The role of semifusinite in plasticity development for a coking coal

To help ascertain the contribution semifusinite makes to plasticity development during carbonization, semifusinite and vitrinite fractions with purities over 90% have been obtained by density gradient centrifugation from a medium-volatile Australian bituminous coal. In-situ 1H NMR, during which the maceral concentrates were heated to 550 °C, has been used to determine the amount and mobility of fluid material developed. At maximum fluidity, the vitrinite fractions generate similar proportions of fluid material as the whole coal, accounting for 30% of the hydrogen, while the semifusinite fractions yield only ca. 15% mobile hydrogen. The mobility of the fluid material is significantly higher for the vitrinite concentrates than for both the whole coal and the semifusinite fractions (T2's of over 70 μs cf. 52 and 45 μs, respectively). For the vitrinite concentrates, the increases in reflectance and the degree of aromatic ring condensation with density correlate with the decreasing mobility of the fluid materi...