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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 effects of temperature, purity, magnetic state, and crystal structure on the thermal conductivity, electrical resistivity, and Seebeck coefficient of iron were obtained from measurements on Armco iron (99.5% pure, ρ300/ρ4.2=11.0) and a high-purity iron (99.95% pure, ρ300/ρ4.2=26.2). The most probable determinate errors of the measurements were thermal conductivity ±1.5%, electrical resistivity ±0.1%, and Seebeck coefficient ±0.9%; and larger absolute errors. Where theory permits, the thermophysical properties of iron are discussed in terms of contributing transport mechanisms. The thermal conductivity of iron can be calculated to ±1.5% between 0° and 910°C from electrical-resistivity measurements and the lattice portion of the thermal conductivity determined in this study.

The thermal conductivities, h, of single-crystal and polycrystalline UO, were measured from 80" to 420°K. The results indicate no observable difference in h between single-crystal and polycrystalline UO,, and both materials have broad peaks in x a t ~2 2 0°K . The results were used with literature values to determine the effect of closed porosity on A. The thermal conductivity of theoretically dense UO, is described phenomenologically from 80" to 140O0K, where conduction is dominated by the phonon component. The phonon conduction is analyzed by comparison with Tho,. This analysis indicates that the high-temperature x is limited by 3-phonon Umklapp scattering processes. Scattering by the disordered spins associated with the paramagnetic U ions contributes a large temperatureindependent phonon scattering term. This mechanism has a mean free path of about 51 A, which implies that grain boundaries and impurities have a relatively insignificant effect on the phonon conduction far above the antiferromagnetic-paramagnetic transition a t -30°K. This implication agrees with the experimental results.

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