Liquid nitrogen 306364 225062538 2008-07-11T18:28:45Z Rjwilmsi 203434 gen fixes + link/fix date fields in cite templates (explanation [[User:Rjwilmsi#My_correction_of_dates_in_templates|here]]) using [[Project:AutoWikiBrowser|AWB]] [[Image:Liquid nitrogen tank.JPG|thumb|A tank of liquid nitrogen, used to supply a [[Cryopreservation|cryogenic freezer]] (for storing laboratory samples at a temperature of about -150 Celsius).]] [[Image:Nitrogen ice cream 0020.jpg|thumb|Liquid nitrogen may be used to prepare "home-made" [[ice cream]], as these students are doing.]] [[Image:Liquid nitrogen dsc04496.jpg|thumb|Liquid nitrogen boiling in a cup]] '''Liquid nitrogen''' (liquid density at the [[triple point]] is 0.707 g/mL) is the liquid produced industrially in large quantities by [[fractional distillation]] of [[liquid air]] and is often referred to by the abbreviation, '''LN<sub>2</sub>'''. It is pure [[nitrogen]], in a liquid state. Liquid nitrogen has the [[UN number]] 1977. Liquid nitrogen boils at {{convert|77|K|0}}, and is a [[cryogenics|cryogenic]] fluid which can cause rapid [[frostbite]] on contact with living tissue. It has a dielectric constant of 1.4.<ref>{{cite web | title = Dielectric Constants | url = http://www.apgsensors.com/ltr2/access.php?file=pdf/dielectric-constants.pdf}}</ref> When appropriately [[Thermal insulation|insulated]] from ambient [[heat]], liquid nitrogen can be stored and transported, for example in [[vacuum flasks]]. Here, the very low temperature is held constant at 77K by slow boiling of the liquid, resulting in the evolution of nitrogen gas. Depending on the size and design, the holding time of vacuum flasks ranges from a few hours to a few weeks. Liquid nitrogen can easily be converted to the solid by placing it in a vacuum chamber pumped by a rotary vacuum pump.<ref>Umrath, W. (1974) Cooling bath for rapid freezing in electron microscopy. Journal of Microscopy 101, 103–105.</ref> Liquid nitrogen freezes at {{convert|63|K|0}}. Despite its reputation, liquid nitrogen's efficiency as a coolant is reduced by the fact that it boils immediately on contact with a warmer object, enveloping the object in insulating nitrogen gas. This effect is known as the [[Leidenfrost effect]] and applies to any liquid in contact with an object significantly hotter than its boiling point. More rapid cooling may be obtained by plunging an object into a slush of liquid and solid nitrogen than into liquid nitrogen alone. That said, liquid nitrogen alone is sufficient for most applications. ==Applications== Liquid nitrogen is a compact and readily transported source of nitrogen gas without pressurization. Further, its ability to maintain temperatures far below the [[freezing point]] of water makes it extremely useful in a wide range of applications, primarily as an open-cycle [[refrigerant]], including: * in [[cryogenics]] * as a source of very dry nitrogen gas * the immersion freezing and transportation of [[food]] products * the [[cryopreservation]] of [[blood]], reproductive cells ([[sperm]] and [[Ovum|egg]]), and other [[biology|biological]] samples and materials * as a cooling supplement for [[overclocking]] a [[central processing unit]], a [[graphics processing unit]], or another type of [[computer hardware]]<ref>{{cite book | title = The Book of Overclocking: Tweak Your PC to Unleash Its Power | first = Scott | last = Wainner | coauthors = Robert Richmond | pages = p. 44 | isbn = 188641176X | publisher = No Starch Press | year = 2003}}</ref> * as a method of freezing water pipes in order to work on them in situations where a valve is not available to block water flow to the work area. * in [[cryotherapy]] for removing unsightly or potentially [[skin cancer|malignant skin lesions]] such as [[wart]]s and [[actinic keratosis]]. * in the process of [[promession]], a way to dispose of the dead. * cooling a [[high-temperature superconductor]] to a temperature sufficient to achieve [[superconductivity]]. * the [[cryonics|cryonic preservation of humans and pets]] in the hope of future reanimation. * as a coolant for [[vacuum pump]] traps and in [[rotovap|controlled-evaporation processes]] in chemistry. ==Safety== Since the liquid to gas expansion ratio of this substance is 1:694,<ref>{{cite web | url = http://www-safety.deas.harvard.edu/services/nitrogen.html | title = Information Specific to Liquid Nitrogen |date=[[30 July]] [[2003]] | publisher = [[Harvard University]]}}</ref> a tremendous amount of force can be generated when liquid nitrogen boils off for whatever reasons. In a well-known accident in 2006 at [[Texas A&M University]], the pressure-relief devices of a tank of liquid nitrogen were sealed with brass plugs. As a result, the tank failed catastrophically, and exploded. The force of the explosion was sufficient to propel the tank through the floor/ceiling immediately above it.<ref>{{cite web | title = Investigative Report on Chemistry 301A Cylinder Explosion | author = Brent S. Mattox | publisher = Texas A&M University | format = reprint | url = http://ehs.ucdavis.edu/ftpd/ucih/chemistry_301a.pdf}}</ref> Due to its extremely low temperature, careless handling of liquid nitrogen may result in [[Cold burn#cold burn|cold burns]]. It should be also borne in mind, that as liquid nitrogen evaporates it will reduce the [[oxygen]] concentration in the [[air]] and might act as an [[asphyxiant]], especially in confined spaces. Nitrogen is odourless, colourless and tasteless, and may produce asphyxia without any sensation or prior warning.<ref name=BCGACOPCP30>British Compressed Gases Association (2000) BCGA Code of Practice CP30. The Safe Use of Liquid nitrogen dewars up to 50 litres. ISSN 0260-4809.[http://www.bcga.co.uk]</ref> Vessels containing liquid nitrogen can [[liquid oxygen| condense oxygen from air]]. The liquid in such a vessel becomes increasingly enriched in oxygen (boiling point = 90 K) as the nitrogen evaporates, and can cause violent oxidation of organic material. ==See also== * [[Computer cooling]] * [[Liquid nitrogen economy]] ==References== {{Refimprove|date=October 2007}} <references/> ==External links== *[http://www.younghotelier.com/interviews/video-cooking-with-liquid-nitrogen-in-the-real-world-tang-restaurant-dubai/ Behind the scenes video] - How liquid nitrogen is used in restaurants for cooking and cocktails [[Category:Nitrogen]] [[Category:Coolants]] [[es:Nitrógeno líquido]] [[fr:Azote liquide]] [[it:Azoto liquido]] [[ja:液体窒素]] [[pl:Ciekły azot]] [[pt:Nitrogênio líquido]] [[zh:液氮]]