20 °C, 9 GHz CW-EPR saturation measurements of five selected Alberta coals

Abstract

This paper reports the first determination of the spin-lattice (Tj) and spin-spin (T~) relaxation times at 20 °C for two subbituminous and three hv bituminous selected Alberta coals using 9 GHz CW-EPR saturation measurements.

Microwave saturation of EPR spectra of oxidised coal

“…The fast spin-lattice relaxation processes are characteristic of the multi-ring aromatic structures (narrow Lorentz 3 lines), and relatively slow spin-lattice relaxation processes occur in simple aromatic coal structures (broad Gauss and broad Lorentz 1 lines). The correlations between the coal structures and the spin-lattice relaxation times were confirmed by EPR and FTIR studies earlier [5,6,[13][14][15][16][17]. The influence of microwave power on the three component lines of the EPR spectra of the studied demineralised lignite is shown in Figure 3.…”

“…The paramagnetic centres of multiring aromatic structures corresponding to the Lorentz 2 lines, which were found in the earlier studied medium-rank coal (85.6 wt% C) [14], did not exist in the coal analysed in this work. The paramagnetic centres located at simple aromatic units of coal are responsible for broad lines [5,6,[13][14][15][16][17]. The paramagnetic centres of multi-ring aromatic units of coal, mainly delocalised π electrons, are responsible for narrow lines [5,6,[13][14][15][16][17].…”

“…Fig. 6 The influence of microwave power on intensities of component lines of the EPR spectra of demineralised Mequinenza lignite and oxidized in O 2 /Na 2 CO 3 system. Notations as in Fig.…”

“…Microwave saturation phenomena of coals and macerals have been observed by many researchers (e.g. [5,6]). The aim of this work was to study the changes in the microwave saturation of EPR spectra of coal upon its oxidation.…”