Application of BIB-SEM technology to characterize macropore morphology in coal

We use broad ion beam (BIB) milling to prepare low-relief polished surfaces of coal samples for high-resolution SEM imaging, in a study of the morphology and distribution of macro- and mesopores. Results show that the BIB-sections of a few square millimeters are not large enough to be statistically representative so that porosity was investigated as a function of maceral type. For a vitrinite maceral type, we found comparably little visible macroporosity within the resolution limits of the SE detector. Less than 2% of all the meso- and macropores studied were found in vitrinites. Pore morphology in an inertinite maceral is dependent on the original maceral. Fusinite yields large, elongated pores (often filled with mineral phases), while macrinite shows comparatively smaller, rounder pores. The distribution of pore sizes follows a similar power law at different magnifications. Our results show that micropores and macropores in coal belong to different populations, with different size distributions and morphologies. BIB-SEM imaging is a useful tool to study meso- and macropore morphology, especially in the size range between 10 nm and 10 mu m, but more maceral types should be characterized for a better characterization of maceral porosity at different stages of coalification. (C) 2013 Elsevier B.V. All rights reserved.