Discussion of the thermal conductivity of particulate materials is dispersed over several decades and a wide range of disciplines. In addition, there is some disparity among the reported values. This paper presents a review of the methodology available for the study of thermal conductivity of particulate materials, with an emphasis on low atmospheric pressures, and an assessment of the dependability of the data previously reported. Both steady state and nonsteady state methods of thermal conductivity measurement are reviewed, delineating the advantages, disadvantages, and sources of error for each. Nonsteady state methods generally are simpler and more efficient. The transient hot wire and differentiated line-heat source are the preferred methods for the laboratory. These methods are better suited for small samples and short measurement times and are therefore the best methods to use for a series of comprehensive studies. Results of previous studies are presented, compared, and evaluated. A good way to assess the relative accuracy is to compare the values of thermal conductivity versus atmospheric pressure obtained from several experimenters. The lowest values of thermal conductivity at vacuum and very low atmospheric pressure, and the steepest slopes on the thermal conductivity versus atmospheric pressure curves, are indicative of the most accurate data. Previous thermal conductivity studies have shown that the thermal conductivity of particulate materials increases with increasing atmospheric pressure, with increasing particle size, and with increasing bulk density of the material. At vacuum, the thermal conductivity of particulate materials is proportional to the cube of the temperature. The temperature dependence of thermal conductivity is much less obvious at higher atmospheric pressures.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/96JE03302

Thermal conductivity measurements of particulate materials 1. A review

The effect of plutonium content on the thermal conductivity of (U, Pu)O2 solid solutions

A re-appraisal of the thermal conductivity of UO2 and mixed (U, Pu) oxide fuels

The heat‐transport properties and heat capacity of UC, UP, and US were determined between room temperature and 600°C. These properties were measured by a transient technique with a laser as a heat pulse source. The thermal conductivity was calculated from the product of the thermal diffusivity, heat capacity, and density. At room temperature the thermal conductivity of the three compounds corrected to theoretical density was found to be 0.057, 0.033, and 0.021 cal sec−1 cm−1°C−1 for UC, UP, and US, respectively. At 600°C the value for UC decreased to 0.041 cal sec−1 cm−1°C−1. The thermal conductivity of UP remained equal to its room‐temperature value and that of US increased to 0.029 cal sec−1 cm−1°C−1. The room‐temperature heat capacity values for the three compounds investigated were all slightly above 12 cal mole−1°K−1. At 600°C the heat capacity of UC increased to 15.2 cal mole−1°K−1, whereas no appreciable changes were found for UP and US at this temperature. The experimental heat‐capacity values wer...

Thermal Conductivity and Heat Capacity of the Monocarbide, Monophosphide, and Monosulfide of Uranium

Various absolute steady-state methods of measuring thermal conductivity can be made to yield, verifiably, experimental results accurate to within ± 2% from 100 to 1200 K, and for conductivity values from 0.1 to 5 W/cmK. This statement is substantiated by a detailed analysis of the results obtained by eight different systems in three laboratories on ten metals: Cu, Ag, Au, Pd, Pt, W, Cr, Armco Iron, and the alloys Nb-10 W and Inconel 702. The experimental systems by which these results were obtained are also briefly described. The achievement of such accuracy, however, requires that careful attention be paid to the design and operation of the experimental apparatus. In general, the thermal conductivity is computed from three parameters: the power developed in a specific heater; the temperature difference due to that heater; and a geometrical factor relating the two through the geometry of the heat flow pattern. The determination of each parameter presents problems of its own; these we outline, and present solutions to them which are often a matter of judicious compromises. However, because the individual problems are not equally severe for the different methods here discussed, the close agreement of the results that we show provides a gratifying reassurance that the experimental approaches and theoretical analysis, including estimates of error, are basically sound.

http://iopscience.iop.org/article/10.1088/0026-1394/7/1/002/pdf

Precise Measurement of Thermal Conductivity at High Temperatures (100–1200 K)

A radial heat flow technique was used to measure the thermal conductivity, k, of polycrystalline UO2in the range -57° to 1100°C. The technique yielded results with a probable accuracy of ±1.5% and a precision of ±0.1% in the range 50° to 1100°C. Meaningful measurements were limited to 1100°C by Pt-90 Pt10Rh thermocouple instability, although the apparatus was structurally sound to 1400°C. The thermal conductivity data up to 1000°C could be explained on the basis of heat transport by phonons. The thermal resistance, l/k, exhibits a linear temperature dependence from 200° to 100°C, which is expected for an insulator well above the Debye temperature. The slope of the l/k-temperature plot is 0.0223 cm w−1 which is independent of impurity content and is associated with three phonon umklapp processes. The intercept is sensitive to impurity content as indicated by the fact that it was decreased by a decrease in the oxygen/uranium ratio. Between 1000° and 1100°C, there is a slight departure of l/k from linearity which may be due to the onset of an electronic contribution. Near room temperature, UO2 has a maximum in k which is apparently caused by the rapid decrease in specific heat below this temperature.

Thermal Conductivity of Uranium Dioxide from ‐57° to 1100°C by a Radial Heat Flow Technique

The thermal conductivity of INOR-8 was measured in a radial heat flow apparatus between 100 and 800 deg C. The results indicated that the thermal conductivity of INOR-8 increases linearly with temperature to about 450 deg C, where an inflection occurs; this is followed by another linear portion with a slightly greater slope. At about 680 deg C, a second larger increase of about 10% was observed, and this was followed by what appeared to be another linear portion. No direct explanation for the behavior is given. The study showed that thermal conductivity measurements are sensitive to internal changes as are specific heat and thermal expansion measurements. A description of the apparatus used is given. (P.C.H.)

T. G. Kollie

Papers

Thermal Conductivity of Uranium Dioxide from ‐57° to 1100°C by a Radial Heat Flow Technique

The thermal conductivity of inor-8 between 100 and 800 c