Paper PS-ThP13
Characterization of a High-Temperature Flowing Oxygen Plasma Afterglow

Thursday, October 18, 2007, 5:30 pm, Room 4C

In the last decade there has been a renewed interest in developing ultra high temperature ceramic composites (UHTCs) as potential construction materials for parts of sharp leading edge hypersonic space vehicles. Oxygen atoms are known to play an important role in this application environment. Oxidation properties of UHTCs have been traditionally studied either in thermal furnaces which provide negligible dissociation of oxygen molecules or in arc-jet tests which dissociates all of them. To attain partially dissociated oxygen environments at low pressures and high temperatures which are better representative of the application environment, we are using a flow reactor downstream to a microwave discharge. To quantify the effect of oxygen atoms on the oxidation mechanism it is necessary to characterize the flow and oxygen plasma afterglow chemistry that the sample is exposed to during oxidation. This work discusses computational and experimental characterization of the reactor over a range of process conditions. There is a lot of uncertainty in the kinetic data available in the literature for high temperature oxygen plasma afterglow chemistry. Sensitivity analysis of the reaction chemistry will be carried out to determine the dominant reaction in the plasma afterglow at relevant pressure and temperature conditions. The output from this model, specifically the oxygen atom concentration reaching the sample, will serve as an input for the subsequent modeling of the oxidation mechanism in the materials oxidized using this set-up. Thus this characterization effort will help in better understanding the high temperature oxygen plasma afterglow chemistry and also the quantitative effect of atomic oxygen on the oxidation properties of various materials.