Diagnostics of carbon gasification by raman microprobe spectroscopy

Abstract

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 (PC) and South African (SA) coal. Samples of the untreated carbons and samples that were heat treated in nitrogen at temperatures in the range 500–2000°C for different times were characterized by (1) thermogravimetric analysis in air at 500°C and in CO 2 at 900 °C 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 nano-meters, 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 sumples of the two carbons that were heat treated up to 1200°C for 30 min holding time. In this range of heat treatment conditions, the ratio between the intensity of the low and high wave numbers correlated satisfactorily with both O 2 and CO 2 char gasification reactivity. Small changes in Raman properties were observed for more severe heat treatments, despite further reactivity loss corresponding to such treatments.