Study on the Differences in the Microstructure between Outburst and Nonoutburst Coal.

Regarding the incomplete understanding of the influence mechanisms of microstructural differences in coal on outburst propensity, this study selected typical outburst and nonoutburst coal samples for comparative experimental investigations. The microchemical and pore structure characteristics of coal samples were systematically characterized through analytical techniques including Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and low-temperature liquid nitrogen adsorption experiments to elucidate how these microstructural features influence their outburst propensity. The results of the study show that outburst coal samples possess a higher degree of aromaticity, with hydrogen atoms migrating to new chemical environments that give rise to abundant, low-crystallinity nascent primary aromatic hydrocarbons and substantial CH generation. Concurrently, the number of oxygen-containing functional groups in the coal is less, and the coal samples have a stronger adsorption capacity for gas. In outburst coal samples, the spatial structure of macromolecular structures is chaotic and disordered, and discontinuities or defects in the microcrystalline framework lead to an increased micropore content. Comparison of the pore structure characteristics of the outburst and nonoutburst coal samples revealed that the outburst coal samples had more total pore volume, more pore content of the coal body per unit volume, and a thinner coal body skeleton, which made the coal body less resistant to damage. The proportion of micropores in the outburst coal samples is even higher and is dominated by fine-necked bottleneck holes and wedge-shaped holes, which increases the resistance to gas desorption and the residual gas content of the coal body and increases the risk of coal and gas outburst. This study provides a theoretical basis for understanding the influence of coal microstructure parameters on coal outburst characteristics.