Abstract
Measurements were made of the velocities of longitudinal ultrasonic waves of frequency 2.5 MHz and selected parameters describing the coal extract structure, such as mean molecular mass, aromaticity factor and concentration of unpaired spins, for the tetrahydrofuran (THF) extract of Indian sub-bituminous Assam coal. The sample of Assam coal (carbon content 80.4 wt%) was collected from the Gondwanaland deposits, where coals are very different from European Carboniferous coals. Results were compared with the data obtained for THF extracts from Polish coals of various rank (64.9–85.6 wt% carbon) and an Indian lignite (54.1 wt% carbon). Absolute temperature coefficients of ultrasonic velocity b and absolute concentration coefficients of ultrasonic velocity a were determined from ultrasonic measurements performed in solutions in THF for THF extracts of brown and bituminous Polish coals, Indian Neyeli lignite and sub-bituminous Assam coal, as well as in solutions in pyridine (PY) for PY extracts from Polish bituminous coals. Correlations between the coefficients b and a and the mean molecular mass of coal extracts were found.
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