Effect of high-temperature environment of mine goaf on pore and fracture of coal

• The coal sample heat-treated under nitrogen produced strip-shaped fractures and debris under the action of thermal stress. • Nitrogen will reduce the process of coal-oxygen reaction to a certain extent. • The coal sample heat-treated under air atmosphere melted and produced more pores. • As the temperature increased, the pore volume of the heat-treated coal sample under air first increased and then decreased. To study the evolution law of pores and fractures in the process of injecting nitrogen to prevent and extinguish fire in the goaf of coal mines. With the help of a self-built high-temperature tube furnace, the coal samples were processed under different temperatures and gas atmospheres. Through comprehensive use of electron microscope scanning, low temperature nitrogen adsorption, and 13 C NMR, the pores and fractures development rules of coal before and after heat treatment were researched. The coal samples heated in nitrogen atmosphere produced many strip-shaped fractures and coal debris, while the coal samples heated in air atmosphere produced many pores and an evident melting phenomenon. In addition, the proportion of carboxyl groups in coal samples heated in nitrogen atmosphere was always greater than that of the coal heated in air atmosphere. The pore specific surface area and volume of coal samples heated under air atmosphere increased significantly, while the degree of development was significantly reduced in nitrogen atmosphere. Thereby weakening the coal-oxygen reaction to a certain extent and inhibiting the generation of harmful gases (CO, CH 4 , etc.), which is conducive to preventing coal spontaneous combustion disasters.