Investigation on the influence factors for preparing mullite-whisker-structured porous ceramic

Abstract Low-density mullite-whiskers-structured porous ceramic can be obtained through ammonium hexafluoroaluminate (AHA) or corn flour adopted as pore-forming agents. The AHA was also used as silicon etchant and source of aluminum. The formation mechanism of sillimanite whiskers and their transformation into mullite whiskers were investigated. The effects of amount and granularity of corn flour doping in the porous ceramic on the bulk density and whisker growth were also investigated. The experimental results demonstrated that sillimanite whiskers were formed by a gas phase reaction via two solid phase processes and mullite whiskers occurred. The mullite transformation starts at 1250 °C, completes at 1450 °C. Pores from burning out of corn flour will promote the growth of gas-derived sillimanite whiskers with the bulk density reduction of the porous ceramic as well as the heat conductivity coefficient. The optimal amount and granularity of corn flour is 50 wt% and 120–160 mesh, respectively. Meanwhile, the prepared mullite-whisker-structured porous ceramic showed low thermal conductivity at the temperature higher than 1250 °C.