DIRECT IMAGING OF COAL PORE-SPACE ACCESSIBLE TO LIQUID-METAL

The pore space in coals which is accessible to a liquid metal such as mercury has been directly imaged for a rank suite ranging from a lignite up to an anthracite. The experimental protocol used was designed to simulate mercury infiltration porosimetry (MIP). A quenchable liquid metal, Wood's alloy (melting point approximately 70-degrees-C), was used in place of mercury. Analysis of each of the samples was performed by scanning electron microscopy. The results indicate that the metal-accessible pores in the lowest rank coal in this report are roughly cylindrical. The spatial distribution of such pores, however, indicate that they constitute a highly rough, topologically complex particle surface, and not an interconnected cylindrical pore network. Volume-pressure relationships derived from MIP result from the pressure-dependent wetting of this coal's surface. Pore space accessible to liquid metals in bituminous and higher rank coals was composed entirely of microcracks. Volume-pressure relationships which apply during MIP analysis for higher rank coals should be quantified in terms of microcrack width, rather than cylindrical pore radius. Finally, hysteresis commonly observed at the conclusion of MIP may reasonably be attributed to variations in width along microcrack surfaces. These irregularities behave like aperture-cavity pores.