| 1. |
- Andersson, Ove, et al.
(författare)
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An ice phase of lowest thermal conductivity
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:20, s. 9612-9617
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Tidskriftsartikel (refereegranskat)abstract
- On pressurizing at temperatures near 130 K, hexagonal and cubic ices transform implosively at 0.8–1 GPa. The phase produced on transformation has the lowest thermal conductivity among the known crystalline ices and its value decreases on increase in temperature. An ice phase of similar thermal conductivity is produced also when high-density amorphous ice kept at 1 GPa transforms on slow heating when the temperature reaches ∼155 K. These unusual formation conditions, the density and its distinguished thermal conductivity, all indicate that a distinct crystal phase of ice has been produced.
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| 2. |
- Andersson, Ove, et al.
(författare)
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Collapse of an ice clathrate under pressure observed via thermal conductivity measurements
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78, s. 174201-
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Tidskriftsartikel (refereegranskat)abstract
- Irreversible transformation of the tetrahydrofuran ice clathrate at 130 K was studied by measuring thermal conductivity k with increase in pressure p. Initially, k increases slowly with p up to 0.75 GPa where it levels off, is roughly constant up to 0.95 GPa, then decreases up to 1.05 GPa. Pressure collapses the clathrate structure, plausibly beginning with lattice distortion, and k increases at 1.05 GPa in a sharp sigmoid-shape manner due to large densification until the transformation is complete at 1.25 GPa. This is the opposite of that found for ice whose k decreases first slowly with increase in p and then rapidly in an inverted sigmoidshape manner [O. Andersson and H. Suga, Phys. Rev. B 65, 140201 (2002)]. At 1.08 GPa and 131 K, k increases with time t (s) according to exp(t /2945), which is also the opposite of the collapse of ice [G. P. Johari and O. Andersson, Phys. Rev. B 70, 184108 (2004)]. The difference in its behavior is attributed to strong phonon scattering from the tetrahydrofuran guest molecules. k of the collapsed clathrate is 30% less than that for the collapsed ice, which is comparable with the 25% lesser k of the tetrahydrofuran-water solution from k of water at ambient pressure. On depressurizing at 130 K, k decreases progressively more rapidly and k of the collapsed state at 0.3 GPa is slightly lower than that of the as-made clathrate, showing that its original structure is not recovered.
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| 3. |
- Andersson, Ove, et al.
(författare)
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Effect of pressure on thermal conductivity and pressure collapse of ice in a polymer-hydrogel and kinetic unfreezing at 1 GPa
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:12, s. 124903-
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Tidskriftsartikel (refereegranskat)abstract
- We report a study of aqueous solutions of poly(vinylalcohol) and its hydrogel by thermal conductivity,κ, and specific heat measurements. In particular, we investigate (i) the changes in the solution and the hydrogel at 0.1 MPa observed in the 350-90 K range and of the frozen hydrogel at 130 K observed in the range from 0.1 MPa to 1.3 GPa, and (ii) the nature of the pressure collapse of ice in the frozen hydrogel and kinetic unfreezing on heating of its high density water at 1 GPa. The water component of the polymer solution on cooling either first phase separates and then freezes to hexagonal ice or freezes without phase separation and the dispersed polymer chains freeze-concentrate in nanoscopic and microscopic regions of the grain boundaries and grain junctions of the ice crystals in the frozen state of water in the hydrogel. The change in κ with temperature at 1 bar is reversible with some hysteresis, but not reversible with pressure after compression to 0.8 GPa at 130 K. At high pressures the crystallized state collapses showing features of. and specific heat characteristic of formation of high density amorphous solid water. The pressure of structural collapse is 0.08 GPa higher than that of ice at 130 K. The slowly formed collapsed state shows kinetic unfreezing or glass-liquid transition temperature at 140 K for a time scale of 1 s. Comparison with the change in the properties observed for ice shows that κ decreases when the polymer is added.
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| 4. |
- Andersson, Ove, et al.
(författare)
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Nature of the pressure-induced collapse of an ice clathrate by dielectric spectroscopy
- 2008
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 129:23
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Tidskriftsartikel (refereegranskat)abstract
- Collapse of an ice clathrate of type II structure containing tetrahydrofuran as guest molecules has been studied at different pressures by dielectric spectroscopy. The sample was pressurized to 1.3 GPa at 130 K and the resulting collapsed state was pressure cycled. The dielectric relaxation time increases at a progressively rapid rate during pressurizing and then decreases slowly on depressurizing, but the dielectric relaxation time does not reach the value of the original state. With increase in pressure, the limiting high frequency permittivity due to orientation of H2O molecules first increases by about 5% until 0.75 GPa and then decreases slightly until 1 GPa, and finally it increases until ~1.2 GPa. The decrease is attributed to the loss of contribution from the reorientational motion of tetrahydrofuran molecules and the increase to densification as the structure mechanically collapses completely in the 1–1.25 GPa range. The relaxation time of the collapsed state is comparable with that of the high-density amorph formed on pressure collapse of ice.
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| 5. |
- Andersson, Ove, et al.
(författare)
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Pressure-induced collapse of ice clathrate and hexagonal ice mixtures formed by freezing
- 2009
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics Publishing LLC. - 0021-9606 .- 1089-7690. ; 131, s. 114503-114513
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Andersson, Ove, et al.
(författare)
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Spontaneous transformation of water's high-density amorph and a two-stage crystallization to ice VI at 1 GPa : a dielectric study
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:24, s. 11662-11671
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric relaxation spectra of a metastable crystal phase formed on implosive and exothermic transformation of pressure-amorphized hexagonal ice have been measured in situ at 0.97 GPa pressure over a range of temperature. The metastable phase showed no relaxation peak at 130 K and 0.97 GPa. When heated at a fixed pressure of 0.97 GPa, it began to transform at ∼ 145 K exothermally to a phase whose relaxation rate and equilibrium dielectric permittivity increased. A second, but slower exothermic transformation also occurred at ∼ 175 K. After keeping at 213 K, the relaxation rate and equilibrium permittivity reached the known values of these two quantities for ice VI. Thus the metastable phase transformed to ice VI in two stages. It is conjectured that the intermediate phase in this transformation could be ice XII. The rate of transformation is not determined by the reorientational relaxation rate of water molecules in the ices
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| 7. |
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| 8. |
- Andersson, Ove, et al.
(författare)
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Time-dependent amorphization of ice at 0.8-0.9 GPa
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP. - 0021-9606 .- 1089-7690. ; 121:8, s. 3936-3938
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Tidskriftsartikel (refereegranskat)abstract
- Thermal conductivity measurements show that ice continues to amorphize for several days when kept at a fixed pressure p in the 0.79–0.88 GPa range, and fixed temperature T in the 127–130 K range. Thermal conductivity k decreases according to a stretched exponential in time, and its limiting long time value k() varies with p and T. At 0.8 GPa and 128 K, k() remains 2.5 times the value observed for high-density amorph. Consequences of these findings for our understanding of amorphization are discussed.
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| 9. |
- Johari, Gyan P, et al.
(författare)
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Water's polyamorphic transitions and amorphization of ice under pressure
- 2004
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Ingår i: Journal of Chemical Physics. - : API. - 0021-9606 .- 1089-7690. ; 120:13, s. 6207-6213
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Tidskriftsartikel (refereegranskat)abstract
- Transformations of water’s high density amorph (HDA) to low density amorph (LDA) and of LDA’s to cubic ice (Ic) have been studied by in situ thermal conductivity κ measurements at high pressures. The HDA to LDA transformation is unobservable at p of 0.07 GPa, indicating that, for a fixed heating rate, an increase in pressure increases the temperature of HDA to LDA transformation and decreases that of LDA to ice Ic, causing thereby the two transformations to merge, and HDA appears to convert directly to ice Ic. Thus either LDA forms but converts extremely rapidly to ice Ic, or LDA does not form. At a fixed p and T, in the range of pressure amorphization of hexagonal ice, κ continues to decrease with time. Therefore, the amorphization of ice Ih is kinetically controlled. When HDA at 1 GPa was heated from 130 to 157 K and densified to very HDA, its κ increased by 3%. Our findings and a scrutiny of earlier reports show that a reversible transition between HDA and LDA does not occur at ∼135 K and ∼0.2 GPa. Since there is no unique HDA, it is difficult to justify the conjecture for a second critical point for water.
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