Boron nitride nanotubes (BNNTs) are a breakout reinforcement, structurally and thermally, needed for hot structures from 1650-2000 °C. BNNTs advance the state-of-the-art being as strong as carbon nanotubes plus superior oxidation and chemical resistance. The highest-quality BNNTs, which we recently started producing at industrial scale by methods improved from what earned our founders NASA Invention of the Year, now embody key performance parameters of being ultra-strong (63 GPa or above), highly flexible, lightweight, pure, highly crystalline (low-defect), molecular ceramic fibers. BNNT offers the strongest and lightest high-temperature reinforcement for ceramic matrix composite (CMC) hot structures, where, protected from oxidation, service temperature of BNNTs is at least 2000 °C. State-of-the-art BNNT reinforcement has significantly improved ceramic, e.g., SiCN, to 3.5x toughness, 2x hardness, 1.3x flexural strength (also SiON and ZrO2). This project adds hafnium oxide (HfO2) to SiCN/BNNT, so HfSiO4 forms a protective coating and protects within the volume to raise temperature thresholds. Project objective is to use BNNTs as sturdy, self-supporting, 3-D shapes infused with the pre-ceramic polymer precursor, SiCN doped with hafnium oxide (HfO2), and pyrolyzed to form a new polymer-derived ceramic (PDC) composite, BNNT/SiCN/HfSiO4. Phase I will develop techniques to fabricate reinforced ceramics for hot structures based on prior proofs-of-concept in other ceramic matrices. Coupons will be delivered for thermal and mechanical tests, arc-jet tests, hot-fire/combustion flame tests, plus complex shapes for additional tests. NASA applications start with uncooled propulsion components, combustion chambers, nozzles, and load-carrying aeroshell structures, leading edges, and heatshields subject to oxidizing environments and/or temperatures of 1650-2000 °C. Defense applications follow, starting with RF-transparent matrices for radar domes on aircraft traveling above Mach 5. Anticipated
Benefits: Uncooled propulsion system components, including hot gas valves, combustion chambers, nozzles, and nozzle extensions, and primary load-carrying aeroshell structures, control surfaces, leading edges, and heatshields, subject to oxidizing environments and/or temperatures in the range of 1650-2000 °C. Defense applications will reinforce RF-transparent ceramics for radar domes, and identical ceramics as for NASA can develop leading edges, control surfaces, and engine components for platforms exceeding Mach 5. Commercial applications need CMCs beyond current SiC/SiC (1400 °C), especially complex rotating shapes for aviation and power-generating turbines where CMCs are still viewed as too brittle.
