This research collaboration between SRI International and Vanderbilt University will systematically investigate the influence of oxygen dissociation on the high temperature oxidation of ultra-high temperature ceramic (UHTC) composites and their constituents. Due to their high melting points and good dimensional stability under intense aerothermal heating, ZrB2/SiC and HfB2/SiC UHTC composites are very promising for sharp leading edge and control surface components of hypersonic vehicles. Research will specifically focus on the effects of atomic oxygen on (1) the boundaries between passive and active oxidation regimes, (2) the kinetics of passive and active oxidation, and (3) the composition, morphology, and optical properties of resulting oxide layers. Oxidation experiments will be conducted at SRI in a vacuum chamber equipped with a high-power microwave discharge for producing atomic oxygen and a CO2 laser for sample heating, as well as in a unique laboratory-scale arc-jet facility. In situ diagnostics will include laser-based and mass spectroscopic species detection for monitoring the presence and concentrations of gaseous reactants and products. Post-oxidation surface analyses will be performed at the University of Vanderbilt using a variety of characterization techniques to examine the composition, structure, and optical properties of oxide layers. The unique high temperature properties of UHTC composites can enable hypersonic vehicle designs with sharp leading edges - designs with much better flight capabilities than traditional blunt-body hypersonic craft. The results of this study will advance the fundamental understanding of UHTC oxidation behavior in dissociated oxygen environments and help pave the way for the application of UHTC components on hypersonic vehicles. The collaboration between SRI and Vanderbilt will also generate significant educational and research opportunities for undergraduate and graduate students, who will participate in all phases of the program. This project is co-funded with AFOSR (6.1).
