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Ice-nine (Ice IX)

Ice-nine crystal

Ice-nine crystal

Ice-nine (ice IX) is the low-temperature equilibrium, slightly denser, structure of ice-three (Space group P41212, cell dimensions 6.692 Å (a) and 6.715 Å (c) at 165 K and 280 MPa [385]). It is metastable in the ice-two phase space and converts to ice-two, rather than back to ice-three, on warming. The change from proton disordered is a partial process starting within ice-three that is only completed at lower temperatures, but with a first-order transition near 126 K[1087]. The hydrogen-bonding is mostly proton-ordered as ice-three undergoes a proton disorder-order transition to ice-nine when rapidly cooled in liquid nitrogen (77 K, so avoiding ice-two formation, see Phase Diagram); ice-three and ice-nine having identical structures apart from the proton ordering [389]. Interactive Jmol structures are given.


The ice-nine, described by Kurt Vonnegut in 'Cat's Cradle' [83], with a freezing point well above ambient temperature under normal atmospheric pressure is, fortunately, an utterly fictitious material, reportedly invented by the Nobel prize winner Irving Langmuir to entertain H. G. Wells. In that novel, it was proposed that this ice was stable and, once formed, could nucleate crystalline ice-nine any liquid water it came into contact with, resulting in a global catastrophe.



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This page was established in 2004 and last updated by Martin Chaplin on 27 October, 2018

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