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 under normal atmospheric pressure is fortunately a completely fictitious material, reportedly invented by the Nobel prize winner Irving Langmuir to entertain H. G. Wells.
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This page was established in 2004 and last updated by Martin Chaplin on 21 July, 2015
