Experimental Study on the Microstructure of Coal with Different Particle Sizes

In the study of coal pore structure, the traditional test method does not consider the influence of coal particle size. During the crushing process, coal samples are affected by crushing stress. While the particle size changes, the change characteristics of pore structure and macromolecular structure are a matter for which systematic research is still lacking. In this paper, mercury injection and liquid nitrogen were used to characterize the pore structure of coal. It was found that the porosity, total pore volume and total specific surface area of the coal increased with the decrease of particle size. However, during this process, the pore volume of macropores and mesopores decreases, while the micropores and transition pores increase significantly, indicating that while the particle size decreases, macropores and mesopores are broken into micropores and transition pores. In addition, the pore structure of samples with a particle size less than 200 mesh changes significantly. With the decrease of coal particle size, the areas of the D peak and G peak of the Raman spectrum increase, indicating that the ordering degree of coal increases. Finally, the statistical results of the peak area of the Fourier infrared spectrum show that alcohol, phenol, ammonia hydroxyl and fatty hydrocarbon CH 2 and CH 3 are greatly reduced, while the out-of-plane deformation vibration of alkyl ether and aromatic structure C–H are significantly increased, which also indicates the transformation of the coal macromolecular structure to an aromatic structure with strong stability.