Aerogeli

Aerogeli are ultralight, highly porous solids formed by replacing the liquid within a gel with a gas, yielding an aerogel. In English the standard plural is aerogels, while in some languages the plural form aerogeli is used to refer to multiple aerogel materials. They are distinguished by extremely low density, high porosity, and very low thermal conductivity.

Structure and properties: Aerogeli consist of a solid three‑dimensional network with interconnected air-filled pores. Densities typically range from about 0.001 to 0.5 g/cm3, and porosity can reach well over 90 percent. Thermal conductivity is among the lowest of solid materials, giving excellent insulation performance. Some silica aerogeli are optically transparent or translucent, but mechanical strength is generally limited; variants may be reinforced or treated to improve stiffness and water resistance. Hydrophobic or hydrophilic surface chemistries can be engineered depending on application.

Production: The common production sequence starts with gel formation from a precursor, followed by solvent exchange and drying. The critical drying step removes liquid without collapsing the pore structure, usually via supercritical drying with carbon dioxide. Ambient pressure drying with surface modification is another approach. Material properties can be tuned by changing the precursor, pore size, and cross-linking density.

Types: Silica aerogels are the most widely studied, but organic polymer aerogels, carbon aerogels, and metal oxide aerogels exist. Composite and reinforced forms are developed to improve mechanical performance or introduce additional functionality.

Applications: Aerogeli are used for thermal insulation in spacecraft, cryogenics, and building envelopes; they also serve as catalyst supports, electrode materials, and lightweight transparent insulation in skylights or windows. They gained prominence after early demonstrations in space exploration missions.

See also: Aerogel.