The Effect of Microsilica and Aluminum Metal Powder on the Densification Parameters, Mechanical Properties and Microstructure of Alumina–Mullite Ceramic Composites

Microsilica, or silica fume, is an amorphous type of silica mostly collected as byproduct of the silicon and ferro-silicon alloy production. In this work, low shrinkage alumina-mullite ceramic composites were prepared from mixtures of calcined alumina, silica fume and aluminum metal powder and sintered at 1550oC for 2 hrs. The influence of silica fume and aluminum powder on the densification parameter, in situ mullite formed and mechanical properties of sintered samples were studied. The phase composition and the microstructural evolution of the sintered samples were also investigated. The results showed that, silica fume enhances the mechanical properties of sintered samples, while the aluminum powder improves the mullite formation process. Ultra low shrinkage (close to zero), and good mechanical properties (CCS ≈ 70 MPa) of alumina-mullite ceramic composites were achieved. Alumina-mullite ceramic composites are considered a promising material for high temperature applications.