XRD analysis of carbon stacking structure in coal during heat treatment

Abstract The fraction of the stacking structure ( P s ) and the average number of aromatic layers ( N ave ) in several raw coals were estimated by X-ray diffraction analysis (Standard Analysis of Coal by XRD: STAC-XRD). STAC-XRD is more appropriate for analyzing coal with low crystallinity than the classical XRD analysis method by using the interlayer spacing of aromatic layers ( d 002 ) and the mean crystallite size along the c axis ( L c ). STAC-XRD was also used to compare the development of the stacking structure in caking coal during heat treatment with that in non-caking coal. After heat treatment at 920 °C, N ave of the caking coals was larger than that of the non-caking coals. The stacking of the aromatic layers in the caking coal temporarily developed at the fluidity stage at 400–440 °C, but in the 440–600 °C range, the release of volatile components partially disordered the stacked layers. The influence of heat-treatment conditions on carbon stacking structure in several kinds of coal was investigated by means of STAC-XRD. The heating rate required for the development of stacking structure in lower-rank coals was slower than that required for higher-rank coals.