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• Friction Welding of Casted SCM440 and Sintered F-05-140 Dissimilar Steels and Their Joint Properties under Various Welding Conditions
  Jisung Lee, Hansung Lee, Eunhyo Song, Byungmin Ahn
  Journal of Powder Materials.2024; 31(5): 414.     CrossRef

The synthesis of porous W by freeze-casting and vacuum drying is investigated. Ball-milled WO₃ powders and tert-butyl alcohol were used as the starting materials. The tert-butyl alcohol slurry is frozen at –25°C and dried under vacuum at –25 and –10°C. The dried bodies are hydrogen-reduced at 800°C and sintered at 1000°C. The XRD analysis shows that WO₃ is completely reduced to W without any reaction phases. SEM observations reveal that the struts and pores aligned in the tert-butyl alcohol growth direction, and the change in the powder content and drying temperature affects the pore structure. Furthermore, the struts of the porous body fabricated under vacuum are thinner than those fabricated under atmospheric pressure. This behavior is explained by the growth mechanism of tert-butyl alcohol and rearrangement of the powders during solidification. These results suggest that the pore structure of a porous body can be controlled by the powder content, drying temperature, and pressure.

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• Fabrication of Porous TiO2 with Aligned Pores Using Tert-Butyl Alcohol Based Freeze Casting
  Eui Seon Lee, Sung-Tag Oh
  Korean Journal of Metals and Materials.2024; 62(12): 929.     CrossRef

The effect of sublimable vehicles on the pore structure of Cu fabricated by freeze drying is investigated. The 5 vol% CuO-dispersed slurries with camphene and various camphor-naphthalene compositions are frozen in a Teflon mold at -25°C, followed by sublimation at room temperature. After hydrogen reduction at 300°C and sintering at 600 °C, the green bodies of CuO are completely converted to Cu with various pore structures. The sintered samples prepared using CuO/camphene slurries show large pores that are aligned parallel to the sublimable vehicle growth direction. In addition, a dense microstructure is observed in the bottom section of the specimen where the solidification heat was released, owing to the difference in the solidification behavior of the camphene crystals. The porous Cu shows different pore structures, such as dendritic, rod-like, and plate shaped, depending on the composition of the camphornaphthalene system. The change in pore structure is explained by the crystal growth behavior of primary camphor and eutectic and primary naphthalene.

Core-shell structured nanoparticles are garnering attention because these nanoparticles are expected to have a wide range of applications. The objective of the present study is to improve the coating efficiency of gold shell formed on the surface of silica nanoparticles for SiO₂@Au core-shell structure. For the efficient coating of gold shell, we attempt an in-situ synthesis method such that the nuclei of the gold nanoparticles are generated and grown on the surface of silica nanoparticles. This method can effectively form a gold shell as compared to the conventional method of attaching gold nanoparticles to silica particles. It is considered possible to form a dense gold shell because the problems caused by electrostatic repulsion between the gold nanoparticles in the conventional method are eliminated.

The effect of the mixing method on the characteristics of hybrid-structure W powder with nano and micro sizes is investigated. Fine WO₃ powders with sizes of ~0.6 μm, prepared by ball milling for 10 h, are mixed with pure W powder with sizes of 12 μm by various mixing process. In the case of simple mixing with ball-milled WO₃ and micro sized W powders, WO₃ particles are locally present in the form of agglomerates in the surface of large W powders, but in the case of ball milling, a relatively uniform distribution of WO₃ particles is exhibited. The microstructural observation reveals that the ball milled WO₃ powder, heat-treated at 750°C for 1 h in a hydrogen atmosphere, is fine W particles of ~200 nm or less. The powder mixture prepared by simple mixing and hydrogen reduction exhibits the formation of coarse W particles with agglomeration of the micro sized W powder on the surface. Conversely, in the powder mixture fabricated by ball milling and hydrogen reduction, a uniform distribution of fine W particles forming nano-micro sized hybrid structure is observed.

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• The Efficiency of Radiation Shielding Sheet to Reduce Radiation Exposure during C-arm Fluoroscopy
  Hosang Jeon, Won Chul Shin, Hee Yun Seol, Yongkan Ki, Kyeong Baek Kim, Ki Seok Choo, Sang Don Lee, Suk-Woong Kang
  Journal of the Korean Fracture Society.2023; 36(4): 111.     CrossRef
• Facile phosphorus-embedding into SnS2 using a high-energy ball mill to improve the surface kinetics of P-SnS2 anodes for a Li-ion battery
  Hongsuk Choi, Seungmin Lee, KwangSup Eom
  Applied Surface Science.2019; 466: 578.     CrossRef
• Hydrogen reduction behavior and microstructural characteristics of WO3 and WO3-NiO powders
  Hyunji Kang, Young-Keun Jeong, Sung-Tag Oh
  International Journal of Refractory Metals and Hard Materials.2019; 80: 69.     CrossRef
• Fabrication of Densified W-Ti by Reaction Treatment and Spark Plasma Sintering of WO3-TiH2 Powder Mixtures
  Hyunji Kang, Heun Joo Kim, Ju-Yeon Han, Yunju Lee, Young-Keun Jeong, Sung-Tag Oh
  Korean Journal of Materials Research.2018; 28(9): 511.     CrossRef

The sol-gel method is the simplest method for synthesizing monodispersed silica particles. The purpose of this study is to synthesize uniform, monodisperse spherical silica nanoparticles using tetraethylorthosilicate (TEOS) as the silica precursor, ethanol, and deionized water in the presence of ammonia as a catalyst. The reaction time and temperature and the concentration of the reactants are controlled to investigate the effect of the reaction parameters on the size of the synthesized particles. The size and morphology of the obtained silica particles are investigated using transmission electron microscopy and particle size analysis. The results show that monodispersed silica particles over a size range of 54-504 nm are successfully synthesized by the sol-gel method without using any additional process. The nanosized silica particles can be synthesized at higher TEOS/H2O ratios, lower ammonia concentrations, and especially, higher reaction temperatures.

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• Nanostructure Construction of SiO₂@Au Core-Shell by In-situ Synthesis
  Mu-Jae Pyeon, Do Kyung Kim, Young-Keun Jeong
  Journal of Korean Powder Metallurgy Institute.2018; 25(5): 420.     CrossRef

Microstructural examination of the Nb-Si-B alloys at Nb-rich compositions is performed. The Nb-rich corner of the Nb-Si-B system is favorable in that the constituent phases are Nb (ductile and tough phase with high melting temperature) and T₂ phase (very hard intermetallic compound with favorable oxidation resistance) which are good combination for high temperature structural materials. The samples containing compositions near Nb-rich corner of the Nb- Si-B ternary system are prepared by spark plasma sintering (SPS) process using T₂ and Nb powders. T₂ bulk phase is made in arc furnace by melting the Nb slug and the Si-B powder compact. The T₂ bulk phase was subsequently ballmilled to powders. SPS is performed at 1300°C and 1400°C, depending on the composition, under 30 MPa for 600s, to produce disc-shaped specimen with 15 mm in diameter and 3 mm high. Hardness tests (Rockwell A-scale and micro Vickers) are carried out to estimate the mechanical property.

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• Fabrication of Nb-Si-B Alloys Using the Pulverized Nb-T₂ Alloy Powder
  Min-Ho Cho, Sung-Jun Kim, Hyun-Ji Kang, Sung-Tag Oh, Young Do Kim, Seong Lee, Myung Jin Suk
  Journal of Korean Powder Metallurgy Institute.2019; 26(4): 299.     CrossRef
• Mechanical properties of Mo-Nb-Si-B quaternary alloy fabricated by powder metallurgical method
  Jong Min Byun, Su-Ryong Bang, Se Hoon Kim, Won June Choi, Young Do Kim
  International Journal of Refractory Metals and Hard Materials.2017; 65: 14.     CrossRef
• Mechanical properties of Mo-Si-B alloys fabricated by using core-shell powder with dispersion of yttria nanoparticles
  Jong Min Byun, Su-Ryong Bang, Won June Choi, Min Sang Kim, Goo Won Noh, Young Do Kim
  Metals and Materials International.2017; 23(1): 170.     CrossRef
• Fabrication of Ta2O5 Dispersion-Strengthened Mo-Si-B Alloy by Powder Metallurgical Method
  Jong Min Byun, Won June Choi, Su-Ryong Bang, Chun Woong Park, Young Do Kim
  JOM.2017; 69(4): 683.     CrossRef
• Rapid consolidation of nanostuctured WC-FeAl3 by pulsed current activated heating and its mechanical properties
  In-Jin Shon, Seok-Jae Lee
  International Journal of Refractory Metals and Hard Materials.2017; 65: 69.     CrossRef

In this study, ternary compound Max Phase Ti₂AlC material was mixed by 3D ball milling as a function of ball milling time. More than 99.5 wt% pure Ti₂AlC was synthesized by using spark plasma sintering method at 1000, 1100, 1200, and 1300°C for 60 min. The material characteristics of synthesized samples were examined with relative density, hardness, and electrical conductivity as a function of sintering temperature. The phase composition of bulk was identified by X-ray diffraction. On the basis of FE-SEM result, a terraced structures which consists of several laminated layers were observed. And Ti₂AlC bulk material obtained a vickers hardness of 5.1 GPa at the sintering temperature of 1100°C.

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• Synthesis and reaction path of Ti‐Al‐C MAX phases by reaction with Ti‐Al intermetallic compounds and TiC
  Hojun Lee, Si Yeon Kim, Young‐In Lee, Jongmin Byun
  Journal of the American Ceramic Society.2023; 106(12): 7230.     CrossRef

SKD11 (ASTM D2) tool steel is a versatile high-carbon, high-chromium, air-hardening tool steel that is characterized by a relatively high attainable hardness and numerous, large, chromium rich alloy carbide in the microstructure. SKD11 tool steel provides an effective combination of wear resistance and toughness, tool performance, price, and a wide variety of product forms. Adding of CNTs increased the performance of mechanical properties more. 1, 3 vol% CNTs was dispersed in SKD11 matrix by mechanical alloying. SKD11 carbon nanocomposite powder was sintered by spark plasma sintering process. FE-SEM, HR-TEM and Raman analysis were carried out for the SKD11 carbon nanocomposites.

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• Study on Effects of Mold Temperature on the Injection Molded Article
  J.-H. Han, Y.-C. Kim
  Archives of Metallurgy and Materials.2017; 62(2): 1271.     CrossRef

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• Synthesis and characterization of N-doped TiO2/ZrO2 visible light photocatalysts
  Ji Young Kim, Chan Soo Kim, Han Kwon Chang, Tae Oh Kim
  Advanced Powder Technology.2011; 22(3): 443.     CrossRef
• Effects of ZrO2 addition on phase stability and photocatalytic activity of ZrO2/TiO2 nanoparticles
  Ji-Young Kim, Chan-Soo Kim, Han-Kwon Chang, Tae-Oh Kim
  Advanced Powder Technology.2010; 21(2): 141.     CrossRef