2006 Volume 92 Issue 3 Pages 122-126
High temperature in-situ EPR studies were carried out to evaluate the thermoplastic and re-solidification characteristics of coal during heat treatment. The change in EPR spectra up on heating demonstrated the differences of coking properties of sample coals. The peak-to-peak height, ΔIpp, of spectra for coking coals showed minimum value at around the maximum fluidity temperature. This decreases in ΔIpp is supposed to result from the relaxation of aggregate structure of coal molecules. At higher temperature range, above the re-solidification temperature of sample coals, the peak-to-peak line width, ΔHpp, decreased with increase in temperature. Since the ΔHpp, is affected with spin-hydrogen interaction and spin exchange interaction, the decreases in the value of ΔHpp indicate the development of polyaromatic structure during heat treatment. In order to evaluate the coking properties of coal quantitatively, curve fitting was attempted for the EPR spectra obtained during heat treatment. The EPR spectra were deconvoluted into three components. The change in spin concentrations calculated from the components clearly exhibited the differences of coking properties of sample coals.