Na_2B_4O_7-Mg_2B_6O_(11)-H_2O体系298.15K时固液相平衡研究

Solid-liquid Phase Equilibria in the Aqueous System Na_2B_4O_7-Mg_2B_6O_(11)-H_2O at 298.5 K

采用等温溶解平衡法研究Na_2B_4O_7-Mg_2B_6O_(11)-H_2O体系在298.15,K时稳定相平衡,并测定其溶解度及物化性质(密度和折光率).根据实验数据绘制稳定相图及物化性质-组成图.研究结果表明:该体系为水合物I型,无复盐及固溶体形成;相图中有1个共饱点E(Na_2B_4O_7·10H_2O+Mg_2B_6O_(11)·15H_2O),对应的液相组成(质量分数)为Na_2B_4O_72.95%、Mg_2B_6O_(11)0.034%;2条单变量溶解度曲线AE和BE;2个单盐结晶区,对应的平衡固相分别为Na_2B_4O_7·10H_2O和Mg_2B_6O_(11)·15H_2O;平衡液相中随着Na_2B_4O_7含量的不断增加,Mg_2B_6O_(11)的溶解度逐渐减小,表明Na_2B_4O_7对Mg_2B_6O_(11)有较强的盐析作用.稳定平衡液相的密度、折光率均随着液相中Na_2B_4O_7质量分数的变化呈有规律的变化.采用经验公式对密度和折光率进行了关联,计算值和实验值吻合较好.

The phase equilibrium of the aqueous system Na2B4O7-Mg2B6O11-H2O has been researched at298.15,K using an iso-thermal dissolution method.The solubility and physico-chemical properties such as density and refractive index were analyzed.Based on the experimental data,the phase diagram at298.15,K and diagrams of physico-chemical properties versus compositions were plotted respectively.The results show that the system at298.15,K belongs to hydrate type I and no double salt or solid solution was generated.There is one invariant point(liquid phase composition is Na2B4O72.95%,,Mg2B6O110.034%,),two univariate curves and two crystallization fields(Na2B4O7·10H2O and Mg2B6O11·15H2O).The concentration of Mg2B6O11decreased with the concentration increase of Na2B4O7,which shows that Na2B4O7has salting-out effect on Mg2B6O11.Physico-chemical properties changed regularly with the increase of Na2B4O7content.Using empirical equations,the calculated values highly match the experimental values.