Processing of Highly Porous, Open-Cell, Microcellular Silicon Carbide Ceramics by Expansion Method Using Expandable Microspheres

Abstract

A refined processing route for producing highly porous, open-cell, microcellular SiC ceramics by the expansion method using expandable microspheres has been demonstrated. The strategy adopted for making microcellular SiC ceramics involved the following steps: (i) fabricating preceramic foams by heating a mixture of polysiloxane, carbon black or phenol resin (used as a carbon source), Al 2 O 3 -Y 2 O 3 (used as a sintering additive), expandable microspheres (used as sacrificial templates), and SiC (an optional inert filler); (ii) cross-linking the polysiloxane in the foamed body; (iii) transforming the polysiloxane and phenol resin by pyrolysis into silicon oxycarbide and carbon, respectively; and (iv) synthesizing SiC by carbothermal reduction. Effects of the carbon source, expandable microsphere content, and inert filler content on microstructure, porosity, and cell density were investigated in this study. By controlling the expandable microsphere and inert filler contents, it was possible to adjust the porosity within a range of 77% to 94%.