Ice II is a
rhombohedral crystalline form of
ice with a highly ordered structure. It is formed from
ice Ih by compressing it at a temperature of 198
K at 300
MPa or by decompressing
ice V. When heated it undergoes transformation to
ice III. Ordinary
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
ice is known as
ice Ih, (in the
Bridgman nomenclature). Different types of ice, from ice II to
ice XIX, have been created in the laboratory at different temperatures and pressures. It is thought that the cores of
icy moons like
Jupiter's Ganymede may be made of ice II.
History
The properties of ice II were first described and recorded by
Gustav Heinrich Johann Apollon Tammann
Gustav Heinrich Johann Apollon Tammann ( – 17 December 1938) was a prominent Baltic German chemist-physicist who made important contributions in the fields of glassy and solid solutions, heterogeneous equilibria, crystallization, and metallurgy ...
in 1900 during his experiments with ice under high pressure and low temperatures. Having produced ice III, Tammann then tried condensing the ice at a temperature between under of pressure. Tammann noted that in this state ice II was denser than he had observed ice III to be. He also found that both types of ice can be kept at normal
atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, ...
in a stable condition so long as the temperature is kept at that of
liquid air, which slows the change in conformation back to ice I
h.
In later experiments by Bridgman in 1912, it was shown that the difference in volume between ice II and ice III was in the range of . This difference hadn't been discovered by Tammann due to the small change and was why he had been unable to determine an
equilibrium curve between the two. The curve showed that the structural change from ice III to ice II was more likely to happen if the medium had previously been in the structural conformation of ice II. However, if a sample of ice III that had never been in the ice II state was obtained, it could be supercooled even below −70 °C without it changing into ice II. Conversely, however, any superheating of ice II was not possible in regards to retaining the same form. Bridgman found that the equilibrium curve between ice II and
ice IV was much the same as with ice III, having the same stability properties and small volume change. The curve between ice II and
ice V was extremely different, however, with the curve's bubble being essentially a straight line and the volume difference being almost always .
Quest for a hydrogen-disordered counterpart of ice II
As ice II is completely hydrogen ordered, the presence of its disordered counterpart is a great matter of interest. Shephard et al. investigated the phase boundaries of NH
4F-doped ices because NH
4F has been reported to be a hydrogen disordering reagent. However, adding 2.5 mol% of NH
4F resulted in the disappearance of ice II instead of the formation of a disordered ice II. According to the DFC calculation by Nakamura et al.
, the phase boundary between ice II and its disordered counterpart is estimated to be in the stability region of liquid water.
See also
*
Ice, for other crystalline forms of ice
References
Water ice
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