用电子自旋共振谱研究我国一些煤的自由基

THE ESR STUDY ON FREE RADICALS IN CHINESE COALS

本文用电子自旋共振谱(ESR)研究了我国十种不同变质程度的煤。电子自旋共振最重要的参数是g值、自由基的浓度、线宽和线形。用这些参数与煤中的碳、氧等元素相关联,发现ESR参数与煤的变质程度有密切关系。

The electron spin resonance (ESR) of 10 coals with different rank has been studied. The ESR parameters of interest are lineshape, linewidth, g value and integrated intensity of the observed signal. All spectra were recorded at room temperature by JES-3BX ESR spectrometer. Polycrystal DPPH was used as the standard for g value and concentration measurements.(1)Spin concentration: The data showed the concentration of unpaired electrons in vitrains increase with increasing carbon content up to approx 93%, after which they decrease rapidly. This suggests the are increasingly delocalised over aromatic rings and stabilised by resonance with the condensation of the ring system. But as electric conductivity increases in coals with more than 93%C, the free radicals will be destabilised.(2)Linewidth: The spectral linewidth are in the range of 4.38-5.85 gauss. It is due to unresolved hyperfine intraction between unpaired electrons and protons in coal. For the vitrains studied, an increase in ESR linewidth was observed in the stage from lignite to lower-rank bituminous coal,followed by a decrease higher-rank bituminous coal to semianthrecite and a sharp increase for anthracite.(3)5 value: The g values are in the range of 2.0026-2.0034. The lower g values are always accompanied with higher C% and lower O% content,because the g values of hydrocarbons radicals are lower than those radicals containing oxygen or other hetero-atoms.The high g values for low-rank coals can be explained by localization of unpaired electrons on hetero-atoms. As the carbon content increases and oxygen content decreases, the g value decreases for the radicals become localised on aromatic hydrocarbons. With the formation of graphitic the g value increases again structure by condensation of aromatic rings.