Progress of Raman spectroscopic investigations on the structure and properties of coal

Raman spectroscopy is a nondestructive and in situ analytical technique that could provide information on the chemical structure and structural ordering of carbonaceous materials. Based on theE(2g)symmetric stretching vibration mode in the aromatic layers (G band, ~1,580 cm(-1)) and the defect structure in graphite (D band, ~1,350 cm(-1)), Raman spectroscopy has been used extensively to characterize the structural features of carbonaceous matters since 1970. Coal is a complex organic compound made up mainly by carbon showing characteristic Raman bands. This article reviews the application of Raman spectroscopy for coal structure characterization under room temperature, to determine its chemical structure, crystallite size, coal rank, and combustion reactivity. Future research for collecting Raman spectra during coal pyrolysis at high temperatures is also discussed. The combination of high-temperature hot stage with Raman spectroscopy technology allows direct collection of Raman spectra at high temperature.