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1
Content available Effect of Milling Time Parameter on the Microstructure and the Thermoelectric Properties of n-Type Bi2Te2.7Se0.3 Alloys
Sharief P., Madavali B., Koo J. M., Kim H. J., Hong S., Hong S.-J.
Archives of Metallurgy and Materials
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2019
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Vol. 64, iss. 2
585-590
EN
Nanostructured thermoelectric materials receiving great attention for its high thermoelectric performance. In this research, nanostructured n-type Bi2 Te2.7 Se0.3 alloys have prepared using high energy ball milling and followed by spark plasma sintering. Also, we have varied ball milling time to investigate milling time parameter on the thermoelectric properties of n-type Bi2 Te2.7 Se0.3 powder. The powders were discrete at 10 min milling and later particles tend to agglomerate at higher milling time due to cold welding. The bulk fracture surface display multi-scale grains where small grains intersperse in between large grains. The maximum Seebeck coefficient value was obtained at 20-min milling time due to their lower carrier density. The κ values were decreased with increasing milling time due to the decreasing trend observed in their κL values. The highest ZT of 0.7 at 350 K was observed for 30-min milling time which was ascribed to its lower thermal conductivity. The Vickers hardness values also greatly improved due to their fine microstructure.
2
Content available Investigation of the Microstructure and Thermoelectric Properties of P-Type BiSbTe Alloys by Usage of Different Revolutions Per Minute (RPM) During Mechanical Milling
Yoon S.-M., Madavali B., Yoon Y.-N., Hong S.-J.
Archives of Metallurgy and Materials
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2017
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Vol. 62, iss. 2B
1167--1171
EN
In this work, p-type Bi0.5Sb1.5Te3 alloys were fabricated by high-energy ball milling (MA) and spark plasma sintering. Different revolutions per minute (RPM)s were used in the MA process, and their effect on microstructure, and thermoelectric properties of p-type Bi0.5Sb1.5Te3 were systematically investigated. The crystal structure of milled powders and sintered samples were characterized using X-ray diffraction. All the powders exhibited the same morphology albeit with slight differences find at 1100 RPM conditions. A slight grain size refinement was observed on the fracture surfaces from 500 to 1100 RPM specimens. The temperature dependence of Seebeck coefficient, electrical conductivity, and power factors were measured as a function of temperature with different RPM conditions. The power factor shows almost same (~3.5 W/mK2 at RT) for all samples due to unchanged Seebeck and electrical conductivity values. The peak ZT of 1.07 at 375K is obtained for 1100 RPM specimen due to low thermal conductivity.
3
Content available Effect of Surfactant Addition on Bi2Te3 Nanostructures Synthesized by Hydrothermal Method
Dharmaiah P., Lee C. H., Madavali B., Hong S.-J.
Archives of Metallurgy and Materials
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2017
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Vol. 62, iss. 2B
1005--1010
EN
In the present work, we have prepared Bi2Te3 nanostructures with different morphologies such as nano-spherical, nanoplates and nanoflakes obtained using various surfactant additions (EG, PVP, and EDTA) by a hydrothermal method. The shape of the nanoparticles can be controlled by addition of surfactants. The samples were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the minority BiOCl phase disappears after maintained pH at 10 with EG as surfactant. SEM bulk microstructure reveals that the sample consists of fine and coarse grains. Temperature dependence of thermoelectric properties of the nanostructured bulk sample was investigated in the range of 300-450K. The presence of nanograins in the bulk sample exhibits a reduction of thermal conductivity and less effect on electrical conductivity. As a result, a figure of merit of the sintered bulk sample reached 0.2 at 400 K. A maximum micro Vickers hardness of 102 Hv was obtained for the nanostructured sample, which was higher than the other reported results.
4
Content available Effect of Ga2O3 Nanoparticles Dispersion on Microstructure and Thermoelectric Properties of p-Type BiSbTe Based Alloys
Kim E.-B., Koo J.-M., Hong S.-J.
Archives of Metallurgy and Materials
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2017
|
Vol. 62, iss. 2B
993--997
EN
In this study, p-type Bi0.5Sb1.5Te3 based nanocomposites with addition of different weight percentages of Ga2O3 nanoparticles are fabricated by mechanical milling and spark plasma sintering. The fracture surfaces of all Bi0.5Sb1.5Te3 nanocomposites exhibited similar grain distribution on the entire fracture surface. The Vickers hardness is improved for the Bi0.5Sb1.5Te3 nanocomposites with 6 wt% added Ga2O3 due to exhibiting fine microstructure, and dispersion strengthening mechanism. The Seebeck coefficient of Bi0.5Sb1.5Te3 nanocomposites are significantly improved owing to the decrease in carrier concentration. The electrical conductivity is decreased rapidly upon the addition of Ga2O3 nanoparticle due to increasing carrier scattering at newly formed interfaces. The peak power factor of 3.24 W/mK2 is achieved for the base Bi0.5Sb1.5Te3 sintered bulk. TheBi0.5Sb1.5Te3 nanocomposites show low power factor than base sample due to low electrical conductivity.
5
Content available Effect of Acid Dissolution Conditions on Recovery of Valuable Metals from Used Plasma Display Panel Scrap
Kim C.- M., Dharmaiah P., Kim H.-S., Koo J.-M., Yoon J.-S., Hong S.-H., Hong S.-J.
Archives of Metallurgy and Materials
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2017
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Vol. 62, iss. 2B
1173--1177
EN
The objective of this particular study was to recover valuable metals from waste plasma display panels using high energy ball milling with subsequent acid dissolution. Dissolution of milled (PDP) powder was studied in HCl, HNO3, and H2SO4 acidic solutions. The effects of dissolution acid, temperature, time, and PDP scrap powder to acid ratio on the leaching process were investigated and the most favorable conditions were found: (1) valuable metals (In, Ag, Mg) were recovered from PDP powder in a mixture of concentrated hydrochloric acid (HCl:H2O = 50:50); (2) the optimal dissolution temperature and time for the valuable metals were found to be 60°C and 30 min, respectively; (3) the ideal PDP scrap powder to acid solution ratio was found to be 1:10. The proposed method was applied to the recovery of magnesium, silver, and indium with satisfactory results.
6
Content available Characterization of Cu and Ni Nano-Fluids Synthesized by Pulsed Wire Evaporation Method
Kim H.-S., Yilmaz F., Dharmaiah P., Lee D.-J, Lee T.-H., Hong S.-J.
Archives of Metallurgy and Materials
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2017
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Vol. 62, iss. 2B
999--1004
EN
In the present work, Cu and Ni nanofluids were synthesized using the pulsed wire evaporation (PWE) method in the different aqueous medias, namely (ethanol and ethylene glycol), and the effects of the aqueous media on the dispersion state, stability, and particle size of nanoparticles were studied. The size and morphology of synthesized nano-particles were investigated by transmission electron microscopy (TEM). Also, the dispersion stability of the nanofluids was evaluated by turbiscan analysis. The TEM results showed that the nano-particles were spherical in shape, and the average particle size was below 100 nm. The average particle size of the Cu nano-particles was smaller than that of Ni, which was attributed to a difference in the specific sublimation energy of the elements. Moreover, ethylene glycol (EG) exhibited higher suspension stability than ethanol. Finally, the dispersion stability of Cu@EG displayed the highest value due to lower particle size and greater viscosity.
7
Content available Microstructure And Thermoelectric Properties Of TAGS-90 Compounds Fabricated By Mechanical Milling Process
Kim H.-S., Babu M., Hong S.-J.
Archives of Metallurgy and Materials
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2015
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Vol. 60, iss. 2B
1231--1234
EN
TAGS-90 compound powder was directly prepared from the elements by high-energy ball milling (HEBM) and subsequently consolidated by a spark plasma sintering (SPS). Effect of milling time on the microstructure and thermoelectric properties of the samples were investigated. The particle size of fabricated powders were decreased with increasing milling time, finally fine particles with ~1μm size was obtained at 90 min. The SPS samples exhibited higher relative densities (>99%) with fine grain size. X-ray diffraction analysis (XRD) and energy dispersion analysis (EDS) results revealed that all the samples were single phase of GeTe with exact composition. The electrical conductivity of samples were decreased with milling time, whereas Seebeck coefficient increased over the temperature range of RT~450°C. The highest power factor was 1.12×10-3 W/mK2 obtained for the sample with 90 min milling at 450°C.
8
Content available Fabrication Of Zn4Sb3 Alloys By A Combination Of Gas-Atomization And Spark Plasma Sintering Processes
Dharmaiah P., Kim H.-S., Lee L. H., Hong S.-J.
Archives of Metallurgy and Materials
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2015
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Vol. 60, iss. 2B
1417--1421
EN
In this study, single phase polycrystalline Zn4Sb3 as well as 11 at.% Zn-rich Zn4Sb3 alloy having ε-Zn4Sb3 (majority phase) and Zn (minority phase) phases bulk samples produced by gas-atomization and subsequently consolidated by spark plasma sintering (SPS) process. The crystal structures were analyzed by X-ray diffraction (XRD) and cross-sectional microstructure were observed by the scanning electron microscopy (SEM). The internal grain microstructure of 11at.% Zn-rich Zn4Sb3 powders shows lamellar structure. Relative density, Vickers hardness and crack lengths were measured to investigate the effect of sintering temperature of Zn4Sb3 samples which are sintered at 653, 673 and 693 K. Relative density of the single phase bulk Zn4Sb3 sample reached to 99.2% of its theoretical density. The micro Vickers hardness of three different sintering temperatures were found around 2.17 – 2.236 GPa.
9
Content available Effect Of Ti Powder Addition On The Fabrication Of TiO2 Nanopowders
Raihanuzzaman R. M., Park H. Y., Ghomashchi R., Kwon T. H., Son H.-T., Hong S.-J.
Archives of Metallurgy and Materials
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2015
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Vol. 60, iss. 2B
1473--1477
EN
Sintered samples of Ti added TiO2 nanopowders were fabricated by combined application of magnetic pulsed compaction (MPC) and sintering. The effect of Ti nano powder on density, shrinkage and hardness of the samples were investigated as part of the study. The optimum processing conditions were found to be around 0.5 GPa MPC pressure and 1450°C sintering temperature, illustrating maximum density, hardness and minimum shrinkage. High pressure compaction using MPC was found to enhance density with increasing MPC pressure up to 0.9 GPa, and significantly reduce the total shrinkage (about 16% in this case) in the sintered bulks compared to other general processes (about 18%). While sintered samples blended with micro Ti showed presence of microstructural cracks, the samples with 1-2% nano Ti had less or no cracks on them. Overall, the inclusion of nano Ti indicated improvement in mechanical properties of TiO2 nanopowders sintered preforms as opposed to micro Ti-added TiO2.
10
Content available Effect Of Different Mechanical Milling Processes On Morphology And Microstructural Changes Of Nano And Micron Al-Powders
Kim H.-S., Madavali B., Eom T.-J., Kim C.- M., Koo J.-M., Lee T. H., Hong S.-J.
Archives of Metallurgy and Materials
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2015
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Vol. 60, iss. 2B
1235--1239
EN
In this research, effect of the various mechanical milling process on morphology and microstructural changes of nano and micron Al-powders was studied. The milling of Al-powders was performed by both high energy and low energy ball milling process. The influence of milling (pulverizing) energy on the structural changes of Al-powders was studied. Al-nanoparticles were agglomerated during the MA and its size was increased with increasing milling while micron Al-powder gets flattened shape during high energy ball milling due to severe plastic deformation. Meanwhile, structural evolution during high energy ball milling of the nano powder occurred faster than that of the micron powder. A slight shift in the position of X-ray diffraction peaks was observed in nano Al-powders but it was un-altered in macro Al-powders. The variation in lattice parameters was observed only for nano Al powders during the high energy ball milling due to lattice distortion.
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