High Temperature Ablation of Vitreous Carbon in a Table-Top Shock Tunnel (TTST)

A table-top shock tunnel (TTST) has been constructed and is intended to allow rapid and low-cost measurements of shock-layer chemistry and material response in well-characterized high-velicity flows. The TTST is based on the production of pulsed hypersonic molecular beams by laser detonation in a conical nozzle. In addition to providing fundamental data for the development of models, the production of controlled shock layers above ablating and non­ablating surfaces and the measurement of their phenomenology provide a means to validate new models. Furthermore, material response can be tested in realistic environments and aid in the development of materials for hypersonics applications. With the use of the TTST, the ablation phenomena of vitreous carbon at high temperatures (1000 - 2000 K) have been investigated in a weak shock layer that is produced with a hypersonic atomic beam of 〜70% Oand 〜30% O₂ with a nominal velocity of 7.6 km s^-1 (for O atoms). Recession of the carbon indicates that the ablation rate initially increases with temperature and then reaches a plateau at higher temperatures. The morphology of the ablated surfaces shows round pits with diameters in the 1-100 μm range, which may be the result of catalytically enhanced reactivity in the vicinity of impurities. These experimental results are appropriate for an initial validation study of a carbon ablation model to be conducted with direct simulation Monte Carlo (DSMC) calculations.