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{{Short description|Chemical element, symbol Ga}}
{{About|the chemical element}}
{{Good article}}
{{Infobox gallium}}
{{Use dmy dates|date=May 2024}}
'''Gallium''' is a [[chemical element]]; it has [[Chemical symbol|symbol]] '''Ga''' and [[atomic number]] 31. Discovered by the French chemist [[Paul-Émile Lecoq de Boisbaudran]] in 1875,<ref>{{Cite book|last=Scerri|first=Eric|title=The Periodic Table: Its Story and Its Significance|publisher=[[Oxford University Press]]|year=2020|isbn=978-0-19-091436-3|pages=149}}</ref> 
elemental gallium is a soft, silvery metal at [[standard temperature and pressure]]. In its liquid state, it becomes silvery white. If enough force is applied, solid gallium may fracture [[conchoidal fracture|conchoidally]]. Since its discovery in 1875, gallium has widely been used to make [[alloy]]s with low melting points. It is also used in [[semiconductor]]s, as a [[dopant]] in semiconductor substrates.

The melting point of gallium, {{convert|29.7646|°C|°F K}}, is used as a temperature reference point. Gallium alloys are used in thermometers as a non-toxic and environmentally friendly alternative to [[Mercury (element)|mercury]], and can withstand higher temperatures than mercury. A melting point of {{convert|-19|°C|°F}}, well below the freezing point of water, is claimed for the alloy [[galinstan]] (62–⁠95% gallium, 5–⁠22% [[indium]], and 0–⁠16% [[tin]] by weight), but that may be the freezing point with the effect of [[supercooling]].

Gallium does not occur as a free element in nature, but rather as gallium(III) compounds in trace amounts in [[zinc]] ores (such as [[sphalerite]]) and in [[bauxite]]. Elemental gallium is a liquid at temperatures greater than {{convert|29.76|°C|°F}}, and will melt in a person's hands at normal human body temperature of {{convert|37.0|°C|°F|abbr=}}.

Gallium is predominantly used in electronics. [[Gallium arsenide]], the primary chemical compound of gallium in electronics, is used in [[microwave]] circuits, high-speed switching circuits, and [[infrared]] circuits. Semiconducting [[gallium nitride]] and [[indium gallium nitride]] produce blue and violet [[light-emitting diode]]s and [[diode laser]]s. Gallium is also used in the production of artificial [[gadolinium gallium garnet]] for jewelry. It has no known natural role in biology. Gallium(III) behaves in a similar manner to [[ferric#Ferric iron and life|ferric]] salts in biological systems and has been used in some medical applications, including pharmaceuticals and [[radiopharmaceuticals]].

==Physical properties==
[[File:Gallium kristallisiert.JPG|thumb|left|Crystallization of gallium from the melt]]
Elemental gallium is not found in nature, but it is easily obtained by [[smelting]]. Very pure gallium is a silvery blue metal that fractures [[conchoidal fracture|conchoidally]] like [[glass]]. Gallium's volume expands by 3.10% when it changes from a liquid to a solid so care must be taken when storing it in containers that may rupture when it changes state. Gallium shares the higher-density liquid state with a short list of other materials that includes [[properties of water|water]], [[silicon]], [[germanium]], [[bismuth]], and [[plutonium]].<ref name="GreenwoodEarnshaw2nd">{{Greenwood&Earnshaw2nd}}</ref>{{rp|222}}
[[File:Liquid gallium pouring.png|thumb|Liquid gallium at {{convert|86|F|}}]]
Gallium forms alloys with most metals. It readily diffuses into cracks or [[grain boundary|grain boundaries]] of some metals such as aluminium, [[aluminium]]–[[zinc]] [[alloy]]s<ref>{{cite journal|title= Grain boundary imaging, gallium diffusion and the fracture behavior of Al–Zn Alloy – An in situ study |author= Tsai, W. L|journal= Nuclear Instruments and Methods in Physics Research Section B |date= 2003 |volume= 199 |pages= 457–463 |doi= 10.1016/S0168-583X(02)01533-1|bibcode= 2003NIMPB.199..457T|last2= Hwu|first2= Y.|last3= Chen|first3= C. H.|last4= Chang|first4= L. W.|last5= Je|first5= J. H.|last6= Lin|first6= H. M.|last7= Margaritondo|first7= G.}}</ref> and [[steel]],<ref>{{cite web|url=https://apps.dtic.mil/sti/citations/ADA365497 |title= Liquid Metal Embrittlement of ASTM A723 Gun Steel by Indium and Gallium|author= Vigilante, G. N.|author2= Trolano, E.|author3= Mossey, C.|publisher= Defense Technical Information Center |date=June 1999|access-date=7 July 2009}}</ref> causing extreme loss of strength and ductility called [[liquid metal embrittlement]].

The [[melting point]] of gallium, at 302.9146&nbsp;K (29.7646&nbsp;°C, 85.5763&nbsp;°F), is just above room temperature, and is approximately the same as the average summer daytime temperatures in Earth's mid-latitudes. This melting point (mp) is one of the formal temperature reference points in the [[International Temperature Scale of 1990]] (ITS-90) established by the [[International Bureau of Weights and Measures]] (BIPM).<ref>{{cite journal |url= http://www.bipm.org/utils/common/pdf/its-90/ITS-90_metrologia.pdf |archive-url=https://web.archive.org/web/20070618131554/http://www.bipm.org/utils/common/pdf/its-90/ITS-90_metrologia.pdf |archive-date=18 June 2007 |url-status=live |title= The International Temperature Scale of 1990 (ITS-90) |last= Preston–Thomas |first= H. |journal= Metrologia |volume= 27 |issue= 1 |pages= 3–10 |date= 1990 |doi= 10.1088/0026-1394/27/1/002 |bibcode= 1990Metro..27....3P |s2cid= 250785635 }}</ref><ref>{{Cite web |url=http://www.bipm.org/en/publications/its-90.html |title=ITS-90 documents at Bureau International de Poids et Mesures}}</ref><ref>{{cite news |url=http://www.cstl.nist.gov/div836/836.05/papers/magnum90ITS90guide.pdf |archive-url=https://web.archive.org/web/20030704215942/http://www.cstl.nist.gov/div836/836.05/papers/magnum90ITS90guide.pdf |url-status=dead |archive-date=4 July 2003 |title=Guidelines for Realizing the International Temperature Scale of 1990 (ITS-90) |last1=Magnum |first1=B. W. |last2=Furukawa |first2=G. T. |publisher=National Institute of Standards and Technology |id=NIST TN 1265 |date=August 1990 }}</ref> The [[triple point]] of gallium, 302.9166&nbsp;K (29.7666&nbsp;°C, 85.5799&nbsp;°F), is used by the US [[National Institute of Standards and Technology]] (NIST) in preference to the melting point.<ref>{{cite journal|access-date=30 October 2016 |title=NIST realization of the gallium triple point |last=Strouse |first=Gregory F. |journal=Proc. TEMPMEKO |volume=1999 |issue=1 |year=1999|pages=147–152 |url=http://ws680.nist.gov/publication/get_pdf.cfm?pub_id=830622}}</ref>

The melting point of gallium allows it to melt in the human hand, and then solidify if removed. The liquid metal has a strong tendency to [[supercooling|supercool]] below its [[melting point]]/[[freezing point]]: Ga [[nanoparticle]]s can be kept in the liquid state below 90&nbsp;K.<ref>{{cite journal |doi=10.1063/1.2221395 |title=Extreme undercooling (down to 90K) of liquid metal nanoparticles |journal=Applied Physics Letters |volume=89 |issue=3 |pages=033123 |year=2006 |last1=Parravicini |first1=G. B. |last2=Stella |first2=A. |last3=Ghigna |first3=P. |last4=Spinolo |first4=G. |last5=Migliori |first5=A. |last6=d'Acapito |first6=F. |last7=Kofman |first7=R. |bibcode=2006ApPhL..89c3123P}}</ref> [[Seed crystal|Seeding]] with a crystal helps to initiate freezing. Gallium is one of the four non-radioactive metals (with [[caesium]], [[rubidium]], and [[mercury (element)|mercury]]) that are known<!--PLEASE DO NOT ADD FRANCIUM; ITS MELTING POINT IS ONLY CALCULATED, AND ITS INTENSE RADIOACTIVITY WOULD MEAN THAT SHOULD YOU HAVE ENOUGH AROUND TO FILL A THERMOMETER, MEASURING ITS TEMPERATURE SHOULD NOT BE YOUR GREATEST CONCERN--> to be liquid at, or near, normal room temperature. Of the four, gallium is the only one that is neither highly reactive (as are rubidium and caesium) nor highly toxic (as is mercury) and can, therefore, be used in metal-in-glass high-temperature thermometers. It is also notable for having one of the largest liquid ranges for a metal, and for having (unlike mercury) a low [[vapor pressure]] at high temperatures. Gallium's boiling point, 2676&nbsp;K, is nearly nine times higher than its melting point on the [[Kelvin|absolute scale]], the greatest ratio between melting point and boiling point of any element.<ref name="GreenwoodEarnshaw2nd"/>{{rp|224}} Unlike mercury, liquid gallium metal [[wetting|wets]] glass and skin, along with most other materials (with the exceptions of quartz, graphite, [[gallium(III) oxide]]<ref>{{cite conference |last1=Chen |first1=Ziyu |last2=Lee |first2=Jeong-Bong |title=2019 IEEE 32nd International Conference on Micro Electro Mechanical Systems (MEMS) |chapter=Gallium Oxide Coated Flat Surface as Non-Wetting Surface for Actuation of Liquid Metal Droplets |year=2019 |pages=1–4 |doi=10.1109/memsys.2019.8870886| isbn=978-1-7281-1610-5 }}</ref> and [[PTFE]]),<ref name="GreenwoodEarnshaw2nd"/>{{rp|221}} making it mechanically more difficult to handle even though it is substantially less toxic and requires far fewer precautions than mercury. Gallium painted onto glass is a brilliant mirror.<ref name="GreenwoodEarnshaw2nd" />{{rp|221}} For this reason as well as the metal contamination and freezing-expansion problems, samples of gallium metal are usually supplied in polyethylene packets within other containers.

<div style="float:left;margin-right:0.5em;">
{|class="wikitable"
|+Properties of gallium for different crystal axes<ref name="anis" />
!Property!!''a''!! ''b'' !! ''c''
|-
|[[Thermal expansion|α]] (~25&nbsp;°C, μm/m)||16||11||31
|-
|[[Electrical resistivity and conductivity|ρ]] (29.7&nbsp;°C, nΩ·m)||543||174||81
|-
|ρ (0&nbsp;°C, nΩ·m)||480||154||71.6
|-
|ρ (77 K, nΩ·m)||101||30.8||14.3
|-
|ρ (4.2 K, pΩ·m)<!-- pico-Ohm, not a typo-->||13.8||6.8||1.6
|}</div>
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]]. Within a unit cell, each atom has only one nearest neighbor (at a distance of 244&nbsp;[[picometre|pm]]). The remaining six unit cell neighbors are spaced 27, 30 and 39&nbsp;pm farther away, and they are grouped in pairs with the same distance.<ref>{{cite journal |last1=Bernasconi |first1=M. |last2=Chiarotti |first2=Guido L. |last3=Tosatti |first3=E. |title=Ab initio calculations of structural and electronic properties of gallium solid-state phases |journal=Physical Review B |date=October 1995 |volume=52 |issue=14 |pages=9988–9998 |doi=10.1103/PhysRevB.52.9988 |pmid=9980044 |bibcode=1995PhRvB..52.9988B }}</ref> Many stable and [[metastability in molecules|metastable]] phases are found as function of temperature and pressure.<ref>{{cite report |last1=Young |first1=David A. |title=Phase diagrams of the elements |date=11 September 1975 |id={{osti|4010212}} |doi=10.2172/4010212 }}</ref>

The bonding between the two nearest neighbors is [[covalent]]; hence Ga<sub>2</sub> [[Dimer (chemistry)|dimers]] are seen as the fundamental building blocks of the crystal. This explains the low melting point relative to the neighbor elements, aluminium and indium. This structure is strikingly similar to that of [[iodine]] and may form because of interactions between the single 4p electrons of gallium atoms, further away from the nucleus than the 4s electrons and the [Ar]3d<sup>10</sup> core. This phenomenon recurs with [[mercury (element)|mercury]] with its "pseudo-noble-gas" [Xe]4f<sup>14</sup>5d<sup>10</sup>6s<sup>2</sup> electron configuration, which is liquid at room temperature.<ref name="GreenwoodEarnshaw2nd"/>{{rp|223}} The 3d<sup>10</sup> electrons do not shield the outer electrons very well from the nucleus and hence the first ionisation energy of gallium is greater than that of aluminium.<ref name="GreenwoodEarnshaw2nd" />{{rp|222}} Ga<sub>2</sub> dimers do not persist in the liquid state and liquid gallium exhibits a complex low-coordinated structure in which each gallium atom is surrounded by 10 others, rather than 11–12 neighbors typical of most liquid metals.<ref>{{cite journal |last1=Yagafarov |first1=O. F. |last2=Katayama |first2=Y. |last3=Brazhkin |first3=V. V. |last4=Lyapin |first4=A. G. |last5=Saitoh |first5=H. |title=Energy dispersive x-ray diffraction and reverse Monte Carlo structural study of liquid gallium under pressure |journal=Physical Review B |date=7 November 2012 |volume=86 |issue=17 |page=174103 |doi=10.1103/PhysRevB.86.174103 |bibcode=2012PhRvB..86q4103Y }}</ref><ref>{{Cite journal |title=Structural Ordering in Liquid Gallium under Extreme Conditions |first1=James W. E.|last1=Drewitt |first2=Francesco |last2=Turci |first3=Benedict J. |last3=Heinen |first4=Simon G. |last4=Macleod |first5=Fei |last5=Qin |first6=Annette K. |last6=Kleppe |first7=Oliver T. |last7=Lord |date=9 April 2020 |journal=Physical Review Letters |volume=124 |issue=14 |pages=145501 |doi=10.1103/PhysRevLett.124.145501 |pmid=32338984 |bibcode=2020PhRvL.124n5501D |s2cid=216177238 |doi-access=free |hdl=1983/d385c37f-dc53-4177-985e-38875b57d8d9 |hdl-access=free}}</ref>

The physical properties of gallium are highly [[Anisotropy|anisotropic]], i.e. have different values along the three major crystallographic axes ''a'', ''b'', and ''c'' (see table), producing a significant difference between the linear (α) and volume [[thermal expansion]] coefficients. The properties of gallium are strongly temperature-dependent, particularly near the melting point. For example, the coefficient of thermal expansion increases by several hundred percent upon melting.<ref name="anis">{{cite book |author=Rosebury, Fred |title=Handbook of Electron Tube and Vacuum Techniques |url=https://books.google.com/books?id=yBmnnaODnHgC&pg=PA26 |date=1992 |publisher=Springer |isbn=978-1-56396-121-2 |page=26}}</ref>

===Isotopes===
{{Main|Isotopes of gallium}}
Gallium has 30 known isotopes, ranging in [[mass number]] from 60 to 89. Only two isotopes are stable and occur naturally, gallium-69 and gallium-71. Gallium-69 is more abundant: it makes up about 60.1% of natural gallium, while gallium-71 makes up the remaining 39.9%. All the other isotopes are radioactive, with gallium-67 being the longest-lived (half-life 3.261&nbsp;days). Isotopes lighter than gallium-69 usually decay through [[beta plus decay]] (positron emission) or [[electron capture]] to isotopes of [[zinc]], while isotopes heavier than gallium-71 decay through [[beta minus decay]] (electron emission), possibly with delayed [[neutron emission]], to isotopes of [[germanium]]. Gallium-70 can decay through both beta minus decay and electron capture. Gallium-67 is unique among the light isotopes in having only electron capture as a decay mode, as its decay energy is not sufficient to allow positron emission.<ref name="Audi">{{NUBASE 2003}}</ref> Gallium-67 and [[gallium-68]] (half-life 67.7&nbsp;min) are both used in [[nuclear medicine]].

==Chemical properties==
{{Main article|Gallium compounds}}
Gallium is found primarily in the +3 [[oxidation state]]. The +1 oxidation state is also found in some compounds, although it is less common than it is for gallium's heavier congeners [[indium]] and [[thallium]]. For example, the very stable GaCl<sub>2</sub> contains both gallium(I) and gallium(III) and can be formulated as Ga<sup>I</sup>Ga<sup>III</sup>Cl<sub>4</sub>; in contrast, the monochloride is unstable above 0&nbsp;°C, [[disproportionating]] into elemental gallium and gallium(III) chloride. Compounds containing Ga–Ga bonds are true gallium(II) compounds, such as [[gallium(II) sulfide|GaS]] (which can be formulated as Ga<sub>2</sub><sup>4+</sup>(S<sup>2−</sup>)<sub>2</sub>) and the [[dioxan]] complex Ga<sub>2</sub>Cl<sub>4</sub>(C<sub>4</sub>H<sub>8</sub>O<sub>2</sub>)<sub>2</sub>.<ref name="GreenwoodEarnshaw2nd"/>{{rp|240}}

===Aqueous chemistry===
Strong acids dissolve gallium, forming gallium(III) salts such as [[gallium(III) nitrate|{{chem|Ga(NO|3|)|3}}]] (gallium nitrate). [[Aqueous]] solutions of gallium(III) salts contain the hydrated gallium ion, {{chem|[Ga(H|2|O)|6|]|3+}}.<ref name="wiberg_holleman">{{cite book |title= Inorganic chemistry |author1= Wiberg, Egon |author2= Wiberg, Nils |author3= Holleman, Arnold Frederick |publisher= Academic Press |date= 2001 |isbn= 978-0-12-352651-9}}</ref>{{rp|1033}} [[Gallium(III) hydroxide]], {{chem|Ga(OH)|3}}, may be precipitated from gallium(III) solutions by adding [[ammonia]]. Dehydrating {{chem|Ga(OH)|3}} at 100&nbsp;°C produces gallium oxide hydroxide, GaO(OH).<ref name="downs">{{cite book |title= Chemistry of aluminium, gallium, indium, and thallium |author= Downs, Anthony John |publisher= Springer |date= 1993 |isbn= 978-0-7514-0103-5}}</ref>{{rp|140–141}}

Alkaline [[hydroxide]] solutions dissolve gallium, forming ''gallate'' salts (not to be confused with identically named [[gallic acid]] salts) containing the {{chem|Ga(OH)|4|-}} anion.<ref name="eagleson" /><ref name="wiberg_holleman" />{{rp|1033}}<ref name="sipos" /> Gallium hydroxide, which is [[amphoteric]], also dissolves in alkali to form gallate salts.<ref name="downs" />{{rp|141}} Although earlier work suggested {{chem|Ga(OH)|6|3-}} as another possible gallate anion,<ref>{{cite book |title= Electrochemistry—Volume 3: Specialist periodical report |author= Hampson, N. A. |editor= Harold Reginald Thirsk |publisher= Royal Society of Chemistry |location= Great Britain |date= 1971 |isbn= 978-0-85186-027-5 |page= 71 |url= https://books.google.com/books?id=vN0Y7KMGqNcC}}</ref> it was not found in later work.<ref name="sipos">{{cite journal |last1= Sipos |first1= P. L. |last2= Megyes |first2= T. N. |last3= Berkesi |year= 2008 |first3= O. |title= The Structure of Gallium in Strongly Alkaline, Highly Concentrated Gallate Solutions—a Raman and {{SimpleNuclide|Ga|71}}-NMR Spectroscopic Study |journal= J Solution Chem |volume= 37 |issue= 10 |pages= 1411–1418 |doi= 10.1007/s10953-008-9314-y |s2cid= 95723025 }}</ref>

===Oxides and chalcogenides===
Gallium reacts with the [[chalcogen]]s only at relatively high temperatures. At room temperature, gallium metal is not reactive with air and water because it forms a [[passivation (chemistry)|passive]], protective [[oxide]] layer. At higher temperatures, however, it reacts with atmospheric [[oxygen]] to form [[gallium(III) oxide]], {{chem|Ga|2|O|3}}.<ref name="eagleson">{{cite book
|title= Concise encyclopedia chemistry
|url= https://archive.org/details/conciseencyclope00eagl
|url-access= registration
|editor= Eagleson, Mary
|publisher= Walter de Gruyter
|date= 1994
|isbn= 978-3-11-011451-5
|page= [https://archive.org/details/conciseencyclope00eagl/page/438 438]
}}</ref> Reducing {{chem|Ga|2|O|3}} with elemental gallium in vacuum at 500&nbsp;°C to 700&nbsp;°C yields the dark brown [[gallium(I) oxide]], {{chem|Ga|2|O}}.<ref name="downs" />{{rp|285}} {{chem|Ga|2|O}} is a very strong [[reducing agent]], capable of reducing [[sulfuric acid|{{chem|H|2|SO|4}}]] to [[hydrogen sulfide|{{chem|H|2|S}}]].<ref name="downs" />{{rp|207}} It disproportionates at 800&nbsp;°C back to gallium and {{chem|Ga|2|O|3}}.<ref name="emeleus_sharpe">{{cite book |title= Advances in inorganic chemistry and radiochemistry |volume= 5 |author= Greenwood, N. N. |editor= Harry Julius Emeléus |editor-link= Harry Julius Emeléus |editor2= Alan G. Sharpe |publisher= Academic Press |date= 1962
|isbn= 978-0-12-023605-3 |pages= 94–95}}</ref>

[[Gallium(III) sulfide]], {{chem|Ga|2|S|3}}, has 3 possible crystal modifications.<ref name="emeleus_sharpe" />{{rp|104}} It can be made by the reaction of gallium with [[hydrogen sulfide]] ({{chem|H|2|S}}) at 950&nbsp;°C.<ref name="downs" />{{rp|162}} Alternatively, {{chem|Ga(OH)|3}} can be used at 747&nbsp;°C:<ref>{{cite book |title= Semiconductors: data handbook |author= Madelung, Otfried |edition= 3rd |publisher= Birkhäuser |date= 2004 |isbn= 978-3-540-40488-0 |pages= 276–277}}</ref>
:2 {{chem|Ga(OH)|3}} + 3 {{chem|H|2|S}} → {{chem|Ga|2|S|3}} + 6 {{chem|H|2|O}}

Reacting a mixture of alkali metal carbonates and {{chem|Ga|2|O|3}} with {{chem|H|2|S}} leads to the formation of ''thiogallates'' containing the {{chem|[Ga|2|S|4|]|2-}} anion. Strong acids decompose these salts, releasing {{chem|H|2|S}} in the process.<ref name="emeleus_sharpe" />{{rp|104–105}} The mercury salt, {{chem|HgGa|2|S|4}}, can be used as a [[phosphor]].<ref>{{cite journal |author= Krausbauer, L. |author2= Nitsche, R. |author3= Wild, P. |year= 1965 |title= Mercury gallium sulfide, {{chem|HgGa|2|S|4}}, a new phosphor |journal= Physica |volume= 31 |issue= 1 |pages= 113–121 |doi= 10.1016/0031-8914(65)90110-2|bibcode= 1965Phy....31..113K}}</ref>

Gallium also forms sulfides in lower oxidation states, such as [[gallium(II) sulfide]] and the green [[gallium(I) sulfide]], the latter of which is produced from the former by heating to 1000&nbsp;°C under a stream of nitrogen.<ref name="emeleus_sharpe" />{{rp|94}}

The other binary chalcogenides, {{chem|Ga|2|Se|3}} and {{chem|Ga|2|Te|3}}, have the [[zincblende (crystal structure)|zincblende]] structure. They are all semiconductors but are easily [[hydrolysis|hydrolysed]] and have limited utility.<ref name="emeleus_sharpe" />{{rp|104}}

===Nitrides and pnictides===
{{Multiple image
|width= 160
|image1= Crystal-GaN.jpg
|image2= Gallium Arsenide (GaAs) 2" wafer.jpg
|footer= Gallium nitride (left) and gallium arsenide (right) wafers
}}
Gallium reacts with ammonia at 1050&nbsp;°C to form [[gallium nitride]], GaN. Gallium also forms binary compounds with [[phosphorus]], [[arsenic]], and [[antimony]]: [[gallium phosphide]] (GaP), [[gallium arsenide]] (GaAs), and [[gallium antimonide]] (GaSb). These compounds have the same structure as [[zinc sulfide|ZnS]], and have important [[semiconductor|semiconducting]] properties.<ref name="wiberg_holleman" />{{rp|1034}} GaP, GaAs, and GaSb can be synthesized by the direct reaction of gallium with elemental phosphorus, arsenic, or antimony.<ref name="emeleus_sharpe" />{{rp|99}} They exhibit higher electrical conductivity than GaN.<ref name="emeleus_sharpe" />{{rp|101}} GaP can also be synthesized by reacting {{chem|Ga|2|O}} with phosphorus at low temperatures.<ref>{{cite book |title= Inorganic Chemistry |author= Michelle Davidson |publisher= Lotus Press |date= 2006 |isbn= 978-81-89093-39-6 |page= 90}}</ref>

Gallium forms ternary [[nitride]]s; for example:<ref name="emeleus_sharpe" />{{rp|99}}
:{{chem|Li|3|Ga}} + {{chem|N|2}} → {{chem|Li|3|GaN|2}}

Similar compounds with phosphorus and arsenic are possible: {{chem|Li|3|GaP|2}} and {{chem|Li|3|GaAs|2}}. These compounds are easily hydrolyzed by dilute [[acid]]s and water.<ref name="emeleus_sharpe" />{{rp|101}}

===Halides===
{{See also|Gallium halides}}
Gallium(III) oxide reacts with [[Halogenation|fluorinating agents]] such as [[hydrogen fluoride|HF]] or [[fluorine|{{chem|F|2}}]] to form [[gallium(III) fluoride]], {{chem|GaF|3}}. It is an ionic compound strongly insoluble in water. However, it dissolves in [[hydrofluoric acid]], in which it forms an [[adduct]] with water, {{chem|GaF|3|·3H|2|O}}. Attempting to dehydrate this adduct forms {{chem|GaF|2|OH·''n''H|2|O}}. The adduct reacts with ammonia to form {{chem|GaF|3|·3NH|3}}, which can then be heated to form anhydrous {{chem|GaF|3}}.<ref name="downs" />{{rp|128–129}}

[[Gallium trichloride]] is formed by the reaction of gallium metal with [[chlorine]] gas.<ref name="eagleson" /> Unlike the trifluoride, gallium(III) chloride exists as dimeric molecules, {{chem|Ga|2|Cl|6}}, with a melting point of 78&nbsp;°C. Equivalent compounds are formed with bromine and iodine, [[gallium(III) bromide|{{chem|Ga|2|Br|6}}]] and [[gallium(III) iodide|{{chem|Ga|2|I|6}}]].<ref name="downs" />{{rp|133}}

Like the other group 13 trihalides, gallium(III) halides are [[Lewis acid]]s, reacting as halide acceptors with alkali metal halides to form salts containing {{chem|GaX|4|-}} anions, where X is a halogen. They also react with [[haloalkane|alkyl halides]] to form [[carbocation]]s and {{chem|GaX|4|-}}.<ref name="downs" />{{rp|136–137}}

When heated to a high temperature, gallium(III) halides react with elemental gallium to form the respective gallium(I) halides. For example, {{chem|GaCl|3}} reacts with Ga to form {{chem|GaCl}}:
:2 Ga + {{chem|GaCl|3}} {{eqm}} 3 GaCl (g)

At lower temperatures, the equilibrium shifts toward the left and GaCl disproportionates back to elemental gallium and {{chem|GaCl|3}}. GaCl can also be produced by reacting Ga with HCl at 950&nbsp;°C; the product can be condensed as a red solid.<ref name="wiberg_holleman" />{{rp|1036}}

Gallium(I) compounds can be stabilized by forming adducts with Lewis acids. For example:
:GaCl + {{chem|AlCl|3}} → {{chem|Ga|+|[AlCl|4|]|-}}

The so-called "gallium(II) halides", {{chem|GaX|2}}, are actually adducts of gallium(I) halides with the respective gallium(III) halides, having the structure {{chem|Ga|+|[GaX|4|]|-}}. For example:<ref name="eagleson" /><ref name="wiberg_holleman" />{{rp|1036}}<ref name="arora">{{cite book
|title= Text Book Of Inorganic Chemistry
|author= Arora, Amit
|publisher= Discovery Publishing House
|date= 2005
|isbn= 978-81-8356-013-9
|pages= 389–399
}}</ref>
:GaCl + {{chem|GaCl|3}} → {{chem|Ga|+|[GaCl|4|]|-}}

===Hydrides===
Like [[aluminium]], gallium also forms a [[hydride]], {{chem|GaH|3}}, known as ''[[gallane]]'', which may be produced by reacting lithium gallanate ({{chem|LiGaH|4}}) with [[gallium(III) chloride]] at −30&nbsp;°C:<ref name="wiberg_holleman" />{{rp|1031}}
:3 {{chem|LiGaH|4}} + {{chem|GaCl|3}} → 3 LiCl + 4 {{chem|GaH|3}}

In the presence of [[dimethyl ether]] as solvent, {{chem|GaH|3}} polymerizes to {{chem|(GaH|3|)|''n''}}. If no solvent is used, the dimer {{chem|Ga|2|H|6}} (''[[digallane]]'') is formed as a gas. Its structure is similar to [[diborane]], having two hydrogen atoms bridging the two gallium centers,<ref name="wiberg_holleman" />{{rp|1031}} unlike α-[[aluminium hydride|{{chem|AlH|3}}]] in which aluminium has a coordination number of 6.<ref name="wiberg_holleman" />{{rp|1008}}

Gallane is unstable above −10&nbsp;°C, decomposing to elemental gallium and [[hydrogen]].<ref name="sykes">{{cite book
|title= Advances in Inorganic Chemistry
|volume= 41
|author1= Downs, Anthony J.
|author2= Pulham, Colin R.
|editor= Sykes, A. G.
|publisher= Academic Press
|date= 1994
|isbn= 978-0-12-023641-1
|pages= 198–199
}}</ref>

===Organogallium compounds===
{{Main|Organogallium chemistry}}
Organogallium compounds are of similar reactivity to [[Organoindium chemistry|organoindium]] compounds, less reactive than [[Organoaluminium chemistry|organoaluminium]] compounds, but more reactive than [[Thallium#Organothallium compounds|organothallium]] compounds.<ref name="GreenwoodEarnshaw2nd"/>{{rp|262-5}} Alkylgalliums are monomeric. [[Lewis acid]]ity decreases in the order Al > Ga > In and as a result organogallium compounds do not form bridged dimers as organoaluminium compounds do. Organogallium compounds are also less reactive than organoaluminium compounds. They do form stable peroxides.<ref>{{cite journal |last1=Uhl |first1=Werner |last2=Reza Halvagar |first2=Mohammad |last3=Claesener |first3=Michael |title=Reducing Ga-H and Ga-C Bonds in Close Proximity to Oxidizing Peroxo Groups: Conflicting Properties in Single Molecules |journal=Chemistry – A European Journal |date=26 October 2009 |volume=15 |issue=42 |pages=11298–11306 |doi=10.1002/chem.200900746 |pmid=19780106 }}</ref> These alkylgalliums are liquids at room temperature, having low melting points, and are quite mobile and flammable. Triphenylgallium is monomeric in solution, but its crystals form chain structures due to weak intermolecluar Ga···C interactions.<ref name="GreenwoodEarnshaw2nd"/>{{rp|262-5}}

Gallium trichloride is a common starting reagent for the formation of organogallium compounds, such as in [[carbometalation|carbogallation]] reactions.<ref>{{cite journal |doi= 10.1002/ejoc.200500512 |volume=2005 |issue=24 |title=GaCl<sub>3</sub> in Organic Synthesis |year=2005 |journal=European Journal of Organic Chemistry |pages=5145–5150 |last1= Amemiya |first1= Ryo}}</ref> Gallium trichloride reacts with [[lithium]] cyclopentadienide in [[diethyl ether]] to form the trigonal planar gallium cyclopentadienyl complex GaCp<sub>3</sub>. Gallium(I) forms complexes with [[arene]] [[ligand]]s such as [[hexamethylbenzene]]. Because this ligand is quite bulky, the structure of the [Ga(η<sup>6</sup>-C<sub>6</sub>Me<sub>6</sub>)]<sup>+</sup> is that of a [[half sandwich compound|half-sandwich]]. Less bulky ligands such as [[mesitylene]] allow two ligands to be attached to the central gallium atom in a bent sandwich structure. [[Benzene]] is even less bulky and allows the formation of dimers: an example is [Ga(η<sup>6</sup>-C<sub>6</sub>H<sub>6</sub>)<sub>2</sub>] [GaCl<sub>4</sub>]·3C<sub>6</sub>H<sub>6</sub>.<ref name="GreenwoodEarnshaw2nd"/>{{rp|262-5}}

==History==
[[File:Gallium drops.ogv|thumbnail|Small gallium droplets fusing together]]
In 1871, the existence of gallium was first predicted by Russian chemist [[Dmitri Mendeleev]], who named it "[[Mendeleev's predicted elements|eka-aluminium]]" from its position in his [[periodic table]]. He also predicted several properties of eka-aluminium that correspond closely to the real properties of gallium, such as its [[density]], [[melting point]], oxide character, and bonding in chloride.<ref>{{cite book |title=The Ingredients: A Guided Tour of the Elements |author=Ball, Philip |publisher=Oxford University Press |page=105 |date=2002 |isbn=978-0-19-284100-1}}</ref>

:{| class="wikitable"
|+ Comparison between Mendeleev's 1871 predictions and the known properties of gallium<ref name="GreenwoodEarnshaw2nd"/>{{rp|217}}
|-
! Property
! Mendeleev's predictions
! Actual properties
|-
! [[Atomic weight]]
| ~68
| 69.723
|-
! Density
| 5.9&nbsp;g/cm<sup>3</sup>
| 5.904&nbsp;g/cm<sup>3</sup>
|-
! Melting point
| Low
| 29.767&nbsp;°C
|-
! Formula of oxide
| M<sub>2</sub>O<sub>3</sub>
| Ga<sub>2</sub>O<sub>3</sub>
|-
! Density of oxide
| 5.5&nbsp;g/cm<sup>3</sup>
| 5.88&nbsp;g/cm<sup>3</sup>
|-
! Nature of hydroxide
| amphoteric
| amphoteric
|}

Mendeleev further predicted that eka-aluminium would be discovered by means of the [[spectroscope]], and that metallic eka-aluminium would dissolve slowly in both acids and alkalis and would not react with air. He also predicted that M<sub>2</sub>O<sub>3</sub> would dissolve in acids to give MX<sub>3</sub> salts, that eka-[[aluminium salt]]s would form basic salts, that eka-aluminium sulfate should form [[alum]]s, and that anhydrous MCl<sub>3</sub> should have a greater volatility than ZnCl<sub>2</sub>: all of these predictions turned out to be true.<ref name="GreenwoodEarnshaw2nd"/>{{rp|217}}

Gallium was discovered using [[spectroscopy]] by French chemist [[Paul-Émile Lecoq de Boisbaudran]] in 1875 from its characteristic spectrum (two [[violet (color)|violet]] lines) in a sample of [[sphalerite]].<ref name="Bois">{{cite journal |title= Caractères chimiques et spectroscopiques d'un nouveau métal, le gallium, découvert dans une blende de la mine de Pierrefitte, vallée d'Argelès (Pyrénées) |first=Paul Émile  |last= Lecoq de Boisbaudran |pages=493–495 |journal= Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences |volume= 81 |date=1875 }}</ref> <!--{{doi|10.1002/andp.18762351216}}--> Later that year, Lecoq obtained the free metal by [[electrolysis]] of the [[Gallium(III) hydroxide|hydroxide]] in [[potassium hydroxide]] solution.<ref name="Weeks" />

He named the element "gallia", from [[Latin]] {{Lang|la|Gallia}} meaning '[[Gaul]]', a name for his native land of France. It was later claimed that, in a multilingual [[pun]] of a kind favoured by men of science in the 19th century, he had also named gallium after himself: {{Lang|fr|Le coq}} is French for 'the rooster', and the Latin word for 'rooster' is {{Lang|la|gallus}}. In an 1877 article, Lecoq denied this conjecture.<ref name="Weeks">{{cite journal |title= The discovery of the elements. XIII. Some elements predicted by Mendeleeff |pages= 1605–1619 |last= Weeks |first= Mary Elvira |author-link=Mary Elvira Weeks |doi=10.1021/ed009p1605 |journal= [[Journal of Chemical Education]] |volume= 9 |issue= 9 |date= 1932 |bibcode= 1932JChEd...9.1605W}}</ref>

Originally, de Boisbaudran determined the density of gallium as 4.7&nbsp;g/cm<sup>3</sup>, the only property that failed to match Mendeleev's predictions; Mendeleev then wrote to him and suggested that he should remeasure the density, and de Boisbaudran then obtained the correct value of 5.9&nbsp;g/cm<sup>3</sup>, that Mendeleev had predicted exactly.<ref name="GreenwoodEarnshaw2nd"/>{{rp|217}}

From its discovery in 1875 until the era of semiconductors, the primary uses of gallium were high-temperature thermometrics and metal alloys with unusual properties of stability or ease of melting (some such being liquid at room temperature).

The development of [[gallium arsenide]] as a [[direct and indirect band gaps|direct bandgap semiconductor]] in the 1960s ushered in the most important stage in the applications of gallium.<ref name="GreenwoodEarnshaw2nd"/>{{rp|221}} In the late 1960s, the [[electronics industry]] started using gallium on a commercial scale to fabricate light emitting diodes, [[photovoltaics]] and semiconductors, while the metals industry used it<ref name="petkof78">{{cite news |last1=Petkof |first1=Benjamin |title=Gallium |url=https://images.library.wisc.edu/EcoNatRes/EFacs2/MineralsYearBk/MinYB197879v1/reference/econatres.minyb197879v1.bpetkof2.pdf |archive-url=https://web.archive.org/web/20210602213700/https://images.library.wisc.edu/EcoNatRes/EFacs2/MineralsYearBk/MinYB197879v1/reference/econatres.minyb197879v1.bpetkof2.pdf |archive-date=2 June 2021 |url-status=live |agency=USGS Minerals Yearbook |publisher=GPO |date=1978}}</ref> to reduce the melting point of [[alloys]].<ref name="azomga">{{cite news |title=An Overview of Gallium |url=https://www.azom.com/article.aspx?ArticleID=1132 |publisher=AZoNetwork |date=18 December 2001}}</ref>

First blue [[gallium nitride]] LED were developed in 1971-1973, but they were feeble.<ref>{{Cite journal |title=History of Gallium–Nitride-Based Light-Emitting Diodes for Illumination |url=https://ieeexplore.ieee.org/document/6582668 |archive-url=https://web.archive.org/web/20240603083529/https://ieeexplore.ieee.org/document/6582668/ |archive-date=3 June 2024 |access-date=2024-12-20 |journal=Proceedings of the IEEE |date=2013 |doi=10.1109/JPROC.2013.2274929 |language=en-US |url-status=live |last1=Nakamura |first1=Shuji |last2=Krames |first2=M. R. |volume=101 |issue=10 |pages=2211–2220 |url-access=subscription }}</ref> Only in the early 1990s [[Shuji Nakamura]] managed to combine GaN with [[indium gallium nitride]] and develop the modern blue LED, now making the basis of ubiquitous white LEDs, which [[Nichia]] commercialized in 1993. He and two other Japanese scientists received a [[Nobel Prize in Physics|Nobel in Physics]] in 2014 for this work.<ref>{{Cite web |title=Why It Was Almost Impossible to Make the Blue LED |url=https://www.getrecall.ai/summary/veritasium/why-it-was-almost-impossible-to-make-the-blue-led |access-date=2024-12-20 |website=Recall |language=en}}</ref><ref>{{Cite journal |last=Nakamura |first=Shuji |date=2015 |title=Background story of the invention of efficient blue InGaN light emitting diodes (Nobel Lecture) |url=https://onlinelibrary.wiley.com/doi/full/10.1002/andp.201500801 |journal=Annalen der Physik |volume=527 |issue=5–6 |pages=335–349 |doi=10.1002/andp.201500801 |bibcode=2015AnP...527..335N |issn=1521-3889}}</ref>

Global gallium production slowly grew from several tens of t/year in the 1970s til ca. 2010, when it passed 100 t/yr and rapidly accelerated,<ref>{{Cite journal |last1=Grandell |first1=Leena |last2=Höök |first2=Mikael |date=2015-09-01 |title=Assessing Rare Metal Availability Challenges for Solar Energy Technologies |journal=Sustainability |language=en |volume=7 |issue=9 |pages=11818–11837 |doi=10.3390/su70911818 |issn=2071-1050 |doi-access=free|bibcode=2015Sust....711818G }}</ref> by 2024 reaching about 450 t/yr.<ref>{{Cite journal |date=2024-11-25 |title=Gallium: Assessing the long term future extraction, supply, recycling and price of using WORLD7, in relation to future technology visions in the European Union |url=https://www.researchsquare.com/article/rs-5390312/v1 |access-date=2024-12-20 |website=www.researchsquare.com |doi=10.21203/rs.3.rs-5390312/v1 |language=en |last1=Sverdrup |first1=Harald Ulrik |last2=Haraldsson |first2=Hördur Valdimar }}</ref>

==Occurrence==
Gallium does not exist as a free element in the Earth's crust, and the few high-content minerals, such as gallite (CuGaS<sub>2</sub>), are too rare to serve as a primary source.<ref name="Frenzel-2016b">{{cite thesis |last1=Frenzel |first1=Max |title=The distribution of gallium, germanium and indium in conventional and non-conventional resources – Implications for global availability |date=2016 |doi=10.13140/rg.2.2.20956.18564 }}{{page needed|date=April 2024}}</ref> The abundance [[Earth#Chemical composition|in the Earth's crust]] is approximately 16.9&nbsp;[[parts per million|ppm]]. It is the 34th most abundant element in the crust.<ref name="Burton">{{cite journal |doi= 10.1016/0016-7037(59)90052-3 |title= The abundances of gallium and germanium in terrestrial materials|first= J. D.|last= Burton |author2= Culkin, F. |author3=Riley, J. P. |journal= Geochimica et Cosmochimica Acta|volume= 16|issue= 1|date= 2007 |pages= 151–180|bibcode= 1959GeCoA..16..151B}}</ref> This is comparable to the crustal abundances of [[lead]], [[cobalt]], and [[niobium]]. Yet unlike these elements, gallium does not form its own ore deposits with concentrations of > 0.1 wt.% in ore. Rather it occurs at trace concentrations similar to the crustal value in zinc ores,<ref name="Frenzel-2016b" /><ref name=FrenzelMeta-2016/> and at somewhat higher values (~ 50&nbsp;ppm) in aluminium ores, from both of which it is extracted as a by-product. This lack of independent deposits is due to gallium's geochemical behaviour, showing no strong enrichment in the processes relevant to the formation of most ore deposits.<ref name="Frenzel-2016b" />

The [[United States Geological Survey]] (USGS) estimates that more than 1&nbsp;million tons of gallium is contained in known reserves of bauxite and zinc ores.<ref name="USGSCS2008" /><ref name="USGSCS2006">{{cite web|url= https://minerals.usgs.gov/minerals/pubs/commodity/gallium/myb1-2006-galli.pdf |archive-url=https://web.archive.org/web/20080509122325/http://minerals.usgs.gov/minerals/pubs/commodity/gallium/myb1-2006-galli.pdf |archive-date=9 May 2008 |url-status=live|title= Mineral Yearbook 2006: Gallium|publisher= United States Geological Survey|access-date= 20 November 2008|first= Deborah A.|last= Kramer}}</ref> Some coal [[flue]] [[dust]]s 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= Xiao-quan, Shan|author2= Wen, Wang|author3= Bei, Wen|name-list-style= amp |journal= [[Journal of Analytical Atomic Spectrometry]]|date= 1992|volume= 7|page= 761 |doi= 10.1039/JA9920700761|issue= 5}}</ref><ref>{{cite web|publisher= West Virginia Geological and Economic Survey |date=2 March 2002|title= Gallium in West Virginia Coals|url= http://www.wvgs.wvnet.edu/www/datastat/te/GaHome.htm |url-status=live |archive-url=https://web.archive.org/web/20020311013523/http://www.wvgs.wvnet.edu/www/datastat/te/GaHome.htm
|archive-date=11 March 2002}}</ref><ref>{{cite journal|author= Font, O|title= Recovery of gallium and vanadium from gasification fly ash|date= 2007|journal= Journal of Hazardous Materials|pmid= 16600480|volume= 139|issue= 3 |doi= 10.1016/j.jhazmat.2006.02.041|pages= 413–23|last2= Querol|first2= Xavier|last3= Juan|first3= Roberto|last4= Casado|first4= Raquel|last5= Ruiz|first5= Carmen R.|last6= López-Soler|first6= Ángel|last7= Coca|first7= Pilar|last8= Peña|first8= Francisco García|bibcode= 2007JHzM..139..413F}}</ref><ref>{{cite journal|title= Elements in Coal Ash and Their Industrial Significance |author= Headlee, A. J. W. |author2= Hunter, Richard G. |name-list-style= amp |pages= 548–551|doi= 10.1021/ie50519a028|volume= 45|date= 1953|journal= Industrial and Engineering Chemistry|issue= 3}}</ref> However, these amounts are not extractable without mining of the host materials (see below). Thus, the availability of gallium is fundamentally determined by the rate at which bauxite, zinc ores, and coal are extracted.

==Production and availability==
[[File:6N Gallium sealed in vacuum ampoule.jpg|thumb|left|99.9999% (6N) gallium sealed in vacuum ampoule]]
Gallium is produced exclusively as a [[by-product]] during the processing of the ores of other metals. Its main source material is [[Bauxite#Source of gallium|bauxite]], the chief ore of [[aluminium]], but minor amounts are also extracted from sulfidic zinc ores ([[sphalerite]] being the main host mineral).<ref name="Frenzel-2016a" /><ref name=FrenzelMeta-2016>{{cite journal |last1=Frenzel |first1=Max |last2=Hirsch |first2=Tamino |last3=Gutzmer |first3=Jens |title=Gallium, germanium, indium, and other trace and minor elements in sphalerite as a function of deposit type — A meta-analysis |journal=Ore Geology Reviews |date=July 2016 |volume=76 |pages=52–78 |doi=10.1016/j.oregeorev.2015.12.017 |bibcode=2016OGRv...76...52F }}</ref>  In the past, certain coals were an important source.

During the processing of [[bauxite]] to [[aluminium oxide|alumina]] in the [[Bayer process]], gallium accumulates in the [[sodium hydroxide]] liquor. From this it can be extracted by a variety of methods. The most recent is the use of [[ion-exchange resin]].<ref name="Frenzel-2016a">{{cite journal|last1=Frenzel|first1=Max|last2=Ketris|first2=Marina P.|last3=Seifert|first3=Thomas|last4=Gutzmer|first4=Jens|date=March 2016|title=On the current and future availability of gallium|journal=Resources Policy|volume=47|pages=38–50|doi=10.1016/j.resourpol.2015.11.005|bibcode=2016RePol..47...38F }}</ref> Achievable extraction efficiencies critically depend on the original concentration in the feed bauxite. At a typical feed concentration of 50&nbsp;ppm, about 15% of the contained gallium is extractable.<ref name="Frenzel-2016a" /> The remainder reports to the [[red mud]] and [[aluminium hydroxide]] streams. Gallium is removed from the ion-exchange resin in solution. Electrolysis then gives gallium metal. For [[semiconductor]] use, it is further purified with [[zone melting]] or single-crystal extraction from a melt ([[Czochralski process]]). Purities of 99.9999% are routinely achieved and commercially available.<ref name="Moskalyk">{{cite journal|last=Moskalyk|first=R. R.|date=2003|title=Gallium: the backbone of the electronics industry|journal=Minerals Engineering|volume=16|issue=10|pages=921–929|doi=10.1016/j.mineng.2003.08.003|bibcode=2003MiEng..16..921M }}</ref>

[[File:Bauxite Jamaica 1984.jpg|thumb|Bauxite mine in [[Jamaica]] (1984)]]
Its by-product status means that gallium production is constrained by the amount of bauxite, sulfidic zinc ores (and coal) extracted per year. Therefore, its availability needs to be discussed in terms of supply potential. The supply potential of a by-product is defined as that amount which is economically extractable from its host materials ''per year'' under current market conditions (i.e. technology and price).<ref>{{cite journal|last1=Frenzel|first1=M|last2=Tolosana-Delgado|first2=R|last3=Gutzmer|first3=J|date=2015|title=Assessing the supply potential of high-tech metals – A general method|journal=Resources Policy|volume=46|pages=45–58|doi=10.1016/j.resourpol.2015.08.002|bibcode=2015RePol..46...45F}}</ref> Reserves and resources are not relevant for by-products, since they ''cannot'' be extracted independently from the main-products.<ref>{{cite journal|last1=Frenzel|first1=Max|last2=Mikolajczak|first2=Claire|last3=Reuter|first3=Markus A.|last4=Gutzmer|first4=Jens|date=June 2017|title=Quantifying the relative availability of high-tech by-product metals – The cases of gallium, germanium and indium|journal=Resources Policy|volume=52|pages=327–335|doi=10.1016/j.resourpol.2017.04.008|bibcode=2017RePol..52..327F |doi-access=free}}</ref> Recent estimates put the supply potential of gallium at a minimum of 2,100&nbsp;t/yr from bauxite, 85&nbsp;t/yr from sulfidic zinc ores, and potentially 590 t/yr from coal.<ref name="Frenzel-2016a" /> These figures are significantly greater than current production (375&nbsp;t in 2016).<ref>{{cite book|url=https://minerals.usgs.gov/minerals/pubs/commodity/gallium/mcs-2017-galli.pdf |archive-url=https://web.archive.org/web/20170427232856/https://minerals.usgs.gov/minerals/pubs/commodity/gallium/mcs-2017-galli.pdf |archive-date=27 April 2017 |url-status=live|title=Gallium – In: USGS Mineral Commodity Summaries|publisher=United States Geological Survey|year=2017}}</ref> Thus, major future increases in the by-product production of gallium will be possible without significant increases in production costs or price. The average price for low-grade gallium was $120 per kilogram in 2016 and $135–140 per kilogram in 2017.<ref name="usgs2018" />

In 2017, the world's production of low-grade gallium was {{Circa|315}} tons—a decrease of 15% from 2016. China, Japan, South Korea, Russia, and Ukraine were the leading producers, while Germany ceased primary production of gallium in 2016. The yield of high-purity gallium was ca. 180 tons, mostly originating from China, Japan, Slovakia, UK and U.S. The 2017 world annual production capacity was estimated at 730 tons for low-grade and 320 tons for refined gallium.<ref name="usgs2018">[https://minerals.usgs.gov/minerals/pubs/commodity/gallium/mcs-2018-galli.pdf Galium]. USGS (2018)</ref>

China produced {{Circa|250}} tons of low-grade gallium in 2016 and {{Circa|300}} tons in 2017. It also accounted for more than half of global [[Light-emitting_diode|LED]] production.<ref name="usgs2018" /> As of July 2023, China accounted for between 80%<ref>{{Cite web |last=Kharpal |first=Arjun |date=4 July 2023 |title=What are Gallium and Germanium? China curbs exports of metals critical to chips and other tech |url=https://www.cnbc.com/2023/07/04/what-are-gallium-and-germanium-china-curbs-exports-of-metals-for-tech.html |access-date=4 July 2023 |website=CNBC |language=en}}</ref> and 95% of its production.<ref>{{Cite web |last=Lamby-Schmitt |first=Eva |title=China verhängt Ausfuhrkontrollen für seltene Metalle |url=https://www.tagesschau.de/wirtschaft/technologie/china-seltene-metalle-100.html |access-date=4 July 2023 |website=Tagesschau |language=de-DE}}</ref>

==Applications==
Semiconductor applications dominate the commercial demand for gallium, accounting for 98% of the total. The next major application is for [[gadolinium gallium garnet]]s.<ref name="Ullmann">Greber, J. F. (2012) "Gallium and Gallium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, {{doi|10.1002/14356007.a12_163}}.</ref> As of 2022, 44% of world use went to light fixtures and 36% to integrated circuits, with smaller shares equal to ~7% going to photovoltaics and magnets each.<ref>{{Cite web |title=Global Gallium consumption distribution by end-use |url=https://www.statista.com/statistics/605987/distribution-of-world-gallium-consumption-by-end-use/ |access-date=2024-12-20 |website=Statista |language=en}}</ref>

===Semiconductors===
[[File:Blue LED and Reflection.jpg|thumb|Gallium-based blue LEDs]]
Extremely high-purity (>99.9999%) gallium is commercially available to serve the [[semiconductor]] industry. [[Gallium arsenide]] (GaAs) and [[gallium nitride]] (GaN) used in electronic components represented about 98% of the gallium consumption in the United States in 2007. About 66% of semiconductor gallium is used in the U.S. in integrated circuits (mostly gallium arsenide), such as the manufacture of ultra-high-speed logic chips and [[MESFET]]s for low-noise microwave preamplifiers in cell phones. About 20% of this gallium is used in [[optoelectronic]]s.<ref name="USGSCS2008">{{cite web|url= http://minerals.usgs.gov/minerals/pubs/commodity/gallium/mcs-2008-galli.pdf |archive-url=https://web.archive.org/web/20080514204029/http://minerals.usgs.gov/minerals/pubs/commodity/gallium/mcs-2008-galli.pdf |archive-date=14 May 2008 |url-status=live|title= Mineral Commodity Summary 2006: Gallium|publisher= United States Geological Survey|access-date= 20 November 2008|first= Deborah A.|last= Kramer}}</ref>

Worldwide, gallium arsenide makes up 95% of the annual global gallium consumption.<ref name="Moskalyk" /> It amounted to $7.5&nbsp;billion in 2016, with 53% originating from cell phones, 27% from wireless communications, and the rest from automotive, consumer, fiber-optic, and military applications. The recent increase in GaAs consumption is mostly related to the emergence of [[3G]] and [[4G]] [[smartphone]]s, which employ up to 10 times the amount of GaAs in older models.<ref name="usgs2018" />

Gallium arsenide and gallium nitride can also be found in a variety of optoelectronic devices which had a market share of $15.3&nbsp;billion in 2015 and $18.5&nbsp;billion in 2016.<ref name="usgs2018" /> [[Aluminium gallium arsenide]] (AlGaAs) is used in high-power infrared laser diodes. The semiconductors gallium nitride and [[indium gallium nitride]] are used in blue and violet optoelectronic devices, mostly [[laser diode]]s and [[light-emitting diode]]s. For example, gallium nitride 405&nbsp;nm diode lasers are used as a violet light source for higher-density [[Blu-ray Disc]] compact data disc drives.<ref>{{cite book |url= https://books.google.com/books?id=pVkhYTzdXgoC&pg=PA150 |pages= 150–151 |title= Advances in Semiconductor Lasers |isbn= 978-0-12-391066-0 |last1= Coleman |first1= James J. |last2= Jagadish |first2= Chennupati |last3= Catrina Bryce |first3= A. |date= 2 May 2012|publisher= Academic Press }}</ref>

Other major applications of gallium nitride are cable television transmission, commercial wireless infrastructure, power electronics, and satellites. The GaN radio frequency device market alone was estimated at $370&nbsp;million in 2016 and $420&nbsp;million in 2016.<ref name="usgs2018" />

[[Multijunction photovoltaic cell]]s, developed for [[satellite]] power applications, are made by [[molecular-beam epitaxy]] or [[metalorganic vapour-phase epitaxy]] of [[thin film]]s of gallium arsenide, [[indium gallium phosphide]], or [[indium gallium arsenide]]. The [[Mars Exploration Rover]]s and several satellites use triple-junction gallium arsenide on germanium cells.<ref>{{cite journal|doi= 10.1016/S0094-5765(02)00287-4 |title= The performance of gallium arsenide/germanium solar cells at the Martian surface |date= 2004 |first= D.|last= Crisp |author2= Pathare, A. |author3=Ewell, R. C. |journal= Acta Astronautica |volume= 54|pages= 83–101|issue= 2|bibcode= 2004AcAau..54...83C}}</ref> Gallium is also a component in [[photovoltaic]] compounds (such as copper indium gallium selenium sulfide {{chem2|Cu(In,Ga)(Se,S)2}}) used in solar panels as a cost-efficient alternative to [[crystalline silicon]].<ref>{{cite journal |title= Material and device properties of single-phase Cu(In,Ga)(Se,S)<sub>2</sub> alloys prepared by selenization/sulfurization of metallic alloys |first= V.|last= Alberts |author2= Titus J. |author3= Birkmire R. W. |journal= Thin Solid Films |volume= 451–452|pages= 207–211 |date= 2003 |doi= 10.1016/j.tsf.2003.10.092|bibcode= 2004TSF...451..207A}}</ref>

===Galinstan and other alloys===
[[File:Galinstan on glass.jpg|thumb|Galinstan easily wetting a piece of ordinary glass]]
[[File:Gallium alloy 3D prints (26519727708).jpg|thumb|Owing to their low melting points, gallium and its alloys can be shaped into various 3D forms using [[3D printing]] and [[additive manufacturing]].]]
Gallium readily [[alloy]]s with most metals, and is used as an ingredient in [[low-melting alloy]]s. The nearly [[eutectic]] alloy of gallium, [[indium]], and [[tin]] is a room temperature liquid used in medical thermometers. This alloy, with the trade-name ''[[Galinstan]]'' (with the "-stan" referring to the tin, {{Lang|la|stannum}} in Latin), has a low melting point of −19&nbsp;°C (−2.2&nbsp;°F).<ref>{{cite journal|doi=10.1007/s00216-005-0069-7|date=Nov 2005|author=Surmann, P|author2=Zeyat, H|title=Voltammetric analysis using a self-renewable non-mercury electrode|volume=383|issue=6|pages=1009–13|issn=1618-2642|pmid=16228199|journal=Analytical and Bioanalytical Chemistry|s2cid=22732411}}</ref> It has been suggested that this family of alloys could also be used to cool computer chips in place of water, and is often used as a replacement for [[Thermal grease|thermal paste]] in high-performance computing.<ref>{{cite web|title= Hot chips chilled with liquid metal|date= 5 May 2005|first= Will|last= Knight|url= https://www.newscientist.com/article.ns?id=dn7348|access-date= 20 November 2008|archive-url= https://web.archive.org/web/20070211083832/https://www.newscientist.com/article.ns?id=dn7348|archive-date= 11 February 2007}}</ref><ref>{{Cite web|url=https://domino.research.ibm.com/library/cyberdig.nsf/papers/AD9B6F5D509CEB3D85257372004FC2C3/$File/rc24372.pdf|title=High Performance Liquid Metal Thermal Interface for Large Volume Production|last=Martin|first=Yves|access-date=20 November 2019|archive-date=9 March 2020|archive-url=https://web.archive.org/web/20200309123838/https://domino.research.ibm.com/library/cyberdig.nsf/papers/AD9B6F5D509CEB3D85257372004FC2C3/$File/rc24372.pdf|url-status=dead}}</ref> Gallium alloys have been evaluated as substitutes for mercury [[dental amalgam]]s, but these materials have yet to see wide acceptance.  Liquid alloys containing mostly gallium and indium have been found to precipitate gaseous CO<sub>2</sub> into solid carbon and are being researched as potential methodologies for [[Carbon capture and storage|carbon capture]] and possibly [[Carbon dioxide removal|carbon removal]].<ref>{{Cite web |title=Technology solidifies carbon dioxide – ASME |url=https://www.asme.org/topics-resources/content/gallium-turns-co2-into-solid |access-date=5 September 2022 |website=www.asme.org |language=en}}</ref><ref>{{Cite web |title=New way to turn carbon dioxide into coal could 'rewind the emissions clock' |url=https://www.science.org/content/article/liquid-metal-catalyst-turns-carbon-dioxide-coal |access-date=5 September 2022 |website=www.science.org |language=en}}</ref>

Because gallium [[wetting|wets]] glass or [[porcelain]], gallium can be used to create brilliant [[mirror]]s. When the wetting action of gallium-alloys is not desired (as in Galinstan glass thermometers), the glass must be protected with a transparent layer of [[gallium(III) oxide]].<ref>{{cite book |url= https://books.google.com/books?id=2EZSAAAAMAAJ|title= Liquid-metals handbook|publisher= U.S. Govt. Print. Off.|date= 1954 |author= United States. Office of Naval Research. Committee on the Basic Properties of Liquid Metals, U.S. Atomic Energy Commission|page= 128}}</ref>

Due to their high [[surface tension]] and [[fluid mechanics|deformability]],<ref>{{cite journal |last1=Khan |first1=Mohammad Rashed |last2=Eaker |first2=Collin B. |last3=Bowden |first3=Edmond F. |last4=Dickey |first4=Michael D. |title=Giant and switchable surface activity of liquid metal via surface oxidation |journal=Proceedings of the National Academy of Sciences |date=30 September 2014 |volume=111 |issue=39 |pages=14047–14051 |doi=10.1073/pnas.1412227111 |doi-access=free |pmid=25228767 |bibcode=2014PNAS..11114047K |pmc=4191764 }}</ref> gallium-based liquid metals can be used to create [[actuator]]s by controlling the surface tension.<ref>{{cite journal |last1=Russell |first1=Loren |last2=Wissman |first2=James |last3=Majidi |first3=Carmel |title=Liquid metal actuator driven by electrochemical manipulation of surface tension |journal=Applied Physics Letters |date=18 December 2017 |volume=111 |issue=25 |doi=10.1063/1.4999113 |bibcode=2017ApPhL.111y4101R |doi-access=free }}</ref><ref>{{cite journal |last1=Liao |first1=Jiahe |last2=Majidi |first2=Carmel |title=Soft actuators by electrochemical oxidation of liquid metal surfaces |journal=Soft Matter |date=2021 |volume=17 |issue=7 |pages=1921–1928 |doi=10.1039/D0SM01851A |pmid=33427274 |bibcode=2021SMat...17.1921L }}</ref><ref>{{cite journal |last1=Liao |first1=Jiahe |last2=Majidi |first2=Carmel |title=Muscle-Inspired Linear Actuators by Electrochemical Oxidation of Liquid Metal Bridges |journal=Advanced Science |date=September 2022 |volume=9 |issue=26 |pages=e2201963 |doi=10.1002/advs.202201963 |pmid=35863909 |pmc=9475532 }}</ref> Researchers have demonstrated the potentials of using liquid metal actuators as [[artificial muscles|artificial muscle]] in robotic actuation.<ref>{{cite journal |last1=Liao |first1=Jiahe |last2=Majidi |first2=Carmel |last3=Sitti |first3=Metin |title=Liquid Metal Actuators: A Comparative Analysis of Surface Tension Controlled Actuation |journal=Advanced Materials |date=January 2024 |volume=36 |issue=1 |pages=e2300560 |doi=10.1002/adma.202300560 |pmid=37358049 |bibcode=2024AdM....3600560L |hdl=20.500.11850/641439 |hdl-access=free }}</ref><ref>{{cite thesis |last= Liao|first= Jiahe|date= 2022|title= Liquid metal actuators|url= https://kilthub.cmu.edu/authors/Jiahe_Liao/4939036|degree= Ph.D.|publisher= Carnegie Mellon University}}</ref>

The [[plutonium]] used in [[plutonium pit|nuclear weapon pits]] is stabilized in the [[allotropes of plutonium|δ phase]] and made machinable by [[Plutonium–gallium alloy|alloying with gallium]].<ref>{{cite web|author=Sublette, Cary |title=Section 6.2.2.1 |date=9 September 2001 |work=Nuclear Weapons FAQ |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq6.html#nfaq6.2 |access-date=24 January 2008}}</ref><ref>{{cite journal|title= Thermochemical Behavior of Gallium in Weapons-Material-Derived Mixed-Oxide Light Water Reactor (LWR) Fuel|first= Theodore M.|last= Besmann|journal= Journal of the American Ceramic Society|volume= 81|pages= 3071–3076 |date= 2005 |doi= 10.1111/j.1151-2916.1998.tb02740.x |issue= 12|url= https://zenodo.org/record/1230603}}</ref>

===Biomedical applications===
Although gallium has no natural function in biology, gallium ions interact with processes in the body in a manner similar to [[Ferric#Ferric iron and life|iron(III)]]. Because these processes include [[inflammation]], a marker for many disease states, several gallium salts are used (or are in development) as [[pharmaceutical drug|pharmaceuticals]] and [[radiopharmacology|radiopharmaceuticals]] in medicine. Interest in the anticancer properties of gallium emerged when it was discovered that <sup>67</sup>Ga(III) citrate injected in tumor-bearing animals localized to sites of tumor. Clinical trials have shown gallium nitrate to have antineoplastic activity against non-Hodgkin's lymphoma and urothelial cancers. A new generation of gallium-ligand complexes such as tris(8-quinolinolato)gallium(III) (KP46) and gallium maltolate has emerged.<ref>{{cite book |doi=10.1515/9783110470734-016 |chapter=16. Copper Complexes in Cancer Therapy |title=Metallo-Drugs: Development and Action of Anticancer Agents |date=2018 |last1=Denoyer |first1=Delphine |last2=Clatworthy |first2=Sharnel A. S. |last3=Cater |first3=Michael A. |series=Metal Ions in Life Sciences |volume=18 |pages=469–506 |pmid=29394029 |isbn=978-3-11-047073-4 }}</ref> [[Gallium nitrate]] (brand name Ganite) has been used as an intravenous pharmaceutical to treat [[hypercalcemia]] associated with tumor [[metastasis]] to bones. Gallium is thought to interfere with [[osteoclast]] function, and the therapy may be effective when other treatments have failed.<ref>{{cite web|url=http://www.cancer.org/docroot/CDG/content/CDG_gallium_nitrate.asp |title=gallium nitrate |url-status=dead |access-date=7 July 2009 |archive-url=https://web.archive.org/web/20090608234315/http://www.cancer.org/docroot/CDG/content/CDG_gallium_nitrate.asp |archive-date=8 June 2009}}</ref> [[Gallium maltolate]], an oral, highly absorbable form of gallium(III) ion, is an anti-proliferative to pathologically proliferating cells, particularly cancer cells and some bacteria that accept it in place of ferric iron (Fe<sup>3+</sup>). Researchers are conducting clinical and preclinical trials on this compound as a potential treatment for a number of cancers, infectious diseases, and inflammatory diseases.<ref>{{cite journal|author= Bernstein, L. R.|author2= Tanner, T.|author3= Godfrey, C.|author4= Noll, B.|name-list-style= amp |title= Chemistry and Pharmacokinetics of Gallium Maltolate, a Compound With High Oral Gallium Bioavailability|journal= Metal-Based Drugs|date= 2000|volume= 7 |issue= 1 |pmid= 18475921|pmc= 2365198 |doi= 10.1155/MBD.2000.33|pages= 33–47|doi-access= free}}</ref>

When gallium ions are mistakenly taken up in place of iron(III) by bacteria such as ''[[Pseudomonas]]'', the ions interfere with respiration, and the bacteria die. This happens because iron is redox-active, allowing the transfer of electrons during respiration, while gallium is redox-inactive.<ref>{{cite web|url= http://www.infoniac.com/health-fitness/trojan-gallium.html|title= A Trojan-horse strategy selected to fight bacteria|date= 16 March 2007|publisher= INFOniac.com |access-date= 20 November 2008}}</ref><ref>{{cite web|url= http://www.medpagetoday.com/InfectiousDisease/GeneralInfectiousDisease/tb/5266|title= Gallium May Have Antibiotic-Like Properties|first= Michael|last= Smith|publisher= MedPage Today|date= 16 March 2007|access-date= 20 November 2008}}</ref>

A complex [[amine]]-[[phenol]] Ga(III) compound MR045 is selectively toxic to parasites resistant to [[chloroquine]], a common drug against [[malaria]]. Both the Ga(III) complex and chloroquine act by inhibiting crystallization of [[hemozoin]], a disposal product formed from the digestion of blood by the parasites.<ref>{{cite journal|pmid=9045684|journal=J. Biol. Chem. |date=1997 |volume=272|issue=10|pages=6567–72|title= Probing the chloroquine resistance locus of Plasmodium falciparum with a novel class of multidentate metal(III) coordination complexes|author=Goldberg D. E.|author2= Sharma V.|author3=Oksman A.|author4=Gluzman I. Y.|author5=Wellems T. E.|author6=Piwnica-Worms D.|doi=10.1074/jbc.272.10.6567|s2cid=3408513 |doi-access=free }}</ref><ref>{{cite book|doi=10.1007/978-3-642-13185-1_7|chapter=Bioorganometallic Chemistry and Malaria|title=Medicinal Organometallic Chemistry|series=Topics in Organometallic Chemistry|date=2010|last1=Biot|first1=Christophe|last2=Dive|first2=Daniel|isbn=978-3-642-13184-4|volume=32|page=155|s2cid=85940061}}</ref>

====Radiogallium salts====
[[Gallium-67]] [[Salt (chemistry)|salts]] such as gallium [[citrate]] and gallium [[nitrate]] are used as [[radiopharmaceutical]] agents in the [[nuclear medicine]] imaging known as [[gallium scan]]. The [[radionuclide|radioactive isotope]] <sup>67</sup>Ga is used, and the compound or salt of gallium is unimportant. The body handles Ga<sup>3+</sup> in many ways as though it were Fe<sup>3+</sup>, and the ion is bound (and concentrates) in areas of inflammation, such as infection, and in areas of rapid cell division. This allows such sites to be imaged by nuclear scan techniques.<ref name="Nordberg" />

[[Gallium-68]], a positron emitter with a half-life of 68 min, is now used as a diagnostic radionuclide in PET-CT when linked to pharmaceutical preparations such as [[DOTATOC]], a [[somatostatin]] analogue used for [[neuroendocrine tumors]] investigation, and [[DOTA-TATE]], a newer one, used for neuroendocrine [[metastasis]] and lung neuroendocrine cancer, such as certain types of ''[[microcytoma]]''. Gallium-68's preparation as a pharmaceutical is chemical, and the radionuclide is extracted by [[elution]] from germanium-68, a [[synthetic radioisotope]] of [[germanium]], in [[gallium-68 generator]]s.<ref>{{cite journal |last1=Banerjee |first1=Sangeeta Ray |last2=Pomper |first2=Martin G. |date=June 2013 |title=Clinical Applications of Gallium-68 |pmc=3664132 |journal=Appl. Radiat. Isot. |volume=76 |pages=2–13 |doi=10.1016/j.apradiso.2013.01.039 |pmid=23522791|bibcode=2013AppRI..76....2B }}</ref>

===Other uses===
'''Neutrino detection''': Gallium is used for [[neutrino detection]]. Possibly the largest amount of pure gallium ever collected in a single location is the Gallium-Germanium Neutrino Telescope used by the [[SAGE (Soviet-American Gallium Experiment)|SAGE experiment]] at the [[Baksan Neutrino Observatory]] in Russia. This detector contains 55–57 tonnes (~9 cubic metres) of liquid gallium.<ref>{{cite web|url= http://ewi.npl.washington.edu/sage/|title= Russian American Gallium Experiment|date= 19 October 2001|access-date= 24 June 2009|archive-url= https://web.archive.org/web/20100705232418/http://ewi.npl.washington.edu/SAGE/|archive-date= 5 July 2010|url-status= dead}}</ref> Another experiment 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 neutrino]]s caused a few atoms of <sup>71</sup>Ga to become radioactive <sup>71</sup>[[germanium|Ge]], which were detected. This experiment showed that the solar neutrino flux is 40% less than theory predicted. This deficit ([[solar neutrino problem]]) was not explained until better solar neutrino detectors and theories were constructed (see [[Sudbury Neutrino Observatory|SNO]]).<ref>{{cite web|url= http://wwwlapp.in2p3.fr/neutrinos/anexp.html#gallex|title= Neutrino Detectors Experiments: GALLEX|date= 26 June 1999|access-date= 20 November 2008}}</ref>

'''Ion source''': Gallium is also used as a [[liquid metal ion source]] for a [[focused ion beam]]. For example, a focused gallium-ion beam was used to create the world's smallest book, ''[[Teeny Ted from Turnip Town]]''.<ref name="pr">[https://www.sfu.ca/mediapr/news_releases/archives/news04110701.htm "Nano lab produces world's smallest book"] {{Webarchive|url=https://web.archive.org/web/20151013010453/https://www.sfu.ca/mediapr/news_releases/archives/news04110701.htm |date=13 October 2015 }}. Simon Fraser University. 11 April 2007. Retrieved 31 January 2013.</ref>

'''Lubricants''': Gallium serves as an additive in [[glide wax]] for skis and other low-friction surface materials.<ref>{{cite patent |inventor1-last=Sugimura |inventor1-first=Kentaro |inventor2-last=Hasimoto |inventor2-first=Shoji |inventor3-last=Ono |inventor3-first=Takayuki |title=Use of a synthetic resin composition containing gallium particles in the glide surfacing material of skis and other applications |issue-date=1995 |patent-number=5069803 |country-code= US}}</ref>

'''Flexible electronics''': Materials scientists speculate that the properties of gallium could make it suitable for the development of flexible and wearable devices.<ref name="Kleiner">{{cite journal |last1=Kleiner |first1=Kurt |title=Gallium: The liquid metal that could transform soft electronics |journal=Knowable Magazine |date=3 May 2022 |doi=10.1146/knowable-050322-2  |doi-access=free |url=https://knowablemagazine.org/article/technology/2022/gallium-liquid-metal-could-transform-soft-electronics |access-date=31 May 2022}}</ref><ref name="Tang">{{cite journal |last1=Tang |first1=Shi-Yang |last2=Tabor |first2=Christopher |last3=Kalantar-Zadeh |first3=Kourosh |last4=Dickey |first4=Michael D. |title=Gallium Liquid Metal: The Devil's Elixir |journal=Annual Review of Materials Research |date=26 July 2021 |volume=51 |issue=1 |pages=381–408 |doi=10.1146/annurev-matsci-080819-125403 |bibcode=2021AnRMS..51..381T |s2cid=236566966 |issn=1531-7331|doi-access=free }}</ref>

'''Hydrogen generation''': Gallium disrupts the [[Passivation (chemistry)|protective oxide layer]] on aluminium, allowing water to react with the aluminium in [[AlGa]] to produce hydrogen gas.<ref name="Amberchan 2022">{{cite journal |last1=Amberchan |first1=Gabriella |last2=Lopez |first2=Isai |last3=Ehlke |first3=Beatriz |last4=Barnett |first4=Jeremy |last5=Bao |first5=Neo Y. |last6=Allen |first6=A’Lester |last7=Singaram |first7=Bakthan |last8=Oliver |first8=Scott R. J. |title=Aluminum Nanoparticles from a Ga–Al Composite for Water Splitting and Hydrogen Generation |journal=ACS Applied Nano Materials |date=25 February 2022 |volume=5 |issue=2 |pages=2636–2643 |doi=10.1021/acsanm.1c04331 }}</ref>

'''Humor''': A well-known [[practical joke]] among chemists is to fashion gallium spoons and use them to serve tea to unsuspecting guests, since gallium has a similar appearance to its lighter homolog aluminium. The spoons then melt in the hot tea.<ref name="Sam Kean2010">{{cite book|author=Kean, Sam|title=The Disappearing Spoon: And Other True Tales of Madness, Love, and the History of the World from the Periodic Table of the Elements|url=https://archive.org/details/disappearingspoo0000kean|date=2010|publisher=Little, Brown and Company|location=Boston|isbn=978-0-316-05164-4|url-access=registration}}</ref>

==Gallium in the ocean==
Advances in trace element testing have allowed scientists to discover traces of dissolved gallium in the Atlantic and Pacific Oceans.<ref name="Dissolved Gallium in the Open Ocean">{{cite journal |last1=Orians |first1=K. J. |last2=Bruland |first2=K. W. |date=April 1988 |title=Dissolved Gallium in the Open Ocean |journal=Nature |volume=332 |issue=21 |pages=717–19|doi=10.1038/332717a0 |bibcode=1988Natur.332..717O |s2cid=4323435 }}</ref> In recent years, dissolved gallium concentrations have presented in the [[Beaufort Sea]].<ref name="Dissolved Gallium in the Open Ocean" /><ref name="Dissolved Gallium in the Beaufort S">{{cite journal |last1=McAlister |first1=Jason A. |last2=Orians |first2=Kristin J. |date=20 December 2015 |title=Dissolved Gallium in the Beaufort Sea of the Western Arctic Ocean: A GEOTRACES cruise in the International Polar Year |journal=Marine Chemistry |volume=177 |issue=Part 1 |pages=101–109 |doi=10.1016/j.marchem.2015.05.007 |bibcode=2015MarCh.177..101M }}</ref> These reports reflect the possible profiles of the Pacific and Atlantic Ocean waters.<ref name="Dissolved Gallium in the Beaufort S" /> For the Pacific Oceans, typical dissolved gallium concentrations are between 4 and 6&nbsp;pmol/kg at depths <~150 m. In comparison, for Atlantic waters 25–28&nbsp;pmol/kg at depths >~350 m.<ref name="Dissolved Gallium in the Beaufort S" />

Gallium has entered oceans mainly through aeolian input, but having gallium in our oceans can be used to resolve aluminium distribution in the oceans.<ref name="Shiller 87–99">{{cite journal |last=Shiller |first=A. M. |date=June 1998 |title=Dissolved Gallium in the Atlantic Ocean |journal=Marine Chemistry |volume=61 |issue=1 |pages=87–99|doi=10.1016/S0304-4203(98)00009-7 |bibcode=1998MarCh..61...87S }}</ref> The reason for this is that gallium is geochemically similar to aluminium, just less reactive. Gallium also has a slightly larger surface water residence time than aluminium.<ref name="Shiller 87–99" /> Gallium has a similar dissolved profile similar to that of aluminium, due to this gallium can be used as a tracer for aluminium.<ref name="Shiller 87–99" /> Gallium can also be used as a tracer of aeolian inputs of iron.<ref name="Dissolved Gallium in the northwest">{{cite journal |last1=Shiller |first1=A. M. |last2=Bairamadgi |first2=G. R. |date=August 2006 |title=Dissolved Gallium in the northwest Pacific and the south and central Atlantic Oceans: Implications for aeolian Fe input and reconsideration of Profiles |journal=Geochemistry, Geophysics, Geosystems |volume=7 |issue=8 |pages=n/a |doi=10.1029/2005GC001118 |bibcode=2006GGG.....7.8M09S |s2cid=129738391 |doi-access=free }}</ref> Gallium is used as a tracer for iron in the northwest Pacific, south and central Atlantic Oceans.<ref name="Dissolved Gallium in the northwest" /> For example, in the northwest Pacific, low gallium surface waters, in the subpolar region suggest that there is low dust input, which can subsequently explain the following [[high-nutrient, low-chlorophyll]] environmental behavior.<ref name="Dissolved Gallium in the northwest" />

==Precautions==
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| NFPA-H = 1
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Metallic gallium is not toxic. However, several gallium compounds are toxic.

Gallium halide complexes can be toxic.<ref>{{cite journal |last1=Ivanoff |first1=C. S. |last2=Ivanoff |first2=A. E. |last3=Hottel |first3=T. L. |date=February 2012 |title=Gallium poisoning: a rare case report. |journal=Food Chem. Toxicol. |volume=50 |issue=2 |pages=212–5 |doi=10.1016/j.fct.2011.10.041 |pmid=22024274}}</ref> The Ga<sup>3+</sup> ion of soluble gallium salts tends to form the insoluble hydroxide when injected in large doses; precipitation of this hydroxide resulted in [[nephrotoxicity]] in animals. In lower doses, soluble gallium is tolerated well and does not accumulate as a poison, instead being excreted mostly through urine. Excretion of gallium occurs in two phases: the first phase has a [[biological half-life]] of 1 hour, while the second has a biological half-life of 25 hours.<ref name="Nordberg">{{cite book |first1=Gunnar F. |last1=Nordberg |first2=Bruce A. |last2=Fowler |first3=Monica |last3=Nordberg |title=Handbook on the Toxicology of Metals |publisher=Academic Press |pages=788–90 |edition=4th |date=7 August 2014 |isbn=978-0-12-397339-9}}</ref>

Inhaled Ga<sub>2</sub>O<sub>3</sub> particles are probably toxic.<ref>{{cite book |doi=10.1016/b978-0-444-52272-6.00474-8 |chapter=Gallium: Environmental Pollution and Health Effects |title=Encyclopedia of Environmental Health |date=2011 |last1=Yu |first1=H.-S. |last2=Liao |first2=W.-T. |pages=829–833 |isbn=978-0-444-52272-6 }}</ref>
{{clear}}

==Notes==
{{Notelist}}

==References==
{{Reflist}}

==External links==
* [http://www.periodicvideos.com/videos/031.htm Gallium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
* [[Safety data sheet]] at [http://www.acialloys.com/wp-content/uploads/msds/ga.html acialloys.com]
* [http://france-gallium.com/photos-gallium.php High-resolution photographs of molten gallium, gallium crystals and gallium ingots under Creative Commons licence]
* [https://www.lenntech.com/periodic/elements/ga.htm Textbook information regarding gallium]
* [https://minerals.usgs.gov/minerals/pubs/commodity/gallium/index.html Environmental effects of gallium]
* [https://www.usgs.gov/centers/national-minerals-information-center/gallium-statistics-and-information Gallium Statistics and Information]
* [https://permanent.fdlp.gov/gpo42065/fs2013-3006.pdf Gallium: A Smart Metal] [[United States Geological Survey]]
* [http://arquivo.pt/wayback/20160515021612/http://jcp.aip.org/resource/1/jcpsa6/v26/i4/p784_s1?isAuthorized=no Thermal conductivity]
* [http://www.impmc.jussieu.fr/%7Eayrinhac/documents/Ga_data.pdf Physical and thermodynamical properties of liquid gallium] (doc pdf)

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[[Category:Gallium| ]]
[[Category:Chemical elements predicted by Dmitri Mendeleev]]
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[[Category:Post-transition metals]]
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[[Category:Materials that expand upon freezing]]
[[Category:Chemical elements with primitive orthorhombic structure]]