Abstract
At present, there are few studies on the development, evolution, and quantitative analysis of internal pores and cracks after heat treatment of coal. On the basis of this, low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray diffraction (XRD) experiments were carried out on five kinds of temperature-treated bituminous coal and anthracite. The pore cracks of coal samples were studied qualitatively and quantitatively using linear fitting and the fractal theory. Through the analysis of the original diffractograms in the XRD experiment, the quantitative analysis of mineral composition in coal was realized. The results show that, with the increase of the temperature, the thermal damage of coal changes obviously and the micromorphology of the coal surface changes from the initial compact structure to the appearance of pores and small cracks and then to the mutual connection and evolution into large cracks. The development of pores and cracks of bituminous coal is more obvious than that of anthracite. Because anthracite has better heat resistance, there is no expansion and crack in its internal structure during the experiment. Through the fractal calculation of the coal nitrogen adsorption capacity, it is obtained that the overall pore volume and specific surface area of bituminous coal and anthracite are positively correlated with the fractal dimension (D 1) of the pore structure and V daf is negatively correlated with the fractal dimension (D 2) of the pore surface. In the temperature range from a normal temperature to 100 °C, the mineral crystal structure inside the coal body changes significantly, a large number of pores appear on the coal surface, and the total pore volume increases accordingly to reach the measured maximum value. The research of this paper is of great significance to reveal the effect of the temperature on coal damage and deformation and crack evolution.