Direct Observation of Nanostructure in Ductile Deformed Coals Using High-Resolution Transmission Electron Microscopy

Ductile deformations damage the macrostructure and impact the nanostructures of coal. New nanostructures can be formed in the layered macromolecular structures by dislocation climb and slip caused by ductile deformation, and the crystallinity of carbon in coals can be affected importantly by the potential energy caused by ductile deformation. In this study, high-resolution transmission electron microscopy (HRTEM) was used to observe the nanostructures of six different types of ductile deformed coals, and its effect on the storage and migration of absorbed gas was discussed. The results show that (1) clear lattice fringe images and nano-sized graphitic carbons with texture similar to carbon nanotubes are observed in ductile deformed coals. The nano-sized graphitic carbons are deemed to be a very low degree of crystallinity of graphite. Futhermore, oxidants (Fe3+ and O-2) observed in Energy Dispersive Spectrometer (EDS) spectra may be the metal catalysts during the nano-sized graphitic carbons formation process; (2) metamorphic grade and tectonic deformation play an important function on coal nanostructures. With the increase of metamorphic grade and tectonic deformation, the macromolecules at the thin edge prone to orientation, growth and realignment, which gradually affect the interior of coal nanostructure, and the layers of nanosized graphitic carbon increase greatly with the ductile deformation rank; (3) strong deformation can affect the coal adsorption capacity by changing the pore size distribution and macromolecular structures. This ultimately makes the adsorption capacity of tectonically deformed coal higher than that of the normal structure coal