Journal of Powder Materials

Y.R. Uhm

6 Articles

Synthesis of Core/shell Structured Ag/C Nano Particles and Properties on Annealing Conditions: S.H. Jun, Y.R. Uhm, C.K. Rhee; J Korean Powder Metall Inst. 2010;17(4):295-301.; DOI: https://doi.org/10.4150/KPMI.2010.17.4.295

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Multi shell graphite coated Ag nano particles with core/shell structure were successfully synthesized by pulsed wire evaporation (PWE) method. Ar and CH_4 (10 vol.%) gases were mixed in chamber, which played a role of carrier gas and reaction gas, respectively. Graphite layers on the surface of silver nano particles were coated indiscretely. However, the graphite layers are detached, when the particles are heated up to 250°C in the air atmosphere. In contrast, the graphite coated layer was stable under Ar and N_2 atmosphere, though the core/shell structured particles were heated up to 800°C. The presence of graphite coated layer prevent agglomeration of nanoparticles during heat treatment. The dispersion stability of the carbon coated Ag nanoparticles was higher than those of pure Ag nanoparticles.

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Fabrication of Carbon-coated Tin Nano-powders by Electrical Wire Explosion in Liquid Media and its Electrochemical Properties
Yoo-Young Kim, Ju-Suck Song, Kwon-Koo Cho
Journal of Korean Powder Metallurgy Institute.2016; 23(4): 317. CrossRef
Study of Mössbauer Spectroscopy for Iron Oxides Synthesized by Pulsed Wire Evaporation (PEW)
Young Rang Uhm
Journal of the Korean Magnetics Society.2014; 24(5): 135. CrossRef

Fabrication and Characterization of Carbon-Coated Cu Nanopowders by Pulsed Wire Evaporation Method: H.M. Lee, J.H. Park, S.M. Hong, Y.R. Uhm, C.K. Rhee; J Korean Powder Metall Inst. 2009;16(4):243-248.; DOI: https://doi.org/10.4150/KPMI.2009.16.4.243

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Carbon-coated Cu nanopowders with core/shell structure have been successfully fabricated by pulsed wire evaporation (PWE) method, in which a mixed gas of Ar/CH_4 (10 vol.%) was used as an ambient gas. The characterization of the samples was carried out using x-ray diffraction (XRD), scanning electron microscope (SEM), and high resolution transmission electron microscope (HRTEM). It was found that the nanoparticles show a spherical morphology with the size ranging of 10-40 nm and are covered with graphite layers of 2-4 nm. When oxygen-passivated Cu nanopowders were annealed under flowing argon gas (600 and 800°C), the crystallinity of Cu_2O phase and the particle size gradually increased. On the other hand, carbon-coated Cu nanopowders remained similar to as-prepared case with no additional oxide or carbide phases even after the annealing, indicating that the metal nanoparticles are well protected by the carbon-coating layers.

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Improved oxidation stability of carbon-coated Ni nanoparticles synthesized by one-step electrical wire explosion
Jun-Hyeok Lee, Byung-Hoon Kim, Gyoung-Ja Lee
Materials Chemistry and Physics.2022; 276: 125410. CrossRef
Fabrication of Ni-free Fe-based Alloy Nano Powder by Pulsed Wire Evaporation in Liquid: Part I. Effect of Wire Diameter and Applied Voltage
Ho-Jin Ryu, Yong-Heui Lee, Kwang-Ug Son, Young-Min Kong, Jin-Chun Kim, Byoung-Kee Kim, Jung-Yeul Yun
Journal of Korean Powder Metallurgy Institute.2011; 18(2): 105. CrossRef
A Study on Thermal Properties of Ethylene Glycol Containing Copper Oxide Nanoparticles
Chang-Kyu Kim, Gyoung-Ja Lee, Chang-Kyu Rhee
Journal of Korean Powder Metallurgy Institute.2010; 17(4): 276. CrossRef
Synthesis and Characterization of Cu Nanofluid Prepared by Pulsed Wire Evaporation Method
Chang-Kyu Kim, Gyoung-Ja Lee, Chang-Kyu Rhee
Journal of Korean Powder Metallurgy Institute.2010; 17(4): 270. CrossRef
Synthesis of Core/shell Structured Ag/C Nano Particles and Properties on Annealing Conditions
S.H. Jun, Y.R. Uhm, C.K. Rhee
Journal of Korean Powder Metallurgy Institute.2010; 17(4): 295. CrossRef
Synthesis and Characterization of Glold Nanofluid Prepared by the Solution Plasma Processing
Yong-Kang Heo, Sang-Yul Lee
Journal of Korean Powder Metallurgy Institute.2010; 17(4): 342. CrossRef

Effect of Alumina Nanooxide Application on Nitrendipine Manufacturing Process: E.J. Chae, Y.R. Uhm, B.S. Han, C.K. Rhee, S.E. Park; J Korean Powder Metall Inst. 2007;14(2):127-131.; DOI: https://doi.org/10.4150/KPMI.2007.14.2.127

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Abstract PDF: The alumina nano powders synthesized by levitational gas condensation (LGC) method were applied to catalyst in manufacturing process of Hanzsch reaction for Nitrendipine. The L-tartaric acid on the surface is carried out with participation of carbonyl fragments, O-H, C-H bonds which affects stereo selectivity, yield on the reagents positively. From the analysis of the IR-spectroscopy, the carbonyl fragments, O-H, and C-H bond were created by the catalytic reaction. From the analysis of the rR-spectroscopy, the carbonyl fragments, O-H, and C-H bond were created by the catalytic reaction. The newly created bonds made a chiral center on the final product.

Study of Mechanically Alloyed Nano Cu-Fe Particles With a Hetero-Structure: Y.R. Uhm, H.M. Lee, C.K. Rhee; J Korean Powder Metall Inst. 2007;14(2):97-100.; DOI: https://doi.org/10.4150/KPMI.2007.14.2.097

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Abstract PDF: The magnetic alloys of Cu-Fe (Cu_50Fe_50,;Cu_80Fe_20;and;Cu_90Fe_10) were prepared by a mechanical alloying method and their structural and magnetic behaviors were examined by X-ray diffraction and Mossbauer spectra. The magnetization curves did not distinctly show the saturation at 70 kOe for the concentrated alloys of Cu_80Fe_20;and;Cu_90Fe_10. The Mossbauer spectrum of Cu_80Fe_20 at room temperature shows one Lorentzian line of the paramagnetic phase, whereas the Mossbauer spectrum of Cu_90Fe_10 consists of sextet Lorentzian line at room temperature and a centered doublet line. The Mossbauer spectra of Cu_90Fe_10 measured in the temperature ranges from 13 to 295 K, implies that Cu_90Fe_10 to consists of two magnetic phases. One superimposed sextet corresponds to the ferromagnetic iron in Cu and the other one indicates the superparamagnetic iron rich phase.

A study on the Particulate Properties of Ti-Ni alloy Nanopowders Prepared by Levitational Gas Condensation Method: B.S. Han, Y.R. Uhm, M.K. Lee, G.M. Kim, C.K. Rhee; J Korean Powder Metall Inst. 2006;13(6):396-400.; DOI: https://doi.org/10.4150/KPMI.2006.13.6.396

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Abstract PDF: The Ti-Ni alloy nanopowders were synthesized by a levitational gas condensation (LGC) by using a micron powder feeding system and their particulate properties were investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) method. The starting Ti and Ni micron powders 150µm were incorporated into the micron powder feeding system. An ingot type of the Ti-Ni ahoy was used as a seed material for the levitation and evaporation reactions. The collected powders were finally passivated by oxidation. The x-ray diffraction experiments have shown that the synthesized powders were completely alloyed with Ti and Ni and comprised of two different cubic and monoclinic crystalline phases. The TEM results showed that the produced powders were very fine and uniform with a spherical particle size of 18 to 32nm. The typical thickness of a passivated oxide layer on the particle surface was about 2 to 3 nm. The specific surface area of the Ti-Ni alloy nanopowders was 60m2/g based on BET method.

Room-temperature Ferromagnetism in Fe-doped Reduced TiO_2-δ: H.M. Lee, C.S. Kim, Y.R. Uhm, C.K. Rhee; J Korean Powder Metall Inst. 2006;13(6):401-407.; DOI: https://doi.org/10.4150/KPMI.2006.13.6.401

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Abstract PDF: Effects of oxygen deficiency on the room temperature ferromagnetism in Fe-doped reduced TiO_2 have been investigated by comparing the air-annealed Ti_0.97Fe_0.03O_2 compound with secondly post-annealed one in vacuum ambience. The air-annealed sample showed a paramagnetic behavior at room temperature. However, when the sample was further annealed in vacuum, a strongly enhanced ferromagnetic behavior was observed at same temperature. M"ossbauer spectra of air-annealed sample at 295K showed a single doublet of Fe3+

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