Preparation of porous mullite ceramics for high-performance thermal insulation via freeze casting

Porous mullite ceramics typically suffer from a performance trade-off between low thermal conductivity and high compressive strength, which often limits their practical applications. In this work, freeze casting was employed to prepare porous mullite ceramics with lamellar structure. The effects of sintering regime and solid content on their microstructure and properties were systematically investigated to achieve the synergistic optimization of thermal insulation and mechanical properties. The results show that samples sintered at 1500 °C for 2 h exhibit an apparent porosity of 63.35% and a compressive strength of 13.83 MPa. At a solid content of 25 vol%, the samples achieve an apparent porosity of 54.62% and a compressive strength of 21.47 MPa with a thermal conductivity as low as 1.16 W/(m·K) at room temperature. In addition, high-temperature fire resistance tests visually demonstrate that porous mullite ceramics possess favorable thermal insulation properties.