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변윤기,최성철,정용근,이상훈 한국세라믹학회 2007 한국세라믹학회지 Vol.44 No.4
High-Quality 1-Dimensional InN single crystalline have been grown by Halide Vapor-Phase Epitaxy on the Au catalyst coated Si substrate using the vapor-liquid-solid growth mechanism. We have been grown 1-dimension InN nanowires having controlled the growth conditions for substrate temperature and gases flow rate. The grown InN nanowire of characteristics for morphologies, crystal structure, and element analysis were carried out by SEM, HR-TEM, and EDS respectively. And the defects of InN crystalline were analyzed by indexing of selective area diffraction pattern with attached HR-TEM. We have successfully obtained the defect-free 1- dimensional InN single crystalline nanowire at the atmosphere pressure.
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공침법으로 제조된 Yttira Doped Ceria분체의 건조방법에 따른 입자특성 고찰
변윤기,이상훈,최성철 한국세라믹학회 2003 한국세라믹학회지 Vol.40 No.8
In synthesis of nano powders, the hard agglomeration for the synthesized powders occurred during the drying processing. In order to avoid hard agglomeration in particles the freeze drying process was used in this experiment. e fabricated the Yttira-Doped Ceria(YDC) nano powder by co-precipitation. Starting materials used in experiments were the cerium(III) nitrate and yttrium(III) nitrate solution with 야-water, which two solutions were mixed and then the precipitated hydroxides were prepared for adding sodium hydroxide. The co-precipitated powders were dried by the thermal drying at 8$0^{\circ}C$ for 24 h and by freeze drying at -4$0^{\circ}C$, 30 mtorr for 72 h. The lattice parameter and crystallite size as a function of calcination temperature was characterized by XRD analysis. The lattice parameter of YDC was decreased with addition amount of yttrium and was estimated as 5.401683 $\AA$ at $700^{\circ}C$. Crystallite size were calculated by XRD-LB method, and morphologies were confirmed with the observation of TEM and SEM. The freeze dried YDC powders had medium diameter of 17 nm with more uniform size distribution than the thermal dried YDC posers, which were mainly ascribed to the difference of agglomerates formation during drying stage.
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변윤기,한경섭,최성철,최도문 한국세라믹학회 2007 한국세라믹학회지 Vol.44 No.3
High-quality one-dimensional GaN nanorods and nanowires were synthesized on Ni-coated c-plan sapphire substrate using halide vapor-phase epitaxy (HVPE). Their structure and optical properties were investigated by X-ray diffraction, scanning and transmission electron microscopy, and photoluminescence techniques. Full substrate coverage of densely packed, uniform, straight and aligned one-dimensional GaN nanowires with a diameter of 80nm were grown at 700~900oC. The X-ray diffraction patterns, transmission electron microscopic image, and selective area electron diffraction patterns indicate that the one-dimensional GaN nanostructures are a pure single crystalline and preferentially oriented in the [001] direction. We observed high optical quality of GaN nanowires by photoluminescence analysis.
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아세트산을 활용한 폐 마그카본(MgO-C) 내화물의 초음파 부상 분리에 관한 연구
변윤기 한국건설순환자원학회 2024 한국건설순환자원학회 논문집 Vol.12 No.1
본 연구에서는 제철공정에서 발생되는 산업폐기물인 폐 MgO-C 내화물로부터 고순도 흑연을 재생하기 위해 산화마그네슘(MgO)을 용해 할 목적으로 사용되는 강 산성용액을 대체하기 위해 상대적으로 약 산성용매인 아세트산 용매를 사용하는새로운 접근 방식을 제시 하였다. 폐내화물에서 MgO만 선택적으로 킬레이트 하는 아세트산의 농도를 달리하고 초음파 부상분리법 통해 높은 실수율 재생 흑연을 정제 회수 할수 있었다. 특히 2 M 아세트산을 용매를 사용 한 경우 흑연의 회수율은99.7 %를 나타내며 회수된 흑연의 순도는 72.7 %로 분석되었으며 물을 용매로 사용한 공정에 대비하여 상당한 개선방법을확보하였다. 또한, 본 연구에서 제시된 기술은 폐내화물 내 MgO와 아세트산의 반응을 통해 아세트산마그네슘을 생산하는방법을 제공하여 고효율의 흑연 정제 및 분리와 마그네슘 추출을 위한 자원을 함께 제공할 수 있을 것으로 기대한다. A novel approach is presented to address issues associated with the use of strong acidic solutions for the leaching of magnesium oxide (MgO) from spent magnesia-carbon refractories. An ultrasonic flotation and separation process is employed, with a mildly acidic solvent, acetic acid, used to selectively chelate MgO from the spent refractories. When using 2 M acetic acid as a solvent, the recovery of the graphite exhibited 99.7 % with high purity of 72.7 %, showing a significant improvement compared to using water as the solvent. Furthermore, the technology presented in this study offers a method for producing magnesium acetate through the reaction of MgO in spent refractory with acetic acid, providing a means for the purification and separation of graphite.
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Influence on the growth temperature for one-dimensional nanostructures by halide vapor-phase epitaxy
최성철,한경섭,변윤기 한양대학교 세라믹연구소 2005 Journal of Ceramic Processing Research Vol.6 No.3
High-quality one-dimensional GaN nanorods and nanowires were synthesized on Ni-coated c-plane sapphire substrates using halide vapor-phase epitaxy (HVPE). Their structure and optical properties were investigated by X-ray diffractometry, scanning and transmission electron microscopy, and photoluminescence techniques. A high density of straight and aligned onedimensional GaN nanowires with a diameter of 80 nm was uniformly formed on the entire substrate at 700 oC. The X-ray diffraction patterns, transmission electron microscope images, and selected area electron diffraction patterns indicate that the one-dimensional GaN nanostructures are pure single crystals and preferentially oriented in the [001] direction. We observed high optical quality of GaN nanowires by photoluminescence analysis.
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