Micro-Raman spectroscopy of carbonized semifusinite and fusinite

The purpose of the study was to present application of micro-Raman spectroscopy for examination of coal macerals and to characterize the internal structure of semifusinite and fusinite heated at 400-1200°C, in an argon atmosphere. Examination was performed on inertinite concentrates prepared from three samples of steam and coking bituminous coals (R_r=0.98-1.42%) from the Upper Silesian Coal Basin of Poland. Fusinite and semifusinite, as well as reactive and non-reactive forms of the latter maceral differ in terms of structural properties, as inferred from the Raman-derived parameters. Behavior of both macerals under heat-treatment is determined by their structural and chemical properties. Carbonization causes rebuilding of macromolecular network of semifusinite and fusinite resulting in the growth of polyaromatic units and, in case of the former maceral, also increases in structural organization. This is followed by significant reflectance increase. Semifusinite carbonized at 1200°C has larger coherent domains and they are more ordered than in fusinite, which results in higher reflectance value. The A_D3+D4/A_ALL ratio may be used as a measure of inertinite reactivity. Significant relationships between random reflectance (R_r) of semifusinite and fusinite and the I_D1/I_G ratio and position of most Raman bands (G, D1, D2 and D3) for the studied temperature range were found.