Papers by Keyword: Transport Property

Abstract: Micro/meso scale modification can bring big changes in macroscale property. The addition of nanofillers makes materials strong, durable and multifunctional/smart. This paper aims at studying mechanical property, durability, electrical property, electromagnetic property and piezoresistivity of concrete with nanosilica (NS), carbon nanotube (CNT), botryoid hybrid carbon material (BHCBM), nanographite platelet (NGP) and nanotip material (spiky spherical nickel particles), respectively. Results demonstrate that the compressive and flexural strengths of concrete show significant increases with the increasing contents of NS. The addition of CNT obviously enhances the transport property of concrete. The BHCBM endows the excellent electrical conductivity with concrete. Both shielding effectiveness and electromagnetic wave absorbing performance of concrete can be achieved by adding NGP. The concrete with nanotip material has ultrahigh piezoresistive response to stress and strain.

Abstract: The band structures and transport properties of Half-Heusler compounds NbFeSb and NbRuSb were studied using ab initio calculations and the Boltzmann transport equation with constant scattering time approximation (CSTA). Both compounds were identified as good p-type thermoelectric materials because of the combination of heavy and light bands in the valence band maximum (VBM). The Seebeck coefficients for NbRuSb were lower than that for NbFeSb; while the electrical conductivities for NbRuSb were little higher than that for NbFeSb. Consequently, the power factors in the p-type regimes for both compounds were similar at a given temperature. NbFeSb and NbRuSb could be efficient materials for thermoelectric generators based on the results in the present investigation.

Abstract: The transport properties of microencapsulated phase change material (MPCM) suspension are helpful for selection of components in the MPCM suspension transport system. The properties of MPCM sample are investigated theoretically. Transport property of MPCM suspension, especially pressure drop in pipe system, has been identified by theoretical analysis. The experimental researches in transport capability and power consumption of MPCM suspension are investigated as well.

Abstract: The physical model and analytical method are put forward for considering the molecular interaction between solid wall and gas fluid when dealing with convective heat transfer in macro/mini/micro channels based on the boundary layer theory concept, the molecular kinetic theory of gases, structural chemistry and continuum hypothesis. The influence rule of wall-fluid intermolecular forces to the transport properties of gases located in boundary layer region is studied applying proposed models. The gas density variation distribution equation including the wall-fluid molecular interaction is derived with continuum media integral approach. The theoretical results show that the fluid diffusion is independent of the wall-fluid interaction but visosity and heat conductivity not. According to the gas molecular density distribution function and molecular dynamics, new formulae were developed for calculating viscidity coefficient and thermal conductivity with wall-fluid interacting effect for a fluid. The research results provide scientific reference for further study and exploitation on fluid flow and heat transfer of mini/micro channels. In addition, the formulae offered in this paper to compute the transport properties of gases are also suitable for fine analysis of boundary layer in macro-scale channels.

Abstract: Sr-doped LaTiO₃ (SLTO) thin epitaxial films on LaAlO₃ (100) have been fabricated by the off-axis rf magnetron co-sputtering system. The dopant Sr²⁺ ions were expected substituting La³⁺ ions in the films to introduce the hole carriers. The X-ray diffraction shows that the [001] direction of the SLTO films is perpendicular to the substrate surface. The in-situ grown specimens were measured the temperature dependence of resistivity and the Hall coefficients to study the transport properties. The Hall measurements show that the carrier is electron for Sr-doping over 16%. The temperature dependence of the resistance shows that the n-type films are metallic and deviate from free electron gas model obviously. We found the behaviour could be well described by the small-polaron coherent motion model.

Abstract: The flow behavior and viscosity of pure aluminum, zinc and Zn-7wt%Al liquids were quantified with the effects of temperature and shear rate by rotational rheometry experiments. These systems exhibited a non-Newtonian, shear thinning and non-thixotropic flow behavior where in the liquid metal viscosity decreases with increasing shear rates. The temperature dependence of viscosity followed the Arrhenius equation. Moreover, at high shear rate regimes the flow resembles a nearly Newtonian behaviour.

Abstract: First-principle calculations were performed for the study of the superconductor MgB₂ and AlB₂. The doping effect of compound Mg_1-xAl_xB₂ was analyzed by supercell method. Band structure, electronic bands structure, total and partial densities of states were calculated and analyzed in detail. Covalent bond effects (CBC) appeared in the electronic bands structure when doping Al to MgB₂. It is found that this CBC effects on Mg_1-xAl_xB₂ samples have prominent relations to superconductivity. The study of the density of state indicates that the superconductivity decreases with the increase of compound Al. In particular, there exists the transition of superconductor to non-superconductor with the change of x. The theoretical predictions agreed well with experimental measurements.

Abstract: The present paper presents the carrier-acoustic phonon scattering rate and charge transport in spherical and TMV viruses. We demonstrate theoretically that the absorption rate changes according to the phonon energy while emission of phonon is limited by the both electron and hole energy. The obtained conductivity for spherical and TMV viruses suggest that the TMV virus is more conducting and therefore may be a good candidate for the connector or wire to be used in the nano- and molecular- electronics . The value of resistance obtained for TMV virus is lower than the resistance of DNA.

Abstract: For more than a decade, skutterudites such as cobalt antimonides have been widely studied as a promising thermoelectric (TE) material for high-temperature applications. High thermoelectric figure of merit (ZT) in this material system can be achieved by suitable doping or by filling the interstitial voids with guest atoms. One of the best improvements in ZT is reported when indium (In) is used as additive to cobalt-antimonide skutterudites, as has been done in this study. Compaction of the grinded powders was carried out by a current-assisted short-term sintering device, which significantly reduces the process time in comparison to conventional hot pressing. Phase homogeneity of the bulk material has been probed by X-ray powder diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX). TE properties (i.e. electrical conductivity, Seebeck coefficient and thermal conductivity) have been analyzed in the temperature range from 300 K to 700 K. The functional homogeneity of the samples was screened by the Potential & Seebeck Microprobe (PSM). Adapted from these results the effect of indium addition to short-term sintered cobalt-antimonide based skutterudites with absence of impurity phases will be discussed.

Abstract: Thermoelectric and galvanomagnetic properties for solid solution based on bismuth and antimony chalcogenides were studied for the optimal compositions and carrier concentrations in the temperature interval 100-240 K. Galvanomagnetic properties were analyzed in the framework of the many–valley energy spectrum model with isotropic and anisotropic scattering of charge carries. The figure-of-merit is shown to be determined with optimal relations between the values of the density-of-states effective mass, the carrier mobility taking into account degeneration of charge carriers, and the lattice thermal conductivity. The figure-of-merit also depends on anisotropy of the constant energy surface and scattering mechanism. Average values of the figure-of-merit through the temperature interval 100-240 K are equal to (2.5-2.65) 10-3 K1 for optimal compositions and carrier concentrations.