Abrupt changes (jumps) in reflectance values and chemical compositions of artificial charcoals and inertinite in coals

Abrupt changes (jumps) in reflectance values and chemical compositions of charcoals during heating experiments in muffle and thermal gravimetric analyzer ovens occur at mean maximum reflectance values of about 0.50-0.60%, 1.10-1.20%, 1.40-1.50'%, 2.20-2.30%, 2.80-2.90% and 3.70-3.90% (R-max). These abrupt changes are similar to the so called 'coalification jumps' in vitrinite or liptinite in coals. Jumps are much more notable in low temperature charcoals (formed at less than 400 degrees C) than in high temperature charcoals (formed at greater than 400 degrees C). Abrupt changes in chemical composition are coincident with jumps in reflectance as evident from sudden decreases or increases in functional groups as determined by FTIR-spectra. The jumps in composition of charcoals (intertinites) during charring experiments explains the multi-modal reflectance distributions commonly documented in coals. The distribution of reflectance values and FTIR spectral characteristics of inertinite in some Western Canadian coals is consistent with a model of charring that incorporates discrete compositional jumps. The 'jumps' in reflectance values and chemical compositions probably reflect progressive breaking of chemical bonds in response to attainment of specific threshold activation energies. (C) 1999 Elsevier Science B.V. All rights reserved.