solgel

Sol-gel, or sol–gel, is a chemical processing method for producing solid materials from small molecules. In this approach a colloidal suspension (sol) transitions into a continuous solid network (gel), commonly forming metal oxides such as silica, titania, and alumina, or their hybrids.

The chemistry centers on hydrolysis and condensation of metal alkoxide precursors, such as tetraethyl orthosilicate (TEOS) or titanium isopropoxide. Water and catalysts promote hydrolysis to M–OH, followed by condensation to M–O–M bonds, creating a three‑dimensional network.

Typical steps include sol preparation, gelation, aging, drying, and, if desired, heat treatment. Films and coatings are deposited by dip, spin, or spray coating; monoliths form in molds. Drying and thermal processing must be controlled to minimize cracking and shrinkage.

Applications span protective and optical coatings, waveguides, porous supports for catalysis, sensors, and ceramic or hybrid materials. The method enables low‑temperature processing and uniform coatings on complex geometries, with hybrids (ORMOSILs) combining organic and inorganic components.

Limitations include drying-induced cracking, porosity control, potential residual organics, and processing times. The field matured in the late 20th century, with Brinker and Scherer’s Sol-Gel Chemistry (1990) providing a foundational reference for materials science and engineering.