The sol-gel process is used for making ceramic and glass materials. It is mainly the transition of a system from a solid to a liquid phase. By using this process, it is possible to make ceramic and glass materials in the following variety of forms: ultra-fine or spherical shaped powders, thin film coatings, ceramic fibers, microporous inorganic membranes, monolithic ceramics and glasses, or extremely porous aerogel materials. By subjecting inorganic metal salts or metal organic compounds to hydrolysis and polymeration, the “sol” is formed.
By further processing the “sol,” a wide variety of ceramic or glass materials are able to be formed. For instance, thin films are capable of being formed by spin-coating a piece of substrate. This is how anti-reflective coatings can be formed. This coating also has potential in being used as a corrosion resistant layer. If the “sol” is poured into a mold, and subjected to drying and heat-treatments, it will form a dense ceramic or glass material. If it is removed from the mold in a “gel” form at supercritical condition, an “aerogel” material is formed.
Fine ceramic powders can be made by precipitation, spray pyrolysis, or emulsion of the “gel” at certain viscosities. A “cryogel” can also be formed by a process of freeze-drying. This “cryogel” can be brought back to it’s identical original form by adding water to it. The importance of sol-gel comes from the wide variety of physical and chemical properties that can be obtained by using different processes. It can be used in everything from sun tan oils to high quality optics. The possibilities of this process have yet to reach their full potential, but the uses seem endless.
