Small angle X-ray scattering study on change of fractal property of Witbank coal with heat treatment

Change in the surface fractal dimension (D-s) of Witbank coal with heat tre atment was studied using small angle X-ray scattering. It was found that D- s changes systematically depending on the temperature and the heating rate. Especially in the pre-softening stage, D-s decreased with increasing tempe rature. From thermogravimetric and differential scanning calorimetric analy ses, we concluded that this was derived from a physical structural change i n coal. It was also found that there are lower limits (F-min) of fractal di stribution of pore surface. Further, these limits change greatly at the thr eshold of the coal softening temperature. It is concluded that the physical structural change of coal takes place at lower temperatures than that thou ght so far, and that D-s and F-min are valuable parameters for representing the structural changes with heat treatment. (C) 2000 Elsevier Science Ltd. All rights reserved.