Self-reinforcement of porous mullite ceramics containing needle-liked whiskers were fabricated from a powder mixture of kaolinite, Al(OH)3 and starch with NH4F as additive. The effects of the sintering temperature and the content of NH4F on porosity, phase composition, strength and microstructure of ceramics were investigated. The formation mechanism of needleliked mullite whiskers by in situ synthesis in ceramic body was discussed. The results indicated that lots of large aspect ratio needle-liked mullite whiskers, especially in the 15% NH4F additive sample, were observed. An interlocking structure was formed by needle-liked mullite whiskers to enhance the mechanical strength of porous mullite ceramic. And as the content of NH4F increasing, the bending strength increased. Comparing to the samples without NH4F additive, porous ceramic fabricated by adding NH4F showed a higher degree of mullitization. The formation mechanism of the needle-liked mullite in the ceramic was attributed to the reaction among NH4F and raw materials.

Keywords: Mullite, Porous ceramic, Ammonium fluoride, Needle-liked, Kaolinite.