Na+, K+//Cl-, B4O2-7-H2O四元体系273 K介稳相平衡

采用等温蒸发法研究了四元体系Na+, K+//Cl-, B4O2-7-H2O 273 K时的介稳相平衡与相图. 测定了该体系273 K平衡液相中各组分的溶解度及平衡液相的密度; 绘制了该体系的介稳相图. 该四元体系273 K相图由5条溶解度单变量线、4个结晶区及2个共饱和点组成. 体系无复盐或固溶体形成. 四个结晶区分别对应单盐NaCl、KCl、K2B4O7·4H2O 和Na2B4O7·10H2O. 共饱点E1处KCl、NaCl及Na2B4O7·10H2O三盐共饱和,所对应的平衡液相组成为w(Cl-)=29.15%, w(B4O2-7)=0.64%, w(K+)=5.97%, w(Na+)=15.55%; 共饱和点E2处盐KCl、Na2B4O7·10H2O和K2B4O7·4H2O的三盐共饱和, 所对应的平衡液相组成为w(Cl-)=22.84%, w(B4O2-7)=10.98%, w(K+)=28.01%, w(Na+)=1.53%. 同体系298 K时的稳定相图相比, 273 K时硼酸钠的结晶区变大, 而硼酸钾、氯化钠结晶区变小.

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

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.