A comprehensive analysis of various structural parameters of Indian coals with the aid of advanced analytical tools

Abstract

An exhaustive structural analysis was carried out on three Indian coals (ranging from sub-bituminous to high volatile bituminous coal) using a range of advanced characterization tools. Detailed investigations were carried out using UV–Visible spectroscopy, X-ray diffraction, scanning electron microscopy coupled energy dispersive spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. The X-ray and Raman peaks were deconvoluted and analyzed in details. Coal crystallites possess turbostratic structure, whose crystallite diameter and height increase with rank. The H/C ratio plotted against aromaticity exhibited a decreasing trend, confirming the graphitization of coal upon leaching. It is also found that, with the increase of coal rank, the dependency of I20/I26 on La is saturated, due to the increase in average size of sp2 nanoclusters. In Raman spectra, the observed G peak (1585 cm−1) and the D2 band arises from graphitic lattices. In IR spectrum, two distinct peaks at 2850 and 2920 cm−1 are attributed to the symmetric and asymmetric –CH2 stretching vibrations. The intense peak at ~1620 cm−1, is either attributed to the aromatic ring stretching of C=C nucleus.