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Almost Nothing
| Article
# : |
20009 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
8 / 1992 |
2,575 Words |
| Author
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Bruce V. Bigelow
Bruce V. Bigelow is a free-lance science writer in San Diego
and a reporter for the San Diego Union-Tribune. |
Aerogel looks as airy as a cloud, but drop some on the floor and it may clang like china.
For more than 60 years, the strange, ethereal substances has been little more than a laboratory curiosity--a ghostly apparition in the annals of materials science.
By the 1970s, the only use found for aerogel was as targets for measuring the energy of particles produced in high-energy accelerators. Today, such highly specialized applications remain the prime commercial use for aerogel, although scientists at Lawrence Livermore National Laboratory have helped NASA develop a space application--catching high-velocity cosmic dust.
Aerogel is a synthetic material produced by removing the solvent from a gel solution in such a manner that the porous aerogel structure remains. As research over the past decade has revealed additional properties of the substance, efforts have been made to install aerogel in everything from lunch buckets to window frames.
A variety of types of aerogel comprise an exotic class of solid foam that is more than 95 percent air. Aerogel, in fact, is the lightest-weight class of solid made by man.
"I sometimes have referred to it as 'my pet cloud,'" says Arlon Hunt, a physicist and leading aerogel researcher at the Lawrence Berkeley Laboratory .
Aerogel has been gaining increasing attention partly because it is classified as the best thermal insulator in the world. A slice half an inch thick can shield a hand from the flame of a blowtorch. Yet that same slice could balance the scales against only a handful of sunflower seeds. It is a contrary image, as if cotton candy could keep molten lava at bay.
Extraordinary properties
Typically, aerogel is made of silica (silicon dioxide)--the same beach sand used to make glass, which, of course, is impervious to liquids and gases. Unlike glass, however, aerogel is porous to liquids and gases because of "large" openings in the irregular molecular scaffolding that forms it. The openings, on the order of one hundred-thousandth (1/100,000) of a millimeter, are less than the wavelength of visible light, which gives silica aerogel an eerie kind of transparency, sometimes called "frozen smoke" by
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