Studies of the dependence of electron spin resonance on heat treatment temperature were carried out for coal carbons made from coals of various rank. The absorption curve of coal carbons changes from Gaussian type to Lorentzian type, the line width decreases and reaches a minimum, and the spin center concentration increases and reaches a maximum, over the range from HTT about 300-400ยฐC to HTT about 700ยฐC. The values of maximum spin center concentration for all coal carbons are of the same order, although for the untreated coals the spin concentration increases with rank. The line width for coal carbons increases rapidly and the spin center concentration decreases rapidly over the range from HTT about 700ยฐC to HTT about 900ยฐC. The estimate of the line width and of the spin center concentration is difficult over the range from HTT about 900ยฐC to HTT about 12OOW. The lines for coal carbons are broad and the changes in line width depend on the type of original coal above HTT about 1200ยฐC. A second maximum in spin center concentration is observed for coal carbons in the range of HTT 1200-2000ยฐC.
The maximum shifts to higher HTT with the increase of rank of the original coal.