Liquid oxygen in a beaker (cropped and retouched)

Liquid oxygen—abbreviated LOx, LOX or Lox in the

aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications. Aerospace engineering consists of aeronautics and astrona ...

, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an application which has continued to the present.

Physical properties

Liquid oxygen has a pale blue color and is strongly paramagnetic: it can be suspended between the poles of a powerful horseshoe magnet. Liquid oxygen has a density of , slightly denser than liquid water, and is cryogenic with a freezing point of and a boiling point of at . Liquid oxygen has an expansion ratio of 1:861 under and , 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 soaked in liquid oxygen, some materials such as coal briquettes, carbon black, etc., can detonate unpredictably from sources of ignition such as flames, sparks or impact from light blows.

Petrochemical Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable ...

s, including

asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term ...

, often exhibit this behavior. The tetraoxygen molecule (O₄) was first predicted in 1924 by

Gilbert N. Lewis Gilbert Newton Lewis (October 23 or October 25, 1875 – March 23, 1946) was an American physical chemist and a Dean of the College of Chemistry at University of California, Berkeley. Lewis was best known for his discovery of the covalent bond a ...

, who proposed it to explain why liquid oxygen defied Curie's law. 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 spins, forming transient O₄ units. 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.

Uses

Liquid oxygen, Bagram Airfield, Afghanistan 4

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 Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

found naturally in air by fractional distillation in a 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.

In rocket propellant

Liquid Oxygen (LOX) ball at the CCAFS SLC-40

Liquid oxygen is the most common cryogenic liquid oxidizer propellant for spacecraft rocket applications, usually in combination with liquid hydrogen, kerosene or methane. Liquid oxygen was used in the first liquid fueled rocket. The

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

V-2 missile also used liquid oxygen under the name ''A-Stoff'' and ''Sauerstoff''. In the 1950s, during the Cold War both the United States' Redstone and

Atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geograp ...

rockets, and the Soviet R-7 Semyorka used liquid oxygen. Later, in the 1960s and 1970s, the ascent stages of the 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: GSLV * JAXA (Japan): H-IIA and H3 (under development) * Roscosmos (Russia): Soyuz-2 and Angara (under development) * ESA ( EU):

Ariane 5 Ariane 5 is a European heavy-lift space launch vehicle developed and operated by Arianespace for the European Space Agency (ESA). It is launched from the Centre Spatial Guyanais (CSG) in French Guiana. It has been used to deliver payloads in ...

and Ariane 6 (under development) * Korea Aerospace Research Institute (

South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...

): KSLV-1 and KSLV-II * United States ** SpaceX: Falcon 9, Falcon Heavy and ''Starship'' (under development) (liquid oxygen chilled to , 10% denser than at boiling temperature) ** United Launch Alliance:

Atlas V Atlas V is an expendable launch system and the fifth major version in the Atlas launch vehicle family. It was originally designed by Lockheed Martin, now being operated by United Launch Alliance (ULA), a joint venture between Lockheed Marti ...

, Delta IV, Delta IV Heavy, Vulcan (under development) **

Northrop Grumman Northrop Grumman Corporation is an American multinational aerospace and defense technology company. With 90,000 employees and an annual revenue in excess of $30 billion, it is one of the world's largest weapons manufacturers and military tec ...

: Antares 230+ ** Blue Origin: New Shepard and

New Glenn New Glenn is a heavy-lift orbital launch vehicle in development by Blue Origin. Named after NASA astronaut John Glenn, design work on the vehicle began in 2012. Illustrations of the vehicle, and the high-level specifications, were initially ...

(under development) ** Rocket Lab:

Electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary partic ...

** Firefly Aerospace: Firefly Alpha ** Virgin Orbit: LauncherOne

History

*By 1845,

Michael Faraday Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic inductio ...

had managed to liquefy most gases then known to exist. Six gases, however, resisted every attempt at liquefactionCryogenics
Scienceclarified.com. Retrieved on 2012-07-22. and were known at the time as "permanent gases". They were oxygen,

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

, nitrogen,

carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

, 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.

References

{{DEFAULTSORT:Liquid Oxygen Rocket oxidizers Cryogenics Oxygen Industrial gases Liquids 1883 in science

Physical properties

Uses

In rocket propellant

History

See also

References