Journal of Powder Materials

Gook-Hyun Ha

11 Articles

Effect of Added B₄C on the Mechanical Properties of WC/Ni-Si Hardmetal: Gil-Geun Lee, Gook-Hyun Ha; J Powder Mater. 2013;20(5):366-370.; DOI: https://doi.org/10.4150/KPMI.2013.20.5.366

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Abstract PDF: The effects of B_4C on the mechanical properties of WC/Ni-Si hardmetal were analyzed using sintered bodies comprising WC(70-x wt.%), Ni (28.5 wt.%), Si (1.5 wt.%), and B_4C (x wt.%), where 0leq_-xleq_-1.2 wt.%. Samples were prepared by a combination of mechanical milling and liquid-phase sintering. Phase and microstructure characterizations were conducted using X-ray diffractometry, scanning electron microscopy, and electron probe X-ray micro analysis. The mechanical properties of the sintered bodies were evaluated by measuring their hardness and transverse rupture strength. The addition of B_4C improved the sinterability of the hardmetals. With increasing B_4C content, their hardness increased, but their transverse rupture strength decreased. The changes of sinterability and mechanical properties were attributed to the alloying reaction between B_4C and the binder metal (Ni, Si).

The Electric and Thermal Properties of Spark Plasma Sintered Bi_0.5Sb_1.5Te₃: Gil-Geun Lee, Young-Hoon Choi, Gook-Hyun Ha; J Korean Powder Metall Inst. 2012;19(4):285-290.; DOI: https://doi.org/10.4150/KPMI.2012.19.4.285

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Abstract PDF: The present study was focused on the analysis of the electric and thermal properties of spark plasma sintered Bi_0.5Sb_1.5Te_3 thermoelectric material. The crystal structure, microstructure, electric and thermal properties of the sintered body were evaluated by measuring XRD, SEM, electric resistivity, Hall effect and thermal conductivity. The Bi_0.5Sb_1.5Te_3 sintered body showed anisotropic crystal structure. The c-axis of the Bi_0.5Sb_1.5Te_3 crystal aligned in a parallel direction with applied pressure during spark plasma sintering. The degree of the crystal alignment increased with increasing sintering temperature and sintering time. The electric resistivity and thermal conductivity of the Bi_0.5Sb_1.5Te_3 sintered body showed anisotropic characteristics result from crystal alignment.

Thermoelectric Properties of Bi₂Te_2.7Se_0.3 Powder Synthesized by an Oxide-Reduction Process: Bae-Gun Park, Gil-Geun Lee, Woo-Yeol Kim, Gook-Hyun Ha; J Korean Powder Metall Inst. 2011;18(5):437-442.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.437

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Abstract PDF: The present study focused on the synthesis of Bi-Te-Se-based powder by an oxide-reduction process, and analysis of the thermoelectric properties of the synthesized powder. The phase structure, chemical composition, and morphology of the synthesized powder were analyzed by XRD, EPMA and SEM. The synthesized powder was sintered by spark plasma sintering. The thermoelectric properties of the sintered body were evaluated by measuring its Seebeck coefficient, electrical resistivity, and thermal conductivity. Bi_2Te_2.7Se_0.3 powder was synthesized from a mixture of Bi_2O_3, TeO_2, and SeO_2 powders by mechanical milling, calcination, and reduction. The sintered body of the synthesized powder exhibited n-type thermoelectric characteristics. The thermoelectric properties of the sintered bodies depend on the reduction temperature. The Seebeck coefficient and electrical resistivity of the sintered body were increased with increasing reduction temperature. The sintered body of the Bi_2Te_2.7Se_0.3 powder synthesized at 360°C showed about 0.5 of the figure of merit (ZT) at room temperature.

Influence of Metal-Coating Layer on an Electrical Resistivity of Thick-Film-Type Thermoelectric Modules Fabricated by a Screen Printing Process: Kyung-Tae Kim, Hye-Young Koo, Gook-Hyun Ha; J Korean Powder Metall Inst. 2011;18(5):423-429.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.423

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Thermoelectric-thick films were fabricated by using a screen printing process of n and p-type bismuth-telluride-based pastes. The screen-printed thick films have approximately 30 µm in thickness and show rough surfaces yielding an empty gap between an electrode and the thick film. The gap might result in an increase of an electrical resistivity of the fabricated thick-film-type thermoelectric module. In this study, we suggest a conductive metal coating onto the surfaces of the screen-printed paste in order to reduce the contact resistance in the module. As a result, the electrical resistivity of the thermoelectric module having a gold coating layer was significantly reduced up to 30% compared to that of a module without any metal coating. This result indicates that an introduction of conductive metal layers is effective to decrease the contact resistivity of a thick-film-typed thermoelectric module processed by screen printing.

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Flexible Thermoelectric Device Using Thick Films for Energy Harvesting from the Human Body
Han Ki Cho, Da Hye Kim, Hye Sun Sin, Churl-Hee Cho, Seungwoo Han
Journal of the Korean Ceramic Society.2017; 54(6): 518. CrossRef

Synthesis of Nano-sized Tungsten Carbide - Cobalt Powder by Liquid Phase Method of Tungstate: Jong-Hoon Kim, Yong-Ho Park, Gook-Hyun Ha; J Korean Powder Metall Inst. 2011;18(4):332-339.; DOI: https://doi.org/10.4150/KPMI.2011.18.4.332

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5 Citations

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Cemented tungsten carbide has been used in cutting tools and die materials, and is an important industrial material. When the particle size is reduced to ultrafine, the hardness and other mechanical properties are improved remarkably. Ultrafine cemented carbide with high toughness and hardness is now widely used. The objective of this study is synthesis of nanostructured WC-Co powders by liquid phase method of tungstate. The precursor powders were obtained by freezen-drying of aqueous solution of soluble salts, such as ammonium metatungstate, cobalt nitrate. the final compositions were WC-10Co. In the case of liquid phase method, it can be observed synthesis of WC-10Co. The properties of powder produced at various temperature, were estimated from the SEM, BET and C/S analyser.

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Development of a new nanocrystalline alloy for X-ray shielding
J. H. Cho, H. K. Lee, M. S. Kim, J. D. Rhim, Y. J. Park
Radiation Effects and Defects in Solids.2018; 173(7-8): 643. CrossRef
Study on dispersibility of thermally stable carbon black particles in ink using asymmetric flow field-flow fractionation (AsFlFFF)
Woonjung Kim, Jihyun Bae, Chul Hun Eum, Jongjin Jung, Seungho Lee
Microchemical Journal.2018; 142: 167. CrossRef
Surface Modification of Carbon Black Using Polymer Resin Synthesized by a Phenyl Radical Reaction
Seungho Lee, Chul Hun Eum, Woon Jung Kim
Journal of the Korean Chemical Society.2016; 60(4): 286. CrossRef
Improvement in Mechanical and Wear Properties of WC-Co by Ultrasonic Nanocrystal Surface Modification Technique
Seung-Chul Lee, Jun-Hyong Kim, Gab-Su Choi, Young-Do Jang, Auezhan Amanov, Young-Sik Pyun
Journal of the Korean Society of Tribologists and Lubrication Engineers.2015; 31(2): 56. CrossRef
Changes in Mechanical Properties of WC-Co by Ultrasonic Nanocrystal Surface Modification Technique
Seung-Chul Lee, Jun-Hyong Kim, Hak-Doo Kim, Gab-Su Choi, Auezhan Amanov, Young-Sik Pyun
Journal of the Korean Society of Tribologists and Lubrication Engineers.2015; 31(4): 157. CrossRef

Synthesis of Bi-Sb-Te-based Thermoelectric Powder by an Oxide-reduction Process: Gil-Geun Lee, Sung-Hyun Kim, Gook-Hyun Ha, Kyung-Tae Kim; J Korean Powder Metall Inst. 2010;17(4):336-341.; DOI: https://doi.org/10.4150/KPMI.2010.17.4.336

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4 Citations

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The present study focused on the synthesis of Bi-Sb-Te-based thermoelectric powder by an oxidereduction process. The phase structure, particle size of the synthesized powders were analyzed using XRD and SEM. The synthesized powder was sintered by the spark plasma sintering method. The thermoelectric property of the sintered body was evaluated by measuring the Seebeck coefficient and specific electric resistivity. The Bi_0.5Sb_1.5Te_3 powder had been synthesized by a combination of mechanical milling, calcination and reduction processes using mixture of Bi_2O_3, Sb_2O_3 and TeO_2 powders. The sintered body of the Bi_0.5Sb_1.5Te_3 powder synthesized by an oxide-reduction process showed p-type thermoelectric characteristics, even though it had lower thermoelectric properties than the sintered body of the Bi_0.5Sb_1.5Te_3 thermoelectric powder synthesized by the conventional melting-crushing method.

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Synthesis of N-type Bi2Te2.7Se0.3 Compounds through Oxide-Reduction Process and Related Thermoelectric Transport Properties
Young Soo Lim, Bae Gun Park, Gil-Geun Lee
Korean Journal of Metals and Materials.2022; 60(6): 463. CrossRef
The Electric and Thermal Properties of Spark Plasma Sintered Bi0.5Sb1.5Te3
Gil-Geun Lee, Young-Hoon Choi, Gook-Hyun Ha
Journal of Korean Powder Metallurgy Institute.2012; 19(4): 285. CrossRef
Synthesis and Characterization of (AgSbTe2)15(GeTe)85Thermoelectric Powder by Gas Atomization Process
Hyo-Seob Kim, Jin-Kyu Lee, Jar-Myung Koo, Byong-Sun Chun, Soon-Jik Hong
Journal of Korean Powder Metallurgy Institute.2011; 18(5): 449. CrossRef
Thermoelectric Properties of Bi2Te2.7Se0.3Powder Synthesized by an Oxide-Reduction Process
Bae-Gun Park, Gil-Geun Lee, Woo-Yeol Kim, Gook-Hyun Ha
Journal of Korean Powder Metallurgy Institute.2011; 18(5): 437. CrossRef

Effect of Hydrogen Reduction Treatment on Room-Temperature Thermoelectric Performance of p-type Thermoelectric Powders: Kyung-Tae Kim, Kyeong-Mi Jang, Gook-Hyun Ha; J Korean Powder Metall Inst. 2010;17(2):136-141.; DOI: https://doi.org/10.4150/KPMI.2010.17.2.136

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Bismuth-telluride based (Bi_0.2Sb_0.8)_2Te_3 thermoelectric powders were fabricated by two-step planetary milling process which produces bimodal size distribution ranging 400;nm;sim;2;µm. The powders were reduced in hydrogen atmosphere to minimize oxygen contents which cause degradation of thermoelectric performance by decreasing electrical conductivity. Oxygen contents were decreased from 0.48% to 0.25% by the reduction process. In this study, both the as-synthesized and the reduced powders were consolidated by the spark plasma sintering process at 350°C for 10 min at the heating rate of 100°C/min and then their thermoelectric properties were investigated. The sintered samples using the reduced p-type thermoelectric powders show 15% lower specific electrical resistivity (0.8;mOmegacdotcm) than those of the as-synthesized powders while Seebeck coefficient and thermal conductivity do not change a lot. The results confirmed that ZT value of thermoelectric performance at room temperature was improved by 15% due to high electric conductivity caused by the controlled oxygen contents present at bismuth telluride materials.

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Influence of Metal-Coating Layer on an Electrical Resistivity of Thick-Film-Type Thermoelectric Modules Fabricated by a Screen Printing Process
Kyung-Tae Kim, Hye-Young Koo, Gook-Hyun Ha
Journal of Korean Powder Metallurgy Institute.2011; 18(5): 423. CrossRef

Fabrication and Thermoelectric Properties of Carbon Nanotube/Bi₂Te₃ Composites: Kyung-Tae Kim, Kyeong-Mi Jang, Kyong-Ju Kim, Gook-Hyun Ha; J Korean Powder Metall Inst. 2010;17(2):107-112.; DOI: https://doi.org/10.4150/KPMI.2010.17.2.107

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Abstract PDF: Carbon-nanotube-embedded bismuth telluride (CNT/Bi_2Te_3) matrix composites were fabricated by a powder metallurgy process. Composite powders, whereby 5 vol.% of functionalized CNTs were homogeneously mixed with Bi_2Te_3 alloying powders, were successfully synthesized by using high-energy ball milling process. The powders were consolidated into bulk CNT/Bi_2Te_3 composites by spark plasma sintering process at 350°C for 10 min. The fabricated composites showed the uniform mixing and homogeneous dispersion of CNTs in the Bi_2Te_3 matrix. Seebeck coefficient of CNT/Bi_2Te_3 composites reveals that the composite has n-type semiconducting characteristics with values ranging -55;µV/K to -95;µV/K with increasing temperature. Furthermore, the significant reduction in thermal conductivity has been clearly observed in the composites. The results showed that CNT addition to thermoelectric materials could be useful method to obtain high thermoelectric performance.

Synthesis of TiC/Co Composite Powder by the Carbothermal Reduction Process: Gil-Geun Lee, Gook-Hyun Ha; J Korean Powder Metall Inst. 2009;16(5):310-315.; DOI: https://doi.org/10.4150/KPMI.2009.16.5.310

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Abstract PDF: Ultra-fine TiC/Co composite powder was synthesized by the carbothermal reduction process without wet chemical processing. The starting powder was prepared by milling of titanium dioxide and cobalt oxalate powders followed by subsequent calcination to have a target composition of TiC-15 wt.%Co. The prepared oxide powder was mixed again with carbon black, and this mixture was then heat-treated under flowing argon atmosphere. The changes in the phase, mass and particle size of the mixture during heat treatment were investigated using XRD, TG-DTA and SEM. The synthesized oxide powder after heat treatment at 700°C has a mixed phase of TiO_2 and CoTiO_3 phases. This composite oxide powder was carbothermally reduced to TiC/Co composite powder by the solid carbon. The synthesized TiC/Co composite powder at 1300°C for 9 hours has particle size of under about 0.4 mum.

Synthesis of Bi-Sb-Te Thermoelectric Nanopowder by the Plasma Arc Discharge Process: Gil-Geun Lee, Dong-Youl Lee, Gook-Hyun Ha; J Korean Powder Metall Inst. 2008;15(5):352-358.; DOI: https://doi.org/10.4150/KPMI.2008.15.5.352

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3 Citations

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The present study focused on the synthesis of a bismuth-antimony-tellurium-based thermoelectric nanopowders using plasma arc discharge process. The chemical composition, phase structure, particle size of the synthesized powders under various synthesis conditions were analyzed using XRF, XRD and SEM. The powders as synthesized were sintered by the plasma activated sintering. The thermoelectric properties of sintered body were analyzed by measuring Seebeck coefficient, specific electric resistivity and thermal conductivity. The chemical composition of the synthesized Bi-Sb-Te-based powders approached that of the raw material with an increasing DC current of the are plasma. The synthesized Bi-Sb-Te-based powder consist of a mixed phase structure of the Bi_0.5Sb_1.5Te_3, Bi_2Te_3 and Sb_2Te_3 phases. This powder has homogeneous mixing state of two different particles in an average particle size; about 100nm and about 500nm. The figure of merit of the sintered body of the synthesized 18.75 wt.%Bi-24.68 wt.%Sb-56.57 wt.%Te nanopowder showed higher value than one of the sintered body of the mechanically milled 12.64 wt.%Bi-29.47 wt.%Sb-57.89 wt.%Te powder.

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Citations to this article as recorded by

Synthesis of N-type Bi2Te2.7Se0.3 Compounds through Oxide-Reduction Process and Related Thermoelectric Transport Properties
Young Soo Lim, Bae Gun Park, Gil-Geun Lee
Korean Journal of Metals and Materials.2022; 60(6): 463. CrossRef
Thermoelectric Properties of Bi2Te2.7Se0.3Powder Synthesized by an Oxide-Reduction Process
Bae-Gun Park, Gil-Geun Lee, Woo-Yeol Kim, Gook-Hyun Ha
Journal of Korean Powder Metallurgy Institute.2011; 18(5): 437. CrossRef
Synthesis of Bi-Sb-Te-based Thermoelectric Powder by an Oxide-reduction Process
Gil-Geun Lee, Sung-Hyun Kim, Gook-Hyun Ha, Kyung-Tae Kim
Journal of Korean Powder Metallurgy Institute.2010; 17(4): 336. CrossRef

Thermoelectric Properties of Bi_0.4Sb_1.6Te₃ Sintered Body Fabricated by Mechanical Grinding Process: Gil-Geun Lee, Sung-Chul Shin, Woo-Yeol Kim, Gook-Hyun Ha; J Korean Powder Metall Inst. 2006;13(5):313-320.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.313

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Abstract PDF: The present study is to analyze the thermoelectric properties of Bi_0.4Sb_1.6Te_3 thermoelectric materials fabricated by the mechanical grinding process. The Bi_0.4Sb_1.6Te_3 powders were prepared by the combination of mechanical milling and reduction treating methods using simply crushed pre-alloyed Bi_0.4Sb_1.6Te_3 powder. The mechanical milling was carried out using the tumbler-ball mill and planetary ball mill. The tumbler-ball milling had an effect on the carrier mobility rather than the carrier concentration, whereas, the latter on the carrier concentration. The specific electric resistivity and Seebeck coefficient decreased with increasing the reduction-heat-treatment time. The thermal conductivity continuously increased with increasing the reduction-heat-treatment time. The figure of merit of the Bi_0.4Sb_1.6Te_3 sintered body prepared by the mechanical grinding process showed higher value than one of the sintered body of the simply crushed powder.

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