Journal of Powder Materials

Chul-Jin Choi

9 Articles

[Korean]
Size Control of Nd-Fe-B Precursor Particles Prepared by Spray Drying and Its Effect on the Magnetic Properties of Nd-Fe-B Alloy Powders after Reduction-Diffusion: Youn-Kyoung Baek, Young-Taek Seo, Jung-Goo Lee, Dong Su Kim, Dong Sik Bae, Chul-Jin Choi; J Korean Powder Metall Inst. 2013;20(5):359-365.; DOI: https://doi.org/10.4150/KPMI.2013.20.5.359

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In this study, we fabricated Nd_2Fe_14B hard magnetic powders with various sizes via spray drying combined with reduction-diffusion process. Spray drying is widely used to produce nearly spherical particles that are relatively homogeneous. Thus, the precursor particles were prepared by spray drying using the aqueous solution containing Nd salts, Fe salts and boric acid with the target stoichiometric composition of Nd_2Fe_14B. The mean particle sizes of the spray-dried powders are in the range from one to seven micrometer, which are adjusted by controlling the concentrations of precursor solutions. After debinding the as-prepared precursor particles, ball milling was also conducted to control the particle sizes of Nd-Fe-B oxide powders. The resulting particles with different sizes were subjected to subsequent treatments including hydrogen reduction, Ca reduction and washing for CaO removal. The size effect of Nd-Fe-B oxide particles on the formation of Nd_2Fe_14B phase and magnetic properties was investigated.

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Research trend in Fabrication of Metastable-phase Iron Nitrides for Hard Magnetic Applications
Kyung Min Kim, Jung-Goo Lee, Kyung Tae Kim, Youn-Kyoung Baek
Journal of Korean Powder Metallurgy Institute.2019; 26(2): 146. CrossRef
Synthesize of Nd₂Fe₁₄B Powders from 1-D Nd₂Fe₁₄B Wires using Electrospinning Process
Nu Si A Eom, Su Noh, Muhammad Aneeq Haq, Bum Sung Kim
Journal of Korean Powder Metallurgy Institute.2019; 26(6): 477. CrossRef

[Korean]
The Effect of Mn Addition on Nitrogenation Behavior and Magnetic Properties of Sm-Fe Alloy Powder Produced by Reduction-diffusion Method: Young-Taek Seo, Youn-Kyoung Baek, Jung-Goo Lee, Chul-Jin Choi; J Korean Powder Metall Inst. 2013;20(1):13-18.; DOI: https://doi.org/10.4150/KPMI.2013.20.1.013

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In the present study, we systematically investigated the effect of Mn addition on nitrogenation behavior and magnetic properties of Sm-Fe powders produced by reduction-diffusion process. Alloy powders with only Sm_2(Fe,Mn)_17 single phase were successfully produced by the reduction-diffusion process. The coercivity of Sm_2(Fe,Mn)_17 powder rapidly increased during nitrogenation and reached the maximum of 637 Oe after 16 hours. After further nitrogenation, it decreased. In contrast, the coercivity of Sm_2Fe_17 powder gradually increased during nitrogenation for 24 hours. The coercivity of Sm_2(Fe,Mn)_17 powder was higher than that of Sm_2Fe_17 powder at the same condition of nitrogenation. It was considered that the Mn addition facilitates the nitrogenation of Sm_2Fe_17 powder and enhances the coercivity.

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Effect of Nb content on Sm2Fe17−xNbx and its nitrides prepared by reduction-diffusion method
Guizhi Yao, Haiming Tian, Cong Zhang, Huan Shi, Shifan Zeng, Sheng Gao, Shuangjiu Feng, Kai Zhu, Xucai Kan, Xiansong Liu
Journal of Materials Science: Materials in Electronics.2024;[Epub] CrossRef

[Korean]
Trend in Research and Development Related to Lean Heavy Rare-earth Permanent Magnets for Next-generation Motors: Jung-Goo Lee, Youn-Kyoung Baek, Ji-Hun Yu, Chul-Jin Choi; J Korean Powder Metall Inst. 2012;19(2):151-159.; DOI: https://doi.org/10.4150/KPMI.2012.19.2.151

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Study on the Demagnetization and Classification of NdFeB Magnets According to Different Heat Treatment Temperatures
Byeong Jun Kim, Ik Keun Park, Young Sung Kim
Journal of the Korean Society of Manufacturing Technology Engineers.2021; 30(2): 119. CrossRef
Low Cost Design Study of Brushless DC Motor for Electric Water Pump Application
Tae-Uk Jung
Journal of Electrical Engineering and Technology.2014; 9(3): 942. CrossRef
Optimized Design of Rotor Considering Cost-Reduction of Small BLDC Motor for the Water Pump
Hoe-Cheon Kim, Tae-Uk Jung
The Transactions of The Korean Institute of Electrical Engineers.2013; 62(4): 495. CrossRef

[Korean]
Manufacturing of Micro Gas Bearing by Fe-Ni Nanopowder and Metal Mold Using LIGA: Soo-Jung Son, Young-Sang Cho, Dae-Jung Kim, Jong-Hyun Kim, Suk-Sang Chang, Chul-Jin Choi; J Korean Powder Metall Inst. 2012;19(2):140-145.; DOI: https://doi.org/10.4150/KPMI.2012.19.2.140

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This paper describes the manufacturing process of tilting pad gas bearing with a diameter of 5 mm and a length of 0.5-1 mm for power MEMS (Micro Electomechanical Systems) applications. The bearing compacts with nanopowder feedstock were prepared by Ni-metal mold with 2-mold system using LIGA process. The effect of the manufacturing conditions on sintering properties of nanopowder gas bearing was investigated. In this work, Fe-45 wt%Ni nanopowder with an average diameter of 30-50 nm size was used as starting material. After mixing the nanopowder and the wax-based binders, the amount of powder was controlled to obtain the certain mixing ratio. The nanopowder bearing compacts were sintered with 1-2 hr holding time under hydrogen atmospheres and under temperatures of 600°C to 1,000°C. Finally, the critical batch of mixed powder system was found to be 70% particle fraction in total volume. The maximum density of the sintered bearing specimen was about 94% of theoretical density.

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A comprehensive review on advancements in compliant structures of gas foil journal bearings
Srusti Priyadarshini, Suraj K Behera
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology.2024; 238(9): 1039. CrossRef

[English]
Fabrication of Ordered or Disordered Macroporous Structures with Various Ceramic Materials from Metal Oxide Nanoparticles or Precursors: Young-Sang Cho, Jun-Hyuk Moon, Young-Kuk Kim, Chul-Jin Choi; J Korean Powder Metall Inst. 2011;18(4):347-358.; DOI: https://doi.org/10.4150/KPMI.2011.18.4.347

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Two different schemes were adopted to fabricate ordered macroporous structures with face centered cubic lattice of air spheres. Monodisperse polymeric latex suspension, which was synthesized by emulsifier-free emulsion polymerization, was mixed with metal oxide ceramic nanoparticles, followed by evaporation-induced self-assembly of the mixed hetero-colloidal particles. After calcination, inverse opal was generated during burning out the organic nanospheres. Inverse opals made of silica or iron oxide were fabricated according to this procedure. Other approach, which utilizes ceramic precursors instead of nanoparticles was adopted successfully to prepare ordered macroporous structure of titania with skeleton structures as well as lithium niobate inverted structures. Similarly, two different schemes were utilized to obtain disordered macroporous structures with random arrays of macropores. Disordered macroporous structure made of indium tin oxide (ITO) was obtained by fabricating colloidal glass of polystyrene microspheres with low monodispersity and subsequent infiltration of the ITO nanoparticles followed by heat treatment at high temperature for burning out the organic microspheres. Similar random structure of titania was also fabricated by mixing polystyrene building block particles with titania nanoparticles having large particle size followed by the calcinations of the samples.

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Fabrication Of Colloidal Clusters Decorated With Dye Molecules For Potential Application As Photonic Molecules
Y.-S. Cho
Archives of Metallurgy and Materials.2015; 60(2): 1221. CrossRef

[English]
Synthesis of Gold Nanoparticles by Chemical Reduction Method for Direct Ink Writing: Young-Sang Cho, Soo-Jung Son, Young-Kuk Kim, Kook-Chae Chung, Chul-Jin Choi; J Korean Powder Metall Inst. 2010;17(5):390-398.; DOI: https://doi.org/10.4150/KPMI.2010.17.5.390

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Aqueous gold nanoparticle dispersion was synthesized by chemical reduction method using diethanolamine as reducing agent and polyethyleneimine as dispersion stabilizer. The synthesis conditions for the stable dispersion of the gold nanoparticle suspension were determined by changing the amount of the reducing agent and dispersant during the wet chemical synthesis procedures. The face centered cubic lattice structure of the gold nanoparticles was confirmed by using X-ray diffraction and the morphologies of the nanoparticles were observed by transmission electron microscope. The synthesized gold nanoparticle dispersion was concentrated by evaporating the dispersion medium at room temperature followed by the addition of ethyleneglycol as humectant for the increase of the elastic properties to obtain gold nanoparticle inks for direct ink writing process. The line patterns were obtained with the gold nanoparticle inks during the writing procedures and the morphologies of the fine patterns were observed by scanning electron microscope.

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Fabrication Of Colloidal Clusters Decorated With Dye Molecules For Potential Application As Photonic Molecules
Y.-S. Cho
Archives of Metallurgy and Materials.2015; 60(2): 1221. CrossRef
Synthesis of Nickel and Copper Nanopowders by Plasma Arc Evaporation
Young-Sang Cho, Jong Woo Moon, Kook Chae Chung, Jung-Goo Lee
Journal of Korean Powder Metallurgy Institute.2013; 20(6): 411. CrossRef
Low Temperature Debinding Process Using Oxygen Plasma for Flexible Printed Electronics
Young-In Lee
Journal of Korean Powder Metallurgy Institute.2012; 19(5): 343. CrossRef
Fabrication of Fecralloy Foil Coated by Fecralloy Nanoparticles Using Electrospray Processing
Jung-Yeul Yun, Sang-Sun Yang, Hye-Young Koo, Hye-Moon Lee
Journal of Korean Powder Metallurgy Institute.2011; 18(6): 526. CrossRef

[Korean]
The Effect of Excess Samarium Oxide on the Preparation of Sm-Fe Alloy Powder by Reduction-diffusion Method: Hun Kwak, Jung-Goo Lee, Chul-Jin Choi; J Korean Powder Metall Inst. 2009;16(5):336-341.; DOI: https://doi.org/10.4150/KPMI.2009.16.5.336

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To produce alloy powders with only Sm_2Fe_17 single phase by reduction-diffusion (R-D) method, the effect of excess samarium oxide on the preparation of Sm-Fe alloy powder during R-D heat treatment was studied. The quantity of samarium oxide was varied from 5% to 50% whereas iron and calcium were taken 0% and 200% in excess of chemical equivalent, respectively. The pellet type mixture of samarium, iron powders and calcium granulars was subjected to heat treatment at 1100°C for 5 hours. The R-D treated pellet was moved into deionized water and agitated to separate Sm-Fe alloy powders. After washing them in deionized water several times, the powders were washed with acetic acid to remove the undesired reaction products such as CaO. By these washing and acid cleaning treatment, only 0.03 wt% calcium remained in Sm-Fe alloy powders. It was also confirmed that the content of unreacted alpha-Fe in Sm_2Fe_17 matrix gradually decreased as the percentage of samarium oxide is increased. However, there was no significant change above 40% excess samarium oxide.

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The Influence of Mechanical Milling on the Structure and Magnetic Properties of Sm-Fe-N Powder Produced by the Reduction-Diffusion Process
Jung-Goo Lee, Seok-Won Kang, Ping-Zhan Si, Chul-Jin Choi
Journal of Magnetics.2011; 16(2): 104. CrossRef

[Korean]
Trend in Research and Development Related to Sm-Fe-N Bonded Magnets: Jung-Goo Lee, Hun Kwak, Chul-Jin Choi, Joon-Chul Yun, Jai-Sung Lee; J Korean Powder Metall Inst. 2009;16(1):1-8.; DOI: https://doi.org/10.4150/KPMI.2009.16.1.001

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Advanced Magnetic Actuation: Harnessing the Dynamics of Sm2Fe17–xCuxN3 Composites
Kangmo Koo, Young-Tae Kwon, Ji Young Park, Yong-Ho Choa
ACS Applied Materials & Interfaces.2024; 16(9): 11872. CrossRef

[Korean]
Fabrication of Micro Component of Metallic Nano Powder Using Polymer Mold: Woo-Seok Lee, Sang-Phil Kim, Hye-Moon Lee, Dong-Sik Bae, Chul-Jin Choi; J Korean Powder Metall Inst. 2007;14(3):202-207.; DOI: https://doi.org/10.4150/KPMI.2007.14.3.202

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Abstract PDF: Novel polymer mold process for fabrication of microcomponents using metal nanopowders was developed and experimentally optimized. Polymer mold for forming green components was produced by using a hard master mold and polydimethylsiloxane (PDMS). In the preparation of metallic powder premix for the green components without any defect, 90 wt.% 17-4PH statinless steel nanopowders and 10 wt.% organic binder were mixed by a ball milling process. The green components with very clear gear shape were formed by filling the powder premix into the PDMS soft mold in surrounding at about 100°C. Cold isostatic pressing (CIP) was very potent process to decrease a porosity in the sintered microcomponent. The microgear fabricated by the improved process showed a good dimension tolerance of about 1.2%.

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