Thermal Conductivity, Electrical Resistivity, and Seebeck Coefficient of Uranium Mononitride

Measurements are reported for the thermal conductivity, λ(80° to 400°K), electrical resistivity, ρ(4.2° to 400°K), and absolute Seebeck coefficient, Q(6° to 400°K), of pressed and sintered uranium mononitride. The measurements between 77° and 400°K were made using an absolute longitudinal heat flow apparatus. These data and literature values for the thermal conductivity and electrical resistivity at higher temperatures were used to separate the electronic and lattice portions of the thermal conductivity. The results indicate that the lattice conductivity peaks in the range 250° to 300°K and that the high-temperature limit of the Lorenz function may be greater than the Sommerfeld value of 2.443 × 10^-8 (V^2°K^-2). The electrical resistivity and the absolute Seebeck coefficient exhibit sharp slope changes near the Néel temperature, T _N(∼50° to 60°K). The Seebeck coefficient has a minimum at 34°K and then rises to a local maximum at 10°K. This low-temperature peak is probably due to magnon drag. The temperature dependence of the electrical resistivity is dominated by the magnetic contribution which increases as T ^2.38±0.08 between 10° and 52°K. The magnetic contribution is constant at high temperatures with an estimated value of 142 μΩ-cm.     

Monoxide-Type Compounds of Uranium and Plutonium: I, Oxycarbides

Oxycarbides having the face-centered cubic MO-type structure were formed by the controlled reduction of mixtures of PuO₂ and UO₂ in helium and in vacuum. Carbon, UC, and U were used as reducing agents. Carbon appeared to be necessary to stabilize the monoxide structure. The maximum oxygen content for essentially single-phase (U_0.9Pu_0.1)(O _x C_{1- x} ) is x = 0.4. Oxycarbide compositions with higher oxygen contents (approaching x = 0.6) can be produced but these products are multiphase containing appreciable quantities of a dioxide, MO_{2- x} in carbon reduction, and MO_{2- x} plus metal in U plus UC reduction. The single-phase oxycarbides lack sufficient water-corrosion resistance to be used as fuels in water-cooled reactors; however, their thermal conductivity appears to be higher than that of the dioxide fuels.     

Synthesis of Sintered Diamond with High Electrical Resistivity and Hardness

Diamond and diamond-ultrafine Co powder mixtures were sintered at 7.7 GPa and 1800° to 2000°C. A well-sintered body with a fine-grained homogeneous microstructure, high hardness, and high electrical resistivity was produced when a diamond-5 vol% Co powder mixture was used as the starting material.     

Thermal Conductivity and Electrical Resistivity of Cemented Transition-Metal Carbides at Low Temperatures

The thermal conductivity, K , and electrical resistivity, ρ, of cemented transition-metal carbides—a class of composites of high toughness—were measured for the first time at cryogenic temperatures. The dependence of these quantities on composition, grain size, and binder content was explored. The major qualitative findings are the following: (1) K for WC/Co grades has a gentle maximum ranging from 80 to 160 W/(m · K) around 150 K; (2) WC/Co has higher values of K and lower values of ρ than TiC _x /NiMo, because of vacancy scattering of electrons and phonons in the latter; (3) grades with larger grains have higher values of K ; (4) grades with higher percentages of binder phase have lower values of K ; (5) the lattice and electronic components of K are comparable for TiC _x /NiMo; (6) multicarbide grades have lower values of K than WC/Co; (7) a Callaway analysis of the lattice component of K identifies scattering of phonons by grain boundaries, point defects, electrons, and other phonons as significant for these materials, with defect scattering dominating in the liquid-nitrogen range.     

Electrical Resistivity of Composites

Percolation and Bruggeman's effective media theories, as they apply to the electrical conductivity of composites, are reviewed, and a general effective media (GEM) equation, which combines most aspects of both percolation and effective media theories, is introduced. It is then shown that the GEM equation quantitatively fits electrical resistivity (conductivity) as a function of the volume fraction data for binary composites. The parameters used to fit the experimental data are the electrical resistivities of the two phases, the percolation threshold for the lower resistivity phase (ô _c ), and an exponent t. Preliminary work, showing how the GEM equation can be used to model the piezoresistivity of composites by postulating that ô _c is a function of the independent variable, is also presented.     

Electrical Resistivity of Refractories

Electrical resistivity was measured on commercially available materials, including high-alumina, magnesia, magnesia-chrome, zircon, and stabilized-zirconia refractories, at temperatures to 2650°F. The tests were made using two-, three-, and four-terminal measurements and the results are discussed. The four-terminal measurements were made by a new method.     

Electrical Resistivity of Titanium-Containing Glasses

Titanium-containing glasses were prepared by fusion of a base glass (BaO·B₂O₃SiO₂) and TiO₂ and/or Ti₂O₃ in Ar. Their resistivities did not vary with melting time and temperature. Interaction of Ti⁴⁺ and Ti³⁺ in the glasses was deduced by spectroscopy, but the valence states in the batch compositions were preserved in the glasses, according to the chemical analysis. Glasses containing either Ti⁴⁺ or Ti³⁺ had very high resistivities, whereas the glass prepared by melting a mixture of a Ti⁴⁺-containing and a Ti³⁺-containing glass had much lower resistivity. All results confirmed the possibility of controlling the resistivity by batch composition for these glasses.     

A Phenomenological Theory of Thermal Diffusivity

Refractories and Industrial Ceramics -     

Electrical Resistivity of Coal and Oil Shales

The physicochemical properties of coal and oil shales are compared: specifically, the ash content, moisture content, porosity, and yield of volatiles. The electrical resistivity of the oil shales, lignite, and coal is compared, as a function of the temperature. On account of their large content of volatiles, lignite and oil shales are characterized by similar electrical resistivity.     

Electrical Conductivity of Uranium Dioxide

The electrical conductivity of nearly stoichiometric single-crystal and polycrystalline uranium dioxide was measured from room temperature to 3000°K. Below approximately 550°K, the curve of log σ versus T ⁻¹ is linear with a calculated activation energy of approximately 0.17 ev. Between 550° and 1250°K, however, the shape of the curve changes; this change varies from one specimen to another. The electrical conductivity increases rapidly with increasing temperature above 1250°K with a change from p -type to n -type conduction. The best linear fit of the log σ versus T ⁻¹ curve above 1400°K is σ= 3.57 × 10³ e ^{−(1.15 ev/KT)}. Above 1900°K, the curve deviates slightly from linearity and is best fit by the equation σ= 2.10 × 10⁻² T ^1.4 e ^{−(0.916 ev/KT)}.     

Sintering and Hot Pressing of Uranium Tetrafluoride

The basic sintering and hot-pressing conditions have been established for UF₄. Either sintering of cold compacted material in argon or direct hot pressing in graphite dies can be used satisfactorily to obtain high-bulk-density compacts. Vacuum sintering is ruled out because of the volatility of the UF₄. The occurrence of black localized areas in both sintered and hot-pressed material is attributed to the internal distortion of fluorine atoms into lattice voids resulting in the formation of strained areas.     

Effect of Impurity and Carrier Concentrations on Electrical Resistivity and Thermal Conductivity of Sic Ceramics Containing BeO

Silicon carbide ceramics with BeO as an additive exhibit unusually high electrical resistivity and thermal conductivity compared to conventional SiC ceramics. Studies concerning the effects of carrier concentration in the SiC grains on electrical properties and thermal conductivity are described. The low carrier concentration in this ceramic is responsible for the high electrical resistivity. The thermal conductivity, however, decreases gradually with increasing impurity concentration.     

Compressive Creep and Hot Hardness of U-Pu Carbides

The compressive creep of carbides having the composition U_0.79Pu_0.21C_1.02 and a sintered density of 11.8 g/cm³ was studied at 1300°, 1400°, and 1500°C and stresses of 2000, 4000, and 6000 psi. The equation which best fitted the data was
   
The dominant creep mechanism was probably grain-boundary sliding. The hardness of monocarbides with various U/Pu ratios was measured from room temperature to 1200°C. Probable mechanisms of deformation are discussed.     

高膨胀系数、低软化温度、高电阻率无铅微晶封接玻璃的研发

介绍了高膨胀系数(α)、低软化温度(Tf,俗称熔点)、高电阻率(ρ)无铅微晶封接玻璃的发展和研究现状。分析了元素周期表中Pb对角线及其邻近元素的氧化物在玻璃中替代PbO的可能性,探讨了富含常见玻璃生成体氧化物、有条件形成玻璃氧化物的无铅微晶封接玻璃。详细讨论了富含Bi2O3微晶封接玻璃的成分设计、制备工艺、主要性质和产品开发情况。得到如下结论:富含PbO的微晶封接玻璃能获得高α、低Tf和高ρ;但因其对环境有害已逐渐被法律所禁止。富含玻璃生成体SiO2、P2O5、B2O3、As2O3、GeO2或Sb2O3系统的无铅微晶封接玻璃,或因其不能同时兼顾高α、低Tf、高ρ(如SiO2、P2O5或B2O3),或因该氧化物的毒性(如As2O3)、成本高(如GeO2),或因其制备条件苛刻(如Sb2O3),而应用受限。有条件玻璃生成体Al、V、Te、Mo、Se和Ti的氧化物中,富含Al2O3的玻璃因α低和Tf高而未发现有作为无铅微晶封接玻璃主要成分的相关报道;其他或者因其毒性(如V2O5)、成本高(如Te、Mo或Se的氧化物)等,不适合作为家用电器电热管用的金属-金属间封接;含TiO2的玻璃因极易析晶及α低而未发现有作为无铅微晶封接玻璃主要成分的相关报道。富含元素周期表中Pb对角线及其邻近元素Sn、In、Tl或Bi氧化物的无铅微晶封接玻璃,或因制备工艺苛刻(如SnO),或因该氧化物的毒性(如Tl2O3)、成本高(如In2O3)而应用受限;富含Bi2O3的无铅微晶封接玻璃,无毒且同时兼具高α、低Tf、高ρ的特点,适用于家用电器中金属-金属间的封接。     

Electrical Resistivity of Titanium Diboride and Zirconium Diboride

The electrical resistivities of hot-pressed samples of Ti_{1- x} Zr _x B₂ ( x = 0.0, 0.3, 0.5, 0.7, 1.0) were measured by a four-point ac technique over the range 298 to 1573 K in an argon atmosphere. The hot-pressed samples for the intermediate compositions were found to be mixtures of two solid-solution phases. The resistivities for all compositions were found to increase linearly with temperature and can be described by ρ( T ) =ρ₂₉₈+φ( T - 298). The room-temperature resistivity ρ298 (μΩ cm) and the temperature coefficient of resistivity φ (nΩ·cm/K) for ZrB₂ were determined to be 7.8 and 10, both of which increase with the content of TiB₂. These values for TiB₂ were determined to be 20.4 and 36, respectively.     

Hot Hardness Behavior of Yttrium Sialon Ceramics

The hot hardness of polycrystalline single-phase α- or β- sialon ceramics declines with increasing temperature, but the measured Vickers hardness (HV1) at 1100°C is still about 1550 and 1300 for the α-sialon and the low-substituted β-sialon materials, respectively. The hardness of 'composite'β- or α-β-sialon ceramics containing a high volume fraction of glassy phase is lower at all temperatures and drops significantly above about 900°C.