History of Aerogels
Many people assume that aerogels are recent products of modern technology. In reality, the first aerogels were prepared in 1931. At that time, Steven S. Kistler set out to prove that a "gel" contained a continuous solid network of the same size and shape as the wet gel.
The obvious way to prove this hypothesis was to remove the liquid from the wet gel without damaging the solid component.
As is often the case, the obvious route included many obstacles. If a wet gel were simply allowed to dry on its own, the gel would shrink, often to a fraction of its original size.
This shrinkage was often accompanied by severe cracking of the gel. Kistler surmised, correctly, that the solid component of the gel was microporous, and that the liquid-vapor interface of the evaporating liquid exerted strong surface tension forces that collapsed the pore structure. Kistler then discovered the key aspect of aerogel production: "Obviously, if one wishes to produce an aerogel [Kistler is credited with coining the term "aerogel"], he must replace the liquid with air by some means in which the surface of the liquid is never permitted to recede within the gel. If a liquid is held under pressure always greater than the vapor pressure, and the temperature is raised, it will be transformed at the critical temperature into a gas without two phases having been present at any time." (S. S. Kistler, J. Phys. Chem. 34, 52, 1932).
The first gels studied by Kistler were silica gels prepared by the acidic condensation of aqueous sodium silicate. However, attempts to prepare aerogels by converting the water in these gels to a supercritical fluid failed. Kistler then tried again by first thoroughly washing the silica gels with water (to remove salts from the gel), and then exchanging the water for alcohol. By converting the alcohol to a supercritical fluid and allowing it to escape, the first true aerogels were formed.
Until now, the aerogels were very fragile material despite their excellent properties. In the year 2000 Aspen Aerogels started the comercial production of aerogel blankets where the fragile aerogel was strengthened with various types of fiber, and by using nanotechnology transformed into extremely ekstremno strong, endurable, thin, low weight and flexible insulation material, 2 - 8 times more effective than traditional insulation materials (lowest K-value), and thus enables large instlation and operational cost savings, which makes aerogels ideal choice for many types of applications.