THE ROLE OF SEMIFUSINITE IN PLASTICITY DEVELOPMENT FOR A COKING COAL

To help ascertain the contribution semifusinite makes to plasticity de velopment during carbonization, semifusinite and vitrinite fractions w ith purities over 90% have been obtained by density gradient centrifug ation from a medium-volatile Australian bituminous coal. In-situ H-1 N MR, during which the maceral concentrates were heated to 550 degrees C , has been used to determine the amount and mobility of fluid material developed. At maximum fluidity, the vitrinite fractions generate simi lar 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 (T-2's of over 70 mu s cf. 52 and 45 mu s, respectively). For the vitrinite concentrates, the increases in refle ctance and the degree of aromatic ring condensation with density corre late with the decreasing mobility of the fluid material. For the coal investigated, the overall contribution of the reactive semifusinite to the fluid phase at maximum fluidity is estimated to be 15% (ca. 4 of the 30% mobile hydrogen observed). Furthermore, there is a reasonably good linear relationship (R-2 > 0.96) between fluidity (for both the p roportion of the fluid material and its mobility or T-2) and density f or all the maceral concentrates investigated, and therefore, samples,v ith very similar petrographic composition can exhibit significantly di fferent fluidity characteristics. Although interactions between macera l groups may take place in the original coal matrix, mixtures of the v itrinite and semifusinite concentratres did not reveal any synergism.