Hierarchical porous (Ta 0.2Nb 0.2Ti 0.2Zr 0.2Hf 0.2)C high-entropy ceramics prepared by a self-foaming method for thermal insulation

To meet the emerging demands for thermal protection materials of hypersonic aircraft, developing porous ultrahigh temperature ceramics with both robust mechanical properties and superior thermal insulation performance is a critical challenge. Herein, we report a novel porous (Ta0.2Nb0.2Ti0.2Zr0.2Hf0.2)C high-entropy carbide (PHEC) ceramic fabricated by a self-foaming method using commercially available metal chloride and furfuryl alcohol as the precursor. The PHEC ceramic is constructed by 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 interface and nanosized pores in the PHEC ceramic. Due to its unique hierarchical structure, the prepared PHEC ceramic has outstanding compressive strength (28.1±2 MPa) and exceptionally low thermal conductivity at room temperature (0.046 W·m−1·K−1). This makes it a promising thermal insulation material in ultrahigh temperature application. This work provides a cost-effective and facility strategy to produce porous ultrahigh temperature ceramics.