Nanopore Structure Analysis of Deformed Coal from Nitrogen Isotherms and Synchrotron Small Angle X-ray Scattering

The characteristics of nanopore structure of 12 deformed coals were studied using N-2 adsorption and synchrotron small-angle X-ray scattering (SAXS) measurements. The ductile deformed coal has greater surface area and pore volume, but smaller pore size than those of brittle deformed coal. The adsorption capacities shows that ductile deformed coal > brittle deformed coal at the relative pressure of 0.2-0.95, which is identical with the PSD (Pore Size Distribution) in different deformed coals. Smaller surface area (S-SAXS) and pore size in brittle deformed coal are calculated from SAXS, which means there are more smaller or closed pores in brittle deformed coal but more small open pores in ductile deformed coal. The fractal dimensions D-1 (P/P-0 range of 0-0.5) and D-2 (P/P-0 range of 0.5-1) obtained from N-2 adsorption represent the pore surface fractal of smaller pore and the pore structure fractal of bigger pore, respectively. Negative correlation between total surface area and D-1 is observed, but positive correlation between S-SAXS and D-s from SAXS. The negative correlation does not fit the fractal theory because of the dominant pores in PSD and changed surface area which affected by adsorption liquid.