CW EPR study of natural Mongolian coals

Abstract

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.