Chemical routes to nanostructured ceramics and composites

Abstract

The sol-gel process represents a chemical synthesis route to fabricate oxidic materials like glasses and ceramics. It is characterized that molecular, oligomeric or colloidal systems can be used as precursors. The synthesis reaction is mainly based on a hydrolysis and condensation reaction. Through the condensation reaction metal oxygen metal bonds are formed leading to a three-dimensional network. While in silica systems in the majority of the cases under acid catalysis a more or less polymeric type of network is built up, in most other cases like alumina, titania, zirconia the first condensation step leads to colloidal systems which may be amorphous or partially crystalline like in titania. The gel formation takes place by aggregation of colloidal particles or further growth of polymer networks.