A novel processing route for developing open-cell, microcellular SiC ceramics has been developed. The strategy adopted for making microcellular SiC ceramics involved the following: (i) fabricating a formed body from a mixture of polysiloxane, phenol resin (used as a carbon source), polymer microbeads (used as sacrificial templates), and Al 2 O 3 -Y 2 O 3 (an optional sintering additive); (ii) cross-linking the polysiloxane in the formed body; (iii) transforming the polysiloxane and phenol resin by pyrolysis into silicon oxycarbide and C, respectively; and (iv) synthesizing SiC by carbothermal reduction. By controlling the microbead and additive contents, it was possible to adjust the porosity so that it ranged from 60% to 95%.

A microcellular ceramic with cell densities >109 cells/cm3 and cells <10 μm was made with a preceramic mixture of polycarbosilane and polysiloxane. The preceramic compact was saturated with gaseous CO2, a large number of cells were nucleated and grown by using a thermodynamic instability induced by a rapid pressure drop, and the microcellular preceramic was transformed into a microcellular ceramic by pyrolysis.

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