Microstructure development and phase evolution of alumina–mullite nanocomposite

In this work, the alumina–mullite composite was prepared using sol–gel derived alumina composite nanopowders. Results revealed the intragranular mullite was embedded in the alumina grain and the intergranular mullite was embedded on the grain boundary. Accordingly, the intragranular mullites (average grain size, 0.3 µm) were smaller than the intergranular mullites (average grain size, 0.5 µm). Moreover, the alumina grains (average grain size, 1.0 µm) are larger than the mullites. Meanwhile, the mullites showed positive results in the prevention of the alumina grains growth, known as the Zener law behavior, and the retardation of densification. The relative density of alumina–mullite that was sintered at 1650 °C for 2 h was obtained as 98.7%. After sintering at 1750 °C for 2 h, the mullite was decomposed.