Journal of Powder Materials

Sung-Tag Oh

13 Articles

Freeze Drying for Porous Mo with Sublimable Vehicles of Eutectic System: Gyu-Tae Lee, Han Gil Seo, Myung-Jin Suk, Sung-Tag Oh; J Powder Mater. 2013;20(4):253-257.; DOI: https://doi.org/10.4150/KPMI.2013.20.4.253

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Freeze drying for porous Mo was accomplished by using MoO_3 powder as the source and camphor-naphthalene eutectic system as the sublimable material. Eutectic composition of camphor-naphthalene slurries with the initial MoO_3 content of 5 vol%, prepared by milling at 55°C with a small amount of oligomeric dispersant, was frozen at -25°C. The addition of dispersant showed improvement of dispersion stability in slurries. Pores were generated subsequently by sublimation of the camphor-naphthalene during drying in air for 48 h. To convert the MoO_3 to metallic Mo, the green body was hydrogen-reduced at 750°C, and sintered at 1100°C for 2 h. The sintered samples, frozen by heated Teflon cylinder, showed large pores with the size of about 40 µm which were aligned parallel to the sublimable vehicles growth direction. The formation of unidirectionally aligned pores is explained by the rejection and accumulation of solid particles in the serrated solid-liquid interface.

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Interaction of Solid Particles with the Solidifying Front in the Liquid-Particle Mixture
Ho-Suk Lee, Kyu-Hee Lee, Sung-Tag Oh, Young Do Kim, Myung-Jin Suk
Journal of Korean Powder Metallurgy Institute.2018; 25(4): 336. CrossRef
Freeze drying for porous Mo with different sublimable vehicle compositions in the camphor-naphthalene system
Sung-Tag Oh, Young Do Kim, Myung-Jin Suk
Materials Letters.2015; 139: 268. CrossRef

Direct Bonding of Cu/AlN using Cu-Cu₂O Eutectic Liquid: Junsung Hong, Jung-Hoon Lee, You-Na Oh, Kwang-Jun Cho, Doh-Hyung Riu, Sung-Tag Oh, Chang-Yong Hyun; J Powder Mater. 2013;20(2):114-119.; DOI: https://doi.org/10.4150/KPMI.2013.20.2.114

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In the DBC (direct bonding of copper) process the oxygen partial pressure surrounding the AlN/Cu bonding pairs has been controlled by Ar gas mixed with oxygen. However, the direct bonding of Cu with sound interface and good adhesion strength is complicated process due to the difficulty in the exact control of oxygen partial pressure by using Ar gas. In this study, we have utilized the in-situ equilibrium established during the reaction of 2CuOrightarrowCu_2O + 1/2 O_2 by placing powder bed of CuO or Cu_2O around the Cu/AlN bonding pair at 1065sim1085°C. The adhesion strength was relatively better in case of using CuO powder than when Cu_2O powder was used. Microstructural analysis by optical microscopy and XRD revealed that the interface of bonding pair was composed of Cu_2O, Cu and small amount of CuO phase. Thus, it is explained that the good adhesion between Cu and AlN is attributed to the wetting of eutectic liquid formed by reaction of Cu and Cu_2O.

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Low-Temperature Sintering Behavior of Aluminum Nitride Ceramics with Added Copper Oxide or Copper
Jin-Geun Hwang, Kyung-Sik Oh, Tai-Joo Chung, Tae-Heui Kim, Yeong-Kyeun Paek
Journal of the Korean Ceramic Society.2019; 56(1): 104. CrossRef

Fabrication of Porous Mo by Freeze-Drying and Hydrogen Reduction of MoO₃/Camphene Slurry: Wonsuk Lee, Sung-Tag Oh; J Korean Powder Metall Inst. 2012;19(6):446-450.; DOI: https://doi.org/10.4150/KPMI.2012.19.6.446

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In order to fabricate the porous Mo with controlled pore characteristics, unique processing by using MoO_3 powder as the source and camphene as the sublimable material is introduced. Camphene-based 15 vol% MoO_3 slurries, prepared by milling at 50°C with a small amount of dispersant, were frozen at -25°C. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at 750°C, and sintered at 1000-1100°C for 1 h. After heat treatment in hydrogen atmosphere, MoO_3 powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about 150µm which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores due to the difference in the camphene growth rate during freezing process. The size of small pores was decreased with increase in sintering temperature, while that of large pores was unchanged. The results are strongly suggested that the porous metal with required pore characteristics can be successfully fabricated by freeze-drying process using metal oxide powders.

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Effect of Heat Treatment Atmosphere on the Microstructure of TiH2-MoO3 Powder Mixtures
Ki Cheol Jeon, Sung Hyun Park, Na-Yeon Kwon, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2016; 23(4): 303. 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
Synthesis and Antifungal Property of Porous Al2O3with Dispersions of Cu Nanoparticles
Ho-Suk Yoo, Min-Sung Kim, Sung-Tag Oh, Chang-Yong Hyun
Journal of Korean Powder Metallurgy Institute.2014; 21(1): 16. CrossRef
Fabrication of Porous Cu-Ni by Freeze Drying and Hydrogen Reduction of CuO-NiO Powder Mixture
Han Gil Seo, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2014; 21(1): 34. 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

Effect of Powder Characteristic and Freeze Condition on the Pore Characteristics of Porous W: Na-Yeon Kwon, Sung-Tag Oh; J Korean Powder Metall Inst. 2012;19(4):259-263.; DOI: https://doi.org/10.4150/KPMI.2012.19.4.259

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Dependence of the freeze-drying process condition on microstructure of porous W and pore formation mechanism were studied. Camphene slurries with WO_3 contents of 10 vol% were prepared by milling at 50°C with a small amount of dispersant. Freezing of a slurry was done in Teflon cylinder attached to a copper bottom plate cooled at -25°C. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at 800°C for 30 min, and sintered in the furnace at 900°C for 1 h. After heat treatment in hydrogen atmosphere, WO_3 powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about 70µm which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores with dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry.

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Fabrication of Porous W-Ti by Freeze-Drying and Hydrogen Reduction of WO3-TiH2 Powder Mixtures
Hyunji Kang, Sung Hyun Park, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2017; 24(6): 472. CrossRef
Synthesis of Aligned Porous Sn by Freeze-Drying of Tin Chloride/camphene Slurry
수룡 방, 승탁 오
Korean Journal of Materials Research.2015; 25(1): 27~31. CrossRef
Effect of Sublimable Vehicle Compositions in the Camphor-NaphthaleneSystem on the Pore Structure of Porous Cu-Ni
Na-Yeon Kwon, Myung-Jin Suk, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2015; 22(5): 362. CrossRef
Porous Mo–30wt.% W alloys synthesized from camphene/MoO3–WO3 slurry by freeze drying and sintering process
Ki Cheol Jeon, Beom Seok Kim, Young Do Kim, Myung-Jin Suk, Sung-Tag Oh
International Journal of Refractory Metals and Hard Materials.2015; 53: 32. CrossRef
Fabrication of Porous Cu-Ni by Freeze Drying and Hydrogen Reduction of CuO-NiO Powder Mixture
Han Gil Seo, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2014; 21(1): 34. CrossRef
Synthesis of porous Cu–Sn using freeze-drying process of CuO–SnO2/camphene slurries
Sung-Tag Oh, Wonsuk Lee, Si Young Chang, Myung-Jin Suk
Research on Chemical Intermediates.2014; 40(7): 2495. 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
Effect of Solidification Condition of Sublimable Vehicles on the Pore Characteristics in Freeze Drying Process
Myung-Jin Suk, Ji Soon Kim, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2014; 21(5): 366. 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
Synthesis of Porous Cu-Sn by Freeze Drying and Hydrogen Reduction Treatment of Metal Oxide Composite Powders
Min-Sung Kim, Ho-Suk Yoo, Sung-Tag Oh, Chang-Yong Hyun
Korean Journal of Materials Research.2013; 23(12): 722. CrossRef
Fabrication of Porous Mo by Freeze-Drying and Hydrogen Reduction of MoO3/Camphene Slurry
Wonsuk Lee, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2012; 19(6): 446. CrossRef

Evaluation of Creep Reliability of Powder Metallurgy and Cast-type Ni-based Superalloy by Using Ultrasonic Wave: Chan-Yang Choi, Jin-Hun Song, Se-Ung Oh, Chung-Seok Kim, Sook-In Kwun, Sung-Tag Oh, Chang-Yong Hyun, Jai-Won Byeon; J Korean Powder Metall Inst. 2012;19(3):215-219.; DOI: https://doi.org/10.4150/KPMI.2012.19.3.215

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Abstract PDF: An attempt was made to evaluate creep reliability of two commercial Ni-based superalloys by using ultrasonic wave. The materials include fine-grained PM alloy fabricated by mechanical alloying and subsequent hot isostatic pressing, and IN738LC cast alloy with a grain size of a few cm. Microstructural parameters (fraction of creep cavity and size of gammaprime precipitates) and ultrasonic parameters (velocity, attenuation) were measured to try to find relationships between them. Ultrasonic velocity decreased with creep cavity formation in PM alloy. On the other hand, no distinct changing trend of ultrasonic velocity was observed for IN738LC alloy. Ultrasonic attenuation was found to have a linear correlation with the size of gammaprime precipitates and was suggested as a potential parameter for monitoring creep reliability of IN738LC alloy.

Fabrication of Porous Cu by Freeze-Drying Method of CuO-Camphene Slurry: Min-Soo Kim, Sung-Tag Oh, Si-Young Chang, Myung-Jin Suk; J Korean Powder Metall Inst. 2011;18(4):327-331.; DOI: https://doi.org/10.4150/KPMI.2011.18.4.327

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In order to fabricate the porous metal with controlled pore characteristics, unique processing by using metal oxide powder as the source and camphene as the sublimable material is introduced. CuO powder was selected as the source for the formation of Cu metal via hydrogen reduction. Camphene-based CuO slurry, prepared by milling at 47°C with a small amount of dispersant, was frozen at -25°C. Pores were generated subsequently by sublimation of the camphene. The green body was hydrogen-reduced at 200°C for 30 min, and sintered at 500-700°C for 1 h. Microstructural analysis revealed that the sintered Cu showed aligned large pore channels parallel to the camphene growth direction, and fine pores are formed around the large pore. Also, it showed that the pore size was controllable by the slurry concentration.

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Freeze drying for porous Mo with different sublimable vehicle compositions in the camphor-naphthalene system
Sung-Tag Oh, Young Do Kim, Myung-Jin Suk
Materials Letters.2015; 139: 268. CrossRef
Effect of Solidification Condition of Sublimable Vehicles on the Pore Characteristics in Freeze Drying Process
Myung-Jin Suk, Ji Soon Kim, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2014; 21(5): 366. CrossRef
Synthesis and Microstructure of Porous Al2O3 with Nano-Sized Cu Dispersions
호석 유, 창용 현, 안기 김
Korean Journal of Materials Research.2013; 23(1): 67~71. CrossRef
Effect of Powder Characteristic and Freeze Condition on the Pore Characteristics of Porous W
Na-Yeon Kwon, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2012; 19(4): 259. CrossRef
Fabrication of Porous Mo by Freeze-Drying and Hydrogen Reduction of MoO3/Camphene Slurry
Wonsuk Lee, Sung-Tag Oh
Journal of Korean Powder Metallurgy Institute.2012; 19(6): 446. CrossRef
Fabrication and Properties of Porous Tungsten by Freeze-Drying Process
영숙 이, 승탁 오
Korean Journal of Materials Research.2011; 21(9): 520~524. CrossRef

Microstructure and Properties of Cu Dispersed Al₂O₃ Nanocomposites Prepared by Pressureless Sintering: Kyong-Hwan Lee, Sung-Tag Oh; J Korean Powder Metall Inst. 2009;16(4):280-284.; DOI: https://doi.org/10.4150/KPMI.2009.16.4.280

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Abstract PDF: The pressureless sintering behavior of Al_2O_3/Cu powder mixtures, prepared from Al_2O_3/CuO and Al_2O_3/Cu-nitrate, has been investigated. Microstructural observation revealed that Al_2O_3 powders with nano-sized Cu particles could be synthesized by hydrogen reduction method. The specimens, pressureless-sintered at 1400°C for 4 min using infrared heating furnace with the heating rate of 200°C/min, showed the relative density of above 90%. Maximum hardness of 16.1 GPa was obtained in Al_2O_3/MgO/Cu nanocomposites. The nanocomposites exhibited the enhanced fracture toughness of 4.3-5.7 MPacdotm1/2, compared with monolithic Al_2O_3. The mechanical properties were discussed in terms of microstructural characteristics.

Synthesis and Properties of Fe-Ni Nano-sized Powders using Metal Nitrates: Min-Hee Joo, Sung-Tag Oh; J Korean Powder Metall Inst. 2009;16(3):191-195.; DOI: https://doi.org/10.4150/KPMI.2009.16.3.191

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Abstract PDF: The calcination and hydrogen-reduction behavior of Fe- and Ni-nitrate have been investigated. Fe_2O_3/NiO composite powders were prepared by chemical solution mixing of Fe- and Ni-nitrate and calcination at 350°C for 2 h. The calcined powders were hydrogen-reduced at 350°C for 30 min. The calcination and hydrogen-reduction behavior of Fe- and Ni-nitrate were analyzed by TG in air and hydrogen atmosphere, respectively. TG and XRD analysis for hydrogen-reduced powders revealed that the Fe_2O_3/NiO phase transformed to FeNi_3 phase at the temperature of 350°. The activation energy for the hydrogen reduction, evaluated by Kissinger method, was measured as 83.0 kJ/mol.

Sintering Behavior and Mechanical Property of Mo Nanopowders: Hai-Gon Kim, Gil-Su Kim, Sung-Tag Oh, Myung-Jin Suk, Young-Do Kim; J Korean Powder Metall Inst. 2007;14(6):386-390.; DOI: https://doi.org/10.4150/KPMI.2007.14.6.386

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Abstract PDF: The sintering behavior and mechanical property of Mo nanopowder was investigated as a function of various sintering condition. Mo oxide nanopowders were milled using a high energy ball-milling process. After the ball milling for 20h, the crystalline size of MoO_3 was about 20 nm. The MoO_3 nanopowders were reduced at the temperature of 800°C without holding time in H_2 atmosphere. The sinterability of Mo nanopowder and commercial Mo powder was investigated by dilatometric analysis. Mo nanopowder and commercial Mo powder were sintered at 1200°C for 1 hand 1500°C for 3 h, respectively. In both specimens the measured relative density was about 95%. But the measured hardness values were 2.34 GPa for nanopowder and 1.87 GPa for commercial powder. Probably due to finer grain size of the sintered body prepared from Mo nanopowder than that prepared using commercial Mo powder. The mean grain sizes were measured to be about 1.4 mm and 6.2 mm, respectively.

Synthesis of SnO₂ Powders by Oxidation Heat Treatment of Nano-sized Sn Powders and Their Microstructural Characteristics: Sung-Tag Oh, Sung-Il Lee, Yeon-Jun Joo; J Korean Powder Metall Inst. 2007;14(5):287-291.; DOI: https://doi.org/10.4150/KPMI.2007.14.5.287

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Abstract PDF: Oxidation behavior and microstructural characteristics of nano-sized Sn powder were studied. DTA-TG analysis showed that the Sn powder exhibited an endothermic peak at 227°C and exothermic peak at 560°C with an increase in weight. Based on the phase diagram consideration of Sn-O system and XRD analysis, it was interpreted that the first peak was for the melting of Sn powder and the second peak resulted from the formation of SnO_2 phase. Microstructural observation revealed that the SnO_2 powder, heated to 1000°C under air atmosphere, consisted of agglomerates with large particle size due to the melting of Sn powder during heat treatment. Finally, fine SnO_2 powders with an average size of 50nm can be fabricated by controlled heat treatment and ultrasonic milling process.

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.

Processing of Nano-Sized Metal Alloy Dispersed Al_2O_3 Nanocomposites: Sung-Tag Oh, Namkung Seok, Jai-Sung Lee, Hyoung-Seop Kim, Sekino Tohru; J Korean Powder Metall Inst. 2001;8(3):157-162.

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Abstract PDF: An optimum route to fabricate the ferrous alloy dispersed Al_2O_3 nanocomposites such as Al_2O_3/Fe-Ni and Al_2O_3/Fe-Co with sound microstructure and desired properties was investigated. The composites were fabricated by the sintering of powder mixtures of Al_2O_3 and nano-sized ferrous alloy, in which the alloy was prepared by solution-chemistry routes using metal nitrates powders and a subsequent hydorgen reduction process. Microstructural observation of reduced powder mixture revealed that the Fe-Ni or Fe-Co alloy particles of about 20 nm in size homogeneously surrounded Al_2O_3, forming nanocomposite powder. The sintered Al_2O_3/Fe-Ni composite showed the formation of FeAl_2O_4 phase, while the reaction phases were not observed in Al_2O_3/Fe-Co composite. Hot-pressed Al_2O_3/Fe-Ni composite showed improved mechanical properties and magnetic response. The properties are discussed in terms of microstructural characteristics such as the distribution and size of alloy particles.

Microstructure and Properties of Nano-Sized Ni-Co Particulate Dispersed Al_2O_3 Matrix Nanocomposites: Sung-Tag Oh, Sando Mutsuo, Niihara Koichi; J Korean Powder Metall Inst. 1998;5(4):334-339.

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Abstract PDF: In purpose of introducing the inverse magnetostrictive properties into the structural ceramics, Al_2O_3 based nanocomposites dispersed with nano-sized Ni-Co particles were studied. The composites were fabricated by the hydrogen reduction and hot-pressing of Al_2O_3 and NiO-CoO mixed powders. The mixtures were prepared by using Ni- and Co-nitrate (Ni(NO_3)_2;cdot;6H_2O;and;Co(NO_3)_2;cdot6H_2O) as source materials for the Ni-Co particles. Microstructural observations revealed that nano-sized Ni-Co particles were dispersed homogeneously at Al_2O_3 grain boundaries. High strength above 1 GPa was obtained for the Al_2O_3/10 wt% Ni-Co nanocomposite fabricated by a controlled powder preparation process. The inverse magnetostrictive response to applied stress was obtained due to the presence of dispersed Ni-Co particles, which indicates a possibility to incorporate new functions into the structural ceramics without loosing the mechanical properties.

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