NACL-H2O SYSTEMS AT TEMPERATURES BELOW 273-K, STUDIES BY DIFFERENTIAL SCANNTI CALORIMETRY

Aqueous solutions of NaCl are studied by differential scanning calorimetry (DSC) during cooling, at scan rate 2 K/min, to 218 K (-55-degrees-C) and subsequent heating to 288 K (+15-degrees-C). Hysteresis effects are reflected in the thermograms. Two exothermic transitions are observed during the cooling, and two endothermic transitions during the heating. The first exotherm is associated with the initial separation of ice from a subcooled NaCl solution. An exothermic transition at 237 K (-36-degrees-C) appears as a pseudo eutectic solidification of a supersaturated NaCl solution. The phase transitions observed are discussed with reference to dehydration of biological cells during cooling.