Alicyclic Structures in Coals

Abstract

X-RAY and other physical and chemical evidence indicates that coals assume a graphitic structure with metamorphism. X-ray diffraction patterns of some meta-anthracites show (hkl) reflexions that arise from the three-dimensional unit cell of a graphite lattice^1,2. For the anthracites, a number of diffraction bands can be detected which coincide with the (hk) reflexions of aromatic layers (having a two-dimensional unit cell of side approximately equal to that of graphite layers)³; the remainder of the bands can be attributed to the (00l) reflexions of these layers packed ‘turbostratically’⁴. Medium- and low-rank coals also give diffuse diffraction patterns that can be indexed as the (hk) and (00l) reflexions of aromatic layers. These observations led to the development of methods for quantitative analysis of X-ray intensity profiles of coals, permitting estimation of bond-lengths, fraction of carbon in aromatic layers (the remainder assumed to be roentgenamorphous), and size distribution and stacking of the layers^3,5,6.