Effects of Fluoride Additives on Synthesis of Porous Mullite Ceramic

摘要

Porous mullite ceramics were synthesized in-situ from a powder mixture of kaolinite, AI(OH)_3 and starch with MgF_2, AIF_3 and NH_4F as additives. The effects of sintering temperature and various fluoride additives on porosity, phase composition and microstructure of porous ceramics were investigated. The mechanisms of additives on forming mullite ceramic have been discussed. The results indicated that MgF_2, AIF_3 and NH_4F additives could promote the degree of the mullitization and the porosity of the mullite ceramics at the temperature range of 1300-1400 °C. Comparing to the sample without adding additive, porous ceramic fabricated by adding MgF_2 showed a rod-like morphology and a needle-like morphology by adding AIF_3 and NH_4F. The mechanism of forming needle-like mullite was due to reactions between additives and the raw materials.