| 1. |
- Andersson, Per, et al.
(författare)
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Effect of guest molecule size on the thermal conductivity and heat capacity of clathrate hydrates
- 1983
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics Publishing (IOPP). - 0022-3719. ; 16:8, s. 1423-1432
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Tidskriftsartikel (refereegranskat)abstract
- Using the transient hot-wire method, we have measured both the thermal conductivity, lambda, and the heat capacity per unit volume, rho cp, for structure II clathrate hydrates of 1,3-dioxolane (DO) and cyclobutanone (CB), and compared the results with similar previous measurements for tetrahydrofuran (THF). All three clathrate hydrates showed a glass-like temperature dependence of lambda. The magnitude of lambda was small, about the same as liquid water, and decreased in the sequence DO-THF-CB which corresponds to an increase in the size of the guest molecule. There was some evidence to support the suggestion that the dominant process in the thermal resistivity was associated with excitation of rotational vibrations of the guest molecules. In all cases, the pressure dependence of lambda was unusually small. We found evidence that there was a phase transition on the CB clathrate hydrate (and almost certainly also in the DO clathrate) at 135K and 1 GPa, which are essentially the same conditions under which we previously found an analogous transition for THF. In each case, the resultant presumably metastable phase may be a new type of clathrate hydrate arising from densification of the host structure. For the three clathrates, our results for rho cp did not depend on the nature of the guest species, and at 0.1 GPa, were the same as previously found for ice Ih.
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| 2. |
- Andersson, Per, et al.
(författare)
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Thermal conductivity, heat capacity and phase diagrams of the trichloroethanes under pressure : II. 1,1,2-trichloroethane
- 1981
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Ingår i: Molecular Crystals and Liquid Crystals. - : Taylor & Francis. - 1542-1406 .- 1563-5287 .- 0026-8941. ; 69:1-2, s. 157-166
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity, λ, the heat capacity per unit volume, ρcp, and the phase diagram of 1,1,2-trichloroethane have been investigated in the temperature range 115 to 300 K and at pressures up to 2.5 GPa. The transient hot-wite method was used for the simultaneous measurement of λ and ρcp. Only solid phases I and II were detected, in agreement with the known phase diagram. A phase I-II transition was detected at about 200K and 0.1 GPa, which are conditions under which it had not priviously been observed. It was doubtful whether phase I could be retained metastably to low temperatures at low pressures with the most rapid cooling rate we were able to employ. The thermal resistivity of phase I was proportioned to temperature. The thermal resistivity of phase II contained an additional constant term, which we inferred to be a residual contribution associated with static structural imperfection in this phase.
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| 3. |
- Andersson, Per, et al.
(författare)
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Thermal conductivity of orientationally-disordered crystals under high pressure
- 1983
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Ingår i: Thermal conductivity 17. - New York : Plenum Publishing. - 0306411776 ; , s. 527-536
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Konferensbidrag (refereegranskat)abstract
- The transient hot-wire method was used to study the effects of temperature and pressure on the thermal conductivity, λ, of several molecular substances showing varying degrees of disorder in molecular orientation. Molecular solids both in the plastic and normal crystal state were investigated as well as a clathrate hydrate. The measurements were made in the temperature range 100 - 450 K and at pressures up to 2.5 GPa. The conductivity results for the different types of crystal studied are discussed in terms of the simple Debye formula. We discuss the unusual glass-like behaviour of λ(T) for the clathrate hydrate in some detail.
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| 4. |
- Andersson, Per, et al.
(författare)
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Thermal resistivity, heat capacity and phase diagram of CBr4 under pressure
- 1980
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Ingår i: Molecular Physics. - : Taylor & Francis. - 0026-8976 .- 1362-3028. ; 39:6, s. 1359-1368
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Tidskriftsartikel (refereegranskat)abstract
- We have measured simultaneously the thermal resistivity and the heat capacity per unit volume for phases I, II, III and IV of CBr4. We have used the transient hot-wire method, and have made measurements over the ranges 170 K to 425 K, and up to 2 GPa. Our results, and other evidence, indicate that I and III are plastic crystal phases, and that there is a significant degree of structural disorder in phase II. Three-phonon interactions probably provide the dominant contribution to the thermal resistivity of phase IV. Using structural analogies with the phases of CCl4, we find that the relative values of the thermal resistivities are roughly as predicted by simple theory.
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| 5. |
- Andersson, Per, et al.
(författare)
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Thermal resistivity of ice Ih near the melting point
- 1980
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics Publishing (IOPP). - 0022-3719 .- 1747-3802. ; 13:4, s. L73-L76
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Tidskriftsartikel (refereegranskat)abstract
- The thermal resistivity r(T) of ice Ih has been re-measured from 120K to as close as practicable to melting. Measurements were made under isobaric conditions at a pressure of 0.07 GPa, and corrected to isochoric conditions. The resultant deviation from the simple theoretical prediction, r/T=constant, has been plausibly accounted for by interaction between optic and acoustic phonons. Thermal resistivity arising from the presence of point defects has been shown to be of negligible importance.
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| 6. |
- Fransson, Åke, et al.
(författare)
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Thermal conductivity, heat capacity and phase stability of solid sodium chlorate (NaClO3) under pressure
- 1983
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics Publishing (IOPP). - 0022-3719. ; 16:15, s. 2861-2869
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity, lambda, and the specific heat capacity at constant pressure, cp, have been measured for solid sodium chlorate (NaClO3) in the temperature range 100-300K. Differential scanning calorimetry (DSC) was used to measure cp at atmospheric pressure, whilst the transient hot-wire method was used to measure simultaneously both lambda and the heat capacity per unit volume, rho cp, up to a pressure of 2 GPa. We found that our measured DSC values of cp exceeded those previously predicted from a lattice dynamical model, consistent with a previous prediction of disorder in Cl atom positions at high temperatures. However, such disorder, if it exists, did not affect the transport of heat, since we found that lambda (T) under isochoric conditions appeared to be determined entirely by three-phonon umklapp interactions. We found no evidence for a phase transition in NaClO3 up to 2 GPa at 300K, contrary to some previous results. However, we did observe an explosive chemical instability to occur at about 1 GPa and 130K.
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| 7. |
- Hopstadius, Bruno, et al.
(författare)
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Invariance of Curie temperature of iron for heating rates up to 10 000 Ks−1
- 1983
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Ingår i: Philosophical Magazine B. - : Taylor & Francis. - 1364-2812 .- 1463-6417. ; 47:6, s. L89-L91
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Tidskriftsartikel (refereegranskat)abstract
- We have shown that the Curie temperature of Fe is unaffected by heating rates up to 10000 Ks−1. This appears to be the first direct evidence, from measurement of bulk properties, that magnetization responds very rapidly to change of temperature through the ferromagnetic—paramagnetic phase transition.
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| 8. |
- Ross, Russell G., et al.
(författare)
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Clathrate and other solid phases in the tetrahydrofuran–water system : thermal conductivity and heat capacity under pressure
- 1982
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Ingår i: Canadian journal of chemistry (Print). - : Canadian Science Publishing. - 0008-4042 .- 1480-3291. ; 60:7, s. 881-892
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Tidskriftsartikel (refereegranskat)abstract
- Solid phases in the tetrahydrofuran–water (THF–H2O) system were investigated in the temperature range 100–260 K and at pressures up to 1.5 GPa. Thermal conductivity, λ, and heat capacity per unit volume, ρcp, were measured, using the transient hot-wire method. We made measurements on solid phases having nominal compositions THF•17H2O, THF•7.1H2O, and THF•4.6H2O, which we refer to as phases α, β, and γ, respectively. Phase α is known to be a structure II clathrate hydrate, and λ for this phase was found to be similar to other crystalline solids which are glass-like in relation to their thermal properties. Low-energy excitations are known to be relevant to the properties of glass-like solids, and, in the case of phase α, were probably rotational vibrations of the THF guest molecules. Phase β was similar, and we inferred that it was probably a structure I clathrate hydrate. Phase γ behaved nearly like a normal crystal phase at low temperatures, but λ became almost independent of temperature near melting. At 1.1 GPa and 130 K, we found evidence that phase α transformed, on pressurization, to a metastable modification which may be a new high-density form of clathrate hydrate. The astrophysical implications of our results were mentioned briefly.
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| 9. |
- Ross, Russell G.
(författare)
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New dimensions in the study of phonon thermal conductivity through the use of high pressure
- 1982
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Ingår i: High Pressure in Research and Industry. ; , s. 95-107
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Konferensbidrag (refereegranskat)abstract
- High pressure is a powerful variable in investigating heat transfer in nonmetallic solids. The effects of phase transitions, and density changes generally, can now be studied using several different techniques of adequate accuracy. Only temperatures > the Debye temperature are considered. Solids for which data are available include relatively simple solids like the alkali and silver halides, as well as many more-complex molecular solids. For the latter, the effects of various forms of structural disorder is a recurrent theme, which can be illustrated by means of solids such as high pressure ices, ammonium chloride, plastic crystal phases and clathrate hydrates.
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| 10. |
- Ross, Russell G., et al.
(författare)
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Thermal conductivity and heat capacity of solid silver bromide (AgBr) under pressure
- 1981
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Ingår i: International journal of thermophysics. - : Plenum Publishing. - 0195-928X .- 1572-9567. ; 2:4, s. 331-340
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity, λ, and the heat capacity per unit volume, ρcp, have been measured for solid silver bromide (AgBr) using the transient hot-wire method. Measurements were made at temperatures in the range 100-400 K and at pressures up to 2 GPa. ρcp was found to be independent of temperature and pressure over these ranges. λ of AgBr was found to be similar to that of AgCl, which was measured previously. For AgBr, only acoustic phonons needed to be taken into account up to 340 K, but optic phonons probably carried some heat at higher temperatures. The Leibfried-Schlömann (LS) formula could describe the ratio λ(AgCl)/λ(AgBr), but not the ratio λ(1 GPa)/λ(0) for either substance. An empirical modification of the LS formula could describe the latter ratios but not the former. Further theoretical developments are required for understanding of λ(P) for even such relatively simple substances as AgCl and AgBr.
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