Experimental study on the metastablle phase equilibria of tine quaternary system Na2CO3-Na2SO4-Na2B4O7-H2O at 273 K

The solubilities and densities of equilibrium solutions in the quaternary system Na2CO3 center dot Na2SO4Na2B4O7 center dot H2O were studied at 273 K by isothermal evaporation method. On the basis of the solubility data, the phase diagram of the system was plotted. The phase diagram consists of two invariant point, five univariant curves and four crystallization fields, which correspond to the salt Na2CO3 center dot 10H(2)O, Na2SO4 center dot 10H(2)O, Na2B4O7 center dot 10H(2)O and 2Na(2)SO(4)center dot Na2CO3. In this system, the double-salt (2Na(2)SO(4)center dot Na2CO3) was formed, and this double-salt also exists in the other quaternary or higher-component systems which contain the Na2CO3 center dot Na2SO4-H2O ternary system. The crystallization forms of sodium carbonate and sodium sulfate are Na2CO3 10H(2)O and Na2SO4 center dot 10H(2)O, respectively. The inextenso molecular fomula of sodium borate is Na2B4O5 (OH)(4)center dot 8H(2)O center dot Na2CO3 has salt-out effect to Na2B4O7 in the solution.