Processing of Microcellular Mullite

A new processing route for manufacturing partially interconnected open‐cell, microcellular mullite ceramics has been developed. The strategy adopted for making microcellular mullite ceramics entailed the following steps: (i) fabricating a formed body from combining polysiloxane, Al 2 O 3 (a reactive filler), polymer microbeads (used as sacrificial templates), and Y 2 O 3 (a sintering additive); (ii) cross‐linking the polysiloxane in the formed body; (iii) transforming the polysiloxane by pyrolysis into SiO 2 ; and (iv) synthesizing mullite by reacting SiO 2 and Al 2 O 3 . By controlling the sintering temperature and the microbead and additive contents, it was possible to adjust the porosity so that it ranged from 38% to 85%. The compressive strengths of the microcellular ceramics with ∼40% and ∼70% porosities were ∼90 and ∼10 MPa, respectively. The superior compressive strengths were attributed to the homogeneous distribution of small (≤20 μm), spherical cells with dense struts in the microcellular ceramics.