Homogeneous nucleation and glass formation in aqueous alkali halide solutions at high pressures

The limit of supercooling determined by homogeneous nucleation has been investigated as a function of pressure for aqueous solutions of the common alkali halides LiCl, NaCl, KCl, CsCl, and KI for dilute solutions. The pressure dependence of the homogeneous nucleation temperature follows the pattern established earlier for H₂O, T_H decreasing curvilinearly until crystallization of ice III becomes favored at ∼2 kbar pressure and T < -90°C. For 1 m solutions the T_H vs. pressure plots are indistinguishable for these salts, implying that the T_H depression, like the freezing point depression, is a colligative property. More concentrated solutions, containing 1 or more mol of salt per 20 mol of water (30 in the case of LiCl), fail to crystallize above ∼1.5 kbar and glassy phases may be obtained below -120°C. The glass transition temperature shows a small positive pressure dependence. At constant alkali chloride concentration and pressure the glass transition temperature is a maximum for NaCl.