Fabrication and morphology control of highly porous mullite thermal insulators prepared by gelation freezing route

Mullite thermal insulators with high porosities of up to 91 vol% were fabricated using a gelation freezing method, resulting in a honeycomb-like morphology with micrometer-sized cells. Mullite particles dispersed gelatin based gels with and without an ice binding protein additives were frozen, dried under vacuum and sintered at 1500 °C. Ice binding proteins could inhibit the formation of large ice crystals and reduce cell size in insulators obtained. The thermal conductivity of the obtained thermal insulators ranged from 0.23 to 0.38 W/mK at room temperature. The compressive strength was measured to be 1.4–21.7 MPa. These properties could be varied by adjusting the process parameters of the gelation freezing. The method proposed here is a promising method of preparing ceramic insulators with very high porosity and improved strength.