Comparative analysis of optical properties of coals by petrography and spectroscopy methods

Abstract

This paper reports determining the grayscale intensity of macerals in the coal lump polished sections oriented along and across the layering of three main groups of sub-bituminous, high volatile bituminous, low volatile bituminous coals. All measurements have been performed in white, red, yellow, green, blue light. The influence of all selected factors and most of their combinations on grayscale intensity is reliable; the most pronounced effects are established for the optical filter color and the maceral type. Comparative analysis of the grayscale intensity data array with the spectra of full reflectance in the visible region and the coefficient of diffuse reflection in the white light of fine powders of the same samples has been carried out. Green light yields a very dark image of vitrinite and liptinite with the grayscale intensity approaching zero. In two of the six samples, the reflectance level of inertinite in yellow light is significantly higher than the grayscale intensity of white light. This anomaly is associated with a hypsochromic shift in the inertinite maximum absorption. The approach used is an alternative method for quantifying the relative changes in reflectivity and position of the diffuse spectral minimum without applying a microspectrometer.

Fractal dimension of the morphology on differently oriented surfaces of coal preparations

“…The work [9] proposes a new method for determining the degree of metamorphism based on the index of gray shade intensity (GI) for microphoto images of lump sections in coal preparations with subsequent digital computer processing. Subsequently, the spectral characteristics of this method were refined [10]. In these works, the choice of maceral for research (vitrinitis) and the orientation of the observation plane in the preparation (cross-section) were justified, which does not contradict existing standards [11].…”

Petrographic and technological aspects of improving the methodology for alternative determination of the degree of carbonification

“…To some extent, this is naturally related to the available equipment. Earlier, in work [6], a statistical analysis of the influence of the spectral characteristics of optical and photometric devices used in the proposed method was carried out. The analysis showed that the influence of all selected factors Color, Macerals, Rank, Bedding, as well as most of their combinations, on the GI indicators significant, and the chosen approach is an alternative method for quantifying relative changes in the reflectivity and position of the diffuse spectral minimum without using a micro spectrometer.…”