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SILICA AEROGEL: Super-Material of the Future?

        Silica Aerogel holds six world records for physical properties. Aerogels are non-toxic nanoporous materials that have the highest thermal insulation value, the lowest density, the highest specific surface area, the lowest refractive index, the lowest speed of sound and the lowest dielectric constant of any solid. Aerogels consist of a foam-like network of molecules that is 99.8% air.

        You might assume that aerogels are a modern invention, but they have actually been around since 1931. Steven. S. Kistler from the College of the Pacific in Stockton, California is credited with inventing and patenting aerogels as well as coining the term "aerogel."

        Aerogel is produced by first making a wet gel, which is an aqueous condensation of sodium silicate. This gel is dried and cooked in an autoclave which removes the liquid from the pores in the gel without collapsing the matrix of nanometer sized hair-like structures within. The framework that is left is the dry aerogel material itself. Since this network of molecules fills space and supports itself, it is considered a solid. With recent advances in sol-gel chemistry over the past few decades, most silica aerogel is now produced from silicon alkoxide. The sol-gel process avoids the formation of unwanted salt byproducts. There are numerous different production methods which all produce aerogels with different properties and characteristics.

        At just three times the density of air, aerogel is the lightest solid ever produced. When produced in a gravitational field, like on the surface of the earth, it has a slight bluish haze, hence the nickname "blue smoke." The slight haze is due to occasional larger pores which detract from its transparency. NASA scientists have produced aerogels in space with the StarDust mission in an attempt to make them transparent. Transparent aerogels, also having the lowest refractive index of any solid, would be nearly invisible in air. This would open up a whole host of new product opportunities, including one inch thick windows with an insulation value equivalent to 15 panes of air-separated glass!

A bullet is supported by a small sample of silica aerogel.

        Aerogel gets its amazing insulation ability because of its large internal surface area. Each molecular "cell" traps heat or cold, insulating like millions of sir-separated panes of glass, on a nano-scale. If a sugar-cube sized piece of aerogel could be unraveled, its internal surface area would add up to cover a basketball court. This is what gives it its tremendous insulating ability.

Matches rest on a thin block of aerogel, protected from the flame beneath.

        The biggest deterrent to the production of aerogel incorporating products today is its high production cost. At $1 - $5 and up for a 1cm cube of the stuff weighing as little as .003g, it is still impractical for most everyday uses. Itís quite pricey for a product made of sand, but research and specialized production methods donít come cheap. There are, however, companies who make flexible blankets, clothing, scientific and cryogenic supplies and super insulations that incorporate aerogel.

        Aerogels offer an enormous number of possibilities for integration into our lives, if costs can be drastically reduced and production increased. Potential uses vary from faster, smaller computer chips, to sleeping bags weighing close to an ounce and rated to "what temperature you got?" Super-insulators for houses, coolers, refrigerators, stoves, electronics, optics, sensors, lightweight structural components and applications not even imagined yet will help to shape our future with this material.

        The widespread use of aerogel insulations instead of fiberglass or polyurethane foam would significantly reduce energy consumption thereby helping the environment and making better use of available resources. Foam insulations also contain ozone-depleting CFCs, so aerogels could be the perfect CFC-free alternative.

        Some safety and environmental concerns do exist with aerogel. Some of the chemicals involved in production are poisonous. There are dangers of an explosion while producing aerogel with some manufacturing techniques that use flammable chemicals, and/or high pressures. High temperature is no longer required, but with older production techniques this also represented a safety concern. At present there is virtually no concern for the disposal of aerogel, but with possible increased production in the future this could also become a concern. It could be recycled, if facilities to do so were put in place.

Aerogel is one of the few solids which can be both porous and transparent, due to its 10-50nm pore size.

        Aerogels could actually help maintain the geometric progression of computer chips for a few more years. As chips get smaller, signals in wires on the chip can actually interfere with one another. Since aerogel has the lowest dielectric constant among solids, it could be used to push wires on chips even closer together, expanding the processing power and reducing the size of tomorrowís chips. The computer industry has an enormous impact on society influencing how we work, communicate, play and live. This influence will grow even larger if computing power continues to follow Mooreís law. 

        Three-dimensional holographic displays using a block of silica aerogel as a display medium, and focusing light in all three planes, could make a still or moving image visible from any side. This would have enormous potential in the entertainment industry as well as in military planning and visualization of the battlefield terrain.

        Companies like Maytag, Bentley, General Motors and Boeing are currently considering aerogel materials for large-scale use as temperature and sound insulation. This would mean higher efficiency consumer products and services on the market. Aerogel is perfect for saving energy, while maintaining the standard of living people have become accustomed to in our modern technological world.

        Nanotechnology offers the prospect of producing aerogels cost and energy efficiently in the future with more advanced production methods. It could even help us to design aerogel materials with better properties than can currently be produced. Since cloudiness is due to imperfections, it should be possible to produce near perfect clarity. 

        Aerogel is an amazing substance with great potential and few risks. It would have an overall positive effect on the progression of technology if it could be produced less expensively. Right now application is severely limited by its high cost. With continuing advances in the field and manufacturing methods, it is hopeful that we will see silica aerogel used more often in the near future. When it comes to super-materials, aerogel is the clear choice!    


REFERENCES
:

2001, Stardust

            http://stardust.jpl.nasa.gov/photo/aerogel.html

1997, Frozen Smoke

            http://science.nasa.gov/newhome/headlines/msad05mar97_1.htm

1995, Aerogel: Energy Efficient Material for buildings

            http://eetd.lbl.gov/newsletter/cbs_nl/nl8/Aerogel.html

2002, Reduced Gravity Aerogel Formation

            http://www.cae.wisc.edu/~aerogel/

1996-2002, Aerogel Materials

            http://www.mkt-intl.com/aerogels/

1999, Aerogel Super-Insulation

            http://www.aspensystems.com/aerogel.html

1997, Will Aerogel Let You Put A 24GHz Computer On Your Desktop By 2006?

            http://science.nasa.gov/newhome/msad/aerogel_update.htm

2002, Aspen Aerogels Inc.

            http://www.aspenaerogels.com

2002, Making Three-Dimensional Holograms Visible From All Sides

            http://www.nasatech.com/Briefs/Apr02/NPO20101.html

1999-2002, Aerogel

            http://www.metafilter.com/mefi/16640

2002, A Brief Histoy of Silica Aerogels

            http://eande.lbl.gov/ECS/aerogels/sahist.htm

2002, Whatís an aerogel?

            http://www.post-gazette.com/healthscience/20021021antarcticsidesci4p4.asp

 

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