Vanessa J. Murray, David Z. Chen, Chenbiao Xu, Pedro Recio, Adriana Carocciolo, Chloe Miossec, Piergiorgio Casavecchia, Savio Poovathingal,Timothy K. Minton
DOI Number XXX-YYY-ZZZ
Conference Number HiSST-2022-122
Molecular beam-surface scattering experiments have been used to obtain fundamental data on gassurface interactions that are central to the ablation of carbon and silicon carbide (SiC) during hypersonic
flight through air. Specifically, the reactions of O and N atoms on high-temperature carbon surfaces
have been studied, and the reactions of O atoms and passive-to-active oxidation phenomena have been
studied on SiC. The reactive scattering dynamics of O on various carbon surfaces suggest that the
oxidation mechanisms on all sp2 types of carbon are similar but that surface morphology influences the
relative importance of the individual mechanisms. In addition to reacting with carbon to produce CO2
(minor product) and CO (major product), oxygen atoms may recombine on the surface to produce O2
with an efficiency that is somewhat lower than that to produce CO. Nitrogen atoms may recombine on
the surface to produce N2 or react to produce CN. The recombination efficiency of N atoms is generally
more than an order of magnitude higher than the reaction efficiency to produce CN. Even a small
percentage of N atoms in the presence of O atoms can increase the reactivity of O atoms on a carbon
surface by more than 50%. Impingement of O atoms on SiC forms an oxide layer at lower temperatures,
which decomposes through the release of SiO and probably Si atoms at approximately 1670 K. With
lower O-atom flux, a graphene-like layer persists on the surface at higher temperatures, but with a
higher O-atom flux, the surface ablates to produce CO and SiO products. By determining individual
chemical mechanisms at a molecular level, as well as their reaction probabilities, ablation models may
be developed that are not tied to a specific test environment.