2806:2F0:91A0:1EB2:3CC9:FFD9:8A6F:263D at 18:03, 1 January 2022

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{{About|the liquid form of the element oxygen|the commercial dietary supplement product|Liquid Oxygen (supplement)}}
{{Redirect|LOX||Lox (disambiguation)}}
{{short description|One of the physical forms of elemental oxygen}}
[[File:Liquid oxygen in a beaker (cropped and retouched).jpg|thumb|Liquid oxygen (pale blue liquid) in a beaker.]]
[[File:Liquid oxygen in a magnet 2.jpg|thumb|When liquid oxygen is poured from a beaker into a strong magnet, the oxygen is temporarily suspended between the magnet poles, owing to its paramagnetism.]]
'''Liquid oxygen'''—abbreviated '''LOx''', '''LOX''' or '''Lox''' in the [[aerospace]], [[submarine]] and [[gas]] industries—is the [[liquid]] form of [[molecular oxygen]]. It was used as the [[Oxidizing agent|oxidizer]] in the first liquid-fueled rocket invented in 1926 by [[Robert H. Goddard]],<ref>{{Cite web|url=https://www.history.com/this-day-in-history/first-liquid-fueled-rocket|title=First liquid-fueled rocket|last=Editors|first=History com|website=HISTORY|language=en|access-date=2019-03-16}}</ref> an application which has continued to the present.

==Physical properties==
Liquid oxygen has a pale blue color and is strongly [[paramagnetism|paramagnetic]]: it can be suspended between the poles of a powerful [[horseshoe magnet]].<ref>{{cite book |author1=Moore, John W. |author2=Stanitski, Conrad L. |author3=Jurs, Peter C. |title=Principles of Chemistry: The Molecular Science |url=https://books.google.com/books?id=ZOm8L9oCwLMC&pg=PA297 |access-date=3 April 2011 |date=21 January 2009 |publisher=Cengage Learning |isbn=978-0-495-39079-4 |pages=297–}}</ref> Liquid oxygen has a density of {{convert|1.141|kg/L|abbr=on|g/ml}}, slightly denser than liquid water, and is [[cryogenics|cryogenic]] with a freezing point of {{convert|54.36|K|abbr=on}} and a boiling point of {{convert|-182.96|C|abbr=on|F K}} at {{convert|1|bar|psi|abbr=on}}. Liquid oxygen has an [[expansion ratio]] of 1:861 under {{convert|1|atm|lk=on}} and {{convert|20|°C|abbr=on}},<ref>[https://web.archive.org/web/20080607160832/http://www.chemistry.ohio-state.edu/ehs/handbook/gases/cryosafe.htm Cryogenic Safety]. chemistry.ohio-state.edu.</ref><ref>[http://www.lindecanada.com/en/aboutboc/safety/cryogenic_liquids/characteristics.php Characteristics]. {{webarchive|url=https://web.archive.org/web/20120218125124/http://www.lindecanada.com/en/aboutboc/safety/cryogenic_liquids/characteristics.php |date=2012-02-18 }}. Lindecanada.com. Retrieved on 2012-07-22.</ref> and because of this, it is used in some commercial and military aircraft as a transportable source of breathing oxygen.

Because of its cryogenic nature, liquid oxygen can cause the materials it touches to become extremely brittle. Liquid oxygen is also a very powerful oxidizing agent: organic materials will burn rapidly and energetically in liquid oxygen. Further, if [[Oxyliquit|soaked in liquid oxygen]], some materials such as coal briquettes, [[carbon black]], etc., can [[Detonation|detonate]] unpredictably from sources of ignition such as flames, sparks or impact from light blows. [[Petrochemical]]s, including [[asphalt]], often exhibit this behavior.<ref>{{cite web |url=https://archive.org/details/23004LiquidOxygenReceiptTransferStorageDisposal |title=Liquid Oxygen Receipt, Handling, Storage and Disposal |publisher=USAF Training Film }}</ref>

The [[tetraoxygen]] molecule (O4) was first predicted in 1924 by [[Gilbert N. Lewis]], who proposed it to explain why liquid oxygen defied [[Curie's law]].<ref>{{cite journal
|last = Lewis
|first = Gilbert N.
|author-link = Gilbert N. Lewis
|year = 1924
|title = The Magnetism of Oxygen and the Molecule O2
|journal = Journal of the American Chemical Society
|volume = 46
|issue = 9
|pages = 2027–2032
|doi = 10.1021/ja01674a008
}}</ref> Modern computer simulations indicate that, although there are no stable O4 molecules in liquid oxygen, O2 molecules do tend to associate in pairs with antiparallel [[spin (physics)|spins]], forming transient O4 units.<ref>{{cite journal
|last = Oda
|first = Tatsuki
|author2 = Alfredo Pasquarello
|year = 2004
|title = Noncollinear magnetism in liquid oxygen: A first-principles molecular dynamics study
|journal = Physical Review B
|volume = 70
|issue = 134402
|pages = 1–19
|doi = 10.1103/PhysRevB.70.134402
|bibcode = 2004PhRvB..70m4402O
|hdl = 2297/3462
|hdl-access = free
}}</ref>

[[Liquid nitrogen]] has a lower boiling point at −196 °C (77 K) than oxygen's −183 °C (90 K), and vessels containing liquid nitrogen can condense oxygen from air: when most of the nitrogen has evaporated from such a vessel, there is a risk that liquid oxygen remaining can react violently with organic material. Conversely, liquid nitrogen or [[liquid air]] can be oxygen-enriched by letting it stand in open air; atmospheric oxygen dissolves in it, while nitrogen evaporates preferentially.

The surface tension of liquid oxygen at its normal pressure boiling point is 13.2 dyn/cm.<ref>J. M. Jurns and J. W. Hartwig (2011). [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110014531.pdf Liquid Oxygen Liquid Acquisition Device Bubble Point Tests With High Pressure LOX at Elevated Temperatures], p. 4.</ref>

==Uses==
[[File:Liquid oxygen, Bagram Airfield, Afghanistan 4.jpg|thumb|A [[U.S. Air Force]] technician transfers liquid oxygen to a [[Lockheed Martin C-130J Super Hercules]] aircraft at the [[Bagram Airfield]], Afghanistan.]]
In commerce, liquid oxygen is classified as an [[industrial gas]] and is widely used for industrial and medical purposes. Liquid oxygen is obtained from the [[oxygen]] found naturally in [[air]] by [[fractional distillation]] in a [[Air separation|cryogenic air separation plant]].

Air forces have long recognized the strategic importance of liquid oxygen, both as an oxidizer and as a supply of gaseous oxygen for breathing in hospitals and high-altitude aircraft flights. In 1985 the USAF started a program of building its own oxygen-generation facilities at all major consumption bases.<ref>Arnold, Mark. [http://www.dtic.mil/get-tr-doc/pdf?AD=ADA581789 1U.S. Army Oxygen Generation System Development]. RTO-MP-HFM-182. dtic.mil</ref><ref>{{cite book|url=https://books.google.com/books?id=LVfaBwAAQBAJ&pg=PA150|title=Advances in Cryogenic Engineering: Proceedings of the 1957 Cryogenic Engineering Conference, National Bureau of Standards Boulder, Colorado, August 19–21, 1957|author=Timmerhaus, K. D.|date=8 March 2013|publisher=Springer Science & Business Media|isbn=978-1-4684-3105-6|pages=150–}}</ref>

=== In rocket propellant ===
{{see also|Liquid rocket propellant}}
[[File:Liquid Oxygen (LOX) ball at the CCAFS SLC-40.jpg|thumb|SpaceX's liquid oxygen ball at [[Kennedy Space Center|Cape Canaveral]]]]
Liquid oxygen is the most common [[Cryogenic fuel|cryogenic]] liquid [[oxidizer]] propellant for [[spacecraft propulsion|spacecraft rocket]] applications, usually in combination with [[liquid hydrogen]], [[kerosene]] or [[liquid methane|methane]].<ref name="nsf20140307">{{cite news |last=Belluscio|first=Alejandro G. |title=SpaceX advances drive for Mars rocket via Raptor power |url=http://www.nasaspaceflight.com/2014/03/spacex-advances-drive-mars-rocket-raptor-power/ |access-date=March 13, 2014 |newspaper=NASAspaceflight.com |date=March 7, 2014 }}</ref><ref name="fg20121120">{{cite news|last=Todd |first=David |title=Musk goes for methane-burning reusable rockets as step to colonise Mars |url=http://www.flightglobal.com/blogs/hyperbola/2012/11/musk-goes-for-methane-burning.html |access-date=November 22, 2012 |newspaper=FlightGlobal Hyperbola |date=November 20, 2012 |quote=‘We are going to do methane,’ Musk announced as he described his future plans for reusable launch vehicles including those designed to take astronauts to Mars within 15 years, ‘The energy cost of methane is the lowest and it has a slight Isp (Specific Impulse) advantage over Kerosene’ said Musk adding, ‘and it does not have the pain in the ass factor that hydrogen has.’ ... SpaceX's initial plan will be to build a lox/methane rocket for a future upper stage codenamed Raptor. ... The new Raptor upper stage engine is likely to be only the first engine in a series of lox/methane engines. |url-status=dead |archive-url=https://web.archive.org/web/20121128070948/http://www.flightglobal.com/blogs/hyperbola/2012/11/musk-goes-for-methane-burning.html |archive-date=November 28, 2012 }}</ref>

Liquid oxygen was used in the [[Robert H. Goddard#First flight|first liquid fueled rocket]]. The [[World War II]] [[V-2 rocket|V-2]] missile also used liquid oxygen under the name [[List of stoffs#List|''A-Stoff'' and ''Sauerstoff'']]. In the 1950s, during the [[Cold War]] both the United States' [[Redstone (rocket)|Redstone]] and [[Atlas (rocket)|Atlas]] rockets, and the [[USSR|Soviet]] [[R-7 Semyorka]] used liquid oxygen. Later, in the 1960s and 1970s, the ascent stages of the [[Saturn (rocket family)|Apollo Saturn rockets]], and the [[Space Shuttle main engines]] used liquid oxygen.

In 2020, many rockets used liquid oxygen: 
* [[Chinese space program]]: [[Long March 5]], and its derivations [[Long March 6]], [[Long March 7]]
* [[Indian Space Research Organisation]]: [[Geosynchronous Satellite Launch Vehicle#Third stage|GSLV]]
* [[JAXA]] (Japan): [[H-IIA]] and [[H3 (rocket)|H3]] (under development)
* [[Roscosmos]] (Russia): [[Soyuz-2]] and [[Angara (rocket family)|Angara]] (under development)
* [[European Space Agency|ESA]] ([[EU]]): [[Ariane 5]] and [[Ariane 6]] (under development)
* [[Korea Aerospace Research Institute]] ([[South Korea]]): [[KSLV-1]] and [[KSLV-II]]
* United States
** [[SpaceX]]: [[Falcon 9]], [[Falcon Heavy]] and [[SpaceX Starship|''Starship'']] (under development) (liquid oxygen chilled to {{Cvt|-207|C|F K}}, 10% denser {{Cvt|1250|g/L|g/ml}}<ref>{{Cite web|title=Oxygen - Density and Specific Weight|url=https://www.engineeringtoolbox.com/oxygen-O2-density-specific-weight-temperature-pressure-d_2082.html?vA=-207&degree=C&pressure=1bar#|access-date=2021-05-19|website=www.engineeringtoolbox.com}}</ref> than at boiling temperature)
** [[United Launch Alliance]]: [[Atlas V]], [[Delta IV]], [[Delta IV Heavy]], [[Vulcan (rocket)|Vulcan]] (under development)
** [[Northrop Grumman]]: [[Antares 230+]]
** [[Blue Origin]]: [[New Shepard]] and [[New Glenn]] (under development)
** [[Rocket Lab]]: [[Electron (rocket)|Electron]]
** [[Firefly Aerospace]]: [[Firefly Alpha]] (under development)
** [[Virgin Orbit]]: [[LauncherOne]]

==History==
*By 1845, [[Michael Faraday]] had managed to liquefy most gases then known to exist. Six gases, however, resisted every attempt at liquefaction<ref>[http://www.scienceclarified.com/Co-Di/Cryogenics.html Cryogenics]. Scienceclarified.com. Retrieved on 2012-07-22.</ref> and were known at the time as "permanent gases". They were oxygen, [[hydrogen]], [[nitrogen]], [[carbon monoxide]], [[methane]], and [[nitric oxide]].
*In 1877, [[Louis Paul Cailletet]] in France and [[Raoul Pictet]] in Switzerland succeeded in producing the first droplets of liquid air.
*In 1883, Polish professors [[Zygmunt Wróblewski]] and [[Karol Olszewski]] produced the first measurable quantity of liquid oxygen.

==See also==
{{Commons category|Liquid oxygen}}
{{div col|colwidth=22em}}
* [[Oxygen storage]]
* [[Industrial gas]]
* [[Cryogenics]]
* [[Liquid hydrogen]]
* [[Liquid helium]]
* [[Liquid nitrogen]]
* [[List of Stoffs]]
* [[Natterer compressor]]
* [[Rocket fuel]]
* [[Solid oxygen]]
* [[Tetraoxygen]]
{{div col end}}

==References==
{{Reflist|30em}}

{{DEFAULTSORT:Liquid Oxygen}}
[[Category:Rocket oxidizers]]
[[Category:Cryogenics]]
[[Category:Oxygen]]
[[Category:Industrial gases]]
[[Category:Liquids]]
[[Category:1883 in science]]

Liquid oxygen - Revision history

2806:2F0:91A0:1EB2:3CC9:FFD9:8A6F:263D at 18:03, 1 January 2022