Aerogel



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Aerogel is a low-density Styrofoam) to the touch.

Aerogel was first created by jam (jelly) jar with gas without causing shrinkage.[2][3]

Aerogels are produced by extracting the liquid component of a gel through supercritical drying. This allows the liquid to be slowly drawn off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation. The first aerogels were produced from Carbon aerogels were first developed in the early 1990s.[4]

Properties

  To the touch, aerogels feel like a light but rigid foam, something between dendritic microstructure, in which spherical particles of average size 2-5 nm are fused together into clusters. These clusters form a three-dimensional highly porous structure of almost fractal chains, with pores smaller than 100 nm. The average size and density of the pores can be controlled during the manufacturing process.

Aerogels are remarkable radiation). They are good convective inhibitors because air cannot circulate throughout the lattice. Silica aerogel is an especially good conductive insulator because silica is a poor conductor of heat—a metallic aerogel, on the other hand, would be a less effective insulator. Carbon aerogel is a good radiative insulator because carbon absorbs the infrared radiation that transfers heat. The most insulative aerogel is silica aerogel with carbon added to it.

Due to its desiccant. Persons handling aerogel for extended periods of time should wear gloves to prevent the appearance of dry brittle spots on their hands.

Since it is 99% air, it appears semi-transparent. The color it does have is due to Rayleigh scattering of the shorter wavelengths of visible light by the nanosized dendritic structure. This causes it to appear bluish against dark backgrounds and whitish against bright backgrounds.

Aerogels by themselves are hydrophilic, but chemical treatment can make them hydrophobic. If they absorb moisture they usually suffer a structural change, such as contraction, and deteriorate, but degradation can be prevented by making them hydrophobic. Aerogels with hydrophobic interiors are less susceptible to degradation than aerogels with only an outer hydrophobic layer, even if a crack penetrates the surface. Hydrophobic treatment facilitates processing because it allows the use of a water jet cutter

Types

   

Silica aerogels

Silica aerogel is the most common type of aerogel and the most extensively studied and used. It is a air is 1.2 mg/cm3[7].

Silica aerogel strongly absorbs infrared radiation. It allows the construction of materials that let light into buildings but trap heat for solar heating.

It has extremely low melting point is 1,473 K (1,200 °C or 2,192 °F).

Silica aerogel holds 15 entries[citation needed] in Guinness World Records for material properties, including best insulator and lowest-density solid.

Carbon aerogels

farads based on a capacitance of 104 F/g and 77 F/cm³. Carbon aerogels are also extremely "black" in the infrared spectrum, reflecting only 0.3% of radiation between 250 nm and 14.3 µm, making them efficient for solar energy collectors.

The term "aerogel" has been incorrectly used to describe airy masses of kevlar and unique electrical properties. These materials are not aerogels, however, since they do not have a monolithic internal structure and do not have the regular pore structure characteristic of aerogels.

Alumina aerogels

Aerogels made with fluoresce at the particle impact site, with amount of fluorescence dependent on impact velocity.

Other aerogels

agar.

Chalcogels are a type of aerogel made of chalcogens (the column of elements on the periodic table beginning with oxygen) such as sulfur and selenium, platinum, and other elements.[9] Research is ongoing, and metals less expensive than platinum have also been used in its creation.

Uses

 

There are a variety of tasks for which aerogels are used. Commercially, aerogels have been used in granular form to add insulation to skylights. After several trips on the Vomit Comet, one research team has shown that producing aerogel in a weightless environment can produce particles with a more uniform size and reduce the Rayleigh scattering effect in silica aerogel, thus making the aerogel less blue and more transparent. Transparent silica aerogel would be very suitable as a thermal insulation material for windows, significantly limiting thermal losses of buildings.

Its high surface area leads to many applications, such as a chemical absorber for cleaning up spills (see paints and cosmetics.

Aerogels are being tested for use in targets for the National Ignition Facility.

Aerogel performance may be augmented for a specific application by the addition of dopants, reinforcing structures, and hybridizing compounds. Using this approach, the breadth of applications for the material class may be greatly increased.

Commercial manufacture of aerogel 'blankets' began around the year 2000. An aerogel blanket is a composite of silica aerogel and fibrous reinforcement that turns the brittle aerogel into a durable, flexible material. The mechanical and thermal properties of the product may be varied based upon the choice of reinforcing fibers, the aerogel matrix, and opacification additives included in the composite.

NASA used aerogel to trap space dust particles aboard the Stardust spacecraft. The particles vaporize on impact with solids and pass through gases, but can be trapped in aerogels. NASA also used aerogel for thermal insulation of the Mars Rover and space suits.[10][11]

Aerogels are also used in particle physics as radiators in Cherenkov effect detectors. ACC system of the Belle detector, used in the Belle Experiment at KEKB, is a recent example of such use. The suitability of aerogels is determined by their low cryogenic liquids or compressed gases. Their low mass is also advantageous for space missions.

phenol formaldehyde resins) are mostly used as precursors for manufacture of carbon aerogels, or when an organic insulator with large surface is desired. They come as high-density material, with surface area about 600 m²/g.

Metal-aerogel nanocomposites can be prepared by impregnating the hydrogel with solution containing ions of the suitable noble or fuel cells.

Aerogel can be used as drug delivery system due to its biocompatibility. Due to its high surface area and porous structure, drugs can be adsorbed from supercritical CO2. The release rate of the drugs can be tailored based on the properties of aerogel.[12][13]

Carbon aerogels are used in the construction of small electrochemical double layer supercapacitors. Due to the high surface area of the aerogel, these capacitors can be 2000 to 5000 times smaller than similarly rated electrolytic capacitors.[14] Aerogel supercapacitors can have a very low impedance compared to normal supercapacitors and can absorb or produce very high peak currents.

Dunlop has recently incorporated aerogel into the mold of its new series of tennis racquets, and has previously used it in squash racquets[15].

Chalcogels has shown promise in absorbing heavy metal pollutants mercury, lead, and cadmium from water.[16]

Aerogel is used to introduce disorder into superfluid 3-helium. [17]

Production

Silica aerogel is made by drying a critical point. A variant on this process involves the direct injection of supercritical carbon dioxide into the pressure vessel containing the aerogel. The end result removes all liquid from the gel and replaces it with gas, without allowing the gel structure to collapse or lose volume.

Aerogel composites have been made using a variety of continuous and discontinuous reinforcements. The high aspect ratio of fibers such as fiberglass have been used to reinforce aerogel composites with significantly improved mechanical properties.

formaldehyde aerogel (RF aerogel) is made in a way similar to production of silica aerogel.

Carbon aerogel is made from a resorcinol-formaldehyde aerogel by its carbon. It is commercially available as solid shapes, powders, or composite paper.

See also

Notes

  1. ^ Taher, Abul (August 19, 2007). Scientists hail ‘frozen smoke’ as material that will change world (Web). News Article. Times Online. Retrieved on August 22, 2007.
  2. ^ Kistler S. S. (1931). "Coherent expanded aerogels and jellies". Nature 127 (3211): 741.
  3. ^ Kistler S. S. (1932). "Coherent Expanded-Aerogels". Journal of Physical Chemistry 36 (1): 52 - 64. doi:10.1021/j150331a003.
  4. ^ Pekala R. W. (1989). "Organic aerogels from the polycondensation of resorcinol with formaldehyde". Journal of Material Science 24 (9): 3221-3227. doi:10.1007/BF01139044.
  5. ^ a b Aerogels Terms. LLNL.
  6. ^ "Lab's aerogel sets world record". LLNL Science & Technology Review. October 2003.
  7. ^ Groom, D.E. Abridged from Atomic Nuclear Properties. Particle Data Group: 2007.
  8. ^ Thermal conductivity from the CRC Handbook of Chemistry and Physics, 85th Ed. section 12, p. 227
  9. ^ Biello, David [http://sciam.com/article.cfm?chanId=sa003&articleId=044B7489-E7F2-99DF-3433709C76B127DF Heavy Metal Filter Made Largely from Air. Scientific American, 2007-07-26. Retrieved on 2007-08-05.
  10. ^ Preventing heat escape through insulation called "aerogel", NASA CPL
  11. ^ Down-to-Earth Uses for Space Materials, The Aerospace Corporation
  12. ^ Smirnova I., Suttiruengwong S., Arlt W. (2004). "Feasibility study of hydrophilic and hydrophobic silica aerogels as drug delivery systems". Journal of Non-Crystalline Solids 350: 54-60. doi:10.1016/j.jnoncrysol.2004.06.031.
  13. ^ From the Research group Pharmaceutical Thermodynamics of Friedrich - Alexander - University Erlangen - Nuremberg
  14. ^ Aerogel Capacitors Support Pulse, Hold-Up, and Main Power Applications
  15. ^ Dunlop Squash Racquets
  16. ^ Carmichael, Mary. First Prize for Weird: A bizarre substance, like 'frozen smoke,' may clean up rivers, run cell phones and power spaceships. Newsweek International, 2007-08-13. Retrieved on 2007-08-05.
  17. ^ Halperin, W. P. and Sauls, J. A., Helium-Three in Aerogel [1].

References

  • NASA's Stardust comet return mission on AEROGEL.
  • J. Fricke, A. Emmerling (1992). "Aerogels—Preparation, properties, applications". Structure & Bonding 77: 37-87. doi:10.1007/BFb0036965.
  • N. Hüsing, U. Schubert (1998). "Aerogels - Airy Materials: Chemistry, Structure, and Properties". Angewandte Chemie International Edition 37 (1/2): 22-196. doi:<22::AID-ANIE22>3.0.CO;2-I 10.1002/1521-3773(19980202)37:1/2<22::AID-ANIE22>3.0.CO;2-I.
  • Pierre A. C., Pajonk G. M. (2002). "Chemistry of aerogels and their applications". Chemical Reviews 102 (11): 4243 - 4266. doi:10.1021/cr0101306.
 
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