C-NEXAFS MICROANALYSIS AND SCANNING-X-RAY MICROSCOPY OF MICROHETEROGENEITIES IN A HIGH-VOLATILE A BITUMINOUS COAL

Carbon near-edge X-ray absorption microanalysis was applied to the study of the chemistry of. macerals in ultrathin sections of a high-volatile A bituminous coal. High-resolution images were obtained by exploiting variations in the intensity of carbon-edge fine structure far contrast. The macerals vitrinite, cutinite, and sporinite were distinguishable based on the relative intensities of two prominent absorption bands. The lower energy band, at 285.5 eV, was assigned to the transition of the core (Is) electron to the valence pi* MO; the absorption intensity correlated with the concentration of aromatic carbon. The higher energy band, near 288 eV, was assigned to a transition of an electron from the core (1s) to a mixed Rydberg/valence (C-H*) state; the intensity of this band correlated with the concentration of aliphatic carbon. Inertinite's inner-shell spectrum was distinct from those of the other macerals by a relatively intense 1s-pi* absorption band; absorption due to transitions to higher energy pi* MO's associated with polynuclear aromatics, moderate absorption near 288 eV, and a shoulder at 289.5 eV which was assigned to oxygen containing functionality. At the highest energies, E similar to 295 eV, absorptions due to transitions to sigma* states were present in the carbon spectra of each maceral type.