Thermo-Electric Properties of Cu and Ni Nanoparticles Packed Beds

Abstract

The hot-wire method and the four-probe resistivity method are applied to probe the thermal conductivity (k) and the electric conductivity (σ) of Cu and Ni nanoparticle packed beds (NPBs). A fitting method based on classical physical theory is devised to separate ke (electronic thermal conductivity) and kp (phonon thermal conductivity) from k at room temperature. Results turn out that kp only accounts for a small proportion of k (4-20%); the proportion decreases with increasing porosity or temperature. Most importantly, this fitting method provides a simple way to separate ke and kp from k at room temperature. The Wiedemann-Franz law is checked and is found to be unsuitable for NPBs. The Lorenz number (L) is calculated from measurements of ke, k, and σ. Results turn out that L is found to be 50-60 times that of the bulk. With a Seebeck coefficient (S) measured, the thermoelectric property of NPBs is also calculated. We find that the NPB possess an advantage in thermoelectric property than bulk, the thermoelectric figure of merit (ZT) of Ni (Cu) NPBs can be 20.17 (1.87) times that of bulk Ni (Cu). The effect of porosity on ZT is also discussed, and results show that a NPB with a small porosity is more preferable as a thermoelectric material. With a small porosity, ZT can be even 1.73 times that of a large porosity. Although metals are not good thermoelectric material, the method in this paper supplies a way to improve the thermoelectric property of other thermoelectric materials.

Multi-Interface-Induced Thermal Conductivity Reduction and Thermoelectric Performance Improvement in a Cu–Ni Alloy

“…This phenomenon has been reported before in Cu-based compounds and composites. ,− According to the electron–gas model, the electronic thermal conductivity can be expressed as where κ B is the Boltzmann constant, m e is the electron mass, τ is the electron relaxation time, n is the concentration of carriers, and T is the absolute temperature. Lin et al proposed that the lattice thermal conductivity is almost negatively dependent on the temperature, which is higher than the Debye temperature (310 K for Cu and 403 K for Ni), that is, κ l ∝ 1/ T . Therefore, the total thermal conductivity (κ T ) can be expressed as where a and b can be obtained by fitting the experimental κ in Figure a, which is shown in Table S2.…”

“…However, the Wiedemann–Franz law fails to distinguish the contribution to total thermal conductivity (Table S1) in this work, which may be mainly attributed to the different relaxation times of phonons and electrons in our samples . This phenomenon has been reported before in Cu-based compounds and composites. ,− According to the electron–gas model, the electronic thermal conductivity can be expressed as where κ B is the Boltzmann constant, m e is the electron mass, τ is the electron relaxation time, n is the concentration of carriers, and T is the absolute temperature. Lin et al proposed that the lattice thermal conductivity is almost negatively dependent on the temperature, which is higher than the Debye temperature (310 K for Cu and 403 K for Ni), that is, κ l ∝ 1/ T .…”

High performance of carbon-particle/bulk-wood bi-layer system for solar steam generation

“…To probe the capacity of the wood to maintain heat, the dry-wood and wet-wood thermal conductivities were both measured. [34][35][36][37][38] The dry-wood thermal conductivity is about 0.37 W·m −1 ·K −1 measured by hot-wire method, [39][40][41][42] much smaller than the one of water which is about 0.60 W·m −1 ·K −1 . [43][44][45][46] The low thermal conductivity can inhibit heat transporting into the bulk water.…”

High cross‐plane thermoelectric performance of carbon nanotube sponge films

“…The main obstacle to increase ZT lies in the interrelated σ and k , thus simultaneously optimization σ and k . The low‐dimensional (two‐dimensional or one‐dimensional) materials offer a route to overcome this difficulty, because of the greatly decreased k and the approximately unchanged σ and S with respect to that of the bulk material …”

“…[3][4][5][6] The main obstacle to increase ZT lies in the interrelated σ and k, thus simultaneously optimization σ and k. [7][8][9] The lowdimensional (two-dimensional or one-dimensional) materials offer a route to overcome this difficulty, because of the greatly decreased k and the approximately unchanged σ and S with respect to that of the bulk material. [10][11][12][13][14] Thanks to the flexible mechanical strength and lightweight, the CNT-based composites have been widely explored as TE materials [15][16][17] and also other materials, such as electric heating materials 18,19 and sensing elements. 20,21 Compared with traditional TE materials based on bismuth and tellurium, CNT-based composites advanced in flexible, [22][23][24][25] while the output electric power is still too low.…”