The sol-gel process generally involves the following steps: 1. Hydrolysis: Precursors, usually metal alkoxides or metal chlorides, are hydrolyzed in the presence of water. 2. Condensation: The hydrolyzed species then undergo condensation reactions, leading to the formation of a three-dimensional network. 3. Gelation: The sol transforms into a gel, a semi-rigid network containing both a liquid and a solid phase. 4. Aging: The gel undergoes aging, where the network further condenses and reorganizes. 5. Drying: The liquid phase is removed, usually by evaporation, to produce a porous solid. 6. Densification: The dried gel can be further heated to improve its mechanical properties and reduce porosity.
