Transpiration cooling performance of carbon fiber oxidation-induced Mullite/Al2O3 porous ceramic composite for hypersonic vehicles

As a candidate for active thermal protection in next-generation hypersonic vehicles, transpiration cooling technology has an excellent capacity to reduce heat. However, it remains constrained by material scarcity with simultaneously adapted permeability and high-temperature endurance. To address this critical bottleneck, we developed an innovative Mullite fiber reinforced Al₂O₃ (Mullite/Al₂O₃) porous ceramic through a carbon fiber oxidation-induced approach combined with grinding-mold pressing-sintering process. The comprehensive properties of the ceramic, such as permeability, pore size distribution, high-temperature resistance, and thermal shock resistance, were systematically investigated. The results showed that the Mullite/Al₂O₃ porous ceramic features low density (1.35 g/cm³), good permeability (1.79 × 10⁻¹³ m²), uniform pore size distributions (3.6–10.3 μm), and excellent temperature resistance (>1500 °C). After 10 thermal shock cycles (1500 °C to 20 °C quenching), the ceramic retained 65.9 % of its initial compressive strength (31.08 MPa) and 52.0 % of its initial flexural strength (13.25 MPa). In addition, oxyacetylene flame tests on nose cones demonstrated remarkable transpiration cooling efficiency under 5.3 MW/m² heat flux. This study demonstrates the effectiveness of the synergistic fabrication strategy integrating carbon fiber oxidation-induced pore generation with mullite fiber reinforced architecture, validating the exceptional performance and thermal protection capacity under extreme aerodynamic heating conditions, providing a viable solution for hypersonic thermal protection systems.