Effects of Heat Treatment on Thermal Conductivity of Highly Porous Copper/Silver Systems

2007 ◽  
Author(s):  
Brian A. Murtha ◽  
Anil K. Kulkarni ◽  
Jogender Singh
Keyword(s):  
Thermal Conductivity ◽  
Heat Treatment ◽  
Porous Material ◽  
Grain Boundaries ◽  
Phonon Scattering ◽  
Particle Diffusion ◽  
Conductive Heat ◽  
Material Particle ◽  
Highly Porous ◽  
Highly Porous Material

The phenomenon of sintering has a significant impact on the thermal conductivity of a highly porous material. Particle diffusion greatly reduces the number of grain boundaries that are normally present in porous materials. In turn, fewer grain boundaries imply fewer sites for phonon scattering during conductive heat transfer. Therefore, during heat treatment of a highly porous material, particle diffusion accounts for a changing thermal conductivity. This occurs with no bulk densificiation of the material. In fact, SEM images show that the microstructure of a porous material changes from many individual particles with small pores between the particles to diffused particles with large pores in between large chunks of material. To model such a phenomenon, standard equations were scaled with unitless weighting functions to account for variable microstructures during heating. By weighting standard equations, the effects of microstructure could be more accurately described as a function of porosity and time.

Thermal Conductivity Measurements of Gas Diffusion Layer Under Controlled Temperature, Humidity and Stress

2009 ◽  
Author(s):  
Jun-ichi Miyamoto ◽  
Junpei Ooyama ◽  
Yoshiaki Yamamoto
Keyword(s):  
Thermal Conductivity ◽  
Porous Material ◽  
Diffusion Layer ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Conductivity Measurements ◽  
Anisotropic Thermal Conductivity ◽  
Plane Direction ◽  
Highly Porous ◽  
Highly Porous Material

In this work, thermal conductivities of gas diffusion layer (GDL) under controlled temperature, humidity and stress are measured. Additionally, we investigated the anisotropic thermal conductivity of GDLs. The experimental results showed that thermal conductivity of in-plane direction was much higher than that of trough-plane direction for all the samples that were measured. This result indicated thermal conductivity of GDLs to be strongly anisotropic since GDL is a highly porous material which contains large amount of air inside the GDL. Moreover, we found that thermal conductivity of GDL in the through-plane direction increased as the compression on the GDL was increased.

scholarly journals Hierarchically structured, highly porous nickel synthesized in sintering–evaporation process from a metal nanopowder and a space holder

2019 ◽  
Vol 484 (4) ◽  
pp. 436-440
Author(s):  
A. G. Gnedovets ◽  
V. A. Zelenskii ◽  
A. B. Ankudinov ◽  
M. I. Alymov
Keyword(s):  
Powder Metallurgy ◽  
Porous Material ◽  
Ammonium Bicarbonate ◽  
Evaporation Process ◽  
Porous Nickel ◽  
Space Holder ◽  
Nickel Nanopowder ◽  
Powder Metallurgy Methods ◽  
Highly Porous ◽  
Highly Porous Material

This paper reports on the creation of a highly porous material with a hierarchical structure using powder metallurgy methods based on nickel nanopowder and ammonium bicarbonate NH4HCO3 as a space holder.

scholarly journals Effect of ZnO and SnO2 Nanolayers at Grain Boundaries on Thermoelectric Properties of Polycrystalline Skutterudites

Nanomaterials ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 2270
Author(s):  
Sang-il Kim ◽  
Jiwoo An ◽  
Woo-Jae Lee ◽  
Se Kwon ◽  
Woo Nam ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Atomic Layer Deposition ◽  
Grain Boundaries ◽  
Thermoelectric Properties ◽  
Phonon Scattering ◽  
Atomic Layer ◽  
Deposition Method ◽  
Plasma Sintering ◽  
Layer Deposition ◽  
Atomic Layer Deposition Method

Nanostructuring is considered one of the key approaches to achieve highly efficient thermoelectric alloys by reducing thermal conductivity. In this study, we investigated the effect of oxide (ZnO and SnO2) nanolayers at the grain boundaries of polycrystalline In0.2Yb0.1Co4Sb12 skutterudites on their electrical and thermal transport properties. Skutterudite powders with oxide nanolayers were prepared by atomic layer deposition method, and the number of deposition cycles was varied to control the coating thickness. The coated powders were consolidated by spark plasma sintering. With increasing number of deposition cycle, the electrical conductivity gradually decreased, while the Seebeck coefficient changed insignificantly; this indicates that the carrier mobility decreased due to the oxide nanolayers. In contrast, the lattice thermal conductivity increased with an increase in the number of deposition cycles, demonstrating the reduction in phonon scattering by grain boundaries owing to the oxide nanolayers. Thus, we could easily control the thermoelectric properties of skutterudite materials through adjusting the oxide nanolayer by atomic layer deposition method.

scholarly journals Revisiting Soil Aquifer Treatment: Improving Biodegradation and Filtration Efficiency Using a Highly Porous Material

Water ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 3593
Author(s):  
Joshua Brooks ◽  
Noam Weisbrod ◽  
Edo Bar-Zeev
Keyword(s):  
Porous Material ◽  
Urban Areas ◽  
Water Reuse ◽  
Filtration Efficiency ◽  
Natural Material ◽  
Soil Aquifer Treatment ◽  
Bacterial Phyla ◽  
Custom Made ◽  
Highly Porous ◽  
Highly Porous Material

Soil aquifer treatment (SAT) is an established and sustainable wastewater treatment approach for water reuse that has been gaining increased attention in various countries around the world. Increasing volumes of domestic wastewater and escalating real estate prices around urban areas emphasize the urgent need to maximize the treatment efficiency by revisiting the SAT setup. In this study, a novel approach was examined to increase biodegradation rates and improve the quality of SAT topsoil effluent. Experiments with midscale, custom-made columns were carried out with sand collected from an operational SAT and a highly permeable natural material with high internal porosity, tuff, which was maturated (i.e., buried in the SAT infiltration basin) for 3 months. The filtration efficiency, biodegradation rates of organic material, microbial diversity, and outflow quality were compared between the operational SAT sand and the tuff using state-of-the-art approaches. The results of this study indicate that biodegradation rates (9.2 µg C g−1d−1) and filtration efficiency were up to 2.5-fold higher within the tuff than the SAT sand. Furthermore, the biofilm community was markedly different between the two media, giving additional insights into the bacterial phyla responsible for biodegradation. The results highlight the advantage of using highly porous material to enhance the SAT filtration efficiency without extending the topsoil volume. Hence, infusing a permeable medium, comprising highly porous material, into the SAT topsoil could offer a simple approach to upgrade an already advantageous SAT in both developed and developing countries.

scholarly journals Thermal transport in nanocrystalline Si and SiGe by ab initio based Monte Carlo simulation

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Lina Yang ◽  
Austin J. Minnich
Keyword(s):  
Thermal Conductivity ◽  
Monte Carlo ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Thermal Transport ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Computational Study ◽  
Phonon Transport ◽  
Nanocrystalline Si

Abstract Nanocrystalline thermoelectric materials based on Si have long been of interest because Si is earth-abundant, inexpensive, and non-toxic. However, a poor understanding of phonon grain boundary scattering and its effect on thermal conductivity has impeded efforts to improve the thermoelectric figure of merit. Here, we report an ab-initio based computational study of thermal transport in nanocrystalline Si-based materials using a variance-reduced Monte Carlo method with the full phonon dispersion and intrinsic lifetimes from first-principles as input. By fitting the transmission profile of grain boundaries, we obtain excellent agreement with experimental thermal conductivity of nanocrystalline Si [Wang et al. Nano Letters 11, 2206 (2011)]. Based on these calculations, we examine phonon transport in nanocrystalline SiGe alloys with ab-initio electron-phonon scattering rates. Our calculations show that low energy phonons still transport substantial amounts of heat in these materials, despite scattering by electron-phonon interactions, due to the high transmission of phonons at grain boundaries, and thus improvements in ZT are still possible by disrupting these modes. This work demonstrates the important insights into phonon transport that can be obtained using ab-initio based Monte Carlo simulations in complex nanostructured materials.

EFFECT OF EMBEDDING NANOPARTICLES ON THERMAL CONDUCTIVITY OF CRYSTALLINE SEMICONDUCTORS: PHONON SCATTERING MECHANISM

2009 ◽  
Vol 08 (06) ◽  
pp. 551-556 ◽  
Author(s):  
K. K. CHOUDHARY ◽  
D. PRASAD ◽  
K. JAYAKUMAR ◽  
DINESH VARSHNEY
Keyword(s):  
Thermal Conductivity ◽  
Grain Boundaries ◽  
Lattice Thermal Conductivity ◽  
Present Model ◽  
Phonon Scattering ◽  
Scattering Mechanism ◽  
Temperature Dependent ◽  
Pure Crystal ◽  
Model Hamiltonian ◽  
Heat Carriers

We evolve a theoretical model for quantitative analysis of decrease in thermal conductivity (κ) by embedding ErAs nanoparticles in In0.53Ga0.47As crystalline semiconductors. The lattice thermal conductivity by incorporating the scattering of phonons with defects, grain boundaries, electrons, and phonons in the model Hamiltonian are evaluated. It is noticed that the ErAs nanoparticles provide an additional scattering mechanism for phonons. The embedding of ErAs nanoparticles in In0.53Ga0.47As crystalline semiconductors, the phonon scattering with point defects and grain boundaries become more efficient, which cause in the decrease of thermal conductivity up to half of its value of pure crystal. Conclusively, the temperature dependent of thermal conductivity is determined by competition among the several operating scattering mechanisms for the heat carriers. Numerical analysis of thermal conductivity from the present model shows similar results as those revealed from experiments.

Effects of heat treatment and sintering additives on thermal conductivity and electrical resistivity in fine-grained SiC ceramics

2002 ◽  
Vol 17 (9) ◽  
pp. 2327-2333 ◽  
Author(s):  
Guo-Dong Zhan ◽  
Mamoru Mitomo ◽  
Amiya K. Mukherjee
Keyword(s):  
Thermal Conductivity ◽  
Heat Treatment ◽  
Electrical Resistivity ◽  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Laser Flash ◽  
Sintering Additives ◽  
Fine Grained ◽  
Resolution Electron ◽  
Thermal And Electrical Properties

The effects of heat treatment and sintering additives on the thermal conductivity and electrical resistivity of fine-grained SiC materials were investigated. The thermal conductivity and the electrical resistivity of dense SiC materials were measured at room temperature by a laser flash technique and a current-voltage method, respectively. The results indicated that the thermal conductivity and electrical resistivity of the SiC materials were dependent on the sintering additives and the resultant microstructure. Annealed materials with oxide additives developed microstructures consisting of elongated grains of various α/β–SiC polytypes. In contrast, annealed materials with oxynitride additives had microstructures consisting of fine equiaxed grains entirely of β–SiC phase. For the annealed materials with oxide additives the observed thermal conductivity was over 110 W/mK. For the annealed materials with oxynitride additives the observed value was 47 W/mK. The electrical resistivity of a hot-pressed material with oxide sintering additives decreased after annealing. For annealed materials with oxynitride additives, the electrical resistivity was even lower. High-resolution electron microscopy revealed a thin amorphous phase along the grain boundaries. Energy dispersive x-ray spectroscopy results showed that there was segregation of both Al and O atoms and a very small amount of Y atoms at grain boundaries. The results indicated that the chemistry and structure of the grain boundary has significant influence on thermal and electrical properties in SiC.

Thermoelectric Properties of AgBiTe2-Ag2Te Composite

1998 ◽  
Vol 545 ◽  
Author(s):  
Y. Takigawa ◽  
T. Imoto ◽  
T. Sakakibara ◽  
K. Kurosawa
Keyword(s):  
Thermal Conductivity ◽  
Composite Materials ◽  
Grain Boundaries ◽  
Thermoelectric Properties ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Lattice Vibrations ◽  
Thermoelectric Devices ◽  
Long Wavelength ◽  
Prepared Composite

AbstractWe prepared composite materials of AgBiTe2 with several contents of Ag2Te small-size grains for applications to thermoelectric devices. By enhancing long-wavelength phonon scattering at the grain boundaries, lattice thermal conductivity (thermal conductivity due to lattice vibrations) decreased 30% and thus the thermoelectric characteristics were significantly improved.

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