Characterization of the chemical structure of tectonically deformed coals

Tectonic deformation damages the macromolecular structures of coal. No evidence can be found of tectonically deformed coal (TDC) structures, in which traces of lattice defects exist. In this study, the mechanisms of ductile deformation and the evolution of the molecular structure have been investigated using coal samples collected from one thrust fault in the Qinan Coal Mine of China. Various characterization methods, such as Raman spectroscopy (Raman), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) imaging, were employed to explore the macromolecular structure parameters and related information that can be derived from coal subjected to ductile deformation. The results show that the full width at half maximum (fwhm parameter) for D1 of ductile deformation coal is greater than that of brittle deformation coal as a result of its high content of defects in the graphitic structure. The difference in the ratio of the -CH- and -CH functional groups indicates that coals that undergo brittle deformation have a much higher content of aliphatic chains compared to coals that undergo ductile deformation. Defects may result from the breaking of C=O bonds in coal macromolecules, given that the maximum energy of broken C=O bonds is less. Hence, the content of C=O functional groups is less in TDCs than in primary structure coals. Evidently, high shearing stress leads to strong ductile deformation, while brittle deformation is related to the breaking of a series of bonds as a result of tensile stress and direct bond breakage. Ductile deformation, which is more likely to be related to point and line defects, leads to the assessed changes in the carbon structure