Bi 2 Te 3 compound has been shown to exhibit the highest thermoelectric figure of merit at 573 K to 673 K. Bi 2 Te 3 samples were synthesized by mechanical alloying (MA) followed by spark plasma sintering (SPS) in this work. The effects of the milling and SPS parameters as well as the specimen thickness were evaluated to obtain the best microstructural and thermoelectric properties. To synthesize Bi 2 Te 3 , Bi and Te powders were mechanically alloyed under argon atmosphere in a stainless-steel vial with a ball-to-powder weight ratio of 15:1 for different durations. The synthesized powders were then sintered using SPS at different temperatures. To characterize the Bi 2 Te 3 powders and bulk samples, x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) analysis were applied. Furthermore, the bandgap energy was measured by ultraviolet-visible (UV-Vis) spectroscopy. Moreover, the Seebeck voltage and electrical conductivity were determined at different temperatures. The experimental results illustrate that, by enhancing the sintering temperature from 623 K to 673 K, the maximum Seebeck coefficient was increased from 136 lV/K to 156 lV/K. To investigate the effect of thickness, specimens were sintered at the optimum temperature of 673 K with thicknesses of 1 mm, 1.5 mm, 2 mm, 3 mm, and 4 mm. The results showed that, by decreasing the thickness, the maximum Seebeck coefficient was increased from 144 lV/K to 166 lV/K while the electrical conductivity was increased from 0.35 9 10 5 S/m to 1.42 9 10 5 S/ m, resulting in an increase in the power factor from 0.76 mW/m-K 2 to 3.94 mW/m-K 2 .
Herein, a powder compacting method was developed to fabricate high porosity micro-and macrocellular copper foams using CaCO 3 space holder. The cold compacted precursors were heated at different temperatures under the nitrogen atmosphere. The effects of precursor compaction pressure, space holder content and sintering temperature on cell microstructure, relative density, compressive and physical properties were investigated. The scanning electron microscopy (SEM) images showed a uniform distribution of interconnected pores with sizes of pores and channels less than 50 microns formed the semi-open cell structure of the fabricated foams. The evaluation of the foaming agent content, 0 to 20 (wt%), in precursor materials showed relatively large changes in the porosity percentage (27%-50%), with the utilitarian strength (43 MPa) and densification strain (40%) of the copper foams. For specimens having 20 wt% CaCO 3 , tuning the sintering temperature (600°C) and compacting pressure (500 MPa) of precursors tailored superior porosity percent (47%), remarkable compressive stress (501 MPa) and high thermal (43.8 W m −1 .k), and electrical conductivity (0.06×10 8 Ω −1 m −1 ) owing to a desirable foaming process. A massive gas release during the CaCO 3 decomposition and the strengthened cell walls of the copper foams during the sintering resulted in the high porosity and strength of the fabricated foams. The presented fabrication method and our results are the core elements for the development of new high porosity metal foams that can help the development of the future application of copper foams for a long-life anode for lithium-ion batteries, catalysis, and thermal and electrical performances as electronic cooling materials.
In the present study high energy ball mill has been conducted to produce Al matrix composite reinforced with silicon carbide (SiC) at different milling time. To evaluate the role of stearic acid content on powder morphology of Al-SiC composite, the material has been fabricated with different stearic acid content, namely 0?1, 0?5, 1 wt-%. The SEM micrographs taken from Al-SiC composite powder show that the size of composite powders depends strictly on both stearic acid content and milling time. At constant milling time the smaller particles have been observed as well as SiC content increases with increasing stearic acid content. The uniformity of composite powders was so much better as stearic acid content increases.
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