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Privacy Overview. Necessary Always Enabled. Intense experimental and computational efforts have been made to find evidence to support the two-liquid model, including proof of the existence of different amorphous phases in compressed ice. The formation, instead, of a metastable amorphous phase suggests that an energy barrier has inhibited the transformation of the solid into the second crystalline structure.
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Such a barrier can be breached if the solid is compressed slowly, which gives time for the structure to relax and for thermodynamic equilibrium to be attained 6. In this scenario, the formation of the amorphous phase would be described as a kinetic effect, because it depends on the amount of time that is given for a transition to occur. The latter two compounds, however, are now known to transform into crystalline structures when compressed under uniform isotropic pressure 7 , 8.
One study 9 generated quasi-hydrostatic conditions using a pressure chamber known as a double-sided dynamic diamond anvil cell, and observed the effects on water both with and without a silicone-based pressure-transmitting medium. Ice was seen to change from one crystal form to another before its amorphization, but observations under true hydrostatic conditions were still desirable. Tulk et al. The authors encapsulated deuterated water in a gasket, which was cooled using boiling liquid nitrogen and placed inside a compression apparatus known as a Paris—Edinburgh press.
Deuterated water contains a heavy isotope of hydrogen, rather than the most abundant isotope, and was used to enhance neutron scattering. The sample was then compressed in incremental steps, and allowed to rest for an hour at each pressure. The resulting diffraction patterns show that HDA ice did not form.
A Bizarre Form of Water May Exist All Over the Universe
These low-temperature phases correspond, respectively, to crystalline phases known as ice III, ice VI and ice VII, which are observed at ambient temperature. Figure 1 The transformation of compressed ice into different crystalline forms.
Red atoms, oxygen; white atoms, hydrogen. The HDA ice that was observed in previous studies therefore formed as a result of kinetic effects. So, is HDA ice similar in structure to liquid water? There are many lines of evidence to consider.
Ice on Blast
A previously reported analysis of the thermodynamics of ice amorphization showed that the observed pressure at which HDA ice forms from normal ice at low temperatures is much higher than the pressure at which normal ice would be expected to melt at the same temperatures HDA ice has been found to transform into an even denser amorphous form when heated 11 , which shows that it is a kinetic product of rapid compression. And a neutron- and X-ray diffraction study of ice decompressed at constant temperatures found that the transformation of HDA ice into LDA ice involves several intermediate amorphous forms, and is therefore not a first-order process Computational studies of the molecular dynamics of ice at constant pressure have also been used to reproduce the main characteristics and behaviours of amorphous ice 6.
A theoretical analysis of data from one study suggests that the transformation of ice into HDA ice is not thermodynamically driven, but is instead the result of a type of instability known as a mechanical or elastic instability that occurs in certain solids This result has been confirmed by experiment The substantial reconstruction that is needed to convert single networks into interpenetrating ones requires a large energy barrier to be overcome.
Nature , — Mishima, O. Nature , 76—78 Gallo, P. Tse, J. Haines, J. Sharma, S.
B 62 , Lin, C. Whalley, E. Loerting, T. Science , — Download references.