Fabrication of Mullite Based Porous Ceramics with Favorable Creep Resistance Utilizing Superplastically Foaming Method

Porous ceramics based on mullite was fabricated using the superplastic foaming method we proposed. When mullite powder was used as the starting material, the porosity was less than 20%. A compacted body was obtained from the constituent metal oxides and the porous body obtained by reaction sintering had a porosity of nearly 50%. The spinel phase and excess silica formed before the formation of mullite were effective in promoting grain boundary sliding and increasing porosity. Additionally, the addition of titania increased the mullite formation temperature, which increased the foaming time and increased the porosity. The obtained mullite-based porous material exhibited strength and thermal conductivity comparable to that of 3YSZ (3 mol% yttria stabilized zirconia) at the same porosity level. Mullite has significant advantages over 3YSZ in terms of cost and creep resistance.