Effective thermal conductivity and electrical conductivity of anisotropic solids of low porosity

Equations are derived to determine the effective thermal and electrical conductivities of anisotropic media of low porosity. The influence of porosity on the thermal and electrical conductivities of anisotropic ternary alloys is established.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 4, pp. 686–692, April, 1976.     

Eddy current measurements of the conductivity of low-conductance composition materials

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 39–41, October, 1990.     

Resistance network-based thermal conductivity model for metal foams

A network model for the estimation of effective thermal conductivity of open-celled metal foams is presented. A nodal network representation of three aluminum foam samples from DUOCEL – 10 ppi, 20 ppi and 40 ppi – is constructed out of X-ray microtomography data obtained by computed tomography (CT) scanning of the samples using a commercial CT scanner. Image processing and 3D skeletonization are performed with commercially available image processing software. The effective thermal conductivity is estimated through a 1D conduction model, representing individual ligaments as an effective thermal resistance using the topological information from the scan data. The effective thermal conductivity data thus obtained are compared with the Lemlich theory and other pore-based models. Further, microstructural characterization of foam features – pore size, ligament thickness, ligament length and pore shapes – is performed. All the three foam samples are observed to have similar pore shapes and volumetric porosity, while the other features scale with the pore size. For a given porosity the computed permeability is found to scale as the square of the pore diameter, as also noted by previous researchers.     

Direct current electrical conductivity of gamma ferric oxide

The study of the direct current electrical conductivity, , of freshly prepared -Fe₂O₃ and that of a sample stored for seven days in static air suggests that -Fe₂O₃ adsorbs oxygen and water from the atmosphere. From infra-red spectra it is deduced that the absorbed water in -Fe₂O₃ is present as the physically adsorbed water and as lattice water. The adsorbed oxygen and physically adsorbed water are removed by heating to 100 C, while the lattice water remains in -Fe₂O₃ even up to 280 C. The removal of lattice water is associated with a decomposition during which some of the hydrogen formed occupies the vacancy sites. This suggested formation of the hydrogen ferrite phase is based on the kink in the log against T ^–1 curve observed at 177 C. This kink is very well resolved for a sample equilibrated at 100 C in normal atmosphere, and the measurements of above 100 C of this sample are done in an N₂ atmosphere. The suggestion that the hydrogen ferrite phase is formed has been substantiated by comparison of the X-ray diffraction patterns of -Fe₂O₃ heated under the different atmospheres. From the log against T ^–1 plot for a sample heated under a nitrogen atmosphere the activation energy is small (< 0.05 eV) up to 215 C, and it is comparatively large (0.95 eV) above 215 C. These results suggest a hopping mechanism for the direct current electrical conductivity of -Fe₂O₃. This suggestion has been substantiated by data of the temperature variation of Seebeck voltage.     

Direct current electrical conductivity of silver-thermosetting polyester composites

The electrical conduction of composites made from unsaturated polyester with silver powder and silver-coated glass spheres is investigated. The samples are generally nonohmic and exhibit switching effects. There is a noted difference in the threshold concentrations for the two types of samples. It is also found that electrical current is conducted via discrete paths.     

Temperature dependence of the electrical conductivity of Salicylaldazinate metal chelates

A study of the temperature dependence of the electrical conductivity of Salicylaldazine and its metal complexes with the d-block elements Ni²⁺, Cu²⁺ and Zn²⁺, is correlated with molecular spectral data. The values of the activation energies obtained from the electrical conductivity measurements, as well as the energy gaps corresponding to the maximum absorption wavelengths in the region of ultraviolet and visible spectra, indicate the important role of chelation in producing the Salicylaldazine semiconducting properties.     

Some steady-state problems in thermal conductivity for a thin metal wire heated by an electrical current

Analysis is made of steady-state problems in thermal conductivity for a thin metal wire heated by an electrical current, including consideration of the temperature dependence of the thermophysical properties of the wire material and of the conditions for heat transfer with the surrounding medium.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 5, pp. 886–894, May, 1977.     

Reconstructing electrical conductivity profiles from variable-frequency eddy current measurements

A method for reconstructing radially varying conductivity profiles in cylindrical conductors is described. Solenoidal driving and sensing coils surround the cylindrical sample and an AC magnetic field applied by the driving solenoid induces axisymmetric eddy currents in the sample. It is shown how a radially varying conductivity profile can be recovered from measurements of the complex impedance recorded as a function of frequency, where impedance here is defined as the ratio of the induced electromotive force (EMF) in the sensing coil to the current in the driving coil. An iterative nonlinear least-squares algorithm is employed to reconstruct the profiles. Demonstrations of the reconstruction method are presented based on both simulated and experimentally recorded impedance data.     

Analytical expression for the total electrical conductivity of unannealed and annealed metal films

Previous studies have shown that the Cottey function constitutes an alternative formulation for the Fuchs-Sondheimer size-effect function, provided that a new parameter is used. This result is used for calculating the effects of scattering at a grain boundary, and a good agreement with the Mayadas-Shatzkes model is found. When background, grain-boundary and external-surface scattering are simultaneously operative, a simple analytical expression for the electrical conductivity of polycrystalline, monocrystalline and columnar metal films can be obtained in the whole experimental domain and may conveniently replace the sophisticated expression of Mayadas and Shatzkes. This expression is similar to that obtained in the framework of the multidimensional models, previously presented. No limitation exists in the value of the electronic specular reflection coefficient, and the theoretical expression is related both to annealed and unannealed films.     

In-situ electrical conductivity measurement of oxidation of tin nanocluster film

An in-situ electrical conductivity measurement of thin films of tin oxide nanoclusters for nano-devices was performed during metal cluster deposition and subsequent oxidation. From the current observation, the percolation threshold and the oxidation process are suggested. During baking at 200 degrees C, tin nanoclusters were transformed into low-conductivity stannous oxide and then into high-conductivity stannic oxide. From electron micrographs, it is suggested that the baking procedure is responsible for changing the oxide state and/or the crystallinity of the individual nanoclusters rather than changing the morphology of the film.     

Thermo-plasticity of metal foams

The thermo-mechanical behaviour of a fluid-filled metal foam is influenced by the characteristics of the solid skeleton and the pore-fluid. During the deformation process both constituents exchange momentum and energy. Based on the theory of porous media a fluid-filled foam is modeled as a binary mixture consisting of a metal skeleton and a pore-gas. The porous solid skeleton is assumed to behave thermo-elasto-plastically. The pore-gas is considered as an ideal gas. For both constituents different phase temperatures and thermo-mechanical coupling mechanisms are taken into account. The resulting system of differential equations is solved using the finite element method. An example demonstrates the applicability and validity of this approach.