagrams of the ternary systems K2SO4 + K2B4O7 + H2O and KCl + K2B4O7 + H2O shows that the supersaturated phenomenon of potassium borate tetrahydrate is significant and easier to appear the metastable behavior.