Thermal conductivity,heat capacity,and thermal diffusivity of selected commercial AlN substrates

The thermal transport properties of four commercially available AlN substrates have been investigated using a combination of steady-state and transient techniques. Measurements of thermal conductivity using a guarded longitudinal heat flow apparatus are in good agreement with published room temperature data (in the range 130–170 W · m^–1 · K^–1). Laser flash diffusivity measurements combined with heat capacity data yielded anomalously low results. This was determined to be an experimental effect for which a method of correction is presented. Low-temperature measurements of thermal conductivity and heat capacity are used to probe the mechanisms that limit the thermal conductivity in AlN.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal conductivity measurements of pacific illite sediment

Results are reported for effective thermal conductivity measurements performed in situ and in core samples of illite marine sediment. The measurements were obtained during a recent oceanographic expedition to a study site in the north central region of the Pacific Ocean. This study was undertaken in support of the U.S. Subseabed Disposal Project, the purpose of which is to investigate the scientific feasibility of using the fine-grained sediments of the sea floor as a repository for high-level nuclear waste. In situ measurements were made and 1.5-m-long hydrostatic piston cores were taken, under remote control, from a platform that was lowered to the sea floor, 5844 m below sea level. The in situ measurement of thermal conductivity was made at a nominal depth of 80 cm below the sediment surface using a specially developed, line-source, needle probe. Thermal conductivity measurements in three piston cores and one box core (obtained several kilometers from the study site) were made on shipboard using a miniature needle probe. The in situ thermal conductivity was approximately 0.91 W · m^–1 · K^–1. Values determined from the cores were within the range 0.81 to 0.89 W · m^–1 · K^–1.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Effective thermal conductivity of a granular bed at elevated temperatures

The effective thermal conductivity of beds of granular material has been investigated experimentally in the temperature range from 373 to 1200° K at a vacuum of 1·10^–4 mm Hg and at atmospheric pressure.     

Establishment of an empirical correlation for estimating the thermal conductivity of igneous rocks

A correlation to predict the thermal conductivity of andesitic igneous rocks is developed from measured data on drill cores from wells from the Los Azufres geothermal field, Mexico. The correlation was developed from density, porosity, and thermal conductivity. Seventeen determinations were made on drill cores extracted at varying depths from 12 wells. Thermal conductivity varied from 1.05 to 2.34 W · m^–1 · K^–1, while bulk density varied from 2050 to 2740 kg · m^–3 and grain density varied from 2610 to 2940 kg · m^–3. Total porosity varied from 1.9 to 24.7%. Two polynomial regressions, one linear and one quadratic, were tested on the thermal conductivity-times-bulk density product, with total porosity as the independent variable. The correlation coefficients and residual mean square deviations were 0.83 and 0.00491 for the linear fit and 0.87 and 0.00425 for the quadratic model, respectively. For porosities up to about 18%, both models showed very close predictions, but for larger values, the quadratic model appeared to be better and it is recommended for the porosity range from 0 to 25%. Furthermore, density and porosity may be determined from drill cuttings, which are more readily available than cores.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal conductivity and heat capacity per unit volume of poly(methyl methacrylate) under high pressure

The thermal conductivity and heat capacity per unit volume of poly(methyl methacrylate) (25 and 350 kg · mol^– in molecular weight) have been measured in the temperature range 155–358 K at pressures up to 2 GPa using the transient hot-wire method. The bulk modulus has been measured up to 1.0 GPa at 294 K and yielded a constant valueg = 3.4 ± 0.3 for the Bridgman parameter. No dependence on molecular weight could be detected in the properties we measured.     

Measurement of the thermal conductivity of molten InSb under microgravity

Thermal conductivity of molten InSb was measured on board the TEXUS-24 sounding rocket by the transient hot-wire method using the originally designed thermal conductivity measurement facility (TCMF). Measurements made through this facility were affected by natural convection on the ground. This natural convection was confirmed to be sufficiently suppressed during a microgravity environment. The thermal conductivity of molten InSb was 15.8 and 18.2 W·m^–1·K^–1 at 830 and 890 K, respectively.     

Thermal conductivity and electrical resistivity of cadmium arsenide (Cd3As2) in the temperature range 4.2–40 K

Results on electrical resistivity and thermal conductivity measured in the temperature range 4.2–40 K are presented for single-crystal and polycrystalline samples of Cd₃As₂. Hall effect has been studied at temperatures of 4.2, 77, and 300 K. The calculated value of the conduction electron concentration was in the range 1.87–1.95 10²⁴m^–3. Electrical resistivity of all investigated samples was independent of temperature up to about 10K and increased slowsly at higher temperatures. The thermal conductivity shows a maximum in the region in which the lattice component of thermal conductivity dominates. The strong anisotropy of the lattice component determines the anisotropy of the total thermal conductivity. The electronic component of thermal conductivity does not exhibit any anisotropy and shows a maximum at a temperature of about 300 K.Paper submitted to the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Thermal conductivity of mica at low temperatures

The thermal conductivity of muscovite and phlogopite has been measured over a temperature range of 3 to 320 K, in directions parallel and perpendicular to the cleavage planes. Both materials showed anisotropic behaviour. The room temperature values for muscovite and phlogopite, respectively, were 4.05 and 3.7 W m^–1 K^–1 for conductivity parallel to the planes, and 0.46 and 0.44 W m^–1 K^–1 perpendicular to the planes. Plots of the variation of thermal conductivity with temperature for both directions in the two materials show a gradual rise in conductivity as the temperature is lowered below room temperature. All four curves reach a peak at about the same temperature of 15 K. The peak values obtained were 12.4 and 7.25 W m^–1 K^–1 parallel to the planes, and 4.7 and 2.05 W m^–1 K^–1 perpendicular to the planes.On leave from Australian Broadcasting Commission.     

Thermal conductivity of pure monoisotopic silicon

The thermal conductivity of pure monoisotopic silicon is estimated by two methods, which give similar results. One estimate, based on the observed thermal conductivity of monoisotopic germanium, yields a maximum of 66 W · cm^–1 · K^–1 at 22 K. The other estimate, based on measurements of natural silicon and on the theoretical isotope scattering rate, yields 75 W · cm^–1 · K^–1 at 22 K, an increase of only 45% over the natural crystal. These values are for crystals of approximately 0.5 cm diameter; smaller crystals yield lower values of the maximum conductivity and smaller isotope effects. Silicon cooled to liquid hydrogen temperature seems promising for high-irradiance laser mirrors. The small gain obtained by using monoisotopic silicon would be substantially greater in cases when the generated phonon distribution is athermal and weighted to higher frequencies. The effective heat transport could then be increased by as much as a factor 60 through the use of monoisotopic silicon.     

Conductivity and strength behaviour of aluminawhisker-zirconia composites

Yttria stabilized zirconia (8 mol%) composites were fabricated by tape casting with either alumina powder or alumina whiskers, and pressureless sintered. Sintering behaviour, ionic conductivity and mechanical strength were analysed. For all compositions analysed, increasing alumina content reduced the sintered density. For whisker-reinforced zirconia, the rigid whiskers prevented matrix densification along their axis. The ionic conductivity was measured by the complex impedance method from 500–1000 °C and the activation energy for ionic conduction calculated over that range. The ionic conductivity of the alumina-zirconia composites decreased with increasing alumina content as expected by the rule of mixtures. However, the ionic conductivity of the whisker-zirconia composites decreased more than expected possibly due to contamination from the whiskers. The strength of the whisker-zirconia composites was also found to be affected by the porosity. At 5 vol%, the average strength was measured at 39.9 kgf mm^–2, which decreased to 24 kgf mm^–2 at 20 vol%.     

Thermal conductivity of sulfur hexafluoride

This paper reports new measurements of the thermal conductivity of sulfur hexafluoride at the nominal temperature of 27.5°C as a function of density in the range up to 200 kg · m^–3. The measurements were performed in a transient, hot-wire instrument. When combined with earlier measurements of the viscosity of the gas, they allow us to calculate the rather large contribution stemming from the internal degrees of freedom. The present measurements compare well with those in the literature. All of them suggest that the excess thermal conductivity is a unique function of density in the present range of states. An empirical correlation of our measurements can serve users in the ranges 0 < t< 100°C and 0 < < 200 kg · m^–3.     

Thermal conductivity of neutron-irradiated MgO

The thermal conductivity of pure and neutron-irradiated MgO has been measured in the temperature range 0.4–80 K and for neutron doses up to 2×10 ¹⁹ n·cm^–2 . Resonance dips in the thermal conductivity vs. temperature curves are observed at 1 and 20 K. It is suggested that the high-temperature dip, which becomes more pronounced with increasing radiation dose, may be a quasilocalized mode resulting from the production ofF-type centers. The low-temperature dip, which fades with increasing neutron dose, may result from the presence of small aggregate centers which give rise to another set of quasilocalized modes. The experimental data for the pure and irradiated crystals are in agreement with calculated curves based on the Debye model of solids. A combined relaxation time for the calculated curves of the irradiated specimens includes a term for the defect scattering rate consisting of two resonance expressions of the Lorentzian form.Supported by the U. S. Atomic Energy Commission.     

Measurement of the enthalpy and specific heat of a Be2C-graphite-UC2 reactor fuel material to 1980 K

The enthalpy and specific heat of a Be₂C-Graphite-UC₂ composite nuclear fuel material have been measured over the temperature range 298–1980 K using both differential scanning calorimetry and liquid argon vaporization calorimetry. The fuel material measured was developed at Sandia National Laboratories for use in pulsed test reactors. The material is a hot-pressed composite consisting of 40 vol% Be₂C, 49.5 vol% graphite, 3.5 vol% UC₂, and 7.0 vol% void. The specific heat was measured with the differential scanning calorimeter over the temperature range 298–950 K, while the enthalpy was measured over the range 1185–1980 K with the liquid argon vaporization calorimeter. The normal spectral emittance at a wavelength of 6.5×10^–5 cm was also measured over the experimental temperature range. The combined experimental enthalpy data were fit using a spline routine and differentiated to give the specific heat. Comparison of the measured specific heat of the composite to the specific heat calculated by summing the contributions of the individual components indicates that the specific heat of the Be₂C component differs significantly from literature values and is approximately 0.56 cal · g^–1 · K ^–1 (2.3×10³J · kg^–1 · K ^–1) for temperatures above 1000 K.     

Thermophysical Parameters of Optical Glass BK 7 Measured by the Pulse Transient Method

This paper is focused on the pulse transient method. The theory of the method and the measuring regime (time window) are analyzed. The results of the analysis are verified on borosilicate crown glass BK7, which is a candidate for a standard for thermal conductivity. Thermal contact and surface effects affect the length of the time window in which the evaluation procedure is applied. The one-point evaluation technique is compared with the results of the fitting procedure that uses the time window found by difference analysis. The values of the thermal conductivity, thermal diffusivity, and specific heat were found to be 1.05 W· m^–1 · K^–1, 0.548 × 10^–6m ^{– 2} · s^–1, and 767 J· kg^–1 · K^–1, respectively, using the one-point evaluation technique.Paper presented at the Sixteenth European Conference on Thermophysical Properties, September 1–4, 2002, London, United Kingdom.     

Knudsen-effect errors with transient line-source measurement in fluids

This paper decribes the Knudsen-effect errors of the transient line-source method used for accurate measurements of the thermal conductivity and thermal diffusivity of fluids. The analysis demonstrates that the instrument can be used with a good accuracy (>0.5%) to lower densities than previously thought. The principal errors are illustrated by measurements on propane in the temperature range 250–300 K at densities less than 9 kg · m^–3.     

Thermal properties of MoSi2 and SiC whisker-reinforced MoSi2

The heat capacity, thermal conductivity and coefficient of thermal expansion of MoSi₂ and 18 vol % SiC whisker-reinforced MoSi₂ were investigated as a function of temperature. The materials were prepared by hot isostatic pressing between 1650 and 1700 °C, the hold time at temperature being 4 h. The heat capacity of MoSi₂ showed an increase from about 0.44 Wsg^–11K^–1 at room temperature to 0.53 at 700 °C. Whisker reinforcement increased heat capacity by about 10%. Thermal conductivity exhibited a decreasing trend from 0.63 Wcm^–1 K^–1 at room temperature to 0.28 Wem^–1 K^–1 at 1400°C. Whiskers reduced conductivity by about 10%. The thermal expansion coefficient increased from 7.42 °C^–1 between room temperature and 200 °C to 9.13 °C^–1 between room temperature and 1200 °C. There was a 10% decrease resulting from the whiskers. The measured data are compared with literature values. The trends in the data and their potential implications for high-temperature aerospace applications of MoSi₂ are discussed.     

Thermal conductivity of B2O3 glass under pressure

The thermal conductivity, , of vitreous boron trioxide was measured, using a hot-wire procedure, from 170 to 570 K and under pressures of up to 1.7 GPa. The thermal conductivity at room temperature and zero pressure was found to be 0.52 W · m^–1 · K^–1. The values of the logarithmic pressure derivative, g = d(ln )/d(ln ), where is the density, were found to be 1.1 for uncompacted glass and 0.7 for glass compacted to 1.2 GPa. The variation of with temperature at constant density was approximately linear, with a positive slope of 1.38×10^–3W·m^–1·K^–2.     

Comparison of thermal conductivity data for partially stabilized zirconia with values derived from thermal diffusivity results

The thermal conductivity of partially stabilized zirconia was measured over the temperature range 320–1273 K using the radial heat flow method. The data have an absolute uncertainty of about ±2% and repeat measurements showed no evidence of changes in the thermal conductivity at high temperatures. This also was true for the thermal diffusivity data, which were obtained in vacuum over the temperature range 300–1473 K. Both sets of thermal conductivity data pass through minima at high temperatures. Quantitative differences were observed in the temperatures and thermal conductivities of the two minima. The results were analyzed by assuming parallel conduction by phonons and photons, and the phonon component was identified by fitting lower-temperature data. Extrapolating this curve allowed identification of the photon contribution to the thermal conductivity at high temperatures. The photon contribution approached a T ³ function and was larger in the thermal conductivity specimens. The difference in the photon contributions correlates with changes in the optical properties of the samples produced during the high temperature measurments.     

The thermal conductivity and heat capacity of gaseous argon

This paper presents new absolute measurements of the thermal conductivity and of the thermal diffusivity of gaseous argon obtained with a transient hot-wire instrument. We measured seven isotherms in the supercritical dense gas at temperatures between 157 and 324 K with pressures up to 70 MPa and densities up to 32 mol · L^–1 and five isotherms in the vapor at temperatures between 103 and 142 K with pressures up to the saturation vapor pressure. The instrument is capable of measuring the thermal conductivity with an accuracy better than 1% and thermal diffusivity with an accuracy better than 5%. Heat capacity results were determined from the simultaneously measured values of thermal conductivity and thermal diffusivity and from the density calculated from measured values of pressure and temperature from an equation of state. The heat capacities presented in this paper, with a nominal accuracy of 5%, prove that heat capacity data can be obtained successfully with the transient hot wire technique over a wide range of fluid states. The technique will be invaluable when applied to fluids which lack specific heat data or an adequate equation of state.     

Thermal conductivity of hydrogen for temperatures between 78 and 310 K with pressures to 70 MPa

The paper presents new experimental measurements of the thermal conductivity of hydrogen. The ortho-para compositions covered are normal, near normal, para, and para-rich. The measurements were made with a transient hot wire apparatus. The temperatures covered the range from 78 to 310 K with pressures to 70 MPa and densities from 0 to a maximum of 40 mol · L^–1. For compositions normal and near normal, the isotherms cover the entire range of pressure, and the temperatures are 78, 100, 125, 150, 175, 200, 225, 250, 275, 294, 300, and 310K. The para measurements include eight isotherms at temperatures from 100 to 275 K with intervals of 25 K, pressures to 12 MPa, and densities from 0 to 12 mol · L^–1. Three additional isotherms at 150, 250, and 275 K cover para-rich compositions with para percentages varying from 85 to 72%. For these three isotherms the pressures reach 70 MPa and the density a maximum of 30 mol · L^–1. The data for all compositions are represented by a single thermal conductivity surface. The data are compared with the experimental measurements of others through the new correlation. The precision (2) of the hydrogen measurements is between 0.5 and 0.8% for wire temperature transients of 4 to 5 K, while the accuracy is estimated to be 1.5%.