Preparation of high strength porous mullite ceramics via combined foam-gelcasting and microwave heating

Porous mullite ceramics with improved mechanical strength were fabricated by using a combined foam-gelcasting and microwave firing method at 1373-1523 K for 30 min. The porous mullite prepared at 1373 K contained 76.6% porosity, and exhibited flexural and compressive strength values as high as respectively 3.8 and 15.2 MPa. Moreover, its thermal conductivity still remained as low as 0.269 W/(m K). These values were comparable or even superior to those of porous mullite ceramics prepared previously via conventional heating at much higher temperatures (1573-1873 K), indicating that it is more beneficial to use microwave heating instead of conventional heating to make high quality porous mullite ceramics at a much lowered temperature.