Ice VII

Ice VII is a cubic crystalline form of ice. It 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 715 K and 10 GPa.[1] It can also be reached in the solid state by increasing the pressure on ice VI at ambient temperature.[2] Like the majority of ice phases (including ice Ih), the hydrogen atom positions are disordered.[3] In addition, the oxygen atoms are disordered over multiple sites.[4][5][6] The structure of ice VII comprises a hydrogen bond framework in the form of two interpenetrating (but non-bonded) sub-lattices.[4]

Ice VII is the only disordered phase of ice that can be ordered by simple cooling,[2] 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.[7] 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;[8] this pressure is substantially higher than that at which water loses its molecular character entirely, forming ice X.

Ordinary water ice is known as ice Ih, (in the Bridgman nomenclature). Different types of ice, from ice II to ice XV, have been created in the laboratory at different temperatures and pressures.

Scientists hypothesize that Ice VII may comprise the ocean floor of extrasolar planets (such as Gliese 436 b and GJ 1214 b) that are largely made of water.[9][10]

Notes

  1. ^ "IAPWS, Release on the pressure along the melting and the sublimation curves of ordinary water substance, 1993". http://www.iapws.org/relguide/meltsub.pdf. Retrieved 2008-02-22. 
  2. ^ a b Johari, G. P.; Lavergne, A. & Whalley, E. (1974), "Dielectric properties of ice VII and VIII and the phase boundary between ice VI and VII", Journal of Chemical Physics 61 (10): 4292, Bibcode 1974JChPh..61.4292J, doi:10.1063/1.1681733 
  3. ^ Petrenko, V. F.; Whitworth, R. W. (2002), The Physics of Ice, New York: Oxford University Press .
  4. ^ a b Kuhs, W. F.; Finney, J. L.; Vettier, C. & Bliss, D. V. (1984), "Structure and hydrogen ordering in ices VI, VII, and VIII by neutron powder diffraction", Journal of Chemical Physics 81 (8): 3612–3623, Bibcode 1984JChPh..81.3612K, doi:10.1063/1.448109 .
  5. ^ Jorgensen, J. D.; Worlton, T. G. (1985), "Disordered structure of D2O ice VII from in situ neutron powder diffraction", Journal of Chemical Physics 83 (1): 329–333, Bibcode 1985JChPh..83..329J, doi:10.1063/1.449867 .
  6. ^ Nelmes, R. J.; Loveday, J. S.; Marshall, W. G.; et al. (1998), "Multisite Disordered Structure of Ice VII to 20 GPa", Physical Review Letters 81 (13): 2719–2722, Bibcode 1998PhRvL..81.2719N, doi:10.1103/PhysRevLett.81.2719 .
  7. ^ Pruzan, Ph.; Chervin, J. C. & Canny, B. (1993), "Stability domain of the ice VIII proton-ordered phase at very high pressure and low temperature", Journal of Chemical Physics 99 (12): 9842–9846, Bibcode 1993JChPh..99.9842P, doi:10.1063/1.465467 .
  8. ^ Hemley, R. J.; Jephcoat, A. P.; Mao, H. K.; et al. (1987), "Static compression of H2O-ice to 128 GPa (1.28 Mbar)", Nature 330 (6150): 737–740, Bibcode 1987Natur.330..737H, doi:10.1038/330737a0 .
  9. ^ University of Liège (2007, May 16). Astronomers Detect Shadow Of Water World In Front Of Nearby Star. ScienceDaily. Retrieved January 3, 2010, from http://www.sciencedaily.com/releases/2007/05/070516151053.htm
  10. ^ David A. Aguilar (2009-12-16). "Astronomers Find Super-Earth Using Amateur, Off-the-Shelf Technology". Harvard-Smithsonian Center for Astrophysics. http://www.cfa.harvard.edu/news/2009/pr200924.html. Retrieved January 23, 2010. 

See also

References

Crystalline forms of ice
Ih · Ic · II · III · IV · V · VI · VII · VIII · IX · X · XI · XII · XIII · XIV · XV
Ice formations
Ice Ages
Ice sports
Other