Catalytic role of mineral matter in structural transformation of anthracites during high temperature treatment

Abstract The ability of anthracites to graphitize is related not only with their microtexture (basic structural units, BSUs, arrangement), but also with the presence of certain inorganic elements that make up part of the coal mineral matter, allowing enhancement of the ordering of that microtexture in carbon materials. It was found that, despite the initial arrangement of the BSUs, the greater the amount of ash content the greater the crystalline ordering ( d 002 X-ray diffraction parameter) achieved by the high temperature treated materials. The mineral matter also promotes the coalescence of the crystallites in the direction of the basal plane ( L a parameter). Moreover, the development of graphite-like particles (flakes, microspheres, and crystalline aggregates) seems to be also related to the presence of inorganic material. The mineral matter present in a set of coal samples was found to lead to the formation of carbides (by carbothermal reactions) during high temperature treatment. The carbides may act as a catalyst and/or as a template for the formation of those graphite-like structures. Further increasing the temperature of treatment allows the catalyst to sublimate or decompose, while the graphitic carbon remains in the sample because it is more stable at higher temperatures.