Mullite

In electrical insulator ceramics (electrical porcelain), mullite provides exceptional high-temperature mechanical stability, low thermal expansion, and good dielectric properties. The controlled formation of a mullite-rich microstructure during firing ensures that the insulator maintains dimensional integrity and mechanical strength under electrical load and thermal cycling.

Mullite has a high melting point (~1840°C) and excellent resistance to high-temperature creep and deformation. When present as a crystalline phase in the ceramic microstructure, it acts as a high-temperature skeletal reinforcement, preventing deformation and maintaining dimensional stability at service temperatures far beyond those of conventional ceramic formulations.

Mullite has a relatively low thermal expansion coefficient (~5×10⁻⁶/°C), which reduces the overall thermal expansion of the ceramic body. This lower expansion improves thermal shock resistance — the ability of the ceramic to withstand rapid temperature changes without cracking — critical for kiln furniture and high-temperature insulators.

Yes. Mullite forms naturally during high-temperature firing of kaolin-containing ceramics when the kaolinite (Al₂Si₂O₅(OH)₄) transforms through metakaolin, spinel, and ultimately mullite at temperatures above ~1000°C. This in-situ mullite formation is the basis for the high-temperature properties of porcelain and electrical ceramics.

Mullite provides its best performance at service temperatures of 1200–1700°C, making it ideal for kiln furniture, high-temperature electrical insulators, and advanced technical ceramics. Below 1000°C, its advantage over conventional aluminosilicate ceramics is less pronounced.