Liquid oxygen

Liquid oxygen
The blue colour of liquid oxygen in a dewar flask

Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.


Physical properties

Liquid oxygen has a pale blue color and is strongly paramagnetic and can be suspended between the poles of a powerful horseshoe magnet.[1] Liquid oxygen has a density of 1.141 g/cm3 (1.141 kg/L) and is cryogenic with a freezing point of 50.5 K (−368.77  °F; −222.65 °C) and a boiling point of 90.19 K (−297.33 °F, −182.96 °C) at 101.325 kPa (760 mmHg). Liquid oxygen has an expansion ratio of 1:861 at 20 °C (68 °F);[2][3] and because of this, it is used in some commercial and military aircraft as a 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. Petrochemicals often exhibit this behavior, including asphalt.

The tetraoxygen molecule (O4) was first predicted in 1924 by Gilbert N. Lewis, who proposed it as an explanation for the failure of liquid oxygen to obey Curie's law.[4] 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.[5]

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.


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 cryogenic air separation plant.

Liquid oxygen is a common liquid oxidizer propellant for spacecraft rocket applications, usually in combination with liquid hydrogen or kerosene. Liquid oxygen is useful in this role because it creates a high specific impulse. It was used in the very first rocket applications like the V2 missile (under the name A-Stoff and Sauerstoff) and Redstone, R-7 Semyorka, Atlas boosters, and the ascent stages of the Apollo Saturn rockets. Liquid oxygen was also used in some early ICBMs, although more modern ICBMs do not use liquid oxygen because its cryogenic properties and need for regular replenishment to replace boiloff make it harder to maintain and launch quickly. Many modern rockets use liquid oxygen, including the main engines on the Space Shuttle.

Liquid oxygen also had extensive use in making oxyliquit explosives, but is rarely used now due to a high rate of accidents.


See also


  1. ^ John W. Moore; Conrad L. Stanitski; Peter C. Jurs (21 January 2009). Principles of Chemistry: The Molecular Science. Cengage Learning. pp. 297–. ISBN 9780495390794. Retrieved 3 April 2011. 
  2. ^ Cryogenic Safety
  3. ^ Characteristics
  4. ^ Lewis, Gilbert N. (1924). "The Magnetism of Oxygen and the Molecule O2". Journal of the American Chemical Society 46 (9): 2027–2032. doi:10.1021/ja01674a008. 
  5. ^ Oda, Tatsuki; Alfredo Pasquarello (2004). "Noncollinear magnetism in liquid oxygen: A first-principles molecular dynamics study". Physical Review B 70 (134402): 1–19. Bibcode 2004PhRvB..70m4402O. doi:10.1103/PhysRevB.70.134402. 
  6. ^ Cryogenics

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Look at other dictionaries:

  • liquid oxygen — n. the light bluish liquid form of oxygen produced by fractionation of liquid air and used as an oxidizer in liquid fueled rockets: oxygen is often stored in this form, which boils at 183°C …   English World dictionary

  • liquid oxygen — Oxygen liquefied by cooling it below −297.4°F (−183°C). Liquid oxygen requires much less volume than gaseous oxygen. This is mainly used for breathing. In some aircraft, it is also used for inflating the g suit. LOX cannot be stored for long… …   Aviation dictionary

  • liquid oxygen — noun a bluish translucent magnetic liquid obtained by compressing gaseous oxygen and then cooling it below its boiling point; used as an oxidizer in rocket propellants • Syn: ↑LOX • Hypernyms: ↑oxygen, ↑O, ↑atomic number 8 * * * noun : a pale… …   Useful english dictionary

  • liquid oxygen — oxygen in liquid form, oxygen chilled to 173 degrees Celsius (provides for easy storage because it has little volume) …   English contemporary dictionary

  • liquid oxygen explosive — oksilikvitas statusas T sritis chemija apibrėžtis Sprogstamoji medžiaga iš pjuvenų, medžio anglių, įmirkytų skystame deguonyje. atitikmenys: angl. liquid oxygen explosive; oxyliquit rus. оксиликвит …   Chemijos terminų aiškinamasis žodynas

  • liquid-oxygen explosive — noun : a blasting explosive that consists essentially of a cartridge containing combustible material (as carbon black or lampblack) and immersed in liquid oxygen shortly before use …   Useful english dictionary

  • liquid oxygen — a clear, pale blue liquid obtained by compressing oxygen and then cooling it below its boiling point: used chiefly as an oxidizer in liquid rocket propellants. Also called lox, LOX [1875 80] * * * …   Universalium

  • liquid oxygen — /lɪkwəd ˈɒksədʒən/ (say likwuhd oksuhjuhn) noun oxygen in its liquid state; a pale blue liquid which boils at 182.9°C; used as an oxidant in rockets. Abbrev.: lox …   Australian-English dictionary

  • liquid oxygen — noun Oxygen in liquid form, as opposed to its gaseous form at standard temperature and pressure …   Wiktionary

  • liquid oxygen — liq′uid ox′ygen n. chem. rkt a clear, pale blue liquid obtained by compressing oxygen and then cooling it below its boiling point Also called lox II …   From formal English to slang

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