Study on micro-mechanical properties of bituminous coal surface based on AFM characterization technology

As a natural porous medium, coal has strong heterogeneity in its microstructure. To further study the differences in microstructure and mechanical properties of different coal bodies, four coal samples with different geological conditions in different mining areas were selected. Atomic force microscopy (AFM) with built-in PF-QNM mode was used to scan the micro surfaces of different coal samples. The results showed that there were significant differences in the micro morphology and mechanical properties between different coal samples. As the degree of metamorphism increased, the number of peaks on the micro surface of coal increased, providing more adsorption sites for gas adsorption. The average modulus of coal increases linearly with the degree of metamorphism. The surface adhesion force of coal shows an inverted U-shaped distribution with the degree of metamorphism, and the average surface adhesion force of medium rank coal is relatively high. The increase in micro surface roughness will increase the actual contact area between coal samples and substances, leading to an increase in adhesion force, while the generation of cracks will increase roughness but reduce micro surface adhesion force.