Novel method of adding seeds for preparation of mullite

Mechanically mixing mullite seeds powder and raw material powder often does not provide a homogeneous mixture. However a well-distributed mixture can be obtained by solution mixing. A novel method of adding mullite seeds was proposed and its influence on the sintering characteristics of mullite was investigated in this paper. A water solution for AlNH₄(SO₄) ₂·12H₂O and a mullite precursor gel were mixed to form a homogeneous solution. After drying and calcining at 1200 °C, a diphasic alumina powders (93.5 wt.% α-Al₂O₃, and well distributed 6.5 wt.% mullite seeds) was obtained. A mullite precursor mixture powders were prepared by mixing the diphasic alumina powders and a silica sol. The initial mullitization temperature and the final mullitization temperature for the mullite precursor mixture powders were 1250 and 1450 °C, respectively. A complete densification specimen can be obtained by hot pressing at 1300 °C for 0.5 h and 8 MPa followed by sintering at 1450 °C for 0.5 h.