Ice perfection and onset of anomalous preservation of gas hydrates

Kuhs, Werner F.; Genov, Georgi; Staykova, Doroteya K.; Hansen, Thomas C.

doi:10.1039/b412866d

Cited by 229 publications

(220 citation statements)

References 29 publications

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“…However, even at 210 K, some cubic stacking sequences persist, disappearing only upon heating to 240 K. The fact that a fraction of cubic sequences persists up to almost 240 K was noticed earlier (23) and is in agreement with the extended temperature range of the transformation into ice I h , as observed by differential thermal analysis (4). The accumulated evidence leaves very little doubt that the changes observed by earlier thermal analysis and diffraction work are related to the progressively disappearing cubic components in the stacking.…”

Section: Aqueous Molecular Soluɵons (17-19)supporting

confidence: 70%

“…Such trigonal crystals have been observed in cirriform clouds (63); triangular growth morphologies were also found in molecular simulations (62). Clearly, a pseudohexagonal crystal shape cannot be taken as evidence for ice I h (23). (ii) Our diffraction data show that crystals of "ice I c " may exist up to ∼240 K in the atmosphere.…”

Section: Discussionmentioning

confidence: 75%

“…We note in this context that a closer inspection of published data of ice formed below ∼240 K often shows deviations from good hexagonal ice--most noticeable in the hexagonal (002) powder peak, which has a higher intensity than expected for ice I h . This becomes most evident in a crystallographic full-pattern Rietveld analysis (23). Ice samples obtained in the temperature range from 190 to 240 K merit close attention in this respect.…”

Section: Discussionmentioning

confidence: 99%

“…21,22). "Ice I c " may also be obtained by decomposing gas hydrates (23)(24)(25)(26). Sample size (i.e., droplet-or pore size) plays an important role in many of these transitions; the formation of "ice I c " is favored in nanometer-sized confined geometry, where it may take place directly from water up to temperatures close to melting.…”

mentioning

confidence: 99%

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Extent and relevance of stacking disorder in “ice I_c”

Kuhs

Sippel

Falenty

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

215

280

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A solid water phase commonly known as "cubic ice" or "ice I c " is frequently encountered in various transitions between the solid, liquid, and gaseous phases of the water substance. It may form, e.g., by water freezing or vapor deposition in the Earth's atmosphere or in extraterrestrial environments, and plays a central role in various cryopreservation techniques; its formation is observed over a wide temperature range from about 120 K up to the melting point of ice. There was multiple and compelling evidence in the past that this phase is not truly cubic but composed of disordered cubic and hexagonal stacking sequences. The complexity of the stacking disorder, however, appears to have been largely overlooked in most of the literature. By analyzing neutron diffraction data with our stacking-disorder model, we show that correlations between next-nearest layers are clearly developed, leading to marked deviations from a simple random stacking in almost all investigated cases. We follow the evolution of the stacking disorder as a function of time and temperature at conditions relevant to atmospheric processes; a continuous transformation toward normal hexagonal ice is observed. We establish a quantitative link between the crystallite size established by diffraction and electron microscopic images of the material; the crystallite size evolves from several nanometers into the micrometer range with progressive annealing. The crystallites are isometric with markedly rough surfaces parallel to the stacking direction, which has implications for atmospheric sciences.

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Section: Aqueous Molecular Soluɵons (17-19)supporting

confidence: 70%

Section: Discussionmentioning

confidence: 75%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Extent and relevance of stacking disorder in “ice I_c”

Kuhs

Sippel

Falenty

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

215

280

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“…3) This term describes the ability of methane hydrate to resist dissociation at temperatures higher than the equilibrium temperature of decomposition. The effect of incomplete dissociation of methane hydrate has been the subject of many experimental studies in the last years (see, for example [4][5][6][7][8][9][10][11][12][13] ). The experiments show the anomalous preservation of methane hydrate at temperatures below 273 K (ice Ih melting point) under ambient pressure with simultaneous formation of ice phase at temperatures above 242 K (beginning of methane hydrate dissociation).…”

Section: Introductionmentioning

confidence: 99%

Modeling the Self-Preservation Effect in Gas Hydrate/Ice Systems

et al. 2007

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Molecular dynamics simulations were performed to investigate the possible role of ice shielding in the anomalous preservation of gas hydrates. Two cases of ice shielding were considered: immersion of hydrate particles into bulk ice Ih and wrapping of similar particles in a thin ice shell. For a microscopic-level model of methane hydrate clusters immersed in bulk ice the excess pressure in the hydrate phase at 250 K was found to be sufficient to shift the gas hydrate into the region of thermodynamic stability on the phase diagram. For the second model the temperature dependence of various properties of the hydrate/ice nanocluster was studied. The surface tension estimates based on the Laplace equation show non-monotonic dependence on temperature, which might indicate the possible involvement of hydrate/ice interfacial phenomena in the self-preservation of gas hydrates.

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