Abstract
In order to explore the differences in the cracking effect of freeze-thaw cycles on coal of different coal grades, this study used liquid nitrogen to carry out freeze-thaw cycle cracking experiments on coal samples of anthracite and long-flame coal with two degrees of metamorphism. By combining a low-temperature nitrogen adsorption experiment and scanning electron microscopy, the surface cracks and pore structure development of water-saturated coal samples before and after freeze-thaw cycles were tested. Scanning electron microscope (SEM) test results show that the freeze-thaw cycle has an obvious destructive effect on the coal matrix. After three freeze-thaw cycles, the anthracite coal sample is obviously damaged, the coal sample is damaged, and the coal chips are peeled off. The surface of a long-flame coal sample is rough, the structure is loose, and the damage of the coal body is more serious by a freeze-thaw cycle. The results of the low-temperature nitrogen adsorption experiment show that the freeze-thaw cycle can effectively promote the development of the pore structure of the coal body. After three freeze-thaw cycles, the specific surface area growth rates of anthracite and long-flame coal samples are 69.57 and 49.13%, respectively. The pore volume growth rates were 73.01 and 35.54%, respectively. The increment of specific surface area and pore volume of the anthracite coal sample is lower than that of the long-flame coal sample, but the growth rate of specific surface area and pore volume of the anthracite coal sample is higher than that of the long-flame coal sample.