Aerogel 423688 224292646 2008-07-08T05:14:13Z Shenstar 7386447 /* Properties */ They are GOOD insulators {{expert-subject|Chemistry}} [[Image:Aerogelbrick.jpg|200px|thumb|right|A 2.5 kg [[brick]] is supported by a piece of aerogel weighing only 2 grams.]] '''Aerogel''' is a low-density [[solid|solid-state]] material derived from [[gel]] in which the liquid component of the gel has been replaced with gas. The result is an extremely low density solid with several remarkable properties, most notably its effectiveness as a [[thermal conductivity|thermal insulator]]. It is nicknamed '''frozen smoke''',<ref Name="Times081907">{{cite web | last =Taher | first =Abul | title = Scientists hail ‘frozen smoke’ as material that will change world | work = News Article | publisher = Times Online | date = 2007-08-19 | url =http://www.timesonline.co.uk/tol/news/uk/science/article2284349.ece | format = Web | accessdate = 2007-08-22 }}</ref> '''solid smoke''' or '''blue smoke''' due to its semi-transparent nature and the way light scatters in the material; however, it feels like [[Polystyrene#Solid foam|expanded polystyrene]] ([[Styrofoam]]) to the touch. Aerogel was first created by [[Steven Kistler]] in 1931, as a result of a bet with Charles Learned over who could replace the liquid inside a [[Fruit preserves|jam]] (jelly) jar with gas without causing shrinkage.<ref>{{cite journal | author = Kistler S. S. | title = Coherent expanded aerogels and jellies | journal = [[Nature]] | year = 1931 | volume = 127 | issue = 3211 | pages = 741 | doi = }} </ref><ref>{{cite journal | author = Kistler S. S. | title = Coherent Expanded-Aerogels | journal = [[Journal of Physical Chemistry]] | year = 1932 | volume = 36 | issue = 1 | pages = 52–64 | doi = 10.1021/j150331a003 }}</ref> 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 [[silica gel]]s. Kistler's later work involved aerogels based on [[alumina]], [[Chromium(III) oxide|chromia]] and [[tin oxide]]. [[Carbon]] aerogels were first developed in the early 1990s.<ref>{{cite journal | author = Pekala R. W. | title = Organic aerogels from the polycondensation of resorcinol with formaldehyde | journal = [[Journal of Material Science]] | year = 1989 | volume = 24 | issue = 9 | pages = 3221–3227 | doi = 10.1007/BF01139044 }} </ref> == Properties == [[Image:Aerogel nasa.jpg|right|thumbnail|200px|[[Peter Tsou]] of [[NASA]]'s [[Jet Propulsion Laboratory]] holding a sample of aerogel]] To the touch, aerogels feel like a light but rigid foam, something between [[Styrofoam]] and the [[Oasis (horticulture)|green floral foam]] used for arranging flowers. Despite what their name may suggest, aerogels are dry materials and do not resemble a gel in their physical properties but a [[nanofoam]]. (The name comes from the fact that they are derived from gels.) Pressing softly on an aerogel typically does not leave a mark; pressing more firmly will leave a permanent dimple. Pressing firmly enough will cause a catastrophic breakdown in the sparse structure, causing it to shatter like glass—a property known as ''[[friability]]''. Despite the fact that it is prone to shattering, it is very strong structurally. Its impressive load bearing abilities are due to the [[dendrite (metal)|dendritic]] microstructure, in which spherical particles of average size 2-5 nm are fused together into clusters. These clusters form a three-dimensional highly [[porosity|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 good [[thermal insulation|thermal insulators]] because they almost nullify three methods of heat transfer ([[convection]], [[heat conduction|conduction]] and [[thermal radiation|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{{Fact|date=June 2008}}. Due to its [[hygroscopic]] nature, aerogel feels dry and acts as a strong [[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 99.8% air, it appears semi-transparent. The color it does have is due to [[Rayleigh scattering]] of the shorter [[wavelength]]s of [[visible light]] by the nanosized dendritic structure. This causes it to appear smoky blue against dark backgrounds and yellowish 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 == [[Image:Aerogel matches.jpg|left|thumbnail|A demonstration of aerogel's insulation properties.]] [[Image:AerogelElliot.jpg|right|thumbnail|Aerogel produced at [[Florida State University]] by Elliot Schwartz and Robert Palmer.]] === Silica aerogels === Silica aerogel is the most common type of aerogel and the most extensively studied and used. It is a [[silica]]-based substance, derived from [[silica gel]]. The world's lowest-density [[solid]] is a silica nanofoam at 1 mg/cm<sup>3</sup><ref name=terms>[http://www.llnl.gov/IPandC/technology/profile/aerogel/Terms/index.php Aerogels Terms]. LLNL.</ref>, which is the evacuated version of the record-aerogel of 1.9 mg/cm<sup>3</sup><ref name="llnl03">"[http://www.llnl.gov/str/October03/NewsOctober03.html Lab's aerogel sets world record]". ''LLNL Science & Technology Review''. October 2003.</ref>. The density of [[air]] is 1.2 mg/cm<sup>3</sup><ref http://pdg.lbl.gov/2007/reviews/atomicrpp.pdf>Groom, D.E. [http://pdg.lbl.gov/2007/reviews/atomicrpp.pdf Abridged from Atomic Nuclear Properties]. Particle Data Group: 2007.</ref>. 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 remarkable thermal insulative properties, having an extremely low [[thermal conductivity]]: from 0.03 [[watt|W]]/[[metre|m]]·[[kelvin|K]]<ref>Thermal conductivity from the [http://hbcpnetbase.com/ CRC Handbook of Chemistry and Physics], 85th Ed. section 12, p. 227</ref> down to 0.004 [[watt|W]]/[[metre|m]]·[[kelvin|K]],<ref name=terms/> which correspond to R-factors of 14 to 105 for 3.5 inch thickness. For comparison, typical wall insulation is 13 for 3.5 inch thickness. Its [[melting point]] is 1,473 K (1,200 °C or 2,192 °F). Silica aerogel holds 15 entries{{Fact|date=August 2007}} in ''[[Guinness World Records]]'' for material properties, including best insulator and lowest-density solid. === Carbon aerogels === [[Carbon]] aerogels are composed of particles with sizes in the [[nanometer]] range, [[covalent bond|covalently bonded]] together. They have very high [[porosity]] (over 50%, with pore diameter under 100 nm) and surface areas ranging between 400–1000 m²/g. They are often manufactured as composite paper: non-woven paper made of [[carbon fiber]]s, impregnated with [[resorcinol]]-[[formaldehyde]] aerogel, and [[pyrolisis|pyrolyzed]]. Depending on the density, carbon aerogels may be electrically conductive, making composite aerogel paper useful for electrodes in [[capacitor]]s or deionization electrodes. Due to their extremely high surface area, carbon aerogels are used to create [[supercapacitor]]s, with values ranging up to thousands of [[farad]]s 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 [[carbon nanotube]]s produced through certain [[chemical vapor deposition]] techniques—such materials can be spun into fibers with strength greater than [[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 [[alumina|aluminium oxide]] are known as [[alumina]] aerogels. These aerogels are used as catalysts, especially when "metal-doped" with another metal. Nickel-alumina aerogel is the most common combination. Alumina aerogels are also examined by [[NASA]] for capturing of hypervelocity particles; a formulation doped with [[gadolinium]] and [[terbium]] could [[fluoresce]] at the particle impact site, with amount of fluorescence dependent on impact velocity. === Other aerogels === [[SEAgel]] is a material similar to organic aerogel, made of [[agar]]. [[Chalcogel]]s are a type of aerogel made of [[chalcogen]]s (the column of elements on the periodic table beginning with oxygen) such as sulfur and selenium, platinum, and other elements.<ref>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]].</ref> Research is ongoing, and metals less expensive than platinum have also been used in its creation. Aerogels made of [[Cadmium selenide]] [[quantum dots]] in a porous 3-D network have recently been developed for use in the semiconductor industry <ref>{{cite journal | author = H.Yu, R.Bellair, R.M.Kannan, S.Brock | title = Engineering Strength, Porosity, and Emission Intensity of Nanostructured CdSe Networks By Altering The Building Block Shape | journal = [[Journal of The American Chemical Society]] | year = 2008 | volume = 130 | issue = 15 | pages = 5054-5055 | doi = 10.1021/ja801212e }}</ref> == Uses == [[Image:Stardust Dust Collector with aerogel.jpg|right|thumbnail|The [[Stardust (spacecraft)|Stardust]] dust collector with aerogel blocks. (NASA)]] There are a variety of tasks for which aerogels are used. *Commercially, aerogels have been used in granular form to add [[Thermal insulation|insulation]] to [[Window#Skylight|skylights]]. *After several trips on the [[Vomit Comet]], one [http://zerogaerogel.com research team] has shown that producing aerogel in a [[weightlessness|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 [[adsorption]]). This feature also gives it great potential as a [[catalyst]] or a catalyst carrier. *Aerogel particles are also used as [[thickening agent]]s in some [[paint]]s 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 material|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)|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 suit]]s.<ref>[http://marsrovers.jpl.nasa.gov/mission/sc_rover_temp_aerogel.html Preventing heat escape through insulation called "aerogel"], ''NASA CPL''</ref><ref>[http://www.aero.org/publications/crosslink/fall2006/backpage.html Down-to-Earth Uses for Space Materials], ''The Aerospace Corporation''</ref> *The [[US Navy]] is evaluating aerogel undergarments as passive thermal protection for divers.<ref>{{cite journal |last=Nuckols |first=M. L. |coauthors=Chao J. C. and Swiergosz M. J. |title=Manned Evaluation of a Prototype Composite Cold Water Diving Garment Using Liquids and Superinsulation Aerogel Materials |journal=US Naval Experimental Diving Unit Technical Report |volume=NEDU-05-02 |date=[[2005]] |url=http://archive.rubicon-foundation.org/3487 |accessdate=2008-04-21 }}</ref> *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 (accelerator)|KEKB]], is a recent example of such use. The suitability of aerogels is determined by their low [[index of refraction]], filling the gap between gases and liquids, and their transparency and solid state, making them easier to use than [[cryogenic]] liquids or compressed gases. Their low mass is also advantageous for space missions. *[[Resorcinol]]-[[formaldehyde]] aerogels (polymers chemically similar to [[phenol formaldehyde resin]]s) 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 metal|noble]] or [[transition metal|transition]] metals. The impregnated hydrogel is then irradiated with [[gamma ray]]s, leading to precipitation of nanoparticles of the metal. Such composites can be used as eg. [[catalyst]]s, sensors, [[electromagnetic shielding]], and in waste disposal. A prospective use of platinum-on-carbon catalysts is in [[fuel cell]]s. *Aerogel can be used as a 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.<ref> {{cite journal | author = Smirnova I., Suttiruengwong S., Arlt W. | title = Feasibility study of hydrophilic and hydrophobic silica aerogels as drug delivery systems | journal = Journal of Non-Crystalline Solids | year = 2004 | volume = 350 | issue = | pages = 54–60 | doi = 10.1016/j.jnoncrysol.2004.06.031 }} </ref><ref>From the [http://www.tvt.cbi.uni-erlangen.de/eng/research/thermo_pharma/thermo_pharmazie_e.htm Research group Pharmaceutical Thermodynamics] of Friedrich - Alexander - University Erlangen - Nuremberg</ref> *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.<ref>[http://powerelectronics.com/portable_power_management/batteries/power_aerogel_capacitors_support/ Aerogel Capacitors Support Pulse, Hold-Up, and Main Power Applications]</ref> 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. <ref>[http://www.pwp.com/squashrackets.asp?id=3&cat=Dunlop%20squash%20rackets Dunlop Squash Racquets]</ref>. *Chalcogels have shown promise in absorbing the heavy metal pollutants mercury, lead and cadmium from water.<ref>Carmichael, Mary. [http://www.msnbc.msn.com/id/20123389/site/newsweek/ 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]].</ref> *Aerogel is used to introduce disorder into superfluid 3-helium. <ref>Halperin, W. P. and Sauls, J. A., Helium-Three in Aerogel [http://arxiv.org/abs/cond-mat/0408593v1].</ref> == Production == Silica aerogel is made by drying a [[hydrogel]] composed of [[colloid]]al [[silica]] in an extreme environment. Specifically, the process starts with a liquid alcohol like [[ethanol]] which is mixed with a [[silicon alkoxide]] [[wiktionary:Precursor|precursor]] to form a [[silicon dioxide]] [[sol gel]] ([[silica gel]]). Then, through a process called [[supercritical drying]], the alcohol is removed from the [[gel]]. This is typically done by exchanging the ethanol for liquid acetone, allowing a better miscibility gradient, and then onto liquid [[carbon dioxide]] and then bringing the carbon dioxide above its [[critical point (chemistry)|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 [[composite]]s with significantly improved mechanical properties. [[Resorcinol]]-[[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 [[pyrolysis]] in [[inert gas]] atmosphere, leaving a matrix of [[carbon]]. It is commercially available as solid shapes, powders, or composite paper. == Safety == Silica-based aerogels are not known to be carcinogenic or toxic. However, they are a mechanical irritant to the eyes, skin, respitatory tract and digestive system. They also can induce dryness of the skin, eyes and mucous membranes. Therefore, it is recommended that protective gear including gloves and eye goggles be worn whenever handling aerogels. <ref>http://www.aspenaerogels.com/products/pdf/Cryogel_x201_MSDS_11_07.pdf</ref> However, safety depends on the material from which the aerogel is made -- it will be carcinogenic or toxic if made from a gel with such characteristics. == See also == * [[Gel]] * [[Nanogel]] * [[Sol gel]] * [[Hydrogel#Hydrogels|Hydrogel]] * [[Xerogel#Xerogels|Xerogel]] * [[SEAgel]] * [[Chalcogel]] == References == {{reflist}} {{refbegin}} * NASA's Stardust comet return mission on [http://stardust.jpl.nasa.gov/tech/aerogel.html AEROGEL.] * {{cite journal | author = J. Fricke, A. Emmerling | title =Aerogels—Preparation, properties, applications | journal= Structure & Bonding | year= 1992 | volume = 77 | issue = | pages= 37–87 | doi = 10.1007/BFb0036965}} * {{cite journal | author = N. Hüsing, U. Schubert | title =Aerogels - Airy Materials: Chemistry, Structure, and Properties | journal= [[Angewandte Chemie International Edition]] | year= 1998 | volume = 37 | issue = 1/2 | pages= 22–45 | doi = 10.1002/1521-3773(19980202)37:1/2<22::AID-ANIE22>3.0.CO;2-I}} *{{cite journal | author = Pierre A. C., Pajonk G. M. | title = Chemistry of aerogels and their applications | journal = [[Chemical Reviews]] | year = 2002 | volume = 102 | issue = 11 | pages = 4243–4266 | doi = 10.1021/cr0101306 }} {{refend}} == External links == {{Commonscat|Aerogel}} * [http://stardust.jpl.nasa.gov/photo/aerogel.html NASA photos of aerogel] * [http://fourier.mech.virginia.edu/~microhx/thermalproperties.html Copy of Lawrence Berkeley National Laboratory page on the Thermal Properties of Silica Aerogels] <!-- original at http://eande.lbl.gov/ECS/aerogels/satcond.htm is now 404 --> * [http://lbl.gov/Science-Articles/Archive/aerogel-insulation.html Another LBL article covering the development of aerogels] * [http://stardust.jpl.nasa.gov/overview/faq.html#aerogel Aerogel FAQ at NASA JPL] * [http://connectexpress.com/~ips/aerogel/faq.html Aerogel FAQ] * "[http://wired.com/news/technology/1,70268-1.html A Solid That's Light As Air]", by Dylan Tweney. ''Wired'', [[23 February]] [[2006]] * [http://neme.org/main/262/Aerosculpture Aer( )sculpture, Using a Space Material as a Sculptural Medium] * [http://science.nasa.gov/newhome/help/tutorials/housefuture.htm Aerogel insulates the The House of the Future?] * [http://aerogel.com/ American company researching and producing flexible aerogel blankets for insulation] * [http://www.airglass.se/ Swedish company researching aerogel glass for windows] * [http://insulatingglass.blogspot.com/ Blog concerned with research, development and manufacture of double glazing insulating glass units with aerogel components] * [http://www.pwp.com/squashrackets.asp?id=3&cat=Dunlop%20squash%20rackets Dunlop develop squash racquets incorporating aerogel] * {{de icon}} [http://www.physikclub.de/projekte-des-physikclubs/projekte-2007-08/aerogele/ Site about producing and working with aerogel] * [http://www.timesonline.co.uk/tol/news/uk/science/article2284349.ece Scientists hail ‘frozen smoke’ as material that will change world] * [http://www.kqed.org/quest/television/view/776 Video of Alex Gash Lawrence Livermore National Laboratory U.S.A. Scientiate showing aerogel and it's properties] * [http://www.solgel.com/articles/april01/aerog1.htm Glass from Aerogels] * [http://www.solgel.com/articles/Dec03/gal2.asp An artistic gallery of Aerogels] [[Category:Insulators]] [[Category:Foams]] [[Category:Gels]] [[Category:Physics articles needing expert attention]] [[Category:Chemistry articles needing expert attention]] [[bs:Aerogel]] [[bg:Аерогел]] [[cs:Aerogel]] [[da:Aerogel]] [[de:Aerogel]] [[el:Αεροπήκτωμα]] [[es:Aerogel]] [[eo:Aeroĝelo]] [[fr:Aérogel]] [[ko:에어로젤]] [[id:Aerogel]] [[it:Aerogel]] [[hu:Aerogél]] [[nl:Aerogel]] [[ja:エアロゲル]] [[no:Aerogel]] [[uz:Aerogel]] [[pl:Aerożel]] [[pt:Aerogel]] [[ru:Аэрогель]] [[sk:Aerogél]] [[sl:Aerogel]] [[sr:Аерогел]] [[su:Aérojél]] [[fi:Aerogeeli]] [[sv:Aerogel]] [[tr:Aerojel]] [[zh:气凝胶]]