Nanoscale Pores in Coal Related to Coal Rank and Deformation Structures

Experimental results show that nanoscale pores in coal are affected by coal rank and deformation structures. In terms of pore volume, the transitional pores occupy the largest proportion, and in terms of specific surface area, the sub-micropores take up the largest proportion. For weak brittle deformed coal (including normal structured coal), when the coal rank increases, the volume and specific surface area of pores in different sizes firstly decrease and then increase. The volume and specific surface area of transitional pores and micropores in coal reach the minimum at about R-O,R-ran = 2.0%. After that, a slow increasing trend is observed. The volume of sub-micropores reaches the minimum at about RO, ran = 1.5% and then shows a trend of rapid growth as coal rank increases. As the degree of coal deformation increases, both pore volume and specific surface area have a significant increase. Under strong tectonic deformation, both the volume and total specific surface area of the nanoscale pores and of sub-micropores increase significantly; the volume of transitional pores increases moderately, and their specific surface area shows a decreasing trend; the volume and specific surface area increments of micropores decline rapidly as the degree of metamorphism increases.