Advanced pulse EPR study of natural Mongolian coals

Abstract

EPR spectra of the studied coals were registered as the first derivative of the microwave absorption versus applied magnetic field. The parameters of the EPR spectra: g-factor, linewidth and integral intensity were evaluated. As mentioned above lower group coals and high rank coals from upper group are declined to the asymmetry and the appearance of dip in the field swept. Consequently, the phenomenon could be assigned to the coal different maceral types that have different spin-spin relaxation times. The relaxation times for the coals have been measured in a few cases. It is well known that relaxation times determine both saturation and linewidth. Coal spin-lattice time, T1, relates with the coal spin concentration and molecular motion and the coal spin-spin relaxation time, T2, relates to the linewidth. The results of T1 and T2 relaxation times of some coals are shown as dependences of linewidth and the elements contents. For the characterization of the paramagnetic species in coal, we have also applied hyperfine sublevel correlation spectroscopy (HYSCORE) method. This method enhances the frequency resolution of the spectrum that makes possible to observe hyperfine structure under the symmetrical, singlet, broad EPR signals.