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#REDIRECT [[Phases of ice#Known phases]] |
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{{ crystal system|cubic 25252525252525#crystalline]] form of [[ice]]. It can be formed from liquid water above 3 [[Pascal (unit)|GPa]atmospheres) by lowering its temperature to room temperature, or by decompressing [[heavy water]] (D<sub>2</sub>O) [[Ice#Phases|ice 25 below 95 K. Ordinary water ice is known as [[ice Ih|ice I<sub>h</sub>]], (in the [[Percy Williams Bridgman|Bridgman]] nomenclature). Different types of ice, from [[ice II]] to [[Superionic water|ice XVIII]], have been creapressures. Ice VII is [[metastable]] over a wide range of temperatures and pressures and transforms low-density [[amorphous ice]] (LDA) above {{Convert|120|K|C}}.<ref>S. Klotz, J. M. Besson, G. Hamel, R. J. Nelmes, J. S. Loveday and W. G. Marshall, Metastable ice VII at low temperature and ambient pressure, Nature 398 (1999) 681–684.</ref> Ice VII has a [[triple point]] with liquid water and ice VI at 355 K and 2.216 GPa, with the melt line extending to at least {{Convert|715|K|C}} and 10 GPa.<ref name="IAPWS">{{cite web | url = http://www.iapws.org/relguide/meltsub.pdf | title = IAPWS, Release on the pressure along the melting and the sublimation curves of ordinary water substance, 1993 | access-date = 2008-02-22 | url-status = dead | archive-url = https://web.archive.org/web/20081006141126/http://www.iapws.org/relguide/meltsub.pdf | archive-date = 2008-10-06 }}</ref> Ice VII can be formed within nanoseconds by rapid compression via shock-waves.<ref>{{cite journal | last1 = Dolan | first1 = D | last2 = Gupta | first2 = Y | title = Nanosecond freezing of water under multiple shock wave compression: Optical transmission and imaging measurements J. Chem. Phys. | volume = 121 | issue = 18 | pages = 9050–9057 | year = 2004 | doi = 10.1063/1.1805499 | pmid = 15527371 | bibcode = 2004JChPh.121.9050D }}</ref><ref>{{cite journal | last1 = Myint | first1 = P | last2 = Benedict | first2 = L | last3 = Belof | first3 = J | title = Free energy models for ice VII and liquid water derived from pressure, entropy, and heat capacity relations | journal = J. Chem. Phys. | volume = 147 | issue = 8 | pages = 084505 | year = 2017 | doi = 10.1063/1.4989582 | pmid = 28863506 | bibcode = 2017JChPh.147h4505M | osti = 1377687 }}</ref> It can also be created by increasing the pressure on ice VI at ambient temperature.<ref name="Johari et al.">{{Citation |first1=G. P. |last1=Johari |first2=A. |last2=Lavergne |first3=E. |last3=Whalley |name-list-style=amp |journal=Journal of Chemical Physics |volume=61 |issue=10 |pages=4292 |year=1974 |title=Dielectric properties of ice VII and VIII and the phase boundary between ice VI and VII |doi=10.1063/1.1681733 |bibcode = 1974JChPh..61.4292J }}</ref> |
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Like the majority of ice phases (including [[ice Ih|ice I<sub>h</sub>]]), the [[hydrogen]] atom positions are disordered.<ref name="Petrenko">{{Citation |first1=V. F. |last1=Petrenko |first2=R. W. |last2=Whitworth |title=The Physics of Ice |publisher=Oxford University Press |location=New York |year=2002 }}.</ref> In addition, the [[oxygen]] atoms are disordered over multiple sites.<ref name="kuhs">{{Citation |first1=W. F. |last1=Kuhs |first2=J. L. |last2=Finney |first3=C. |last3=Vettier |first4=D. V. |last4=Bliss |name-list-style=amp |journal=Journal of Chemical Physics |volume=81 |issue=8 |pages=3612–3623 |year=1984 |title=Structure and hydrogen ordering in ices VI, VII, and VIII by neutron powder diffraction |doi=10.1063/1.448109 |bibcode = 1984JChPh..81.3612K }}.</ref><ref name="jorgensen">{{Citation |first1=J. D. |last1=Jorgensen |first2=T. G. |last2=Worlton |journal=Journal of Chemical Physics |volume=83 |issue=1 |pages=329–333 |year=1985 |title=Disordered structure of D<sub>2</sub>O ice VII from in situ neutron powder diffraction |doi=10.1063/1.449867 |bibcode = 1985JChPh..83..329J |url=https://zenodo.org/record/1232091 }}.</ref><ref name="nelmes">{{Citation |first1=R. J. |last1=Nelmes |first2=J. S. |last2=Loveday |first3=W. G. |last3=Marshall |journal=[[Physical Review Letters]] |volume=81 |issue=13 |pages=2719–2722 |year=1998 |title=Multisite Disordered Structure of Ice VII to 20 GPa |doi=10.1103/PhysRevLett.81.2719 |bibcode=1998PhRvL..81.2719N|display-authors=etal}}.</ref> The structure of ice VII comprises a [[hydrogen bond]] framework in the form of two interpenetrating (but non-bonded) sublattices.<ref name="kuhs"/> Hydrogen bonds pass through the center of the water hexamers and thus do not connect the two lattices. Ice VII has a density of about 1.65 g cm<sup>−3</sup> (at 2.5 GPa and {{Convert|25|C|F K}}),<ref>D. Eisenberg and W. Kauzmann, The structure and properties of water (Oxford University Press, London, 1969); (b) The dodecahedral interstitial model is described in L. Pauling, The structure of water, In Hydrogen bonding, Ed. D. Hadzi and H. W. Thompson ([[Pergamon Press]] Ltd, London, 1959) pp 1–6.</ref> which is less than twice the [[cubic ice]] density as the intra-network O–O distances are 8% longer (at 0.1 MPa) to allow for interpenetration. The cubic unit cell has a side length of 3.3501 Å (for D<sub>2</sub>O, at 2.6 GPa and {{Convert|22|C|F K}}) and contains two water molecules.<ref name="jorgensen"/> |
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Ice VII is the only disordered phase of ice that can be ordered by simple cooling,<ref name="Johari et al."/><ref>Note: ice I<sub>h</sub> theoretically transforms into proton-ordered [[ice XI]] on geologic timescales, but in practice it is necessary to add small amounts of KOH catalyst.</ref> and it forms (ordered) [[ice VIII]] below 273 K up to ~8 GPa. Above this pressure, the VII–VIII transition temperature drops rapidly, reaching 0 K at ~60 GPa.<ref name="pruzan">{{Citation |first1=Ph. |last1=Pruzan |first2=J. C. |last2=Chervin |first3=B. |last3=Canny |name-list-style=amp |journal=Journal of Chemical Physics |volume=99 |issue=12 |pages=9842–9846 |year=1993 |title=Stability domain of the ice VIII proton-ordered phase at very high pressure and low temperature |doi=10.1063/1.465467 |bibcode = 1993JChPh..99.9842P }}.</ref> Thus, ice VII has the largest stability field of all of the molecular phases of ice. The cubic oxygen sub-lattices that form the backbone of the ice VII structure persist to pressures of at least 128 GPa;<ref name="hemley">{{Citation |first1=R. J. |last1=Hemley |first2=A. P. |last2=Jephcoat |first3=H. K. |last3=Mao |journal=[[Nature (journal)|Nature]] |issue=6150 |volume=330 |pages=737–740 |year=1987 |title=Static compression of H<sub>2</sub>O-ice to 128 GPa (1.28 Mbar) |doi=10.1038/330737a0 |bibcode = 1987Natur.330..737H |s2cid=4265919 |url=https://zenodo.org/record/1233067 |display-authors=etal}}.</ref> this pressure is substantially higher than that at which water loses its molecular character entirely, forming [[ice X]]. In high pressure ices, protonic diffusion (movement of protons around the oxygen lattice) dominates molecular diffusion, an effect which has been measured directly.<ref>{{cite journal|last=Katoh|first=E.|s2cid=38999963|title=Protonic Diffusion in High-Pressure Ice VII|journal=Science|date=15 February 2002 |volume=29=5558|issue=5558|pages=1264–1266|doi=10.1126/science.1067746|bibcode = 2002Sci...295.1264K|pmid=11847334}}</ref> |
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==Natural occurrence== |
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Scientists hypothesize that ice VII may comprise the ocean floor of [[Europa (moon)|Europa]] as well as [[Exoplanet|extrasolar planets]] (such as [[Gliese 436 b]], and [[Gliese 1214 b]]) that are largely made of water.<ref>University of Liège (2007, May 16). Astronomers Detect Shadow Of Water World In Front Of Nearby Star. ScienceDaily. Retrieved Jan. 3, 2010, from {{cite web |url=https://www.sciencedaily.com/releases/2007/05/070516151053.htm |title=Astronomers Detect Shadow of Water World in Front of Nearby Star |access-date=2018-04-22 |url-status=live |archive-url=https://web.archive.org/web/20170821212607/https://www.sciencedaily.com/releases/2007/05/070516151053.htm |archive-date=2017-08-21 }}</ref><ref>{{cite web |url=http://www.cfa.harvard.edu/news/2009/pr200924.html |title=Astronomers Find Super-Earth Using Amateur, Off-the-Shelf Technology |author=David A. Aguilar |date=2009-12-16 |publisher=Harvard-Smithsonian Center for Astrophysics |access-date=January 23, 2010 |url-status=live |archive-url=https://www.webcitation.org/66sgAVTw2?url=http://www.cfa.harvard.edu/news/2009/pr200924.html |archive-date=April 13, 2012 }}</ref> |
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In 2018, ice VII was identified among [[Inclusion (mineral)|inclusions]] found in natural diamonds. Due to this demonstration that ice VII exists in nature, the [[International Mineralogical Association]] duly classified ice VII as a distinct [[mineral]].<ref>{{cite journal|url=http://www.sciencemag.org/news/2018/03/pockets-water-may-lay-deep-below-earth-s-surface|title=Pockets of water may lay deep below Earth's surface|author=Sid Perkins|journal=Science|date=2018-03-08|access-date=March 8, 2018|url-status=live|archive-url=https://web.archive.org/web/20180308220310/http://www.sciencemag.org/news/2018/03/pockets-water-may-lay-deep-below-earth-s-surface|archive-date=March 8, 2018}}</ref> The ice VII was presumably formed when water trapped inside the diamonds retained the high pressure of the deep [[mantle (geology)|mantle]] due to the strength and rigidity of the diamond lattice, but cooled down to surface temperatures, producing the required environment of high pressure without high temperature.<ref>{{cite news|last1=Netburn|first1=Deborah|title=What scientists found trapped in a diamond: a type of ice not known on Earth|url=http://www.latimes.com/science/sciencenow/la-sci-sn-water-in-diamonds-20180308-story.html|access-date=12 March 2018|work=Los Angeles Times|url-status=live|archive-url=https://web.archive.org/web/20180312003000/http://www.latimes.com/science/sciencenow/la-sci-sn-water-in-diamonds-20180308-story.html|archive-date=12 March 2018}}</ref> |
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==References== |
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{{reflist|30em}} |
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==External links== |
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* {{cite web |first=Maren |last=Hunsberger |title=A New State of Water Reveals a Hidden Ocean in Earth's Mantle |date=September 21, 2018 |work=[[Seeker (media company)|Seeker]] |url=https://www.youtube.com/watch?v=pgm4z8vJVVk |archive-url=https://ghostarchive.org/varchive/youtube/20211221/pgm4z8vJVVk |archive-date=2021-12-21 |url-status=live|via=[[YouTube]] }}{{cbignore}} |
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* {{cite web |first=Marcus |last=Woo |date=July 11, 2018 |title=The Hunt for Earth's Deep Hidden Oceans |work=[[Quanta Magazine]] |url=https://www.quantamagazine.org/the-hunt-for-earths-deep-hidden-oceans-20180711 }} |
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{{ice}} |
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{{Portal bar|Geology|Oceans|Astronomy|Stars|Spaceflight|Outer space|Solar System|Science}} |
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{{DEFAULTSORT:Ice Vii}} |
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[[Category:Water ice]] |
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[[Category:Cubic minerals]] |
[[Category:Cubic minerals]] |
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Latest revision as of 11:21, 28 April 2024
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