21 / 2023-05-14 11:24:08

Influence law and failure mechanism of adsorbed gas on coal microcrystal structure

Coal; Gas; Microcrystalline structure; Molecular dynamics simulation

Exploring the influence laws and failure mechanisms of adsorbed gas on the microcrystalline structure of coal is helpful to prevent gas accidents in coal mines. Five kinds of coal samples were studied by elemental analysis, solid-state ¹³C nuclear magnetic resonance, X-ray photoelectron spectroscopy, X-ray diffraction, isothermal adsorption experiments, and molecular dynamics simulation. The results showed that adsorbed methane destroyed the microcrystalline structure of coal, decreased the ductility L_a, and increased the aromatic layer interlayer spacing d₀₀₂. On the one hand, methane molecules need to absorb heat to maintain diffusion movement, which is provided by the release of coal molecules. The energy of coal molecules decreased, which made the order of microcrystalline structure decrease and the aromatic lamellae twist. On the other hand, the methane molecules preferentially adsorbed on the aromatic structure, which led to an increase in intermolecular force and collision probability between them. And methane molecules move in Knudsen diffusion between aromatic layers. This led to a large-amplitude twisting of the aromatic structure in the microcrystalline structure and a loosening of the aromatic ring arrangement.