The slight colour it does have is due to Rayleigh scattering of the shorter wavelengths of visible light by the nano-sized dendritic structure. People handling aerogel for extended periods should wear gloves to prevent the appearance of dry brittle spots on their skin. Owing to its hygroscopic nature, aerogel feels dry and acts as a strong desiccant. Aerogels are poor radiative insulators because infrared radiation (which transfers heat) passes through them. (Silica aerogel is an especially good insulator because silica is also a poor conductor of heat a metallic or carbon aerogel, on the other hand, would be less effective.) They are good convective inhibitors because air cannot circulate through the lattice. They are good conductive insulators because they are composed almost entirely of gases, which are very poor heat conductors. The dearth of solid material allows aerogel to be almost weightless.Īerogels are good thermal insulators because they almost nullify two of the three methods of heat transfer – conduction (they are mostly composed of insulating gas) and convection (the microstructure prevents net gas movement). Aerogels have a porous solid network that contains air pockets, with the air pockets taking up the majority of space within the material. The average size and density of the pores can be controlled during the manufacturing process.Īerogel is a material that is 99.8% air. These clusters form a three-dimensional highly porous structure of almost fractal chains, with pores just under 100 nm. Its impressive load-bearing abilities are due to the dendritic microstructure, in which spherical particles of average size 2–5 nm are fused together into clusters. Despite the fact that it is prone to shattering, it is very strong structurally. Pressing extremely firmly will cause a catastrophic breakdown in the sparse structure, causing it to shatter like glass (a property known as friability), although more modern variations do not suffer from this. Pressing softly on an aerogel typically does not leave even a minor mark pressing more firmly will leave a permanent depression. Aerogels have excellent insulating properties, and the flower is protected from the heat of the flame.ĭespite the name, aerogels are solid, rigid, and dry materials that do not resemble a gel in their physical properties: the name comes from the fact that they are made from gels. Ī flower resting on a piece of silica aerogel, which is suspended over a flame from a Bunsen burner. Carbon aerogels were first developed in the late 1980s. Kistler's later work involved aerogels based on alumina, chromia and tin dioxide. The first aerogels were produced from silica gels. This allows the liquid to be slowly dried off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation. Īerogels are produced by extracting the liquid component of a gel through supercritical drying or freeze-drying. The first documented example of an aerogel was created by Samuel Stephens Kistler in 1931, as a result of a bet with Charles Learned over who could replace the liquid in "jellies" with gas without causing shrinkage. Silica aerogels feel like fragile expanded polystyrene to the touch, while some polymer-based aerogels feel like rigid foams. Aerogels can be made from a variety of chemical compounds.
The result is a solid with extremely low density and extremely low thermal conductivity. Aerogels are a class of synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure.
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