Aerogels are not an exotic type of gel. An aerogel is a solid, highly porous material, with a number of very special properties. The high volume of pores in an aerogel give it very low density and very light weight, as the material is mostly air. Some aerogels are over 99% air. Despite being extremely lightweight, aerogels are very strong, and can support up to 2000 times their own weight. Different types of aerogels each have their own unique properties, as well.
How Aerogels Are Made
An aerogel begins with a gel, which is a structure consisting of tiny pores that are filled with a liquid. Under normal circumstances, if the liquid is removed from a gel, the porous framework that contained the liquid will collapse. A process known as supercritical drying makes it possible to remove the liquid part of a gel without collapsing the solid framework, by replacing the liquid with a gas. The resulting structure is an aerogel.
Aerogels can be manufactured from a number of different materials. It is not the type of material used, but the unique, porous structure of the material that makes something an aerogel. The properties of an aerogel vary, depending on the material used. For example, aerogels made of silica are nearly transparent, with a slight blue tint, earning them the nickname “blue smoke”. Carbon aerogels, on the other hand, are a non-transparent black, and metal oxide aerogels come in a variety of opaque and transparent colors.
How Aerogels Are Used
The unique properties of aerogels make them especially useful in many situations. The abundance of pores in the material create a great deal of total surface area. This makes aerogel useful in cleaning up chemical spills, or as a purification product, such as an air or water purifier or desalination system.
Silica aerogel is the best thermal insulator known. The electronics of NASA’s Mars Rovers were insulated with silica aerogel. Applications such as cryogenics and oil pipeline insulation also use silica aerogel. Because it is nearly transparent, silica aerogel could be useful in insulating windows, once the cost of producing it comes down.
Carbon aerogels can be made electrically conductive, and are used in electrodes, capacitors, supercapacitors, and fuel cells. The black color of carbon aerogels also make them useful as solar collectors.
Although they are very strong, aerogels also tend to be quite brittle. Force must be gently and evenly applied or an aerogel will crumble. Pure aerogels, therefore, are not useful as structural components. A technique called crosslinking can increase the strength and flexibility of aerogels, at the cost of increasing density and reducing surface area. Crosslinked aerogels could be used as structural components for a number of applications, including aircraft, spacecraft, and even armor.
The unique qualities of aerogels make them useful in many other high-tech situations, including particle physics experiments, and the collection of space dust for NASA. As the cost of manufacturing aerogels comes down, however, they will increasingly become part of our everyday lives.
