Fabrication and Properties of Low-Shrinkage Reaction-Bonded Mullite

Mullite ceramics were fabricated according to the recently developed reaction-bonded Al2O3 (RBAO) technology. Green compacts consisting of mechanically alloyed Al, SiC, and Al2O3 were heat-treated in two steps. During the first hold at 1200°C, Al and SiC were oxidized to form Al2O3 and SiO2. On further heating, mullite was formed which then sintered during the second hold at 1550°C. All reactions involved in the process were associated with volume expansions that almost compensated for the shrinkage on sintering. Processing details and microstructure development are discussed. Reaction-bonded mullite ceramics exhibit high fracture strength, e.g., 290 MPa at a density of 97% of theoretical density.