Rafał Morga

Vitrinite reflectance property change during heating under inert conditions

Abstract The aim of the study was to determine optical properties of vitrinite, subjected to temperatures within the range of 400–1200 °C for durations of 1–7 h, in an argon atmosphere. The samples of vitrinite concentrate (Vt content 90%, R r =1.17%) were inserted in the furnace at room temperature and subjected to a heating rate of 60 °C/min. To assess the effects of the experiment, random reflectance as well as apparent maximum and minimum reflectances of vitrinite were measured on the raw and thermally treated concentrates. Employing the method and computer programme of W.E. Kilby, the true maximum, intermediate and minimum reflectances of vitrinite as well as reflectance anisotropy and Reflectance-Indicating Surface (RIS) shapes were evaluated. Transformation of vitrinite subjected to heating is influenced more by the increase of temperature than the time applied. During the plastic stage (400–500 °C), vitrinite is subjected to substantial chemical and physical alteration. It is manifested by chemical decomposition, significant mass loss and mesophase appearance. Porosity, relief, reflectance and bireflectance of the vitrinite grains increase with heating. At the temperature of 1200 °C, random vitrinite reflectance reaches 6.62% with bireflectance of 3.46%. Mesophase at 1200 °C was characterised by mean reflectance equal to 9.25% and a bireflectance of 13.35%. The reflectance character of vitrinite changes from biaxial negative into biaxial positive–negative. However, the original RIS shape, resulting from the tectonic regime during the main phase of coalification, is not fully transformed until heated to 1200 °C. Reflectance character of mesophase is consistently biaxial negative. The internal structure of mesophase is thought to be better organised than the internal structure of vitrinite.

Relationship between the maximum and the random reflectance of vitrinite for coal from the Upper Silesian Coal Basin (Poland)

Abstract The relationship between the maximum and random reflectance of vitrinite, Rmax and Rr, for Upper Silesian coal is represented by the equation: Rmax=1.090Rr−0.052. When the random reflectance is higher than 0.90%, the difference between Rmax and Rr values becomes significant. Rmax is a more precise rank indicator, the standard deviation is much smaller than the standard deviation of the random reflectance value, which is larger due to the optical anisotropy of vitrinite.