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Pressure-induced collapse of ice clathrate and hexagonal ice mixtures formed by freezing
Umeå University, Faculty of Science and Technology, Department of Physics.
Department of Materials Science and Engineering, McMaster University, Hamilton, Canada.
2009 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, 114503-114513 p.Article in journal (Refereed) Published
Abstract [en]

We report thermal conductivity κ measurements of the pressure-induced collapse of two mixtures of ice and tetrahydrofuran (THF) clathrate hydrate formed by freezing aqueous solutions, THF·23 H2O and THF·20 H2O, one containing twice as much excess water than the other. On pressurizing, κ of the solid mixture first decreases at the onset pressure of 0.8 GPa, as occurs for collapse of pure ice, reaches a local minimum at a pressure of 1.0 GPa, and then increases as occurs for the collapse of the pure clathrate THF·17 H2O. This shows that in the apparently homogeneous mixture, the ice and the clathrate collapse as if the two were in a mechanically mixed state. The manner in which the clathrate aggregate can arrange in the solid indicates that ice occupies the interstitial space in the tightly packed aggregates and H2O molecules belonging to the lattice of one form hydrogen bond with that of the other, a feature that is preserved in their collapsed states. On decompression, the original clathrate is partially recovered in the THF·20 H2O mixture, but the collapsed ice does not transform to the low density amorph. We surmise that on irreversible transformation to the original clathrate, the aggregates expand. Any pressure thus exerted on the small domains of the collapsed ice with a hydrogen bonded interface with the clathrate aggregates could prevent it from transforming to the low density amorph. Measurements of κ are useful in investigating structural collapse of crystals when dilatometry is unable to do so, as κ seems to be more sensitive to pressure-induced changes than the volume.

Place, publisher, year, edition, pages
American Institute of Physics Publishing LLC , 2009. Vol. 131, 114503-114513 p.
National Category
Condensed Matter Physics
Research subject
URN: urn:nbn:se:umu:diva-30451DOI: 10.1063/1.3225603OAI: diva2:283411
Available from: 2009-12-25 Created: 2009-12-25 Last updated: 2013-08-13Bibliographically approved

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