ADVANCED LIGHTWEIGHT CERAMIC FOAMS FOR HYPERSONIC VEHICLES

ZrC-ZrB<sub>2</sub>-based ultrahigh-temperature ceramic (UHTC) foams were prepared by preceramic route using preceramic precursor resin, viz., boron-functionalized polyzirconoxane and polyurethane (PU) foam as the template. The structure and chemical composition of the as-procured preceramic precursor resin were analyzed using different analytical techniques for validating the resin for ceramic conversions. The Fourier transform infrared and nuclear magnetic resonance spectra confirmed the presence of phenolic carbon attached to oxygen, phenolic aromatic protons, olefinic protons, and Zr-O-B moieties in the polymer backbone. The weight percentages of C, H, N, Zr, and B were obtained as 60, 6.4, 1.3, 7.8, and 1.4, respectively, by carbon hydrogen nitrogen and inductively coupled plasma-atomic emission spectrometer. Thermogravimetric analysis and pyrolysis gas chromatograph mass spectrometer (Py GC-MS) results indicated that the precursor is a low molecular weight resin dissolved in low volatile solvents. The ceramic residue of the cured resin at 900°C was 50.5 wt. % and hence has the potential for use as a precursor resin for making ceramic products. The final UHTC foams were characterized for structural, chemical, and morphological properties and confirmed the formation of crystalline ZrC-ZrB<sub>2</sub> with an open cell structure. The thermo-oxidative stability of the UHTC foam was tested and characterized for its final morphology. The ZrC-ZrB<sub>2</sub> foams can find applications as thermal insulating core in thermal protection system (TPS) systems and as porous membrane for transpiration cooling of combustion chambers of hypersonic vehicles.