Gasification Studies of Graphite Surface by Scanning Tunneling Microscopy

Carbon-gas reactions have been an important area of study over the past two decades. The basic mechanisms of carbon gasification are essential to understanding coal gasification. However, the studies of the inhibition and catalysis of carbon gasification have raised technical issues which have not been fully addressable until now. Some of these issues for catalytic gasification include: the effective particle size of the catalysts; the exact nature of bi-metallic catalysts; the interaction between carbon surfaces, gas, and catalyst; the percentage of the catalyst which is active; and catalyst deactivation mechanisms. The scanning tunneling microscope (STM) can address some of these issues. The purpose of this paper is to describe some preliminary work on applying STM to characterizing gasified carbon surfaces. Highly ordered pyrolytic graphite (HOPG) was gasified at 650° C for a net weight loss of 5 and 30%. The study has identified the tendency to develop high oxidation rate perpendicular to the basal plane despite the unfavorable thermodynamics of attack in this direction. The initial attack does not develop in the expected hexagonal pattern which develops after 5% burnoff. Oxygen on the surface can be identified by study of bond lengths in cross sectional analysis. Additional work is required to identify the exact nature of the oxygen structures, but the techniques developed in this study demonstrate that it is possible to follow gasification with the STM.