Sugar blowing induced honeycomb porous mullite powders with low thermal conductivity and thermal stability

Mullite powder has excellent thermal stability and low thermal conductivity, which make it ideal for thermal insulation, aerospace, and refractory applications. However, conventional synthesis methods have limitations in controlling the microstructure and properties of materials. Herein, a simple sugar blowing method was used to successfully prepare highly porous mullite powders with a three-dimensional honeycomb structure. The honeycomb porous structure was attributed to the synergistic effect of glucose and NH 4 Cl, which caused the matrix to blow and expand. This synergistic effect promoted a pressure-equilibrium between the internal gas and the surrounding matrix, resulting in a controlled expansion and self-organization into hexagonal pore geometries. The effects of glucose/NH 4 Cl molar ratio and synthesis temperature on the microstructure and thermal stability of mullite powders were investigated. Mullite powder prepared with a glucose/NH 4 Cl molar ratio of 1:4 at 1200 °C exhibited the lowest thermal conductivity (0.0456 W·m −1 ·K −1 ), which was directly attributed to its hexagonal honeycomb pore structure. The structure reduced thermal conductivity through the dual mechanism of reduced solid-phase conduction and enhanced phonon scattering. It also showed excellent thermal stability even at synthesis temperatures up to 1400 °C. This work provides new possibilities for designing and manufacturing advanced insulation materials.