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소결분위기 변환온도가 Al<sub>2</sub>O<sub>3</sub>/Cu 나노복합재료의 미세조직과 파괴강도에 미치는 영향
오승탁,윤세중,Oh Sung-Tag,Yoon Se-Joong 한국분말야금학회 2004 한국분말재료학회지 (KPMI) Vol.11 No.5
The microstructure and mechanical property of hot-pressed $Al_2O_3/Cu$ composites with a different temperature for atmosphere changing from H$_{2}$ to Ar have been studied. When atmosphere-changed from H$_{2}$ to Ar gas at 145$0^{\circ}C$, the hot-pressed composite was characterized by inhomogeneous microstructure and low fracture strength. On the contrary, when atmosphere-changed at low temperature of 110$0^{\circ}C$ the composite showed more homogeneous microstructure, higher fracture strength and smaller deviation in strength. Based on the thermodynamic consideration and microstructural analysis, it was interpreted that the Cu wetting behavior relating to the formation of CuAlO$_{2}$ is probably responsible for strong dependence of microstructure on atmosphere changing temperature. The reason for a strong sensitivity of fracture strength and especially of its deviation to atmosphere changing temperature was explained by the microstructural inhomogeneity and by the role of CuAlO$_{2}$ phase on the interfacial bonding strength.
원료분말에 따른 Al<sub>2</sub>O<sub>3</sub>/CuO 분말혼합체의 수소환원 거동 및 미세조직 특성
오승탁,김정남,강계명,Oh Sung-Tag,Kim Jung-Nam,Kang Kae-Myung 한국재료학회 2004 한국재료학회지 Vol.14 No.10
The reduction behavior of $Al_{2}O_3/CuO$ powder mixtures, prepared from $Al_{2}O_3/CuO$ or $Al_{2}O_3/Cu-nitrate$, was investigated by using thermogravimetry and hygrometry. The powder characteristics were examined by BET, XRD and TEM. Also, the influence of powder characteristics on the microstructure and properties of hot-pressed composites was analyzed. The formation mechanism of nano-sized Cu dispersions was explained based on the powder characteristics and reduction kinetics of oxide powders. In addition, the dependence of the microstructure and mechanical properties of hot-pressed composites on powder characteristics is discussed in terms of the initial size and distribution of Cu particles. The practical implication of these results is that an optimum processing condition for the design of homogeneous microstructure and required properties can be established.
Cu 첨가량이 Al<sub>2</sub>O<sub>3</sub>/Cu 나노복합재료의 미세조직과 기계적 성질에 미치는 영향
오승탁,윤세중,Oh Sung-Tag,Yoon Se-Joong 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.1
The effect of Cu content on microstructure and mechanical properties of nano-sized Cu dispersed $Al_2O_3(Al_2O_3/Cu)$ nanocomposites was investigated. The nanocomposites with Cu content of 2.5 to 10 vol% were prepared by reduction and hot-pressing of $Al_2O_3/CuO$ powder mixtures. The nanocomposites with Cu content of 2.5 and 5vol% exhibited the maximum fracture strength of 820MPa and enhanced toughness compared with monolithic $Al_2O_3$. The strengthening was mainly attributed to the refinement of $Al_2O_3$ matrix grains. The toughening mechanism was discussed by the observed microstructural feature based on crack bridging.
나노크기 Sn 분말의 산화열처리에 의한 SnO<sub>2</sub>분말의 합성 및 미세조직 특성
오승탁,이성일,주연준,Oh, Sung-Tag,Lee, Sung-Il,Joo, Yeon-Jun 한국분말야금학회 2007 한국분말재료학회지 (KPMI) Vol.14 No.5
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 $227^{\circ}C$ and exothermic peak at $560^{\circ}C$ 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 $1000^{\circ}C$ 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.
나노크기 금속입자가 분산된 Al<sub>2</sub>O<sub>3</sub> 나노복합재료의 제조 및 마모거동
오승탁,윤세중,정영근,Oh Sung-Tag,Yoon Se-Joong,Jeong Young-Keun 한국재료학회 2005 한국재료학회지 Vol.15 No.8
Microstructure and wear behavior of A1203-based nanocomposites with Cu and Ni-Co dispersions were investigated. $Al_2O_3/Cu$ and $Al_2O_3/Ni-Co$ nanocomposites were fabricated by hydrogen reduction and sintering method using metal oxide and metal nitrates. The nanocomposites showed increased mechanical properties compared with monolithic $Al_2O_3$. In particular, high toughness and hardness were measured for the $Al_2O_3/Ni-Co$ nanocomposite consolidated by spark plasma sintering. A minimum value of wear coefficient comparable to the monolithic $Al_2O_3$ was obtained for $Al_2O_3/Ni-Co$ nanocomposite. Wear behavior is discussed in terms of microstructure and mechanical properties of nanocomposites
WO3/Camphene 슬러리의 동결건조 공정에서 동결제의 응고거동이 기공구조에 미치는 영향
오승탁 ( Sung Tag Oh ),이규태 ( Gyu Tae Lee ),이근재 ( Kun Jae Lee ),석명진 ( Myung Jin Suk ) 대한금속재료학회(구 대한금속학회) 2014 대한금속·재료학회지 Vol.52 No.3
This paper describes the effect of the solidification behavior of camphene on the pore structure of porous W fabricated via a freeze-drying process. Camphene slurries with 10 and 15 vol% WO3 were prepared by milling at 50 ℃ with a small amount of dispersant. Porous W with unidirectionally aligned pore channels was prepared by freeze-drying of slurry and heat treatment in a hydrogen atmosphere. The sintered specimen with 10 vol% WO3 showed large pores with a size of about 100 μm which were aligned parallel to the growth direction of camphene. The internal wall of large pores had relatively small pores. In the slurry with 15 vol% WO3, large pores were not observed in the sintered body, and only small pores existed. The difference in the pore size in the two specimens is explained on the basis of the growth characteristics of the camphene dendrite depending on the amount of particles in the slurry.
김정현,오승탁,이영인,Kim, Jeong Hyun,Oh, Sung-Tag,Lee, Young-In 한국분말재료학회 (*구 분말야금학회) 2021 한국분말재료학회지 (KPMI) Vol.28 No.3
The (Ga<sub>1-x</sub>Zn<sub>x</sub>)(N<sub>1-x</sub>O<sub>x</sub>) solid solution is attracting extensive attention for photocatalytic water splitting and wastewater treatment owing to its narrow and controllable band gap. To optimize the photocatalytic performance of the solid solution, the key points are to decrease its band gap and recombination rate. In this study, (Ga<sub>1-x</sub>Zn<sub>x</sub>)(N<sub>1-x</sub>O<sub>x</sub>) nanofibers with various Zn fractions are prepared by electrospinning followed by calcination and nitridation. The effect of the composition and crystallinity of electrospun oxide nanofibers on the morphology and optical properties of the obtained solid-solution nanofibers are systematically investigated. The results show that the final shape of the (Ga<sub>1-x</sub>Zn<sub>x</sub>) (N<sub>1-x</sub>O<sub>x</sub>) material is greatly affected by the crystallinity of the oxide nanofibers before nitridation. The photocatalytic properties of (Ga<sub>1-x</sub>Zn<sub>x</sub>)(N<sub>1-x</sub>O<sub>x</sub>) with different Ga:Zn atomic ratios are investigated by studying the degradation of rhodamine B under visible light irradiation.
상압소결법으로 제조한 Cu 입자 분산 Al<sub>2</sub>O<sub>3</sub> 나노복합재료의 미세조직 및 특성
이경환,오승탁,Lee, Kyong-Hwan,Oh, Sung-Tag 한국분말야금학회 2009 한국분말재료학회지 (KPMI) Vol.16 No.4
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 $1400^{\circ}C$ for 4 min using infrared heating furnace with the heating rate of $200^{\circ}C$/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 $MPa{\cdot}m^{1/2}$, compared with monolithic $Al_2O_3$. The mechanical properties were discussed in terms of microstructural characteristics.
CuO-Camphene 슬러리의 동결건조에 의한 Cu 다공체 제조
김민수,오승탁,장시영,석명진,Kim, Min-Soo,Oh, Sung-Tag,Chang, Si-Young,Suk, Myung-Jin 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.4
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 $47^{\circ}C$ with a small amount of dispersant, was frozen at $-25^{\circ}C$. Pores were generated subsequently by sublimation of the camphene. The green body was hydrogen-reduced at $200^{\circ}C$ for 30 min, and sintered at $500-700^{\circ}C$ 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.
이영숙,오승탁,Lee, Young-Sook,Oh, Sung-Tag 한국재료학회 2011 한국재료학회지 Vol.21 No.9
Porous W with controlled pore characteristics was fabricated by a freeze-drying process. $WO_3$ powder and camphene were used as the source materials of W and sublimable vehicles, respectively. Camphene slurries with $WO_3$ contents of 10 and 15 vol% were prepared by milling at $50^{\circ}C$ with a small amount of oligomeric polyester dispersant. Freezing of a slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at $-25^{\circ}C$ while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at $800^{\circ}C$ for 30 min and sintered in a furnace at $900^{\circ}C$ for 1 h under a hydrogen atmosphere. Microstructural observation revealed that all of the sintered samples were composed of only W phase and showed large pores which were aligned parallel to the camphene growth direction. The porosity and pore size increased with increasing camphene content. The difference in the pore characteristics depending on the slurry concentration may be explained by the degree of powder rearrangement in the slurry. The results strongly suggest that a porous metal with the required pore characteristics can be successfully fabricated by a freeze-drying process using metal oxide powders.