Poly-cyclic Aromatic Structural Study of Sub-bituminous Assam Coal using X-ray Pair Distribution Function

Coal is a very complex heterogeneous material. It consists of both organic and inorganic matter. The X-ray diffraction patterns of coals are produced by distinct components in the coal, which include diffraction from the organic matrix and mineral components in it. The contribution from the organic component of coal shows the amorphous scattering which describes the short-range structure of the small polycyclic aromatic (PCA) unit in it. X-ray scattering study is one of the most important techniques to describe the structure of coal. This paper related to the distribution of carbon atoms in a single poly-cyclic aromatic (PCA) layer (graphene) in Tirap coal from Assam, India. The pair distribution function (PDF) analysis performed indicates no evidence of any graphite like structure in this coal. The aromatic fraction in this coal is 74% with aliphatic fraction correspondingly estimated to be 26%. The average carbon atom has 2.6 nearest carbon atom neighbors at an average bond distance 1.50 Å. The first significant maximum of pair distribution function is at 1.5 Å which relates to the C-C aliphatic bond length. The second maximum at 2.6 Å which relates to the distance between carbonatoms of aliphatic chains that located across one carbon atom. The γ-band is observed at a d-value 4.24 Å.