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동결건조 공정에서 동결제의 응고조건이 기공특성에 미치는 영향
석명진,김지순,오승탁,Suk, Myung-Jin,Kim, Ji Soon,Oh, Sung-Tag 한국분말야금학회 2014 한국분말재료학회지 (KPMI) Vol.21 No.5
The present study demonstrates the effect of solidification condition on the pore structure in freeze drying process using the slurries of CuO/sublimable vehicles. Camphene and Camphor-45 wt% naphthalene based slurries with 14 vol% CuO powder were frozen into a mold at $-25^{\circ}C$, followed by sublimation at room temperature. The green bodies were hydrogen-reduced and sintered at $500^{\circ}C$ for 1 h. The porous Cu specimen, frozen the CuO/camphene slurry into the heated mold of the upper part, showed large pores with unidirectional pore channels and small pores in their internal wall. Also, it was observed that the size of large pores was decreasing near the bottom part of specimen. The change of pore structure depending on the freezing condition was explained by the nucleation behavior of camphene crystals and rearrangement of solid powders during solidification. In case of porous Cu prepared from CuO/Camphor-naphthalene system, the pore structure exhibited plate shape as a replica of the original structure of crystallized vehicles with hypereutectic composition.
일방향응고시킨 Pivalic Acid-Ethanol 계에서의 Dendrite의 성장
석명진 ( Myung Jin Suk ),박영민 ( Young Min Park ) 한국주조공학회 2011 한국주조공학회지 Vol.31 No.4
Transparent organic materials have been frequently used as an analog of the solidifying metallic materials, because their transparency permits an in-situ observation of the microstructural development during solidification through optical microscopy. Pivalic acid (PVA)-ethanol system showing an anisotropic property in solid-liquid interfacial energy and interface kinetics was adopted in the present experiment, and the detailed experiments performed are as follows: ① variation of dendrite tip temperature with growth velocity, ② correlation between primary dendrite arm spacing (λ1) and the growth orientation away from the heat flow direction (tilt angle: θ), ③ variation of dendrite tip radius (R) with growth velocity (V), ④ dendrite tip stability parameter (σ*) and its dependence on the concentration. Concerning the correlation between the dendrite tip temperature and growth velocity the present result is well suited to Hunt-Lu equation. As the tilt angle increases, the average primary dendrite spacing tends to increase.
논문 : Pivalic Acid-Ethanol 및 Succinonitrile-Salol 계에서의 수지상정 선단의 형상
석명진 ( Myung Jin Suk ),박영민 ( Young Min Park ),오승탁 ( Sung Tag Oh ),장시영 ( Si Young Chang ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.7
The shape of a dendrite tip has long been approximated by a paraboloid of revolution, but many attempts have been made as well to more accurately match the dendrite tip profile using other mathematical functions: power function, 4th order polynomial, and hyperbolic function. In the present work, dendrite tip shapes were matched by parabolic function. The differences between the dendrite tip shapes of pivalic acid(PVA)-ethanol(Eth) and succinonitrile(SCN)-salol systems, characterized by anisotropic and isotropic solid-liquid interfacial properties, respectively, were quantitatively treated using shape parameters. The PVA-Eth system showed a slightly higher Z/R value than the SCN-salol system, their Z/R values lying in the range 2-4. (Z is the distance from the tip beyond which the parabolic fit starts to deviate from the profile, and R the tip radius.) λP is the distance from the tip beyond which side branching starts to appear, and is larger in the PVA-Eth system than the SCNsalol system. λP is different for both sides of the 2-dimensional dendrite profile. The difference of λP between both sides of the dendrite is larger for PVA-Eth system than for SCN-salol, implying that the dendrite of PVA-Eth is less symmetric than that of SCN-salol.
Camphor-Naphthalene 동결제 조성이 Cu-Ni 다공체의 기공구조에 미치는 영향
권나연,석명진,오승탁,Kwon, Na-Yeon,Suk, Myung-Jin,Oh, Sung-Tag 한국분말야금학회 2015 한국분말재료학회지 (KPMI) Vol.22 No.5
The effect of sublimable vehicle composition in the camphor-naphthalene system on the pore structure of porous Cu-Ni alloy is investigated. The CuO-NiO mixed slurries with hypoeutectic, eutectic and hypereutectic compositions are frozen into a mold at $-25^{\circ}C$. Pores are generated by sublimation of the vehicles at room temperature. After hydrogen reduction at $300^{\circ}C$ and sintering at $850^{\circ}C$ for 1 h, the green body of CuO-NiO is completely converted to porous Cu-Ni alloy with various pore structures. The sintered samples show large pores which are aligned parallel to the sublimable vehicle growth direction. The pore size and porosity decrease with increase in powder content due to the degree of powder rearrangement in slurry. In the hypoeutectic composition slurry, small pores with dendritic morphology are observed in the sintered Cu-Ni, whereas the specimen of hypereutectic composition shows pore structure of plate shape. The change of pore structure is explained by growth behavior of primary camphor and naphthalene crystals during solidification of camphor-naphthalene alloys.
김세훈,석명진,김영도,Kim, Se-Hoon,Suk, Myung-Jin,Kim, Young-Do 한국분말야금학회 2009 한국분말재료학회지 (KPMI) Vol.16 No.4
3-D shape soft magnetic composite parts can be formed by general compaction method of powder metallurgy. In this study, the results on the high density nanostructured Fe-Si/Fe composite prepared by a warm compaction method were presented. Ball-milled Fe-25 wt.%Si powder, pure Fe powder and Si-polymer were mixed and then the powder mixture was compacted at various temperatures and pressures. Pore free density of samples up to 95% theoretical value has been obtained. The warm compacted sample prepared at 650 MPa and 240$^{\circ}C$ had highest compaction properties in comparison with other compacts prepared at 300, 400 MPa and room temperature and 120$^{\circ}C$. The magnetic properties such as core loss, magnetization saturation and coercivity were measured by B-H curve analyzer and vibration sample magnetometer.
기공형성제 PMMA와 WO<sub>3</sub> 분말 성형체의 열처리를 이용한 W 다공체 제조
전기철,김영도,석명진,오승탁,Jeon, Ki Cheol,Kim, Young Do,Suk, Myung-Jin,Oh, Sung-Tag 한국분말야금학회 2015 한국분말재료학회지 (KPMI) Vol.22 No.2
Porous W with controlled pore structure was fabricated by thermal decomposition and hydrogen reduction process of PMMA beads and $WO_3$ powder compacts. The PMMA sizes of 8 and $50{\mu}m$ were used as pore forming agent for fabricating the porous W. The $WO_3$ powder compacts with 20 and 70 vol% PMMA were prepared by uniaxial pressing and sintered for 2 h at $1200^{\circ}C$ in hydrogen atmosphere. TGA analysis revealed that the PMMA was decomposed at about $400^{\circ}C$ and $WO_3$ was reduced to metallic W at $800^{\circ}C$. Large pores in the sintered specimens were formed by thermal decomposition of spherical PMMA, and their size was increased with increase in PMMA size and the amount of PMMA addition. Also the pore shape was changed from spherical to irregular form with increasing PMMA contents due to the agglomeration of PMMA in the powder mixing process.
CNTs 합성을 통해 향상된 비표면적을 갖는 Ti 다공체의 제조
최혜림,변종민,석명진,오승탁,김영도,Choi, Hye Rim,Byun, Jong Min,Suk, Myung-Jin,Oh, Sung-Tag,Kim, Young Do 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.3
This study is performed to fabricate a Ti porous body by freeze drying process using titanium hydride ($TiH_2$) powder and camphene. Then, the Ti porous body is employed to synthesize carbon nanotubes (CNTs) using thermal catalytic chemical vapor deposition (CCVD) with Fe catalyst and methane ($CH_4$) gas to increase the specific surface area. The synthesized Ti porous body has $100{\mu}M$-sized macropores and $10-30{\mu}m$-sized micropores. The synthesized CNTs have random directions and are entangled with adjacent CNTs. The CNTs have a bamboo-like structure, and their average diameter is about 50 nm. The Fe nano-particles observed at the tip of the CNTs indicate that the tip growth model is applicable. The specific surface area of the CNT-coated Ti porous body is about 20 times larger than that of the raw Ti porous body. These CNT-coated Ti porous bodies are expected to be used as filters or catalyst supports.
공정 계 동결제 슬러리의 동결건조 공정에 의한 Mo 다공체 제조
이규태,서한길,석명진,오승탁,Lee, Gyu-Tae,Seo, Han Gil,Suk, Myung-Jin,Oh, Sung-Tag 한국분말야금학회 2013 한국분말재료학회지 (KPMI) Vol.20 No.4
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 $55^{\circ}C$ with a small amount of oligomeric dispersant, was frozen at $-25^{\circ}C$. 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 $750^{\circ}C$, and sintered at $1100^{\circ}C$ for 2 h. The sintered samples, frozen by heated Teflon cylinder, showed large pores with the size of about 40 ${\mu}m$ 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.
다양한 동결제를 이용하여 동결건조 공정으로 제조한 Cu 다공체의 기공구조 특성
이규휘,오승탁,석명진,정영근,Lee, Gyuhwi,Oh, Sung-Tag,Suk, Myung-Jin,Jeong, Young-Keun 한국분말야금학회 2020 한국분말재료학회지 (KPMI) Vol.27 No.3
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℃, followed by sublimation at room temperature. After hydrogen reduction at 300℃ and sintering at 600 ℃, 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.