Modification of liquid phase and microstructure of sintered mullite by different additives

In the field of ceramics, mullite has drawn plenty of attention due to its low thermal expansion and thermal conductivity as well as its high chemical stability and creep resistance. This work reported the mineral phase, liquid phase, and microstructure evolution of the sintered mullite, using coal‐series kaolin as the raw material and potash feldspar as well as phosphorus pentoxide as additives. The effects of K2O and P2O5 on the content and viscosity of the liquid phase in mullite were calculated using FactSage 8.1. The results showed that the introduction of K2O could inhibit the formation of cristobalite effectively. Adding K2O and P2O5 improved the content of the liquid phase formed during the calcination process. After introducing K2O and P2O5, mullite developed acicular and columnar structures, with average lengths of 9.76 and 7.97 µm, respectively. Furthermore, introducing K2O and P2O5 improved the physical properties of mullite significantly.