Editing Argon (section)

==Applications==
[[Image:Argon.jpg|thumb|right|upright=0.8|Cylinders containing argon gas for use in extinguishing fire without damaging server equipment]]

Argon has several desirable properties:
* Argon is a chemically [[inert gas]].
* Argon is the cheapest alternative when [[nitrogen]] is not sufficiently inert.
* Argon has low [[thermal conductivity]].
* Argon has electronic properties (ionization and/or the emission spectrum) desirable for some applications.

Other [[noble gas]]es would be equally suitable for most of these applications, but argon is by far the cheapest. It is inexpensive, since it occurs naturally in air and is readily obtained as a byproduct of [[cryogenic]] [[air separation]] in the production of [[liquid oxygen]] and [[liquid nitrogen]]: the primary constituents of air are used on a large industrial scale. The other noble gases (except [[helium]]) are produced this way as well, but argon is the most plentiful by far. The bulk of its applications arise simply because it is inert and relatively cheap.

===Industrial processes===
Argon is used in some high-temperature industrial processes where ordinarily non-reactive substances become reactive. For example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning.

For some of these processes, the presence of nitrogen or oxygen gases might cause defects within the material. Argon is used in some types of [[arc welding]] such as [[gas metal arc welding]] and [[gas tungsten arc welding]], as well as in the processing of [[titanium]] and other reactive elements. An argon atmosphere is also used for growing crystals of [[silicon]] and [[germanium]].

{{See also|shielding gas}}
Argon is used in the poultry industry to [[asphyxiant gas|asphyxiate]] birds, either for mass culling following disease outbreaks, or as a means of slaughter more humane than [[electronarcosis|electric stunning]]. Argon is denser than air and displaces oxygen close to the ground during [[inert gas asphyxiation]].<ref>{{Unbulleted list citebundle|
{{cite news
 |last        = Fletcher
 |first       = D. L.
 |title       = Slaughter Technology
 |url         = http://ps.fass.org/cgi/reprint/78/2/277.pdf
 |work        = Symposium: Recent Advances in Poultry Slaughter Technology
 |access-date  = 1 January 2010
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20110724195609/http://ps.fass.org/cgi/reprint/78/2/277.pdf
 |archive-date = 24 July 2011
}}|{{cite journal|last1=Shields|first1=Sara J.|last2=Raj|first2=A. B. M.|s2cid=11301328|title=A Critical Review of Electrical Water-Bath Stun Systems for Poultry Slaughter and Recent Developments in Alternative Technologies|journal=Journal of Applied Animal Welfare Science|volume=13|issue=4|year=2010|pages=281–299|issn=1088-8705|doi=10.1080/10888705.2010.507119|pmid=20865613|citeseerx=10.1.1.680.5115}}}}</ref> Its non-reactive nature makes it suitable in a food product, and since it replaces oxygen within the dead bird, argon also enhances shelf life.<ref name="FraquezaBarreto2009">{{cite journal|last1=Fraqueza|first1=M. J.|last2=Barreto|first2=A. S.|title=The effect on turkey meat shelf life of modified-atmosphere packaging with an argon mixture|journal=Poultry Science|volume=88|issue=9|year=2009|pages=1991–1998|issn=0032-5791|doi=10.3382/ps.2008-00239|pmid=19687286|doi-access=free}}</ref>

Argon is sometimes used for [[Gaseous fire suppression|extinguishing fires]] where valuable equipment may be damaged by water or foam.<ref name="SuKim2001">{{cite journal|last1=Su|first1=Joseph Z.|last2=Kim|first2=Andrew K.|last3=Crampton|first3=George P.|last4=Liu|first4=Zhigang|title=Fire Suppression with Inert Gas Agents|journal=Journal of Fire Protection Engineering|volume=11|issue=2|year=2001|pages=72–87|issn=1042-3915|doi=10.1106/X21V-YQKU-PMKP-XGTP}}</ref>

===Scientific research===
Liquid argon is used as the target for neutrino experiments and direct [[dark matter]] searches. The interaction between the hypothetical [[Weakly interacting massive particles|WIMP]]s and an argon nucleus produces [[scintillation (physics)|scintillation]] light that is detected by [[photomultiplier tubes]]. Two-phase detectors containing argon gas are used to detect the ionized electrons produced during the WIMP–nucleus scattering. As with most other liquefied noble gases, argon has a high scintillation light yield (about 51 photons/keV<ref>
{{cite journal
 |display-authors= 4
 |author= Gastler, Dan
 |author2= Kearns, Ed
 |author3= Hime, Andrew
 |author4= Stonehill, Laura C.
 |author5= Seibert, Stan
 |author6= Klein, Josh
 |author7= Lippincott, W. Hugh
 |author8= McKinsey, Daniel N.
 |author9= Nikkel, James A
 |s2cid= 6876533
 |date= 2012
 |title=Measurement of scintillation efficiency for nuclear recoils in liquid argon
 |doi= 10.1103/PhysRevC.85.065811
 |journal= Physical Review C
 |volume= 85
 |issue= 6
 |pages= 065811
 |arxiv=1004.0373
|bibcode = 2012PhRvC..85f5811G }}</ref>), is transparent to its own scintillation light, and is relatively easy to purify. Compared to [[xenon]], argon is cheaper and has a distinct scintillation time profile, which allows the separation of electronic recoils from nuclear recoils. On the other hand, its intrinsic beta-ray background is larger due to {{chem|39|Ar}} contamination, unless one uses argon from underground sources, which has much less {{chem|39|Ar}} contamination. Most of the argon in Earth's atmosphere was produced by electron capture of long-lived {{chem|40|K}} ({{chem|40|K}} + e<sup>−</sup> → {{chem|40|Ar}} + ν) present in natural potassium within Earth. The {{chem|39|Ar}} activity in the atmosphere is maintained by cosmogenic production through the knockout reaction {{chem|40|Ar}}(n,2n){{chem|39|Ar}} and similar reactions. The half-life of {{chem|39|Ar}} is only 269&nbsp;years. As a result, the underground Ar, shielded by rock and water, has much less {{chem|39|Ar}} contamination.<ref>
{{Cite journal|author= Xu, J.
 |author2= Calaprice, F.
 |author3= Galbiati, C.
 |author4= Goretti, A.
 |author5= Guray, G.
 |s2cid= 117711599
 |name-list-style= amp
 |date= 26 April 2012
 |title=A Study of the Residual {{Chem|39|Ar}} Content in Argon from Underground Sources
 |journal= Astroparticle Physics
 |volume= 66
 |issue= 2015
 |pages= 53–60
 |arxiv=1204.6011 |display-authors=etal|doi= 10.1016/j.astropartphys.2015.01.002
 |bibcode= 2015APh....66...53X
 }}</ref> Dark-matter detectors currently operating with liquid argon include [[DarkSide (dark matter experiment)|DarkSide]], [[WIMP Argon Programme|WArP]], [[ArDM]], [[Cryogenic Low-Energy Astrophysics with Neon|microCLEAN]] and [[DEAP]]. Neutrino experiments include [[ICARUS (experiment)|ICARUS]] and [[MicroBooNE]], both of which use high-purity liquid argon in a [[time projection chamber]] for fine grained three-dimensional imaging of neutrino interactions.

At Linköping University, Sweden, the inert gas is being utilized in a vacuum chamber in which plasma is introduced to ionize metallic films.<ref>{{Cite web|title=Plasma electrons can be used to produce metallic films|url=https://phys.org/news/2020-05-plasma-electrons-metallic.html|date=May 7, 2020|website=Phys.org|access-date=May 8, 2020}}</ref> This process results in a film usable for manufacturing computer processors. The new process would eliminate the need for chemical baths and use of expensive, dangerous and rare materials.

===Preservative===
[[File:CsCrystals.JPG|thumb|A sample of [[caesium]] is packed under argon to avoid reactions with air]]
Argon is used to displace oxygen- and moisture-containing air in packaging material to extend the shelf-lives of the contents (argon has the [[E numbers|European food additive code]] E938). Aerial oxidation, hydrolysis, and other chemical reactions that degrade the products are retarded or prevented entirely. High-purity chemicals and pharmaceuticals are sometimes packed and sealed in argon.<ref name="pmid17099243">{{cite journal |vauthors=Ilouga PE, Winkler D, Kirchhoff C, Schierholz B, Wölcke J|date=November 2007 |title=Investigation of 3 industry-wide applied storage conditions for compound libraries|journal=Journal of Biomolecular Screening|volume=12 |issue=1 |pages=21–32 |doi=10.1177/1087057106295507|pmid=17099243 |doi-access=free }}</ref>

In [[winemaking]], argon is used in a variety of activities to provide a barrier against oxygen at the liquid surface, which can spoil wine by fueling both microbial metabolism (as with [[acetic acid bacteria]]) and standard [[redox]] chemistry.

Argon is sometimes used as the propellant in [[aerosol]] cans.

Argon is also used as a preservative for such products as [[varnish]], [[polyurethane]], and paint, by displacing air to prepare a container for storage.<ref>Zawalick, Steven Scott "Method for preserving an oxygen sensitive liquid product" {{US patent|6629402}} Issue date: 7 October 2003.</ref>

Since 2002, the American [[National Archives]] stores important national documents such as the [[United States Declaration of Independence|Declaration of Independence]] and the [[United States Constitution|Constitution]] within argon-filled cases to inhibit their degradation. Argon is preferable to the helium that had been used in the preceding five decades, because helium gas escapes through the intermolecular pores in most containers and must be regularly replaced.<ref>
{{cite web
 |url=https://www.archives.gov/press/press-kits/charters.html#pressrelaese1
 |title=Schedule for Renovation of the National Archives Building
 |access-date=7 July 2009
}}</ref>

===Laboratory equipment===
{{See also|Air-free technique}}
[[Image:Glovebox.jpg|thumb|[[Glovebox]]es are often filled with argon, which recirculates over scrubbers to maintain an [[oxygen]]-, [[nitrogen]]-, and moisture-free atmosphere]]

Argon may be used as the [[inert gas]] within [[Schlenk line]]s and [[glovebox]]es. Argon is preferred to less expensive nitrogen in cases where nitrogen may react with the reagents or apparatus.

Argon may be used as the carrier gas in [[gas chromatography]] and in [[electrospray ionization mass spectrometry]]; it is the gas of choice for the plasma used in [[Inductively coupled plasma|ICP]] [[spectroscopy]]. Argon is preferred for the sputter coating of specimens for [[scanning electron microscopy]]. Argon gas is also commonly used for [[sputter deposition]] of thin films as in [[microelectronics]] and for [[microfabrication|wafer cleaning in microfabrication]].

===Medical use===
[[Cryosurgery]] procedures such as [[cryoablation]] use liquid argon to destroy tissue such as [[cancer]] cells. It is used in a procedure called "argon-enhanced coagulation", a form of argon [[plasma torch|plasma beam]] [[electrosurgery]]. The procedure carries a risk of producing [[gas embolism]] and has resulted in the death of at least one patient.<ref>{{cite web
 |url=http://www.mdsr.ecri.org/summary/detail.aspx?doc_id=8248
 |title=Fatal Gas Embolism Caused by Overpressurization during Laparoscopic Use of Argon Enhanced Coagulation
 |date=24 June 1994
 |publisher=MDSR
 |access-date=10 January 2007
 |archive-date=12 July 2021
 |archive-url=https://web.archive.org/web/20210712040208/http://www.mdsr.ecri.org/summary/detail.aspx?doc_id=8248
 |url-status=dead
 }}</ref>

Blue [[argon laser]]s are used in surgery to weld arteries, destroy tumors, and correct eye defects.<ref name="emsley" />

Argon has also been used experimentally to replace nitrogen in the breathing or decompression mix known as [[Argox (breathing gas)|Argox]], to speed the elimination of dissolved nitrogen from the blood.<ref>
{{cite journal
 |author=Pilmanis Andrew A.
 |author2=Balldin U. I.
 |author3=Webb James T.
 |author4=Krause K. M.
 |title=Staged decompression to 3.5 psi using argon–oxygen and 100% oxygen breathing mixtures
 |journal=Aviation, Space, and Environmental Medicine 
 |volume=74 |issue=12 |pages=1243–1250
 |date=2003
 |pmid=14692466|url=https://www.researchgate.net/publication/8945687
}}</ref>

===Lighting===
[[File:ArTube.jpg|thumb|upright=0.8|Argon [[gas-discharge lamp]] forming "Ar", the symbol for argon]]

[[Incandescent light]]s are filled with argon, to preserve the [[electrical filament|filaments]] at high temperature from oxidation. It is used for the specific way it ionizes and emits light, such as in [[plasma globe]]s and [[Calorimeter (particle physics)|calorimetry]] in experimental [[particle physics]]. [[Gas-discharge lamp]]s filled with pure argon provide lilac/violet light; with argon and some mercury, blue light. Argon is also used for blue and green [[argon laser|argon-ion lasers]].

===Miscellaneous uses===
Argon is used for [[thermal insulation]] in [[Insulated glazing|energy-efficient windows]].<ref>
{{cite web
 |url=http://www.finehomebuilding.com/how-to/articles/understanding-energy-efficient-windows.aspx
 |title=Energy-Efficient Windows
 |access-date=1 August 2009
 |publisher=FineHomebuilding.com
|date=February 1998
 }}</ref> Argon is also used in technical [[scuba diving]] to inflate a [[dry suit]] because it is inert and has low thermal conductivity.<ref name="IEEE2008">{{cite journal
 |author=Nuckols M. L.
 |author2=Giblo J.
 |author3=Wood-Putnam J. L.
 |title=Thermal Characteristics of Diving Garments When Using Argon as a Suit Inflation Gas
 |journal=Proceedings of the Oceans 08 MTS/IEEE Quebec, Canada Meeting
 |date=15–18 September 2008
 |url=http://archive.rubicon-foundation.org/7962
 |access-date=2 March 2009
 |archive-url=https://web.archive.org/web/20090721035810/http://archive.rubicon-foundation.org/7962
 |archive-date=21 July 2009
 |url-status=usurped
 }}</ref>

Argon is used as a propellant in the development of the [[Variable Specific Impulse Magnetoplasma Rocket]] (VASIMR). Compressed argon gas is allowed to expand, to cool the seeker heads of some versions of the [[AIM-9 Sidewinder]] missile and other missiles that use cooled thermal seeker heads. The gas is [[AIM-9 Sidewinder#Design|stored at high pressure]].<ref>{{cite web
 |url=http://home.wanadoo.nl/tcc/rnlaf/aim9.html 
 |title=Description of Aim-9 Operation 
 |access-date=1 February 2009 
 |publisher=planken.org 
 |archive-url=https://web.archive.org/web/20081222025556/http://home.wanadoo.nl/tcc/rnlaf/aim9.html 
 |archive-date=22 December 2008 
 |url-status=dead 
}}</ref>

Argon-39, with a half-life of 269 years, has been used for a number of applications, primarily [[ice core]] and [[ground water]] dating. Also, [[potassium–argon dating]] and related [[Argon argon dating|argon-argon dating]] are used to date [[Sedimentary rock|sedimentary]], [[Metamorphic rock|metamorphic]], and [[igneous rock]]s.<ref name="emsley" />

Argon has been used by athletes as a doping agent to simulate [[Hypoxia (environmental)|hypoxic]] conditions. In 2014, the [[World Anti-Doping Agency]] (WADA) added argon and [[xenon]] to the list of prohibited substances and methods, although at this time there is no reliable test for abuse.<ref>{{cite news |title=WADA amends Section S.2.1 of 2014 Prohibited List |url=https://www.wada-ama.org/en/media/2014-05/wada-amends-section-s21-of-2014-prohibited-list#.VARJ3WNqOIl |date=31 August 2014 |access-date=1 September 2014 |archive-date=27 April 2021 |archive-url=https://web.archive.org/web/20210427160909/https://www.wada-ama.org/en/media/2014-05/wada-amends-section-s21-of-2014-prohibited-list#.VARJ3WNqOIl |url-status=dead }}</ref>