Some recent developments in aqueous sol-gel processing

In this overview we describe the recent use of aqueous sol-gel processing for the preparation of ceramics that have very different end-uses. Zirconia nanofiltration membranes with 50% rejection of solutes at a molecular weight of about 1000 have been produced using zirconia sols containing inorganic polymeric "particles" and evaluated on the pilot-plant scale. Microporous alumina- and zirconia-pillared clays having a large and hydrothermally stable interlayer spacing (2 nm) and specific surface area (approximately 400 m(2) g(-1)) have been prepared using similar polymeric sols. These have been produced on the 20 kg scale and evaluated for catalytic applications. Cathodoluminescent phosphor powders, based on the doped-yttrium aluminium gallium oxide system, have been synthesized for high resolution displays using a combination of aqueous sol-gel precursors and aerosol techniques to produce particles of controlled size and shape. Finally, ceramic stains for decorating ceramic bodies have been synthesized using this method, not only in powder form but also for direct application to ceramic ware by ink-jet printing. These examples illustrate the versatility of aqueous sol-gel processing for the preparation of a wide range of ceramic compositions and forms.