Inference on carbon atom arrangement in the turbostatic graphene layers in Tikak coal (India) by X-ray pair distribution function analysis

Abstract

This paper communicates the distribution of carbon atoms in a single poly-cyclic aromatic (PCA) layer (graphene) in Tikak 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 is observed to be 74% with the aliphatic fraction correspondingly estimated to be 26% in this coal. The average carbon atom has 2.5 nearest carbon atom neighbours at an average bond distance of 1.50 Å. The average stacking height of the parallel aromatic layers (Lc) and the average diameter of the aromatic layers (La) are estimated to be 9.86 Å and 4.80 Å, respectively. For this coal, the average number of stacking layers and the average number of atoms per layer are estimated to be four and eight respectively. In addition, the gamma band is observed at a d-value of 4.34 Å. The comparison of the atom-pair correlation function to simulated one-dimensional structure function calculated for a model compound benzene (C6H6) also indicates that C6 unit is the major components in this coal. The average carbon atom has at least one and one nearest aryl and alkyl C-C atom pairs separated by 1.39 and 1.54 Å respectively. [Received: January 30, 2010; Accepted: March 21, 2010]