The structural alignment of coal and the analogous case of Argonne Upper Freeport coal

Abstract

It has long been recognized that coal is somewhat aligned. Multiple techniques imply a structural alignment but its quantification has been challenging. Moreover, discrepancies exist among techniques as to whether low-rank coals are aligned. The extent of structural alignment for the rank range was quantified directly via image analysis of high-resolution transmission electron micrograph lattice fringes. Alignment was quantified, for each coal, by the contribution to the total fringe length within the prominent 45° of orientation over random orientation (1/4 of the possible orientations). It was evident that there is structural alignment across the rank range. Thus it is time for the community to desist from making the erroneous statement that: low-rank coals are randomly oriented. The slight orientation was similar for low-rank Beulah-Zap lignite and Illinois No. 6 bituminous coals (24% and 22%) with Pocahontas (lvb) coal showing slightly greater (39%) alignment with extensive alignment (65%) in the case of an anthracite coal. The degree of ordering is illustrated with the aid of false-color lattice fringe images and Rose diagrams. The fringe contribution 90° opposed to the maximum length contribution had the minimum or near minimum percentage length contribution for all coals except Upper Freeport and to a lesser degree Illinois No. 6. For the Upper Freeport coal the alignment is lower than expected given its mvb rank (14% over random) and is attributed to a variant of T-stacking for the small aromatic moieties sited perpendicular and between horizontal displaced fringes.