Abstract
Vitrinite from Polish medium-rank coal (85.6 wt% C) heated in an inert atmosphere at 300–650°C was investigated by electron paramagnetic resonance in the X-band (9.3 GHz). The e.p.r. spectra of the vitrinite, recorded using different microwave powers, were approximated by superposition of a Gauss line and two Lorentz lines. The g factor, linewidth of the components and their fraction in the total spectrum were determined. A sharp increase in total concentration of paramagnetic centres after heating above 550°C was observed. Strong quenching and production of paramagnetic centres with broad Gauss and broad Lorentz lines above 550°C were detected. The heating of the vitrinite only slightly influenced the amount of paramagnetic centres with narrow Lorentz lines. The saturation behaviour of the all measured e.p.r. lines depended on heat-treatment temperature.
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