ADVANCED ELECTRON PARAMAGNETIC RESONANCE (EPR) TECHNIQUES FOR THE STUDY OF COAL STRUCTURE

Publisher Summary This chapter describes the advanced electron paramagnetic resonance (EPR) techniques for the study of coal structure. The chapter presents a few experiments that were performed on two series of samples: (1) the isolated coal macerals and (2) a series of as-received samples of Argonne Premium Coal samples. The pulsed EPR experiments were run at microwave frequencies from 9.1–9.4 GHz. The relaxation measurements were performed at room temperature, while the double resonance measurements were done at −100K. For the double resonance experiments, the frequency of the radio-frequency field used to excite the protons was swept from 1 to 30 MHz. The relaxation properties of the isolated vitrinite macerals as a function of coal rank probe the interactions of radicals in the coal. Instantaneous diffusion contributes to phase memory loss in higher rank coals and can be separated from the asymptotic phase coherence decay rate, Tml−1, which is the EPR analog of T2. The Tle−1values are more than an order of magnitude smaller than Tml−1 in all cases.