| 1. |
- Brydsten, Ulf, et al.
(författare)
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Hot strip determination of the thermal conductivity tensor and heat capacity of crystals
- 1983
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Ingår i: International journal of thermophysics. - : Plenum Publishing. - 0195-928X .- 1572-9567. ; 4:4, s. 369-387
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Tidskriftsartikel (refereegranskat)abstract
- A method of determining the principal thermal conductivities and the specific heat capacity for an anisotropic crystal is presented, tested, and discussed. Two parallel metal strips are deposited onto a plane face of the specimen. One strip serves as a heater, the other as a temperature sensor. A pulse of constant dc power is applied to the heater, and the response at the sensor is measured by means of an ac bridge, monitored by a lock-in amplifier. The experiment is on-line with a PDP-11/34 computer system. The expression for the temperature rise in case of infinitely long strips is fitted to the sensor temperature data. In the isotropic case one experiment yields both thermal conductivity and heat capacity. In an anisotropic case experiments have to be performed with two or three different strip orientations, if all principal thermal conductivities are to be determined. A precision of 0.1% is readily obtained, and the method is thus valuable in cases where small changes in thermal conductivity are to be determined. We estimate that the accuracy generally obtainable is about 2% as regards thermal conductivity and heat capacity. The accuracy in determining thermal diffusivities is mainly limited by geometrical factors and may ultimately be better than 1%. Results are given for isotropic CaF2 and anisotropic SiO2 at 300 K.
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| 2. |
- Hopstadius, Bruno, et al.
(författare)
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High Speed Scanning Calorimetry for Amorphous Alloys
- 1983
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Ingår i: International journal of thermophysics. - : Plenum Publishing. - 0195-928X .- 1572-9567. ; 4:3, s. 235-252
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Tidskriftsartikel (refereegranskat)abstract
- A high speed scanning calorimeter has been developed for simultaneous measurements of heat capacity and electrical resistivity of thin strips. The system was designed for amorphous alloys but can be used for other materials as well. The specimen is heated by an electrical current at rates ranging from 250 to 40,000 K s-1, and the temperature is sensed by an IR pyrometer ranging down to room temperature. The maximum data acquisition rate is 50 kHz. Operational characteristics of the system are given, and various phenomena that affect design and operation are discussed. Data are taken for some Metglas alloys, Glass transition and crystallization temperatures as well as rough viscosity data are evaluated. At high heating rates the glass transition is spread over a wide temperature range. The formation of metastable crystalline phases can be bypassed so that stable phases form directly from the amorphous state.
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| 3. |
- 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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| 4. |
- 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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