Gallium 12241 223615080 2008-07-04T22:07:16Z Lightbot 7178666 Units/dates/other {{distinguish2|the plant genus, [[Galium]]}} {{For|computer graphics|Gallium 3D}} {{Infobox gallium}}'''Gallium''' ({{pronEng|ˈgæliəm}}) is a [[chemical element]] that has the symbol '''Ga''' and [[atomic number]] 31. A soft silvery metallic [[poor metal]], gallium is a brittle solid at low temperatures but liquefies slightly above [[room temperature]] and will melt in the hand. It occurs in trace amounts in [[bauxite]] and [[zinc]] ores. An important application is in the compounds [[gallium nitride]] and [[gallium arsenide]], used as a [[semiconductor]], most notably in [[light-emitting diode]]s (LEDs). == Notable characteristics == Elemental gallium is not found in nature, but it is easily obtained by [[smelting]]. Very pure gallium metal has a brilliant silvery color and its solid metal fractures [[Conchoidal fracture|conchoid]]ally like [[glass]]. Gallium metal expands by 3.1 percent when it solidifies, and therefore storage in either glass or metal containers is avoided, due to the possibility of container rupture with freezing. Gallium shares the higher-density liquid state with only a few materials like [[germanium]], [[bismuth]], [[antimony]] and [[water]]. Gallium also [[Liquid metal embrittlement|attacks]] most other metals by [[diffusion|diffusing]] into their metal [[crystal structure|lattice]]. Gallium for example diffuses into the [[grain boundary|grain boundaries]] of [[Aluminium|Al]]/[[Zinc|Zn]] [[alloy]]s<ref>{{cite journal | title = Grain boundary imaging, gallium diffusion and the fracture behavior of Al–Zn Alloy – An in situ study | author = W. L. Tsai, Y. Hwu, C. H. Chen, L. W. Chang, J. H. Je, H. M. Lin, G. Margaritondo | journal = Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms | year = 2003 | volume = 199 | issue = | pages = 457–463 | doi = 10.1016/S0168-583X(02)01533-1 }}</ref> or steel.<ref>{{cite web | url = http://stinet.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA365497 | title = Liquid Metal Embrittlement of ASTM A723 Gun Steel by Indium and Gallium | author = Vigilante, G. N., Trolano, E., Mossey, C. | publisher = Defense Technical Information Center |date=Jun 1999}}</ref>, making them very brittle. Also, gallium metal easily alloys with many metals,{{Fact|date=February 2007}} and was used in small quantities in the core of the first atomic bomb to help stabilize the plutonium crystal structure.<ref>{{cite web |author=Sublette,Cary |title=Section 6.2.2.1 |date=2001-09-09 |work=Nuclear Weapons FAQ |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq6.html#nfaq6.2 |accessdate=2008-01-24 }}</ref> The [[melting point]] temperature of 29.76 °C allows the metal to be melted in one's hand. This metal has a strong tendency to [[supercooling|supercool]] below its [[melting point]]/[[freezing point]], thus necessitating [[seed crystal|seeding]] in order to solidify. Gallium is one of the metals (with [[caesium]], [[rubidium]], [[francium]] and [[mercury (element)|mercury]]) which are liquid at or near normal room temperature, and can therefore be used in metal-in-glass high-temperature [[thermometer]]s. It is also notable for having one of the largest liquid ranges for a metal, and (unlike mercury) for having a low [[vapor pressure]] at high temperatures. Unlike mercury, liquid gallium metal [[Wetting|wets]] glass and skin, making it mechanically more difficult to handle (even though it is substantially less toxic and requires far fewer precautions). For this reason as well as the metal contamination problem and freezing-expansion problems noted above, samples of gallium metal are usually supplied in polyethylene packets within other containers. Gallium does not [[crystal]]lize in any of the simple [[crystal structure]]s. The stable phase under normal conditions is [[orthorhombic]] with 8 atoms in the conventional [[unit cell]]. Each atom has only one nearest neighbor (at a distance of 244 [[picometre|pm]]) and six other neighbors within additional 39 pm. Many stable and [[metastability in molecules|metastable]] phases are found as function of temperature and pressure. The bonding between the nearest neighbors is found to be of [[covalent]] character, hence Ga<sub>2</sub> [[dimer]]s are seen as the fundamental building blocks of the crystal. The compound with [[arsenic]], [[gallium(III) arsenide|gallium arsenide]] is a [[semiconductor]] commonly used in [[light-emitting diode]]s. High-purity gallium is dissolved slowly by [[mineral acid]]s. Gallium has no known biological role, although it might be involved in metabolism stimulation. <ref>{{cite web | url = http://www.webelements.com/webelements/scholar/elements/gallium/biological.html | title = Scholar Edition: gallium: Biological information | author = Mark Winter | publisher = The University of Sheffield and WebElements Ltd, UK}}</ref> == History == Gallium (the [[Latin]] ''Gallia'' means "[[Gaul]]," essentially modern [[France]]) was discovered [[spectroscopy|spectroscopically]] by [[Lecoq de Boisbaudran]] in 1875 by its characteristic spectrum (two [[violet (color)|violet]] lines) in an examination of a [[zinc blende]] from the [[Pyrenees]]. Before its discovery, most of its properties had been predicted and described by [[Dmitri Mendeleev]] (who had called the hypothetical element "[[Mendeleev's predicted elements|eka-aluminium]]") on the basis of its position in his [[periodic table]]. Later, in 1875, Boisbaudran obtained the free metal by [[electrolysis]] of its [[hydroxide]] in [[potassium hydroxide]] solution. He named the element "gallia" after his native land of [[France]]. It was later claimed that, in one of those multilingual [[pun]]s so beloved of men of science in the early 19th century, he had also named gallium after himself, as his name, "Le coq," is the French for "the [[rooster]]," and the [[Latin]] for "rooster" is "''gallus''"; however, in an 1877 article Le coq denied this supposition. == Occurrence == Gallium does not exist in free form in nature, nor do any high-gallium minerals exist to serve as a primary source of extraction of the element or its compounds. Gallium is found and extracted as a trace component in [[bauxite]], [[coal]], [[diaspore]], [[germanite]], and [[sphalerite]]. The [[United States Geological Survey]] ([[United States Geological Survey|USGS]]) estimates gallium reserves based on 50 ppm by weight concentration in known reserves of bauxite and zinc ores. Some [[flue]] [[dust]]s from burning coal have been shown to contain small quantities of gallium, typically less than 1 % by weight.<ref>{{cite journal | title = Determination of gallium in coal and coal fly ash by electrothermal atomic absorption spectrometry using slurry sampling and nickel chemical modification | author = Shan Xiao-quan, Wang Wen and Wen Bei | journal = [[J. Anal. At. Spectrom.]] | year = 1992 | volume = 7 | pages = 761–764 | doi = 10.1039/JA9920700761}}</ref><ref>{{cite web | publisher = West Virginia Geological and Economic Survey |date=2002-03-02 | title = Gallium in West Virginia Coals | url = http://www.wvgs.wvnet.edu/www/datastat/te/GaHome.htm}}</ref><ref>{{cite journal | author = O. Font, X. Querol, R. Juan, R. Casado, C. R. Ruiz, A. Lopez-Soler, P. Coca and F. G. Pena | title = Recovery of gallium and vanadium from gasification fly ash | year = 2007 | journal = [[Journal of Hazardous Materials]] | volume = 139 | issue = 3 | pages = 413–423 | doi = 10.1016/j.jhazmat.2006.02.041}}</ref><ref>{{cite journal |title = Elements in Coal Ash and Their Industrial Significance| author =A. J. W. Headlee and Richard G. Hunter| pages = 548–551|doi = 10.1021/ie50519a028 | volume = 45 | issue = 3| year = 1953 | journal =Industrial and Engineering Chemistry}}</ref> Most gallium is extracted from the crude [[aluminium hydroxide]] solution of the [[Bayer process]] for producing alumina and aluminium. A [[mercury (element)|mercury]] cell [[electrolysis]] and [[hydrolysis]] of the [[amalgam]] with [[sodium hydroxide]] leads to sodium gallate. Electrolysis then gives gallium metal. For [[semiconductor]] use, further purification is carried out using [[zone melting]], or else single crystal extraction from a melt ([[Czochralski process]]). Purities of 99.9999% are routinely achieved and commercially widely available. One chemist estimated in 2007 that at the current rate of usage, the world's supply of gallium would be exhausted by about the year 2017.<ref>[http://www.idtechex.com/products/en/articles/00000591.asp Augsberg University Calculate When Our Materials Run Out] retrieved May 4, 2008</ref> == Applications == Semiconductor and electronic industry. The semiconductor applications are the main reason for the low-cost commercial availability of the extremely high-purity (99.9999+%) metal: *As a component of the semiconductor [[Gallium(III) arsenide|gallium arsenide]], the most common application for gallium is analog [[integrated circuit]]s{{Fact|date=February 2008}}, with the second largest use being [[optoelectronic]] devices (mostly [[laser diode]]s and [[LED|light-emitting diodes]].) *Gallium is used widely as a [[dopant]] to [[doping (semiconductor)|dope]] [[semiconductor]]s and produce solid-state devices like [[transistor]]s. *Gallium is the rarest component of new [[photovoltaic]] compounds (such as copper indium gallium selenium sulfide or Cu(In,Ga)(Se,S)<sub>2</sub>, recently announced by South African researchers) for use in solar panels as an alternative to [[crystalline silicon]], which is currently in short supply. As a wetting, and alloy improvement agent: *Because gallium [[wetting|wets]] glass or [[porcelain]], gallium can be used to create brilliant [[mirror]]s. *Gallium readily [[alloy]]s with most metals, and has been used as a component in [[low-melting alloy]]s. The [[plutonium]] used in [[Nuclear weapon design#Plutonium_pit|nuclear weapon pits]] is machined by alloying with gallium to stabilize the [[allotropy|allotrope]]s of plutonium. *Gallium added in quantities up to 2% in common [[solder]]s can aid wetting and flow characteristics. As part of an energy storage mechanism: * Aluminium is reactive enough to reduce water to [[hydrogen]], being oxidized to [[aluminium oxide]]. However, the aluminium oxide forms a protective coat which prevents further reaction. When gallium is alloyed with aluminium, the coat does not form, thus the alloy can potentially provide a solid hydrogen source for transportation purposes, which would be more convenient than a pressurized hydrogen tank. Resmelting the resultant aluminium oxide and gallium mixture to metallic aluminium and gallium and reforming these into electrodes would constitute most of the energy input into the system, while electricity produced by a hydrogen fuel cell could constitute an energy output.<ref>{{cite press release | url = http://www.purdue.edu/uns/x/2007a/070410Gorehydrogen.html | title = Purdue Energy Center symposium to pave the road to a hydrogen economy |date=2007-04-10 | publisher = [[Purdue University]]}}</ref><ref>{{cite news | publisher = PhysOrg.com | url = http://www.physorg.com/news98556080.html | title = New process generates hydrogen from aluminum alloy to run engines, fuel cells |date=2007-05-16}}</ref>The thermodynamic efficiency of the aluminium smelting process is said to be approximately 50 percent.{{Fact|date=October 2007}} Therefore, at most no more than half the energy that goes into smelting aluminium could be recovered by a fuel cell. For liquid alloys: *It has been suggested that a liquid gallium-[[tin]] alloy could be used to cool computer chips in place of water. As it conducts heat approximately 65 times better than water it can make a comparable [[coolant]]. [http://www.newscientist.com/article.ns?id=dn7348] *Gallium is used in some high temperature thermometers. *A liquid Gallium-Indium-Tin alloy has been used in activating Aluminum. Activated Aluminum reacts with water generating Hydrogen and steam. This reaction is considered a feasible process in the hydrogen economy. Biomedical applications: *A low temperature liquid [[eutectic]] alloy of gallium, [[indium]], and [[tin]], is widely available in medical thermometers (fever thermometers), replacing problematic mercury. This alloy, with the trade name ''[[Galinstan]]'' (with the "-stan" referring to the tin), has a freezing point of &minus;20°C. *Gallium [[salt]]s such as gallium [[citrate]] and gallium [[nitrate]] are used as [[radiopharmaceutical]] agents in [[nuclear medicine]] imaging. (The form or salt is not important, since it is the free dissolved gallium ion Ga<sup>3+</sup> which is active). For these applications, a [[radionuclide|radioactive isotope]] such as <sup>67</sup>Ga is used. The body handles Ga<sup>3+</sup> in many ways as though it were iron, and thus it is bound (and concentrates) in areas of inflammation, such as infection, and also areas of rapid cell division. This allows such sites to be imaged by nuclear scan techniques. See [[gallium scan]]. This use has largely been replaced by [[fluorodeoxyglucose]] (FDG) for [[positron emission tomography]], "PET" scan. *[[Gallium maltolate]] is in clinical and preclinical trials as a potential treatment for cancer, infectious disease, and inflammatory disease. <ref>{{cite journal |author = L. R. Bernstein, T. Tanner, C. Godfrey, B. Noll | title = Chemistry and pharmacokinetics of gallium maltolate, a compound with high oral gallium bioavailability | journal = Metal Based Drugs | year = 2000 | volume = 7 | pages = 33–48 | doi = 10.1155/MBD.2000.33}}</ref> *Much research is being devoted to gallium alloys as substitutes for mercury [[dental amalgam]]s, but these compounds have yet to see wide acceptance. *Research is being conducted to determine whether gallium can be used to fight bacterial infections in people with [[cystic fibrosis]]. Gallium is similar in size to iron, an essential nutrient for respiration. When gallium is mistakenly picked up by bacteria such as ''[[Pseudomonas]]'', the bacteria's ability to respire is interfered with and the bacteria die. The mechanism behind this is that iron is redox active, which allows for the transfer of electrons during respiration, but gallium is redox inactive. <ref>[http://www.infoniac.com/health-fitness/trojan-gallium.html A Trojan-horse strategy selected to fight bacteria]</ref><ref>[http://www.medpagetoday.com/InfectiousDisease/GeneralInfectiousDisease/tb/5266 Gallium May Have Antibiotic-Like Properties]</ref> Miscellaneous: *[[Magnesium]] [[gallate]] containing impurities (such as Mn<sup>2+</sup>), is beginning to be used in [[ultraviolet]]-activated [[phosphor]] powder. *[[Neutrino]] detection. Possibly the largest amount of pure gallium ever collected in a single spot was the [[GALLEX]] neutrino detector operated in the early 1990s in an Italian mountain tunnel. The detector contained 12.2 tons of watered gallium-71. Solar neutrinos caused a few atoms of Ga-71 to become radioactive [[Germanium|Ge]]-71, which were detected. The solar neutrino flux deduced was found to have a deficit of 40% from theory. This was not explained until better solar neutrino detectors and theories were constructed (see [[SNO]]).[http://wwwlapp.in2p3.fr/neutrinos/anexp.html#gallex] *As a [[liquid metal ion source]] for a [[focused ion beam]]. == Precautions == While not considered toxic, the data about gallium are inconclusive. Some sources suggest that it may cause [[dermatitis]] from prolonged exposure; other tests have not caused a positive reaction. Like most metals, finely divided gallium loses its luster. Powdered gallium appears grey. When gallium is handled with bare hands, the extremely fine dispersion of liquid gallium droplets which results from wetting skin with the metal may appear as a grey skin stain. ==See also== * [[:category:Gallium compounds|Gallium compounds]] == References == *[http://periodic.lanl.gov/elements/31.html Los Alamos National Laboratory &ndash; Gallium] *[http://www.webelements.com/webelements/elements/text/Ga/key.html Webelements: detailed information on gallium] <references/> == External links == {{Commons|Gallium}} {{wiktionary|gallium}} *[http://www.webelements.com/webelements/elements/text/Ga/index.html WebElements.com &ndash; textbook information on gallium] *[http://www.pniok.de/ga.htm Picture in the Element collection from Heinrich Pniok] *[[Material safety data sheet]] at [http://www.acialloys.com/msds/ga.html acialloys.com] *[http://www.lenntech.com/Periodic-chart-elements/Ga-en.htm www.lenntech.com &ndash; textbook information regarding gallium] *[http://minerals.usgs.gov/minerals/pubs/commodity/gallium/index.html environmental effects of gallium] *[http://minerals.usgs.gov/minerals/pubs/commodity/gallium/460798.pdf Price development of gallium 1959-1998] *[http://www.physorg.com/news107446364.html Technology produces hydrogen by adding water to an alloy of aluminum and gallium] *[http://www.pse-mendelejew.de/bilder/ga.jpg pure Gallium crystals ~99,9999% picture in the element collection from Heinrich Pniok] {{clear}} {{compact periodic table}} [[Category:Chemical elements]] [[Category:Poor metals]] [[Category:Coolants]] [[Category:Gallium]] <!-- interwiki --> [[af:Gallium]] [[ar:غاليوم]] [[bn:গ্যালিয়াম]] [[be:Галій]] [[bs:Galijum]] [[bg:Галий]] [[ca:Gal·li]] [[cs:Gallium]] [[co:Galliu]] [[cy:Galiwm]] [[da:Gallium]] [[de:Gallium]] [[et:Gallium]] [[el:Γάλλιο]] [[es:Galio]] [[eo:Galiumo]] [[eu:Galio]] [[fa:گالیوم]] [[fr:Gallium]] [[fur:Gali]] [[ga:Gailliam]] [[gv:Gallium]] [[gl:Galio]] [[ko:갈륨]] [[hy:Գալիում]] [[hi:गैलिअम]] [[hr:Galij]] [[io:Galio]] [[id:Galium]] [[is:Gallín]] [[it:Gallio (elemento)]] [[he:גליום]] [[jv:Galium]] [[sw:Gali]] [[ht:Galyòm]] [[ku:Galyûm]] [[la:Gallium]] [[lv:Gallijs]] [[lb:Gallium]] [[lt:Galis]] [[jbo:fasyjinme]] [[hu:Gallium]] [[ml:ഗാലിയം]] [[nl:Gallium]] [[ja:ガリウム]] [[no:Gallium]] [[nn:Gallium]] [[oc:Galli]] [[uz:Galliy]] [[pl:Gal]] [[pt:Gálio]] [[qu:Galyu]] [[ru:Галлий]] [[scn:Galliu (elementu)]] [[simple:Gallium]] [[sk:Gálium]] [[sl:Galij]] [[sr:Галијум]] [[sh:Galijum]] [[fi:Gallium]] [[sv:Gallium]] [[ta:காலியம்]] [[th:แกลเลียม]] [[vi:Gali]] [[tr:Galyum]] [[uk:Галій]] [[zh:镓]]