The evolutionary characteristics and mechanisms of coal chemical structure in micro deformed domains under sub-high temperatures and high pressures

Abstract To understand the physic-chemical evolutionary characteristics and mechanisms of coal chemical structure, sub-high temperature and high pressure coal deformation experiments were conducted by using the self-developed TRTP-2000 experimental system. The micro deformed features and the macromolecular structural characteristics of experimental samples were detected by various in-situ methods. With the decrease of strain rate, the ductile deformation features in samples gradually become distinct. Brittle deformation lead to the breakage of oxygen functional groups and side chains through the coupling of mechanochemistry and frictional thermal energy. Ductile deformation with a higher strain rate resulted in a total increase in aromatic carbon, a relative decrease in the disorder degree of the molecular structure, and a reduction in secondary structure defects respectively. While the excessive strain energy accumulation under ductile deformation at a lower strain rate can lead to the dislocation and slip of the aromatic layer in coal molecular structure and an increase in secondary structure defects. Besides, the alteration of coal molecular structure may increase the ultra micropore volume within coal that is critical for the retention of CBM.