Solid-Liquid Phase Equilibria of Organic Compounds Under High Pressures

利用新设计的高压光学容器，研究了有机化合物二元混合物在278 ~ 343 K温度和500 MPa压力下的固液相平衡。测量温度、压力和成分的不确定度分别在0.1 K、0.5 MPa和0.001摩尔分数以内系统研究：(1)简单共晶体系：苯+环己烷，苯+ 2-甲基-2-丙醇；(2)分子间化合物形成体系：四氯化碳+苯，四氯化碳+对二甲苯；(3)部分固溶体体系：-甲基萘+ -甲基萘；(4)完全固溶体体系：氯苯+溴苯。仪器和实验方法在高压容器中进行，有一对光学窗口。将已知成分的样品液引入平衡容器，浸入恒温控制在0.05 K以内的液浴中，并逐渐压缩。从视觉上观察到相变和固液共存实验结果与讨论在相图的所有情况下，恒定组分下的冻结温度随压力的增加而单调增加。共晶温度向更高温度转变，共晶成分向冻结温度压力系数较大的组分的更丰富成分转变。在形成分子间化合物的体系中，发现全等熔点变为非全等熔点，并且有一种化合物在高压下消失。固液共存曲线可以用一个新提出的方程令人满意地与所有系统相关联。

Solid-liquid phase equilibria of the binary mixtures of organic compounds have been investigated at temperatures from 278 to 343 K and pressures up to 500 MPa using a high-pressure optical vessel newly designed. The uncertainties in the measurements of temperature, pressure and composition are within 0.1 K, 0.5 MPa and 0.001 mole fraction, respectively.1 Systems investigated(1) simple eutectic systems : benzene + cyclohexane, benzene + 2-methyl-2-propanol(2) systems with formation of intermolecular compounds : carbon tetrachloride + benzene, carbon tetrachloride + p-xylene(3) partial solid solution system : -methylnaphthalene + -methylnaphthalene(4) complete solid solution system : chlorobenzene + bromobenzene2 Apparatus and experimental proceduresThe measurements were performed in a high-pressure vessel with a couple of optical windows. The sample liquid of a known composition was introduced in the equilibrium vessel, which was immersed in a liquid bath thermostatically controlled within 0.05 K, and was compressed gradually. The phase transition and solid-liquid coexistence were observed visually.3 Experimental results and discussionThe freezing temperature at a constant composition increases monotonously with increasing pressure in all cases of phase diagrams. The eutectic temperature shifts to higher temperature, and the eutectic composition shifts to richer composition of the component whose pressure coefficient of freezing temperature is larger. In the systems forming intermolecular compounds, it is found that the congruent melting point turns to the incongruent melting point, and that one compound disappears under high pressure. The solid-liquid coexistence curve can be correlated satisfactorily by an equation newly proposed for all systems.