| 1. |
- 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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| 2. |
- 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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| 3. |
- Forsman, Hans, et al.
(författare)
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Dielectric relaxation of glycerol and n-propyl alcohol at high pressure
- 1986
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Ingår i: Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics. - : Royal Society of Chemistry. - 0300-9238. ; 82:5, s. 857-868
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Tidskriftsartikel (refereegranskat)abstract
- The dielectric relaxation of glycerol and n-propyl alcohol in the supercooled liquid state has been investigated at frequencies from 5 Hz to 13 MHz and at pressures up to 1 GPa. The high-pressure dielectric cell and the measurement procedures are described in detail. A significant broadening of the loss peak is observed for both liquids with increasing pressure. The results are discussed in terms of a many-body relaxation theory which accounts for increasing correlation of the relaxing dipoles at high pressure.
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| 4. |
- Forsman, Hans, et al.
(författare)
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Thermal conductivity and heat capacity of n-heptane, n- and iso-propyl-alcohol at high pressure
- 1982
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Ingår i: Physica B+C. - : Elsevier. - 0378-4363. ; 114:3, s. 287-294
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity, λ, and the heat capacity per unit volume, ρcp, of three molecular liquids, i.e. n-heptane, n-propyl-alcohol and iso-propyl-alcohol, were measured. We used a transient hot-wire method, and the measurements were carried out in a piston-cylinder apparatus with a simple high-pressure cell of novel design. For each substance two isotherms, at room temperature and above, were investigated up to 1.0 GPa. On pressurization a positive sign of the isobaric temperature coefficient of λ, (∂(ln λ)/∂T)P, was observed only for iso-propyl-alcohol. For all three liquids the isothermal volume coefficient of λ, g = -(∂(ln λ)/(∂(ln V)))T, was found to be in the range 2.7–3.1. The isothermal pressure dependence of heat capacity per unit mass was found to be small, except for iso-propyl-alcohol, where a 10–15% decrease in cp was observed. The experimental values of cp were compared with theoretical calculations based on thermodynamics.
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| 5. |
- Håkansson, Björn, et al.
(författare)
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Improved hot-wire procedure for thermophysical measurements under pressure
- 1988
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 59:10, s. 2269-2275
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Tidskriftsartikel (refereegranskat)abstract
- A new and simplified version of the circuitry for the transient hot‐wire method is presented. The circuitry provides a wide range of currents allowing probe wires of various diameters to be used in order to match the thermal properties of the specimen to be investigated. The analysis of the temperature increase during the heat pulse is based on the exact solution for a heated wire immersed in a medium. Data are corrected for varying power. The method was tested by computer simulations and by measurements of the thermal conductivity (λ) and the heat capacity per unit volume (ρcp ) of glycerol at room temperature and atmospheric pressure, and for CsCl and NaCl at room temperature and at pressures up to 2 GPa. The results on glycerol and CsCl are in excellent agreement with previous works. The inaccuracy in λ and ρcp is estimated as 1%–2% and 3%–5%, respectively, but the standard deviation of the measurements is as low as 0.2% for λ and 1% for ρcp. The improved procedure makes it possible to detect systematic errors caused by reflection of the heat pulse from the walls of the high‐pressure cell. This error, which reveals itself by a curvature of the residual, defined as the difference between fitted function and data, was demonstrated in the case of NaCl. A theoretical estimate of the influence of perturbations due to reflection was also carried out and it was found that the error mainly affects the value of ρcp.
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| 6. |
- Ross, Russell George, et al.
(författare)
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Thermal conductivity and heat capacity of solid AgCl under pressure
- 1981
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Ingår i: International journal of thermophysics. - : Plenum Publishing. - 0195-928X .- 1572-9567. ; 2:3, s. 289-300
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Tidskriftsartikel (refereegranskat)abstract
- Using the transient hot-wire method, measurements were made for solid AgCl of both the thermal conductivity, λ, and the heat capacity per unit volume, ρcp, where ρ is the mass density. Measurements were made in the temperature range 100 to 400 K, and at pressures up to 2 GPa. cp(P,T) could be adequately described if the acoustic modes were represented by a Debye model and the optic modes by an Einstein model. Analysis of λ(T) showed that only acoustic modes needed to be taken into account up to 300 K, but that optic modes were increasingly effective in carrying heat at higher temperatures. λ(P) was adequately described by the Lawson formula, but not by the Leibfried-Schlömann formula, to which it is formally equivalent. Agreement with experiment could be achieved by two different modifications of the Leibfried-Schlömann formula, although neither has a firm theoretical basis.
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| 7. |
- Ross, Russel George, et al.
(författare)
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Thermal conductivity of solids and liquids under pressure
- 1984
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Ingår i: Reports on progress in physics (Print). - : IOP Publishing. - 0034-4885 .- 1361-6633. ; 47:10, s. 1347-1402
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Forskningsöversikt (övrigt vetenskapligt/konstnärligt)abstract
- Thermal conductivity of solids and liquids under pressure is covered in this review. Experimental techniques are critically considered and compared, and an introduction to theory is provided. Results are presented and discussed for ionic crystals, normal molecular crystals, plastic crystal phases, clathrate hydrates, polymers and glass-formers, liquids, covalent and semiconducting crystals, rocks and metals. Special attention is given to isochoric conditions, change of crystal structure and molecular orientational disorder. Available reliable measurements at pressures up to a few GPa indicate the need for theoretical development, especially in connection with molecular crystals and ferromagnetic metals.
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| 8. |
- Ross, Russell G., et al.
(författare)
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Unusual PT dependence of thermal conductivity for a clathrate hydrate
- 1981
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 290:5804, s. 322-323
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Tidskriftsartikel (refereegranskat)abstract
- Molecular clathrate solids1 are crystals with peculiar and interesting properties. Their characteristic feature2 is that one chemical species, the ‘host’, forms a strongly bonded structure, which encages individual molecules of a second ‘guest’ species. There is virtually no chemical bonding between host and guest molecules. The guests are, nevertheless, firmly constrained by high energy barriers. X-ray and neutron diffraction experiments have shown that clathrates have a periodic structure typical of crystalline solids. A clathrate hydrate2 is a host substance consisting of H2O molecules which form an ice-like, hydrogen-bonded structure. Huge geological deposits of clathrate hydrates containing natural gas are known to exist2,3—these deposits may be exploitable, and in searching for clathrate hydrates knowledge of the thermal conductivity, λ, will be important. We present here a preliminary account of the first measurements of λ versus pressure (P) and temperature (T) for a clathrate hydrate. We studied a clathrate hydrate encaging molecules of tetrahydrofuran. Thermal conductivity was measured using the transient hot-wire method4. The accuracy of the measurements was 3% and the precision 1%. The temperature dependence was found to be unusual in that λ(T) has a positive slope (Fig. 1), a feature never before observed with crystalline organic materials. Furthermore, when λ was measured versus P, it was found unexpectedly that λ (P) was constant—behaviour never before reported for a non-metallic material.
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