Macromolecular Structural Responses of Coking Coal to Stress Strain Environments Based on High-Resolution Transmission Electron Microscopy

In China, most coal seams have experienced multiple phases of tectonics, which increase the complexity of the coal porosity. The responses of macromolecular structures to stress-strain environments are the key to understanding the complexity of coal porosity caused by tectonism. This study investigated the macromolecular structural response of coking coal to different stress-strain environments. The calculation and analysis of high-resolution transmission electron microscopy (HRTEM) test results for six coking coals with different deformation types and degrees were performed. The results showed that the macromolecular structure of coking coal has different responses to stress- strain environments. The lattice fringe length, curvature, and d(002) parameters are not prominently governed by certain principles increasing shear and toughness. Furthermore, the lattice fringe tends to be consistent with the deformation. However, the lattice fringe during ductile deformation in the main direction is arranged nearly parallel on the plane. In shear deformation, the lattice fringes are arranged parallel in the principal direction. This phenomenon is caused by the directional screening of the macromolecular structure of coking coal by stress. Under the action of tectonic stress, the structure hindering tectonic stress is destroyed, and the structure grows in other directions gradually under the promotion of tectonic stress. As a result, the direction of the whole lattice fringe gradually converges under stress screening after tectonic stress is applied. Therefore, the direction tends to be consistent with the strengthening of the deformation. The response of the other parameters is slow, showing the coexistence of the old and new orders of direction. The directivity of the macromolecular structure of coal is an important index for reflecting the types and degrees of tectonic deformation.