Journal of Powder Materials

Yong-Ho Choa

11 Articles

Luminescent Characteristics of CdSe Quantum Dot Phosphor Depending on Se Precursor Ratio: Nu Si A Eom, Taek-Soo Kim, Yong-Ho Choa, Bum Sung Kim; J Korean Powder Metall Inst. 2012;19(6):442-445.; DOI: https://doi.org/10.4150/KPMI.2012.19.6.442

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The quantum dots (QD) have unique electrical and optical properties due to quantum dot confinement effect. The optical properties of QDs are decided by various synthesis conditions. In a prior QDs study, a study on the QDs size with synthesis condition such as synthesis time and temperature is being extensively researched. However, the research on QDs size with composition ratio has hitherto received scant attention. In order to evaluate the ratio dependence of CdSe crystal, synthesis ratio of Se precursor is changed from 16.7 mol%Se to 44 mol%Se. As the increasing Se ratio, the band gap was increased. This is caused by red shift of emission. We confirmed optical property of CdSe QDs with composition ratio.

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Synthesis and analysis CdSe/ZnS quantum dot with a Core/shell Continuous Synthesis System Using a Microfluidic Reactor
Myung Hwan Hong, So Young Joo, Lee-Seung Kang, Chan Gi Lee
Journal of Korean Powder Metallurgy Institute.2018; 25(2): 132. CrossRef
Multimodal luminescence properties of surface-treated ZnSe quantum dots by Eu
Ji Young Park, Da-Woon Jeong, Kyoung-Mook Lim, Yong-Ho Choa, Woo-Byoung Kim, Bum Sung Kim
Applied Surface Science.2017; 415: 8. CrossRef
Optical Characteristics of CdSe/ZnS Quantum Dot with Precursor Flow Rate Synthesized by using Microreactor
Ji Young Park, Da-Woon Jeong, Won Ju, Han Wook Seo, Yong-Ho Choa, Bum Sung Kim
journal of Korean Powder Metallurgy Institute.2016; 23(2): 91. CrossRef

Synthesis and Characterization of Cu Nanowires Using Anodic Alumina Template Based Electrochemical Deposition Method: Young-In Lee, Yong-Ho Choa; J Korean Powder Metall Inst. 2012;19(5):367-372.; DOI: https://doi.org/10.4150/KPMI.2012.19.5.367

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Abstract PDF: Single crystalline Cu nanowires with controlled diameters and aspect ratios have been synthesized using electrochemical deposition within confined nanochannels of a porous anodic aluminium oxide(AAO) template. The diameters of nano-sized cylindrical pores in AAO template were adjusted by controlling the anodization conditions. Cu nanowires with diameters of approximately 38, 99, 274 nm were synthesized by the electrodeposition using the AAO templates. The crystal structure, morphology and microstructure of the Cu nanowires were systematically investigated using XRD, FE-SEM, TEM and SAED. Investigation results revealed that the Cu nanowires had the controlled diameter, high aspect ratio and single crystalline nature.

Synthesis of SnO₂ Nanotubes Via Electrospinning Process and Their Application to Lithium Ion Battery Anodes: Young-In Lee, Yong-Ho Choa; J Korean Powder Metall Inst. 2012;19(4):271-277.; DOI: https://doi.org/10.4150/KPMI.2012.19.4.271

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SnO_2 nanotubes were successfully synthesized using an electrospinning technique followed by calcination in air. The nanotubes were the single phase nature of SnO_2 and consisted of approximately 14 nm nanocrystals. SEM and TEM characterizations demonstrated that uniform hollow fibers with an average outer diameter of around 124 nm and wall thickness of around 25 nm were successfully obtained. As anode materials for lithium ion batteries, the SnO_2 nanotubes exhibited excellent cyclability and reversible capacity of 580mAhg-1 up to 25 cycles at 100mAg-1 as compared to SnO_2 nanoparticles with a capacity of sim200mAhg-1. Such excellent performance of the SnO_2 nanotube was related to the one-dimensional hollow structure which acted as a buffer zone during the volume contraction and expansion of Sn.

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Fabrication of Nanowire by Electrospinning Process Using Nickel Oxide Particle Recovered from MLCC
Haein Shin, Jongwon Bae, Minsu Kang, Kun-Jae Lee
journal of Korean Powder Metallurgy Institute.2023; 30(6): 502. CrossRef
A study on the synthesis of tin oxide crystalline by the liquid reduction precipitation method and hydrothermal process
Il-Jeong Park, Geon-Hong Kim, Dae-Weon Kim, Hee-Lack Choi, Hang-Chul Jung
Journal of the Korean Crystal Growth and Crystal Technology.2016; 26(3): 95. CrossRef
Improvement of Triboelectric Efficiency using SnO2 Friction Layer for Triboelectric Generator
No Ho Lee, Jae Rok Shin, Ji Een Yoo, Dong Hun You, Bon-Ryul Koo, Sung Woo Lee, Hyo-Jin Ahn, Byung Joon Choi
Journal of Korean Powder Metallurgy Institute.2015; 22(5): 321. CrossRef

Research on Synthesis and Sintering Behavior of Nano-sized (Pb, La)TiO₃ Powders Using Mechano Chemical Process: Young-In Lee, Yong-Sung Goo, Jong-Sik Lee, Yong-Ho Choa; J Korean Powder Metall Inst. 2010;17(2):101-106.; DOI: https://doi.org/10.4150/KPMI.2010.17.2.101

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Abstract PDF: In this study, we successfully synthesized a nano-sized lanthanum-modified lead-titanate (PLT) powder with a perovskite structure using a high-energy mechanochemical process (MCP). In addition, the sintering behavior of synthesized PLT nanopowder was investigated and the sintering temperature that can make the full dense PLT specimen decreased to below 1050°C by using Bi_2O_3 powder as sintering agent. The pure PLT phase of perovskite structure was formed after MCP was conducted for 4 h and the average size of the particles was approximately 20 nm. After sintered at 1050 and 1150°C, the relative density of PLT was about 93.84 and 95.78%, respectively. The density of PLT increased with adding Bi_2O_3 and the specimen with the relative densitiy over 96% were fabricated below 1050°C when 2 wt% of Bi_2O_3 was added.

Fabrication and Characterization of Porous Nickel Membrane for High Precision Gas Filter by In-situ Reduction/Sintering Process: Nam-Hoon Kim, Han-Bok Song, Sung-Churl Choi, Yong-Ho Choa; J Korean Powder Metall Inst. 2009;16(4):262-267.; DOI: https://doi.org/10.4150/KPMI.2009.16.4.262

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Disk type porous nickel membrane was fabricated by in-situ reduction/sintering process using compacted NiO/PMMA (PMMA; Polymethyl methacrylate) mixture at 800°C in hydrogen atmosphere. The porosity (49sim58%) of these membrane was investigated as an amount of PMMA additive. The thermal decomposition and reduction behavior of NiO/PMMA were analyzed by TG/DTA in hydrogen atmosphere and the activation energy for the hydrogen reduction of NiO and thermal degradation of PMMA was calculated as 61.1 kJ/mol, evaluated by Kissinger method. Finally, the filtering performance and pressure drop were measured by particle counting system.

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Fabrication of Porous Ni by Freeze Drying and Hydrogen Reduction of NiO/Camphene Slurry
Jae-Hun Jeong, Sung-Tag Oh, Chang-Yong Hyun
Journal of Korean Powder Metallurgy Institute.2019; 26(1): 6. CrossRef
Fabrication of Porous W by Heat Treatment of Pore Forming Agent of PMMA and WO3 Powder Compacts
Ki Cheol Jeon, Young Do Kim, Myung-Jin Suk, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2015; 22(2): 129. CrossRef
Fabrication of Porous Cu by Freeze-drying Process of Camphene Slurry with CuO-coated Cu Powders
Su-Ryong Bang, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2014; 21(3): 191. CrossRef
Fabrication of Porous Ti by Freeze-Drying and Heat Treatment of TiH2/Camphene Slurries
한길 서, 명진 석, 영도 김, 승탁 오
Korean Journal of Materials Research.2013; 23(6): 339~343. CrossRef
Freeze Drying for Porous Mo with Sublimable Vehicles of Eutectic System
Gyu-Tae Lee, Han Gil Seo, Myung-Jin Suk, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2013; 20(4): 253. CrossRef

Development and Application of Metal Nanoparticles for Printed Electronics: Application to Metal Ink in Ink-Jet Technology: Kun-Jae Lee, Yong-Ho Choa; J Korean Powder Metall Inst. 2008;15(2):81-86.; DOI: https://doi.org/10.4150/KPMI.2008.15.2.081

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Synthesis of Eu³⁺ Doped (Y,Gd)BO₃ Powder by Mechanochemical Process: Hee-Sub Won, Wan-Jae Lee, Je-Seok Kim, Gun-Young Hong, Kun-Jae Lee, Yong-Ho Choa; J Korean Powder Metall Inst. 2008;15(2):136-141.; DOI: https://doi.org/10.4150/KPMI.2008.15.2.136

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The mechanochemical process were employed to prepare the red phosphors (Y,Gd)BO_3:Eu3+. The main factors affecting particle size, particle distribution, and luminescent properties of the product were investigated in details. Particles sized around 200-600 nm are formed after intensive milling. The phosphors were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectrum. Results revealed that phosphors with different morphology, small particle size and high luminescence intensity could be obtained by mechanochemical process.

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Photoluminescence Properties of Green Phosphor Y1-xBO3:Tbx3+Synthesized by Solid-state Reaction Method
Shin-Ho Cho
Journal of the Korean Institute of Electrical and Electronic Material Engineers.2011; 24(8): 659. CrossRef

Functionalization of Fe₃O₄ Nanoparticles and Improvement of Dispersion Stability for Seperation of Biomolecules: Min-Jung Kim, Guk-Hwan An, Borami Lim, Hee-Taik Kim, Yong-Ho Choa; J Korean Powder Metall Inst. 2007;14(4):256-260.; DOI: https://doi.org/10.4150/KPMI.2007.14.4.256

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Abstract PDF: The surface of magnetite (Fe_3O_4) nanoparticles prepared by coprecipitation method was modified by carboxylic acid group of poly(3-thiophenacetic acid (3TA)) and meso-2,3-dimercaptosuccinic acid (DMSA). Then the lysozyme protein was immobilized on the carboxylic acid group of the modification of the magnetite nanoparticles. The magnetite nanoparticles are spherical and the particle size is approximately 10 nm. We measured quantitative dispersion state by dispersion stability analyzer for each Fe_3O_4 nanoparticles with and without surface modification. The concentration of lysozyme on the modified magnetite nanoparticles was also investigated by a UV-Vis spectrometer and compared to that of magnetite nanoparticles without surface modification. The functionalized magnetite particles had higher enzymatic capacity and dispersion stability than non-functionalized magnetite nanoparticles.

Synthesis of γ-Fe₂O₃ Nanoparticles by Low-pressure Ultrasonic Spraying: Chang-Woo Lee, Soon-Gil Kim, Yong-Ho Choa, Jai-Sung Lee; J Korean Powder Metall Inst. 2007;14(1):19-25.; DOI: https://doi.org/10.4150/KPMI.2007.14.1.019

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Abstract PDF: This study was focused on the optimization of low-pressure ultrasonic spraying process for synthesis of pure gamma-Fe_2O_3 nanoparticles. As process variables, pressure in the reactor, precursor concentration, and reaction temperature were changed in order to control the chemical and microstructural properties of iron oxide nanoparticles including crystal phase, mean particle size and particle size distribution. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies revealed that pure gamma-Fe_2O_3 nanoparticles with narrow particle size distribution of 5-15 nm were successfully synthesized from iron pentacarbonyl (Fe(CO)_5) in hexane under 30 mbar with precursor concentrations of 0.1M and 0.2M, at temperatures over 800°C. Also magnetic properties, coercivity (H_c) and saturation magnetization (M_s) were reported in terms of the microstructure of particles based on the results from vibration sampling magnetometer (VSM).

Effect of Sintering Temperature on Microstructure and Mechanical Properties of Cu Particles Dispersed Al₂O₃ Nanocomposites: Young-Keun Jeong, Sung-Tag Oh, Yong-Ho Choa; J Korean Powder Metall Inst. 2006;13(5):366-370.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.366

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Abstract PDF: The microstructure and mechanical properties of hot-pressed Al_2O_3/Cu composites with a different sintering temperature have been studied. The size of matrix grain and Cu dispersion in composites increased with increase in sintering temperature. Fracture toughness of the composite sintered at high temperature exhibited an enhanced value. The toughness increase was explained by the thermal residual stress, crack bridging and crack branching by the formation of microcrack. The nanocomposite, hot-pressed at 1450°C, showed the maximum fracture strength of 707 MPa. The strengthening was mainly attributed to the refinement of matrix grains and the increased toughness.

Design of Nanocluster Based Material with Catalytic Properties: Nakayama Tadachika, Chang-Yeoul Kim, Sekino Tohru, Yong-Ho Choa, Kusunose Takafumi, Hayashi Yamato, Niibara Koichi; J Korean Powder Metall Inst. 2001;8(3):197-200.

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Abstract PDF: Modified inert gas condensation method was used to produce the nanocluster composites of CuO/CeO_2. High-resolution TEM, SEM and catalytic measurements have been used to characterize the samples and study the synergistic effect between the CuO phase and CeO_2(ceria) support. By varying the He pressure, the heating temperature and configuration of the heating boats inside the modified gas condensation chamber, nanoclusters of varying sizes, shapes and composition can be produced. The composition and nanostructured morphology were shown to influence the catalytic properties of the system. A copper content around 10 at% with a morphology that favors high-energy surfaces of ceria is shown to be beneficial for a high catalytic activity.

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