Phase Transitions of Water in Zeolite Pores

Phase transition temperatures of water are experimentally determined for the case in which ice melts in the pores of zeolite (natural mineral) with a pore size of 0.2–2 nm. Three temperatures with a sharp change in the heat capacity and extremes of low-frequency electrical fluctuations are found when moistened material is heated from –150 to 100°C, the values of which are –20, 43, and 86°C. These values are associated with the melting of polygonal structures containing from five to seven water molecules.