One-dimensional description of the average polycyclic aromatic unit in Pocahontas No. 3 coal: an X-ray scattering study

Abstract

The radial distribution method was used to examine the non-crystalline portion of a low-volatile bituminous coal, Pocahontas No. 3, from Buchanan County, VA, USA. This coal, one of the Argonne Premium Coal Sample Program, was used as received for X-ray absorption/diffraction/scattering experiments. The diffraction due to the crystalline minerals contained in the coal and due to the graphene layering peak was removed from the amorphous scattering component. The latter was fitted to the self-scattering curve constructed from the scattering factor for carbon and the difference was Fourier transformed to obtain the one-dimensional structural details of the average short-range structural unit in this coal. Interpretation of the radial distribution indicates that the average structural unit is ∼ 80% aromatic and consists of polycyclic six-membered rings which are predominantly, if not exclusively, planar. In addition, the average graphene layer has a diameter of ∼ 7.7 Å. The radial distribution function results compare favourably with those obtained by 13C NMR spectroscopy.