Calorimetric Study of the Glassy State. IV. Heat Capacities of Glassy Water and Cubic Ice

TLDR

The study measured heat capacities of amorphous, cubic, and hexagonal ice from 20 K to 250 K using a vapor‑condensation calorimeter. A glass transition at ~135 K was observed, marked by a 35 J mol⁻¹ K⁻¹ jump and a 1.64 kJ mol⁻¹ exothermic crystallization; subsequent cubic‑to‑hexagonal transformation between 160–210 K occurred in two steps with activation energies of 21.3 and 44.7 kJ mol⁻¹ and released ~160 J mol⁻¹.

Abstract

Abstract By making use of the vapor-condensation type calorimeter, the heat capacity measurements of amorphous, cubic and hexagonal ices were made between 20°K and 250°K. The glass transition phenomenon was found near 135°K with the sudden change of the heat capacity amounting to 35 J/(mol°K). The drastic crystallization with the exothermic effect which amounts to 1.64 kJ/mol was then followed at this temperature. The transformation of the cubic crystal to the hexagonal one was confirmed to occur in the temperature region from 160 to 210°K and to proceed in two steps with the activation energies of 21.3 and 44.7 kJ/mol, respectively. The amount of the exothermic effect accompanying this transformation was found to be about 160 J/mol.