- Ice XII
Ice XII is a
metastable , dense,crystalline phase ofsolid water . It is a type ofice . It was first reported in1996 by C. Lobban, J.L. Finney and W.F. Kuhs and after initial caution was properly identified in1998 .It was first obtained by cooling
liquid water to 260 K at a pressure of 0.55 GPa; it was discovered existing within the phase stability region ofice V . Later research showed that ice XII could be created outside that range. Pure ice XII can be created from ice Ih at 77 K by rapid compression (0.81-1.00 GPa/min) or by warminghigh density amorphous ice at pressures between 0.8 and 1.6 GPa. The proton-ordered form of ice XII isice XIV .While it is similar in density (1.29 g/cm3 at 127 K) to
ice IV (also found in theice V space) it exists as atetragonal crystal . Topologically it is a mix of seven- and eight-membered rings, a 4-connected net (4-coordinatesphere packing) -- the densest possible arrangement withouthydrogen bond interpenetration .Ordinary water ice is known as ice Ih, (in the Bridgman nomenclature). Different types of ice, from ice II to ice XIV, have been created in the laboratory at different temperatures and pressures.
References
* C. Lobban, J.L. Finney and W.F. Kuhs, The structure of a new phase of ice, Nature 391, 268-270, 1998
*cite web |url=http://www.lsbu.ac.uk/water/ice_xii.html |title=Ice-twelve and ice-fourteen structures |accessdate=2008-01-02 |author=Chaplin, Martin |date=2007-07-01 |work=Water Structure and Science
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