Water in Coal Pores: Low-Temperature Heat Capacity Behavior of the Moisture in Wyodak Coal

Abstract

The low-temperature heat capacity behavior of naturally occuring water in Wyodak coal indicates that there are two types of water present. More than two-thirds is "nonfreezable," displaying no evidence of a phase transition in the neighborhood of 273 K where normal bulk water melts. The remainder is "freezable," displaying a somewhat distorted heat capacity peak, which is indicative of a phase transition. This evidence suggests that the nonfreezable water is either adsorbed on the internal surfaces of the coal or is in smaller pores, whereas the freezable water is in larger pores. Parallels to the heat capacity behavior of the coal-water system include the water in a porous ceramic, water in the mineral endellite, and water in the protein collagen.