Macroporous ceramics by colloidal templating

We describe a novel method of fabricating macroporous ceramics employing colloidal dispersions of ultrafine ceramic particles with latex particles as the templates. The colloidal particles form a particulate gel on drying and the fill the voids of the ordered latex templates. Subsequent removal of the template by calcination results in the formation of an ordered macroporous ceramic. The process has significant advantages over the traditional sol-gel process employing alkoxide precursors. Most importantly, the much lower shrinkage (less than 10%) compared to the sol-gel process (typically 25-30%) enabled us to produce larger pieces of the sample (approximately 3×2×0.5 mm³). The larger shrinkage involved in the sol-gel process often results in small (<0.5 mm) and fragile pieces of the macroporous material. Moreover, the sol-gel process often produces amorphous material which has to be subsequently heat treated to induce crystallization. The ability to choose crystalline colloidal particles in our method obviates the need for heat treatment to achieve crystallinity. We have synthesized a variety of materials such as macroporous silica, titania, alumina and recently have also extended the approach to macroporous silicon which is not amenable to the sol-gel process.