1998 Volume 31 Issue 5 Pages 700-705
The oxidative reaction of OH radicals or O atoms with carbon black (CB) particles is studied by using a silent discharge reactor operated at room temperature and atmospheric pressure. The CB particles are oxidized by OH radicals or O atoms to produce approximately corresponding amounts of CO and CO2 through the silent discharge reactor. The OH radicals and O atoms are generated from the dissociation of H2O and O2 by silent discharge, respectively. The concentration of OH radicals is measured by resonance absorption spectroscopy while that of O atoms is estimated from a computer simulation by taking into consideration molecular dissociative reactions by electron impact.
The amount of CB particles oxidized gradually decreases in the high H2O concentration range in spite of an increase in OH radical concentration. It is considered that the surface reactivity of the CB particles decreases upon adsorption of H2O on their surfaces. On the other hand, the amount of CB particles oxidized with addition of O2 is almost independent of the O2 concentration. The CO and CO2 concentrations produced are correlated with that of O atoms, which is estimated from O3 concentration. These results indicate that the O atoms are much more reactive than the O3 molecules for oxidation of CB particles.
The sticking coefficient for oxidation of CB particles by OH radicals or O atoms is calculated from the experimental results. The OH radicals are more reactive than O atoms when H2O concentration is under 0.6%. However, beyond this value, the sticking coefficient of OH radicals suddenly decreases, and then becomes lower than that of O atoms.