R. S. Graves

Absolute Seebeck coefficient of platinum from 80 to 340 K and the thermal and electrical conductivities of lead from 80 to 400 K

The absolute Seebeck coefficient of platinum was determined from 80 to 340 K by direct comparsion to lead. Results of this comparison disagree with previous results which have been used for the calculation of absolute values for other materials. The thermal conductivity λ and electrical resistivity ρ of the lead standard were also determined. The electrical resistivity could be described with a modified Gruneisen‐Bloch equation which allows for the effect of thermal expansion on the Debye temperature ΘD. The ratio λρ/T was within 1% of the Sommerfeld value of 2.443×10−8 (V/K)2 from 1.0 to 5.0 ΘD.

The thermal conductivity of AISI 304L stainless steel

A compilation and critical analysis of the thermal conductivity (γ) of AISI 304 stainless steel (SS) between 100 and 1707 K has been given in the literature. The author represented his “recommended” values of λ by an inflection in the A versus temperature relationship between 300 and 500 K. Because a physical mechanism had not been identified that would produce such a temperature dependence in γ of 304 SS, interest was generated in the possible existence of an as yet undiscovered phenomenon that might cause such an inflection. Consequently, experimental verification of the inflection was sought. The present paper presents recent measurements of λ, the electrical resistivity, and the absolute Seebeck coefficient of 304L SS from 300 to 1000 K and of the thermal diffusivity (α) from 297 to 423 K. The λ values computed from the a measurements were within ± 1.6% of the directly measured λ An inflection was not observed in the temperature dependence of λ between 300 and 500 K. After careful evaluation and because a physical mechanism still has not been identified which would produce such an inflection, the authors conclude that the inflection in the λ vs T relationship reported in the literature was caused by the data analysis technique.

Thermal conductivity, electrical resistivity, and Seebeck coefficient of high‐purity chromium from 280 to 1000 K

The thermal conductivity λ, electrical resistivity ρ, and Seebeck coefficient S of a high‐purity Cr specimen (ρ273/ρ4.2=380) were measured from 285 to 1000 K. The ρ and S of two other Cr specimens (ρ273/ρ4.2=380 and 58) were determined from 300 to 1300 K. The ρ and S results from the three specimens are in excellent agreement and all three properties agree to within experimental uncertainty with previous low‐temperature results on the same specimens over the temperature range of overlap. Near T′ N (300–320 K), the present λ results are within 0.7% of the previous data and indicate that λρ/T should be smooth to within 1%. At high temperature, the present λ data are about 8% above those of Powell and Tye but the ratios of λρ/T agree to within 2% up to 1000 K. These new data on pure Cr are compared to calculations from standard transport theory and to previous results from W and Mo.

Experimental determination of the phonon and electron components of the thermal conductivity of bcc iron

A study of the factors which affect the thermal conductivity of αFe and its solutions is described. The results of these experiments define the phonon and electronic components of the thermal conductivity of pure αFe fairly well between 90 and 400 K. Also, the phonon conductivity can be analyzed to identify the strengths of electron‐phonon and phonon‐phonon scattering, and the latter resistance is in good agreement with theoretical estimates. The scattering of phonons by electrons is intermediate between the small values for noble metals and the strong scattering found in Nb and Ta. An experimental estimate of the electron‐phonon mass enhancement factor, 0.4, is derived from the results. Finally, reexamination of the data for ten solid solution alloys suggests that both phonon‐scattering mechanisms are influenced by the alloying elements.

Transport properties of high purity, polycrystalline titanium diboride

Thermal conductivity data for several TiB2 samples are presented and the results for one sample extend from 80 to 400 K. These results show that the thermal conductivity attains a maximum value of about 130 W/m K at 140 K. An analysis of the results shows that this is caused by the electronic component of the thermal conductivity and that phonon conduction is also probably significant. Seebeck coefficient values agreed with the results of previous studies. The electrical resistivity of one sample was also determined to 1800 K. These results can be described by the Bloch–Gruneisen equation if the effect of thermal expansion is included.

The effects of Cr2O3 and Fe2O3 additions on the thermal conductivity of Al2O3

Thermal conductivity data for a series of Al2O3, Al2O3‐Cr2O3, Al2O3‐Fe2O3, and Al2O3‐Cr2O3‐Fe2O3 samples are reported. The results, which span the temperature range 300–360 K, show that grain size has an important effect on the thermal conductivity of Al2O3, and this effect is larger than would be anticipated from standard theories. Results for seven Al2O3‐based solid solutions were examined in terms of a Callaway formula, and it was found that the point defect relaxation times were principally dependent on solute content and the mass difference between the solute and solvent. The data support a theory that suggests that a heavy atom in a light matrix scatters less effectively than a light atom in a heavy matrix. The data do not show that isolated point defects are more effective phonon scatterers than point defects in a concentrated solution.Thermal conductivity data for a series of Al/sub 2/O/sub 3/, Al/sub 2/O/sub 3/-Cr/sub 2/O/sub 3/, Al/sub 2/O/sub 3/-Fe/sub 2/O/sub 3/, and Al/sub 2/O/sub 3/-Cr/sub 2/O/sub 3/-Fe/sub 2/O/sub 3/ samples are reported. The results, which span the temperature range 300--360 K, show that grain size has an important effect on the thermal conductivity of Al/sub 2/O/sub 3/, and this effect is larger than would be anticipated from standard theories. Results for seven Al/sub 2/O/sub 3/-based solid solutions were examined in terms of a Callaway formula, and it was found that the point defect relaxation times were principally dependent on solute content and the mass difference between the solute and solvent. The data support a theory that suggests that a heavy atom in a light matrix scatters less effectively than a light atom in a heavy matrix. The data do not show that isolated point defects are more effective phonon scatterers than point defects in a concentrated solution.

Effects of temperature and composition on the thermal and electrical conductivities of Ni3Al

The results of a study of the thermal conductivity, electrical resistivity, and Seebeck coefficient of Ni3Al are described. The thermal and electrical conductivities are sensitive to composition and attain their maximum values in well‐ordered, stoichiometric Ni3Al. Nonstoichiometry (antisite defects), and Fe (a substitutional solute) and B (an interstitial solute) contents are all about equally effective in reducing the transport properties. Even for stoichiometric Ni3Al, the temperature variation of the thermal and electrical conductivities resembles that of an alloy, and this is attributed to scattering associated with the loss of ferromagnetic order at ∼60 K. Experimental data and a theoretical analysis show that phonon conduction is an important part of the thermal conductivity and not very sensitive to composition or stoichiometry.

Precision measurements of the thermal conductivity, electrical resistivity, and Seebeck coefficient from 80 to 400 K and their application to pure molybdenum

A longitudinal heat‐flow technique for precise measurement of thermal conductivity, electrical resistivity, and Seebeck coefficient over the temperature range from 80 to 400 K is described. The basis of the technique is the use of a calibrated platinum resistance thermometer to provide in situ calibrations of specimen thermocouples. The total determinate errors at 273 K are ± 0.23% for electrical resistivity, ± 0.49% for thermal conductivity, and ± 0.07 μV/K for the Seebeck coefficient when Pt wire is used as the reference. Experimental results on two high‐purity molybdenum specimens with cross‐sectional areas differing by a factor of four are presented to demonstrate the system precision and low level of indeterminate erros.

Thermal Measurement of In-Situ and Thin-Specimen Aging of Experimental Polyisocyanurate Roof Insulation Foamed with Alternative Blowing Agents

This paper reports apparent thermal conductivity (k) values from field and laboratory aging tests on a set of industry-produced, experimental polyisocyanurate (PIR) laminated boardstock foamed with hydrochlorofluorocarbons (HCFCs) as alternatives to chlorofluorocarbon (CFC). The PIR boards were blown with five gases: CFC-11, HCFC-123, HCFC-14lb, and 50/50 and 65/35 blends of HCFC-123/HCFC-14lb. The k-values were determined from 0 to 50{degree}C (30 to 120{degree}F) using techniques that meet ASTM C 114 (Thin Heater Apparatus) and ASTM C 518 (Heat Flow Meter Apparatus). Results on laminate boards with facers provide an independent laboratory check on the increase in k observed for field exposure in the ORNL Roof Thermal Research Apparatus (RTRA). The observed laboratory increase in k was between 8% and 11% for a 240 day field exposure in the RTRA. A thin-specimen aging procedure established the long-term thermal resistance of gas-filled foams. Thin specimens were planed from the industry-produced boardstock foams and aged at 24 and 65{degree}C (75{degree}F and 150{degree}F) for up to 300 days. An exponential dependency of k with the quantity (diffusion coefficient X time){sup {1/2}}/ thickness, provide effective diffusion coefficients for air components into the foams and blowing agent out of the foams. The foams blown with alternative blowing agents exhibited k-values 3 to 16% (average 9.4%) above CFC-11 foams under similar conditions. Field exposures were conducted on specimens under single ply EPDM membranes in the RTRA for over 400 days. Hourly averages of panel temperature and heat flux were analyzed to obtain K as a function of mean temperature on a week by week basis. The relative performance of test specimens of HCFC-14B under a black and under a white membrane is reported. 29 refs., 10 figs., 10 tabs.

Effect of point defects on the phonon thermal conductivity of bcc iron

The effects of low concentrations of seven different substitutional impurities on the phonon thermal conductivity of iron were determined at 300 K. Of the seven solutes, Ni caused the smallest reduction and W the greatest. The data were analyzed on the basis of Callaway’s model, and the resulting impurity scattering was compared with theory. The data show that phonon scattering from the local strain field associated with point defects is smaller than predicted from theory, but not negligible. The results are consistent with theoretical formulas that show that mass difference and lattice‐strain scattering can either reinforce or cancel.