Editing Cryogenics (section)

{{short description|Study of the production and behaviour of materials at very low temperatures}}
{{redirect|Low temperature physics|the journal|Low Temperature Physics (journal)}}
{{for-multi|cryopreservation of humans|Cryonics|the band|Cryogenic (band)}}
[[File:Liquidnitrogen.jpg|thumb|[[Liquid nitrogen|Nitrogen is a liquid]] under {{convert|-195.8|C|K}}. ]]
In [[physics]], '''cryogenics''' is the production and behaviour of materials at very low [[temperature]]s.

The 13th [[International Institute of Refrigeration]]'s (IIR) International Congress of Refrigeration (held in Washington, DC in 1971) endorsed a universal definition of "cryogenics" and "cryogenic" by accepting a threshold of {{convert|120|K|C}} to distinguish these terms from conventional refrigeration.<ref>International Dictionary of Refrigeration, http://dictionary.iifiir.org/search.php, {{Webarchive|url=https://web.archive.org/web/20191001210219/http://dictionary.iifiir.org/search.php|date=2019-10-01}}.</ref><ref>ASHRAE Terminology, https://www.ashrae.org/technical-resources/free-resources/ashrae-terminology.</ref><ref>"Cryogenics is usually defined as the science and technology dealing with temperatures less than about 120 K [4, 5], although this review does not adhere to a strict 120 K definition." K. D. Timmerhaus, R. Reed. ''Cryogenic Engineering: Fifty Years of Progress''. Springer Science+Business Media LLC (2007), chapter: 1.2, The Beginning of Cryogenics, p. 7.</ref><ref>{{cite web | url=https://trc.nist.gov/cryogenics/aboutCryogenics.html | title=About Cryogenics | quote=In terms of the Kelvin scale the cryogenic region is often considered to be that below approximately 120 K (−153 C).}}</ref> This is a logical dividing line, since the normal [[boiling point]]s of the so-called permanent [[gas]]es (such as [[helium]], [[hydrogen]], [[neon]], [[nitrogen]], [[oxygen]], and normal [[air]]) lie below 120&nbsp;K, while the [[Freon]] refrigerants, [[hydrocarbon]]s, and other common refrigerants have boiling points above 120&nbsp;K.<ref>{{Cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/dichlorodifluoromethane#section=Chemical-and-Physical-Properties|title=DICHLORODIFLUOROMETHANE at Pubchem}}</ref><ref>{{Cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/propane#section=Boiling-Point|title=PROPANE at Pubchem}}</ref>

Discovery of [[superconducting]] materials with critical temperatures significantly above the boiling point of nitrogen has provided new interest in reliable, low-cost methods of producing high-temperature cryogenic refrigeration. The term "high temperature cryogenic" describes temperatures ranging from above the boiling point of liquid nitrogen, {{convert|-195.79|°C|K °F|2}}, up to {{convert|-50|°C|K °F|0}}.<ref>J. M. Nash, 1991, "Vortex Expansion Devices for High Temperature Cryogenics", Proceedings of the 26th Intersociety Energy Conversion Engineering Conference, Vol. 4, pp. 521–525.</ref> The discovery of superconductive properties is first attributed to [[Heike Kamerlingh Onnes]] on July 10, 1908, after they were able to reach a temperature of 2&nbsp;K. These first superconductive properties were observed in mercury at a temperature of 4.2&nbsp;K.<ref>{{Citation |last=Radebaugh |first=R. |title=Historical Summary of Cryogenic Activity Prior to 1950 |date=2007 |work=Cryogenic Engineering |pages=3–27 |editor-last=Timmerhaus |editor-first=Klaus D. |series=International Cryogenics Monograph Series |place=New York, New York |publisher=Springer |language=en |bibcode=2007cren.book....3R |doi=10.1007/0-387-46896-x_1 |isbn=978-0-387-46896-9 |editor2-last=Reed |editor2-first=Richard P. |doi-access=free}}.</ref>

Cryogenicists use the [[Kelvin]] or [[Rankine scale|Rankine]] temperature scale, both of which measure from [[absolute zero]], rather than more usual scales such as [[Celsius]] which measures from the freezing point of water at sea level<ref>Celsius, Anders (1742) [https://archive.org/stream/kungligasvenskav1317kung#page/170/mode/2up/search "Observationer om twänne beständiga grader på en thermometer"] (Observations about two stable degrees on a thermometer), ''Kungliga Svenska Vetenskapsakademiens Handlingar'' (Proceedings of the Royal Swedish Academy of Sciences), '''3''': 171–180 and [https://archive.org/stream/kungligasvenskav1317kung#page/232/mode/2up Fig. 1.]</ref><ref name="EOC 1">[[Don Rittner]]; Ronald A. Bailey (2005): [https://books.google.com/books?id=Y2MNUNFg-8gC&pg=PA43 ''Encyclopedia of Chemistry.''] [[Facts On File]], [[Manhattan]], New York City, p. 43.</ref> or [[Fahrenheit]] which measures from the freezing point of a particular brine solution at sea level.<ref name=":0">[https://www.britannica.com/science/Fahrenheit-temperature-scale Fahrenheit temperature scale], Encyclopædia Britannica Online. 25 September 2015.</ref><ref>{{cite web|title=Fahrenheit: Facts, History & Conversion Formulas|url=https://www.livescience.com/39916-fahrenheit.html|access-date=2018-02-09|website=Live Science}}</ref>