aerogel

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aerogel,

any of a group of extremely light and porous solid materials; the lightest is less than four times as dense as dry air. Aerogels are produced from certain gels (see colloidcolloid
[Gr.,=gluelike], a mixture in which one substance is divided into minute particles (called colloidal particles) and dispersed throughout a second substance. The mixture is also called a colloidal system, colloidal solution, or colloidal dispersion.
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) by heating the gel under pressure, which causes the liquid in the gel to become supercritical (in a state between a liquid and a gas) and lose its surface tension. In this state, the liquid may be removed from the gel by applying additional heat, without disrupting the porous network formed by the gel's solid component. Silica-, melamine-, and carbon-based aerogels have been produced. Silica-based aerogels are among the lightest, and some, nicknamed "solid smoke" or "frozen smoke," are nearly transparent. Heavier aerogels were first developed in 1931 and have been used to detect high-energy particles emitted by particle acceleratorsparticle accelerator,
apparatus used in nuclear physics to produce beams of energetic charged particles and to direct them against various targets. Such machines, popularly called atom smashers, are needed to observe objects as small as the atomic nucleus in studies of its
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. Newer, lighter aerogels with relatively high insulating properties are being tested as substitutes for the chlorofluorocarbonchlorofluorocarbons
(CFCs), organic compounds that contain carbon, chlorine, and fluorine atoms. CFCs are highly effective refrigerants that were developed in response to the pressing need to eliminate toxic and flammable substances, such as sulfur dioxide and ammonia, in
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 foams used as refrigerator insulation and as replacements for the air between the panes of double-glazed windows; other aerogels are being used as filters.

aerogel

[′e·rō‚jel]
(chemistry)
A porous solid formed from a gel by replacing the liquid with a gas with little change in volume so that the solid is highly porous.