MICROSCOPE PHOTOMETRY IN STUDIES OF THE MOLECULAR-STRUCTURE OF CARBONIZED BITUMENS AND PYROBITUMENS

Four bitumens and pyrobitumens (gilsonite, grahamite, impsonite and shungite), varying considerably in their initial properties, have been carbonized over the temperature range 0–1400 °C. Reflectances of the carbonized products in air and immersion oil were measured at 546 nm using a conventional microscope photometer, and the effective bireflectances. refractive indices and absorption coefficients calculated for the samples from the reflectances. The results obtained support an earlier suggestion that the derived optical data can be used to supplement X‐ray lattice parameters as a means of tracing the general course of molecular and structural organization of organic materials when these are carbonized, viz: (a) continuously rising bireflectance and absorption coefficient with rise of preparation temperature respectively indicate progressive ordering of the aromatic lamellae and increasing average diameter of the sheets of aromatic layers forming the‘crystallites’; while (b) systematic changes of the effective refractive index point to interruptions in the growth of the heights of the aromatic‐layer stacks in the crystallites. The optical variations are paralleled by changes in the patterns of the X‐ray lattice parameters for the same samples, which estimate directly the aromatic‐layer diameters (La), the average number of aromatic layers in the stacks (Lc) and the average spacing of the aromatic layers (d). Although the trends followed by the optical properties of the carbonized products of the bitumens and pyrobitumens are generally similar, in detail they show variations that can be related to the initial character of the fresh materials. The carbonization process, as it affects bitumens and pyrobitumens, is briefly discussed in the light of these results. 1979 Blackwell Science Ltd