Absorption of Ultra-violet and Visible Light by Ultra-thin Sections of Vitrinite from a High-volatile Bituminous Coal

Abstract

IT is a commonly held view that coals contain aromatic structures and that they become more graphite-like with increase in rank. X-ray studies have tended to confirm this concept ; however, recent work¹ has shown that small (about 100 atoms or less) aromatic and tetrahedral structures that have comparable numbers of atoms give rise to overlapping X-ray diffraction patterns in the angular regions of the (10), (11) and (20) reflexions of graphite-like layers. The question of distinguishing between the two types of structures will have to be resolved eventually by rigorous and more detailed X-ray or electron diffraction studies. Knowledge of other physical and chemical properties would be of great help in such structural analyses. It has been reported² that the extinction coefficients of a high-volatile A bituminous vitrinite in ultra-violet and visible light are too low to admit of an appreciable content of condensed aromatic structures. A detailed study of absorption became possible when we succeeded in cutting ultra-thin sections of coals of various ranks and in accurately measuring their thickness and refractive index by interferometry³.