Editing Ice (section)

==={{anchor|Phases}}Phases===
{{Main|Phases of ice}}

[[File:Phase diagram of water.svg|thumb|[[Semi-log plot|Log-lin]] pressure-temperature [[phase diagram]] of water. The [[Roman numeral]]s correspond to some ice phases listed below.]]
[[File:3D representation of several phases of water.jpg|thumb|An alternative formulation of the phase diagram for certain ices and other phases of water<ref>{{cite journal |last1=David |first1=Carl |title=Verwiebe's '3-D' Ice phase diagram reworked |journal=Chemistry Education Materials |date=8 August 2016 |url=https://opencommons.uconn.edu/chem_educ/94/ }}</ref>]]

Most liquids under increased pressure freeze at ''higher'' temperatures because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: for some pressures higher than {{convert|1|atm|MPa|abbr=on}}, water freezes at a temperature ''below'' {{cvt|0|C|F}}. Ice, water, and [[water vapour]] can coexist at the [[triple point]], which is exactly {{cvt|273.16|K|C}} at a pressure of 611.657&nbsp;[[Pascal (unit)|Pa]].<ref>{{cite journal |last1=Wagner |first1=Wolfgang |last2=Saul |first2=A. |last3=Pruss |first3=A. |title=International Equations for the Pressure Along the Melting and Along the Sublimation Curve of Ordinary Water Substance |journal=Journal of Physical and Chemical Reference Data |date=May 1994 |volume=23 |issue=3 |pages=515–527 |doi=10.1063/1.555947 |bibcode=1994JPCRD..23..515W }}</ref><ref>{{cite journal|doi=10.1256/qj.04.94 | volume=131 | issue=608 | title=Review of the vapour pressures of ice and supercooled water for atmospheric applications | year=2005 | journal=Quarterly Journal of the Royal Meteorological Society | pages=1539–1565 | last1 = Murphy | first1 = D. M.| bibcode=2005QJRMS.131.1539M | s2cid=122365938 | url=https://zenodo.org/record/1236243 | doi-access=free }}</ref> The [[kelvin]] was defined as {{sfrac|1|273.16}} of the difference between this triple point and [[absolute zero]],<ref>{{cite web|url=http://www1.bipm.org/en/si/base_units/|title=SI base units|publisher=Bureau International des Poids et Mesures|access-date=31 August 2012|url-status=live|archive-url=https://web.archive.org/web/20120716202131/http://www.bipm.org/en/si/base_units/|archive-date=16 July 2012}}</ref> though this definition [[2019 revision of the SI|changed]] in May 2019.<ref>{{cite web |url=https://www.bipm.org/utils/common/pdf/SI-statement.pdf |title=Information for users about the proposed revision of the SI |publisher=Bureau International des Poids et Mesures |access-date=6 January 2019 |archive-date=21 January 2018 |archive-url=https://web.archive.org/web/20180121160000/https://www.bipm.org/utils/common/pdf/SI-statement.pdf |url-status=dead }}</ref> Unlike most other solids, ice is difficult to [[Superheating|superheat]]. In an experiment, ice at −3&nbsp;°C was superheated to about 17&nbsp;°C for about 250 [[picosecond]]s.<ref>{{cite journal|journal=Nature|volume=439|pages=183–186|year=2006| doi=10.1038/nature04415|pmid=16407948|title=Ultrafast superheating and melting of bulk ice|bibcode=2006Natur.439..183I|last1=Iglev|first1=H.|last2=Schmeisser|first2=M.|last3=Simeonidis|first3=K.|last4=Thaller|first4=A.|last5=Laubereau|first5=A.|issue=7073|s2cid=4404036}}</ref>

Subjected to higher pressures and varying temperatures, ice can form in nineteen separate known crystalline phases at various densities, along with hypothetical proposed phases of ice that have not been observed.<ref name="Metcalfe-2021">{{cite news|last1=Metcalfe|first1=Tom|date=9 March 2021|title=Exotic crystals of 'ice 19' discovered|language=en|work=Live Science|url=https://www.livescience.com/exotic-ice-19-discovered.html}}</ref> With care, at least fifteen of these phases (one of the known exceptions being ice X) can be recovered at ambient pressure and low temperature in [[metastable]] form.<ref>{{cite journal|last=La Placa|first=S. J.|author2=Hamilton, W. C.|author3=Kamb, B.|author4=Prakash, A.|year=1972|title=On a nearly proton ordered structure for ice IX|journal=Journal of Chemical Physics|volume=58|issue=2|pages=567–580|doi=10.1063/1.1679238|bibcode = 1973JChPh..58..567L }}</ref><ref>{{cite journal|last=Klotz|first=S.|author2=Besson, J. M.|author3=Hamel, G.|author4=Nelmes, R. J.|author5=Loveday, J. S.|author6=Marshall, W. G.|year=1999|title=Metastable ice VII at low temperature and ambient pressure|journal=Nature|volume=398|issue=6729|pages=681–684|doi=10.1038/19480|bibcode = 1999Natur.398..681K |s2cid=4382067}}</ref> The types are differentiated by their crystalline structure, proton ordering,<ref>{{cite web|url=https://www.uwgb.edu/dutchs/Petrology/Ice%20Structure.HTM|title=Ice Structure|last=Dutch|first=Stephen|publisher=University of Wisconsin Green Bay|access-date=12 July 2017|url-status=dead|archive-url=https://web.archive.org/web/20161016143124/http://www.uwgb.edu/dutchs/petrology/Ice%20Structure.HTM|archive-date=16 October 2016}}</ref> and density. There are also two metastable phases of ice under pressure, both fully hydrogen-disordered; these are Ice IV and Ice XII. Ice XII was discovered in 1996. In 2006, Ice XIII and Ice XIV were discovered.<ref>{{cite journal |last1=Salzmann |first1=Christoph G. |last2=Radaelli |first2=Paolo G. |last3=Hallbrucker |first3=Andreas |last4=Mayer |first4=Erwin |last5=Finney |first5=John L. |title=The Preparation and Structures of Hydrogen Ordered Phases of Ice |journal=Science |date=24 March 2006 |volume=311 |issue=5768 |pages=1758–1761 |doi=10.1126/science.1123896 |pmid=16556840 |bibcode=2006Sci...311.1758S |s2cid=44522271 }}</ref> Ices XI, XIII, and XIV are hydrogen-ordered forms of ices I{{sub|h}}, V, and XII respectively. In 2009, ice XV was found at extremely high pressures and −143&nbsp;°C.<ref>{{cite magazine|url=http://www.sciencenews.org/view/generic/id/47258/title/A_very_special_snowball|title=A Very Special Snowball|author=Sanders, Laura|magazine=Science News|date=11 September 2009|access-date=11 September 2009|url-status=live|archive-url=https://web.archive.org/web/20090914174027/http://www.sciencenews.org/view/generic/id/47258/title/A_very_special_snowball|archive-date=14 September 2009}}</ref> At even higher pressures, ice is predicted to become a [[metal]]; this has been variously estimated to occur at 1.55&nbsp;TPa<ref>{{cite journal |last1=Militzer |first1=Burkhard |last2=Wilson |first2=Hugh F. |title=New Phases of Water Ice Predicted at Megabar Pressures |journal=Physical Review Letters |date=2 November 2010 |volume=105 |issue=19 |page=195701 |doi=10.1103/PhysRevLett.105.195701 |pmid=21231184 |arxiv=1009.4722 |bibcode=2010PhRvL.105s5701M |s2cid=15761164 }}</ref> or 5.62&nbsp;TPa.<ref>{{cite journal|author=MacMahon, J. M.|title=Ground-State Structures of Ice at High-Pressures|doi=10.1103/PhysRevB.84.220104|arxiv=1106.1941|bibcode=2011PhRvB..84v0104M|year=1970|journal=Physical Review B|volume=84|issue=22|pages=220104|s2cid=117870442}}</ref>

As well as crystalline forms, solid water can exist in amorphous states as [[amorphous solid water]] (ASW) of varying densities. In outer space, hexagonal crystalline ice is present in the [[ice volcano]]es,<ref>{{cite news|url=https://www.nytimes.com/2004/12/09/science/09ice.html|title=Astronomers Contemplate Icy Volcanoes in Far Places|author=Chang, Kenneth|work=The New York Times|date=9 December 2004|access-date=30 July 2012|url-status=live|archive-url=https://web.archive.org/web/20150509123243/http://www.nytimes.com/2004/12/09/science/09ice.html|archive-date=9 May 2015}}</ref> but is extremely rare otherwise. Even icy moons like [[Ganymede (moon)|Ganymede]] are expected to mainly consist of other crystalline forms of ice.<ref>{{cite journal |url=http://www.jhuapl.edu/techdigest/TD/td2602/Prockter.pdf |title=Ice in the Solar System |author=Prockter, Louise M. |journal=Johns Hopkins APL Technical Digest |volume=26 |issue=2 |year=2005 |page=175 |url-status=dead |archive-url=https://web.archive.org/web/20150319063545/http://www.jhuapl.edu/techdigest/TD/td2602/Prockter.pdf |archive-date=19 March 2015 |access-date=21 December 2013 }}</ref><ref name=showman1997>{{Cite journal | doi = 10.1006/icar.1997.5778| title = Coupled Orbital and Thermal Evolution of Ganymede| journal = Icarus| volume = 129| issue = 2| pages = 367–383| year = 1997| last1 = Showman | first1 = A. | bibcode = 1997Icar..129..367S| url = http://www.lpl.arizona.edu/~showman/publications/showman-etal-1997.pdf}}</ref> Water in the [[interstellar medium]] is dominated by amorphous ice, making it likely the most common form of water in the universe.<ref name="stanley">{{cite journal|last1=Debennetti|first1=Pablo G. |last2=Stanley |first2=H. Eugene |year=2003 |title=Supercooled and Glassy Water |journal=Physics Today |volume=56 |issue=6 |pages=40–46 |bibcode=2003PhT....56f..40D|doi=10.1063/1.1595053 |url=http://polymer.bu.edu/hes/articles/ds03.pdf |access-date=19 September 2012 }}</ref>  Low-density ASW (LDA), also known as hyperquenched glassy water, may be responsible for [[noctilucent clouds]] on Earth and is usually formed by [[vapor deposition|deposition]] of water vapor in cold or vacuum conditions.<ref>{{cite journal |last1=Lübken |first1=F.-J. |last2=Lautenbach |first2=J. |last3=Höffner |first3=J. |last4=Rapp |first4=M. |last5=Zecha |first5=M. |title=First continuous temperature measurements within polar mesosphere summer echoes |journal=Journal of Atmospheric and Solar-Terrestrial Physics |date=March 2009 |volume=71 |issue=3–4 |pages=453–463 |doi=10.1016/j.jastp.2008.06.001|bibcode=2009JASTP..71..453L }}</ref> High-density ASW (HDA) is formed by compression of ordinary ice I{{sub|h}} or LDA at GPa pressures. Very-high-density ASW (VHDA) is HDA slightly warmed to 160&nbsp;K under 1–2&nbsp;GPa pressures.<ref>{{cite journal|doi=10.1039/b108676f|title=A second distinct structural "state" of high-density amorphous ice at 77 K and 1 bar|year=2001|author1-link=Thomas Loerting|last1=Loerting|first1=Thomas|last2=Salzmann|first2=Christoph|last3=Kohl|first3=Ingrid|last4=Mayer|first4=Erwin|last5=Hallbrucker|first5=Andreas|s2cid=59485355|journal=Physical Chemistry Chemical Physics |volume=3 |pages=5355–5357 |issue=24 |bibcode=2001PCCP....3.5355L }}</ref>

Ice from a theorized superionic water may possess two crystalline structures. At pressures in excess of {{convert|500000|bar|psi}} such ''superionic ice'' would take on a [[body-centered cubic]] structure. However, at pressures in excess of {{convert|1000000|bar|psi}} the structure may shift to a more stable [[face-centered cubic]] lattice. It is speculated that superionic ice could compose the interior of ice giants such as Uranus and Neptune.<ref name=Phys.org-2013-04-25>{{cite news |website=Phys.org |url=http://phys.org/news/2013-04-phase-dominate-interiors-uranus-neptune.html |title=New phase of water could dominate the interiors of Uranus and Neptune |first=Lisa |last=Zyga |date=25 April 2013}}</ref>