To characterize chemical structure of oxidized coal, solid state 13C NMR spectra were acquired for two kinds of coal X and Y before and after estimation of their self-heating property by using R70 apparatus. It was found that coal X with higher oxgen concentration reached 80°C in shorter time than coal Y. The oxygen functional group most generated in coal Y during oxidation was found to be aldehyde and ketone, while that in coal X was found to be carbonyl. It is suggested that generation of aldehyde and ketone, and carbony might occur at less than 80°C. In addition, it is indicated that the kinds of oxidation reactions were diffrent between coal X and Y.
