Temperature dependence of the solidification enthalpy as experimentally determined between 245 and 203 K for montmorillonite-water systems

• Solidification enthalpy was determined for water in pores of montmorillonites.
• Solidification below 245 K involves formation of flat “ice plates”.
• Mass of the formed ice was calculated from BJH differential curves.
• Exchangeable cation and sample extensive parameters are statistically insignificant.
• The proposed empirical relationship enables prediction of enthalpy change to 203 K.

The temperature dependence of the solidification enthalpy change was determined for water confined in the pores of three homoionic forms of montmorillonite by the use of Differential Scanning Calorimetry (DSC). A model of the montmorillonite-water system was proposed, in which most of the micropores are slit-like in shape and the solidification process below 245 K involves the formation of flat “ice plates” with cylindrical interphase. The solidification heat associated with an exothermic freezing peak is proportional to the mass of ice formed. The latter was calculated from the pore size distribution differential curves measured for the same system by the use of the nitrogen adsorption at 77 K and calculated using the method of Barrett, Joyner, and Halenda (BJH).A good qualitative compatibility between the low temperature exothermic peaks and the peaks on the curves dm/dT obtained from the BJH data was observed. Statistical analysis of the enthalpy change values determined between 245 and 200 K showed an insignificance of the kind of homoionic form and sample parameters such as dry mass, water mass and the mass water content. A general empirical relationship is proposed enabling the prediction of the enthalpy change between 273 and 203 K.