Characterization of thermal annealing effects on the evolution of coke carbon structure using Raman spectroscopy and X-ray diffraction

摘要

An experimental study was conducted to monitor the evolution of coke carbon structure during thermal annealing in a temperature range from 1 273 to 2 473K in a bench-scale reactor. Coke carbon structure was characterized by using Raman Spectroscopy and the X-ray Diffraction. The Raman spectra of most of the cokes displayed two broad peaks G* (1 620cm~(-1)) and D* (1 360cm"1). Both Raman peaks were deconvo-luted into five peaks namely G, D, D', R_1 and R_2. On the basis of area under the respective band peaks, new structural parameters were obtained to quantify graphitic (G), graphitic defect (D) and random (R) carbon fractions of cokes. XRD analysis was used to show that stack height carbon crystallite, Lc, of coke increases with increasing annealing temperature while the impact of annealing duration was not significant particularly up to 1 873 K. On the other hand, average carbon crystallite width, La, did not improve significantly up to 1 873 K, and increased rapidly after subsequent rise in the annealing temperature. It appears that during annealing up to 1 873 K, modification of coke carbon structure could occur due to loss of basal carbon as a consequence of in-situ gasification. The lateral expansion of carbon crystallite, La, was related to relative intensity or shape of Raman band peaks such that both parameters did not change significantly up to an annealing temperature of 1 873 K. At higher annealing temperatures, La values of coke increased with decreasing D/G ratio. Lateral expansion of carbon crystallite was attributed to progressive reduction of defects of graphitic carbon of coke, which can be monitored by D fraction of Raman Analysis. Combined Raman and XRD analysis suggested that rapid graphitization of coke may not occur along all dimensions until the annealing temperature exceeds 1 873 K. Combining XRD and Raman analysis would provide a comprehensive evaluation of the evolution of coke carbon structure at different temperatures and their subsequent implications on the efficiency of various ironmaking operations.