Advanced pulse EPR study of natural Mongolian coals

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.Белорусский Республиканский Фонд Фундаментальных Исследовани

Advanced pulse EPR study of natural Mongolian coals

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.Белорусский Республиканский Фонд Фундаментальных Исследовани

A Study of Defects and Impurities in Doped Detonation Nanodiamonds by EPR, Raman Scattering, and XRD Methods

Samples of detonation nanodiamonds modified during the synthesis by adding doping elements in various ways have been studied by spectroscopic methods (electron paramagnetic resonance, Raman scattering, and X-ray diffraction). For the first time, the presence of P1 centers in detonation nanodiamond crystals has been indirectly demonstrated. The authors discuss the nature and distribution of spins as observed by the electron paramagnetic resonance, the composition of phases and size of the coherent scattering region, and crystal density (calculated by the X-ray method) of the detonation nanodiamond samples at hand

CW EPR study of natural Mongolian coals

Various EPR spectra of the studied coals were registered, e.g. symmetric or asymmetric, narrow and broad singlet. The EPR parameters of the spectra obtained in a flow of nitrogen gas are compared to the parameters in an air presence. The differences were observed in the EPR parameters such as line shape, peak-to-peak amplitude, line width and g-factor. As mentioned above the most of the cw EPR spectra of the studied coals are declined to asymmetry that can be from the complexity of the spin system. Therefore, complex character of the coal EPR spectrum is often visible at higher microwave powers, when some components partly saturated and the intensities of the others relatively increased. For this purposes, EPR microwave power saturation for each coal sample was measured. The dependence provides a measure of the interaction strength of the radical with the environment. In both cases EPR spectra of the studied coals are saturated differently. The saturation curve shows the one of components saturation character or broad (in the presence of air mostly) or narrow (in the flow of nitrogen gas mostly). The saturation curve shows the one of components saturation character or broad (in the presence of air mostly) or narrow (in the flow of nitrogen gas mostly). The EPR spectra with two components in the coal has discussed in many of works that mainly attributed to two types of macerals (fusain and vitrain, respectively) in the coal. This is also proved by the dependences of atomic hydrogen-carbon ratio of the studied coals that particularly the lower group coals show the complexity in their EPR spectra. The narrow component is alleged to the presence of fusain (or inertinite) that is composed mainly of fusinite or carbonized woody plant tissue. One can also assign it to the coal spontaneous combustion since the same EPR property has observed on particular samples taken from the place where the coal self-inflammation center is. It is clear from the measurement results that the broad line is much more easily saturated, exposing a relatively weaker narrow line at high microwave power. The appearance of the narrow line is coal rank independent.Белорусский Республиканский Фонд Фундаментальных Исследовани