Optical properties of oxidized resinite

Abstract

Resinite concentrate from a subbituminous coal ( R oil = 0.45%) was oxidized in air for 1 h intervals at fixed temperatures between 50 and 400 °C. The oxidized residues were examined using reflected white and fluorescent light microscopy. Three phases of oxidation were observed. Phase I (50–125°C) was marked by an oxidation rim with lower reflectance than the main mass of resinite, perhaps indicating chemisorption and decomposition of the chemisorbed components. Phase II (150–350°C) was apparent from the development of two oxidation rims, the outer of higher and the inner of lower reflectance than the main mass of resinite, perhaps indicating an ‘oxycoal’ phase. Phase III (〉 350° C) was marked by a sharp increase in reflectance of the outer oxidation rim and a similarity in reflectance between the inner oxidation rim and main mass of resinite, perhaps indicating a ‘combustion phase’. The fluorescence properties (colour, wavelength of maximum intensity and red-green quotient) of the oxidation rims shifted from green towards the red region of the spectrum with increasing oxidation temperature and were a good indicator of the progress of oxidation.