Acta Phys. -Chim. Sin. ›› 2008, Vol. 24 ›› Issue (03): 471-474.doi: 10.3866/PKU.WHXB20080321

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Metastable Phase Equilibria of the Quaternary System Na+, K+//Cl-, B4O2-7-H2O at 273 K

ZENG Ying; WANG Rui-Lin; LIN Xiao-Feng; PENG Yun   

  1. College of Materials and Chemistry &Chemical Engineering, Chengdu University of Technology, Chengdu 610059, P. R. China
  • Received:2007-09-20 Revised:2007-10-17 Published:2008-03-10
  • Contact: ZENG Ying

Abstract: The metastable phase equilibria of the quaternary system Na+, K+//Cl-, B4O2-
7-H2O were studied at 273 K by isothermal evaporation method. Solubilities and densities of the equilibrium solution of this system were determined. According to the experimental data, the metastable equilibrium phase diagram was plotted. The phase diagram of the system consists of five univariant curves, four crystallization fields and two invariant points. No double salt or solid solution was formed. The four crystallization fields were corresponding to single salt NaCl, KCl, K2B4O7·4H2O and Na2B4O7·10H2O, respectively. Invariant point E1 was saturated with salt KCl, NaCl and Na2B4O7·10H2O, the mass fraction composition of the equilibrium solution corresponding to E1 is w(Cl-)=29.15%, w(B4O2-7)=0.64%, w(K+)=5.97%, w(Na+)=15.55%, while that of point E2 was w(Cl-)=22.84%, w(B4O2-7)=10.98%, w(K+)=28.01%, w(Na+)=1.53%. Point E2 is saturated with salt KCl, Na2B4O7·10H2O and K2B4O7·4H2O. Compared with the stable phase diagram at 298 K, the crystallization field of Na2B4O7·10H2O became large at 273 K in this system, whereas the crystallization fields of K2B4O7·4H2O and NaCl became small.

Key words: Quaternary system, Metastable phase equilibrium, Borate, 273 K