ELASTIC BEHAVIOR OF COALS STUDIED BY MERCURY POROSIMETRY

Mercury porosimetry has been widely used to study the pore structures of coals. One of the difficulties in using this approach for characterizing pore size distributions involves the 'correction' of the apparent intrusion volumes for coal compressibility. This paper presents results which use the mercury porosimetry technique to draw conclusions concerning the elastic properties of coals. Both dry and moist coals and lignites are observed to have apparent compressibilites between about 2.6 and 8.5 GPa, typical of glassy solids. Hysteresis behaviour is observed on repeated compression-decompression cycles and suggests that coal behaves like a macromolecular material under dynamic stressing conditions. This means that the compressibility is an apparent quantity, and depends on the method used to obtain it. The magnitude of the observed hysteresis effect also suggests that the coal dissipates a large fraction of the mechanical energy input during compression. It is believed that most of the dissipation results from frictional processes associated with the steric difficulty of reorganizing the network structure.