Water contained in brown coals generally consists of three different types, i.e. free, bound and non-freezable waters. In swelling experiments with water, volumetric change of coal was found to be reversible for free water in adsorption and desorption processes, while irreversible for the other types of waters. The freezing properties of water in a coal sample were measured by a ^1H-NMR in a temperature range from 170 to 293K. The amount of water condensed in the coal pores, C_<PW>, was defined as that of water which freezes below 250K. Since C_<PW> of the water-swollen coal changed reversibly for free water in adsorption and desorption processes and irreversibly for the other types, the irreversibility of the volume change could be explained in terms of the irreversible change in the pore structure of coal induced by drying. The freezing point distribution (FPD) of the pore water was obtained by fitting Gaussian functions to the temperature dependent change in the amount of nonfreezable water. A modified Gibbs-Thompson equation was used to determine the pore size distributions estimated by FPD. The reduction of C_<PW> well corresponded to volumetric reduction of pores whose radius was larger than 1nm.
