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To meet the emerging demands for thermal protection materials for hypersonic aircraft, developing porous ultrahigh-temperature ceramics with both robust mechanical properties and superior thermal insulation performance is a critical challenge. Herein, we report novel porous (Ta0.2Nb0.2Ti0.2Zr0.2Hf0.2)C high-entropy carbide (PHEC) ceramics fabricated by a self-foaming method using commercially available metal chloride and furfuryl alcohol (FA) as precursors. The PHEC ceramics are constructed of microspheres with a size of 2 µm, leading to a high porosity of 91.3% and an interconnected frame. These microspheres consist of high-entropy carbide grains (20 nm), resulting in abundant interfaces and nanosized pores in the PHEC ceramics. Due to its unique hierarchical structure, the prepared PHEC ceramics have outstanding compressive strength (28.1±2 MPa) and exceptionally low thermal conductivity (κT, 0.046 W·m−1·K−1) at room temperature. This makes it a promising thermal insulation materials for ultrahigh temperature applications. This work provides a cost-effective and facile strategy for producing porous ultrahigh-temperature ceramics.

Abstract A dense ZrB2 particles reinforced glass (ZrB2/SiO2) coating was prepared on the SiC coated carbon/carbon composites by a facile sol-dipping approach. The prepared ZrB2/SiO2 coating could protect the composites from being oxidized for 160 h at 1773 K with a weight loss of 6.9 mg/cm2. The flexural strength retention ratio of the ZrB2/SiO2 coated composites is 87% after oxidation for 160 h at 1773 K. The continuous SiO2 glass layer embedded with the submicron ZrSiO4 particles was formed during oxidation. This was helpful to lower the diffusion rate of oxygen and improve the stability of SiO2 glass film, thus improving the oxidation resistance of the coated samples. After thermal cycles between 1773 K and room temperature for 15 times, penetrated cracks formed in the coating. The weight loss of the ZrB2/SiO2 coated sample presented linear relationship, and the final weight loss per unit area was 6.35 mg/cm2. The generation of the penetrative cracks and the debonded coating interface resulted in the failure of the ZrB2/SiO2 coating.