Diagnostics of carbon gasification by Raman microprobe spectroscopy

The objective of this study is to examine the possibility of using Raman microprobe spectroscopy to investigate the effects of heat treatment on the evolution of reactivity and morphology of carbons. In this study, two carbons were used: petroleum coke IPC) and South African ISA) coal. Samples of the untreated carbons and samples that were heat treated in nitrogen at temperatures in the range 500-2000 degreesC for different times were characterized by (1) thermogravimetric analysis ill air at 500 degreesC and in CO2 at 900 degreesC and (2) Raman microprobe spectroscopy in the range 200-2500 cm(-1). The effects of mineral matter on Raman spectra were found to be negligible. Since the Raman scattering depth is a few tens of nanometers, it is believed that a carbon layer larger than that coats mineral matters. A good correlation was found between gasification reactivity and Raman properties for samples of the two carbons that were heat treated up to 1200 degreesC for 30 min holding time. In this range of heat treatment conditions, the ratio between the intensity of die low and high wave numbers correlated satisfactorily with both O-2 and CO2 char gasification reactivity. Small changes in Raman properties were observed for more severe heat treatments, despite further reactivity loss corresponding to such treatments.