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Fabrication of microcellular SiCN ceramics from templated polyvinylsilazane with expandable microspheres.

The microcellular SiCN ceramics with high porosity and high surface area were fabricated from polysilazane as a viscous SiCN ceramic precursor and expandable microspheres as a self-sacrificial template. The fabrication steps were composed of (1) forming of expandable microsphere compact, (2) infiltrating polysilazane into the compact, (3) foaming and curing, (4) pyrolysis in N2 gas. The microcellular structures and properties of the obtained ceramic products depended on the foaming and curing conditions as well as the pyrolysis temperature. When foamed and cured at 120 degrees C for 30 min, then pyrolyzed at 1000 degrees C in N2, the microcellular product exhibited the largest cell size 9.3 microm with the lowest cell densities 2.2 x 108 cells/cm2, 93% of porosity and surface area of 356 m2/g. Furthermore, the higher temperature pyrolysis at 1300 degrees C induced significant change in the microcellular morphology by reducing the cell size with thicker wall and the cell density. Finally, it demonstrated an efficient way of manufacturing highly porous microcellular ceramics with no etching process using a polyvinylsilazane and expandable microspheres for catalytic supporting application.