Exploring the spatial heterogeneity of coal pore structure via synchrotron radiation SAXS

Mesoscale pore structures fundamentally govern the adsorption, transport, and mechanical behavior of coal, yet characterizing their spatial heterogeneity remains a challenge. This study employs multi-point synchrotron small-angle X-ray scattering (SAXS) to probe the pore systems of six coals of different ranks and origins. Results show a spectrum of structural characteristics: the 1/3 coking coals exhibit highly isotropic pores (geometric radii: 3.06~5.65 nm), whereas anthracite and meager lean coal display pronounced anisotropy. Quantitative analysis reveals a clear heterogeneity ranking: anthracite shows the greatest spatial variation, with pore orientation angles varying by up to 23.4° and the radius of gyration ranging over 2.61 nm across measured positions. Furthermore, grinding and pelletization are found to eliminate anisotropy and reduce micropore scattering, also slightly decreasing the representative pore size (e.g., radius of gyration decreased from 8.54 nm to 8.39 nm for coking coal), while larger pores remain statistically unaffected. This work not only quantifies the spatial heterogeneity of coal pores but also reveals the profound impact of sample preparation, demonstrating that accurate characterization must account for both geological origin and physical morphology. These findings underscore the critical value of multi-point SAXS in elucidating coal's complex pore network.