Micro-Raman Spectroscopy Study of 32 Kinds of Chinese Coals: Second-Order Raman Spectrum and Its Correlations with Coal Properties

Coal property and structures of 32 kinds of Chinese coals were investigated from the insights of second-order Raman spectrum using micro-Raman spectroscopy. A new deconvolution method for the second-order Raman spectrum of coal has been established, and the spectrum from 2100 to 3400 cm–1was curve-fitted by eight Gaussian bands successfully. The results indicate that the bands at 3060 and 2810 cm–1are sensitive to the volatiles content in coal and the bands at 2925, 2670, and 2480 cm–1are related to the more ordered structures of coal. Reasonable correlations between the second-order Raman bands area ratios and coal property parameters have been found, and an effectively comprehensive method for evaluating the coal property based on a second-order Raman spectrum has been built. The results reveal that the C–H and amorphous carbon structures increase with the increase of volatile content in the coal but have no obvious relationship with the fixed carbon content. Besides, the order degree of coal structure has a good positive correlation with the ratio of fixed carbon to volatiles content in the coal. This study demonstrates that the second-order Raman spectrum can reveal useful structure information on coal and provide a new approach for evaluating coal properties.