Oxidation and nitridation of vitreous carbon at high temperatures.

Molecular beam-surface scattering experiments were used to obtain fundamental data on gas-surface interactions that are central to the ablation of carbon during hypersonic flight through air. Continuous beams containing O or N atoms with incident velocities of ∼2000 m s−1 were directed at a vitreous carbon surface at temperatures in the range, 800–1873 K, and the products that desorbed from the surface were detected with a rotatable mass spectrometer detector as a function of their velocity and scattering angle. All products exhibited the dynamical characteristics of thermal desorption. The efficiencies of the gas-surface interactions, both reactive and non-reactive, were quantified as a function of surface temperature. In addition to reacting with carbon to produce CO 2 (minor product) and CO (major product), oxygen atoms may recombine on the surface to produce O 2 with an efficiency that is somewhat lower than that to produce CO. Nitrogen atoms may recombine on the surface to produce N 2 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. The quantitative reaction efficiencies reported here are useful for the development of air-carbon models for hypersonic ablation. Image 1 [ABSTRACT FROM AUTHOR]