INTRINSIC RATES OF NOX-CARBON REACTIONS

The noncatalytic reactions of NO2, NO, N2O, and O2 with graphite between 400 and 700-degrees-C have been studied by scanning tunneling microscopy to obtain quantitative kinetics by measuring the number and size of monolayer pits on the basal plane versus temperature and time. At low temperature, the reaction initiates exclusively from the point defects on the basal plane to form monolayer pits. The monolayer etching rates follow the order of r(NO2) > r(N2O) > r(NO) > r(O2). The activation energies for these reactions are determined to be 60, 90, 74, and 127 kJ/ mol, respectively. At high temperatures, instead of the recession of the monolayer pits, direct abstraction of the atoms on the basal plane of graphite becomes significant. This produces more active sites for monolayer pit nucleation, thus enhancing the total rate of reaction. N2O has the highest rate of basal plane attack. The rates of basal plane abstraction follow the order of R(N2O) > R(NO) > R(O2) > R(NO2). Also, the formation of stable (CN)x polymer during the graphite-NO(x) reaction below 700-degrees-C has been confirmed by transmission electron microscopy, atomic force microscopy, Auger electron spectroscopy, and electron energy loss spectroscopy.