Processing and Properties of Cellular Silica Synthesized by Foaming Sol‐Gels

A novel process for fabricating lightweight, cellular ceramics from sols is presented. The process utilizes the rapid viscosity change during gelation to stabilize the structure of a foamed silica sol. Manipulation of gel viscosity and foaming agent concentration resulted in a minimum cell size of 90 μm at 31% density and minimum density of 17% with average cell size of 400 μm. The flexural strength compared favorably with space shuttle tiles and sintered hollow glass spheres. From −50° to 150°C, the dielectric constant ranged from 1.51 to 1.55 for a 20% dense foam and was slightly dispersive, whereas the dielectric loss was comparable with fused silica.