Freezing: Difference between revisions

'''Freezing''' is a [[phase transition]] in which a [[liquid]] turns into a [[solid]] when its [[temperature]] is lowered below its [[freezing point]]. In accordance with the internationally established definition, ''freezing'' means the solidification phase change of a liquid or the liquid content of a substance, usually due to [[cooling]].<ref>{{cite web |title=freezing |website=International Dictionary of Refrigeration |url=http://dictionary.iifiir.org/search.php |access-date=2022-11-03 |archive-date=2019-10-01 |archive-url=https://web.archive.org/web/20191001210219/http://dictionary.iifiir.org/search.php |url-status=dead }}</ref><ref>{{cite web |title=freezing |website=ASHRAE Terminology |url=https://terminology.ashrae.org/?letter=F |access-date=2022-11-03 |website=ASHRAE Terminology}} — via [https://www.ashrae.org/technical-resources/free-resources/ashrae-terminology https://www.ashrae.org/teches/free-resources/ashrae-terminology]</ref>

In spite of the [[second law of thermodynamics]], crystallization of pure liquids usually begins at a lower temperature than the [[melting point]], due to high [[activation energy]] of [[Nucleation#Homogeneous nucleation|homogeneous nucleation]]. The creation of a nucleus implies the formation of an interface at the boundaries of the new phase. Some energy is expended to form this interface, based on the [[surface energy]] of each phase. If a hypothetical nucleus is too small, the energy that would be released by forming its volume is not enough to create its surface, and nucleation does not proceed. Freezing does not start until the temperature is low enough to provide enough energy to form stable nuclei. In presence of irregularities on the surface of the containing vessel, solid or gaseous impurities, pre-formed solid crystals, or other nucleators, [[Nucleation#Heterogeneous nucleation often dominates homogeneous nucleation|heterogeneous nucleation]] may occur, where some energy is released by the partial destruction of the previous interface, raising the supercooling point to be near or equal to the melting point. The melting point of [[water]] at 1 atmosphere of pressure is very close to {{convert|0|°C|°F K|abbr=on}}, and in the presence of [[Nucleation|nucleating substances]] the freezing point of water is close to the melting point, but in the absence of nucleators water can [[Supercooling|supercool]] to {{convert|-40|C|F K}} before freezing.<ref>{{cite journal | vauthors = Lundheim R | title = Physiological and ecological significance of biological ice nucleators | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 357 | issue = 1423 | pages = 937–43 | date = July 2002 | pmid = 12171657 | pmc = 1693005 | doi = 10.1098/rstb.2002.1082 }}</ref><ref>{{cite journal | vauthors = Franks F | s2cid = 25606767 | title = Nucleation of ice and its management in ecosystems | journal = Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences | volume = 361 | issue = 1804 | pages = 557–74; discussion 574 | date = March 2003 | pmid = 12662454 | doi = 10.1098/rsta.2002.1141 | url = http://rsta.royalsocietypublishing.org/content/361/1804/557.long | format = [[PDF]] | bibcode = 2003RSPTA.361..557F }}</ref> Under high pressure (2,000 [[Atmosphere (unit)|atmosphere]]s) water will supercool to as low as {{convert|-70|C|F K}} before freezing.<ref>{{Cite journal |vauthors=Jeffery CA, Austin PH |date=November 1997 |title=Homogeneous nucleation of supercooled water: Results from a new equation of state | vauthors = Jeffery CA, Austin PH | journal=Journal of Geophysical Research | volume=102 | issue=D21 | pages= 25269–25280 |date= November 1997 | doi=10.1029/97JD02243 | bibcode=1997JGR...10225269J | citeseerx=10.1.1.9.3236 |doi=10.1029/97JD02243}}fortaste and nutrition.</ref>

Freezing is almost always an [[exothermic]] process, meaning that as liquid changes into solid, heat and pressure are released. This is often seen as counter-intuitive,<ref>[http://www.sciam.com/article.cfm?id=what-is-an-exothermic-rea What is an exothermic reaction?] ''Scientific American'', 1999</ref> since the temperature of the material does not rise during freezing, except if the liquid were [[supercooled]]. But this can be understood since heat must be continually removed from the freezing liquid or the freezing process will stop. The energy released upon freezing is a [[latent heat]], and is known as the [[enthalpy of fusion]] and is exactly the same as the energy required to [[melting|melt]] the same amount of the solid.

Three species of bacteria, ''[[Carnobacterium pleistocenium]]'', as well as ''[[Chryseobacterium greenlandensis]]'' and ''[[Herminiimonas glaciei]]'', have reportedly been revived after surviving for thousands of years frozen in ice.{{Cn|date=October 2024}}

Freezing is a common method of [[food preservation]] that slows both food decay and the growth of [[micro-organism]]s. Besides the effect of lower temperatures on [[reaction rate]]s, freezing makes water less available for [[bacteria]] growth. Freezing is one of the oldest and mosta widely used methodsmethod of food preservation;. sinceFreezing asgenerally long ago as 1842, freezing has been used in an ice and salt brine. In freezing,preserves flavours, smell and nutritional content generally remain unchanged. Freezing became commercially applicable after the advent (introduction) of mechanical refrigeration. Freezing has been successfully employed for long term preservation of many foods providing a significantly extended shelf-life. Freezing preservation is generally regarded as superior to canning and dehydration with respect to retention in sensory attributes and nutritive attributes.viable

*[http://www.ameslab.gov/mpc/video VideoV]used[http://www.ameslab.gov/mpc/video of an intermetallicnic compound solidifying/freezing] {{Webarchive|url=https://web.archive.org/web/20151210223620/http://www.ameslab.gov/mpc/video |date=2015-12-10 }}