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전기선폭발법으로 제조된 텅스텐 분말의 산소 조성이 방전플라즈마소결 거동에 미치는 영향
김철희,이성,김병기,김지순,Kim, Cheol-Hee,Lee, Seong,Kim, Byung-Kee,Kim, Ji Soon 한국분말야금학회 2014 한국분말재료학회지 (KPMI) Vol.21 No.6
Effect of oxygen content in the ultrafine tungsten powder fabricated by electrical explosion of wire method on the behvior of spark plasma sintering was investigated. The initial oxygen content of 6.5 wt% of as-fabricated tungsten powder was reduced to 2.3 and 0.7 wt% for the powders which were reduction-treated at $400^{\circ}C$ for 2 hour and at $500^{\circ}C$ for 1h in hydrogen atmosphere, respectively. The reduction-treated tungsten powders were spark-plasma sintered at $1200-1600^{\circ}C$ for 100-3600 sec. with applied pressure of 50 MPa under vacuum of 0.133 Pa. Maximun sindered density of 97% relative density was obtained under the condition of $1600^{\circ}C$ for 1h from the tungsten powder with 0.7 wt% oxygen. Sintering activation energy of $95.85kJ/mol^{-1}$ was obtained, which is remarkably smaller than the reported ones of $380{\sim}460kJ/mol^{-1}$ for pressureless sintering of micron-scale tungsten powders.
유기 킬레이터들을 이용한 구리 식각에 대한 반응성 평가
김철희,임은택,박찬호,박성용,이지수,정지원,김동욱,Kim, Chul Hee,Lim, Eun Taek,Park, Chan Ho,Park, Sung Yong,Lee, Ji Soo,Chung, Chee Won,Kim, Dong Wook 한국재료학회 2021 한국재료학회지 Vol.31 No.10
The reactivity evaluation of copper is performed using ethylenediamine, aminoethanol, and piperidine to apply organic chelators to copper etching. It is revealed that piperidine, which is a ring-type chelator, has the lowest reactivity on copper and copper oxide and ethylenediamine, which is a chain-type chelator, has the highest reactivity via inductively coupled plasma-mass spectroscopy (ICP-MS). Furthermore, it is confirmed that the stable complex of copper-ethylenediamine can be formed during the reaction between copper and ethylenediamine using nuclear magnetic resonance (NMR) and radio-thin layer chromatography. As a final evaluation, the copper reactivity is evaluated by wet etching using each solution. Scanning electron micrographs reveal that the degree of copper reaction in ethylenediamine is stronger than that in any other chelator. This result is in good agreement with the evaluation results obtained by ICP-MS and NMR. It is concluded that ethylenediamine is a prospective etch gas for the dry etching of the copper.
아연도금 강판의 $CO_2$ 레이저-TIG 하이브리드 용접에 관한 연구 Part 1 : 용접현상분석
김철희,최웅용,채현병,김정한,이세헌,Kim, Cheol-Hee,Choi, Woong-Yong,Chae, Hyun-Byung,Kim, Jeong-Han,Rhee, Se-Hun 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.4
In lap welding of zinc-coated steel, porosity formation is one of most significant weld defects, which is caused by zinc vapor generated between the steel sheets. Various solutions have been proposed in the past years but development of more effective method is a worthwhile subject to be investigated. In this study, autogenous laser welding and laser-TIG hybrid welding was applied to the lap welding of zinc-coated steel without gap, and weld pool behaviors were observed by using high speed camera and the porosity generation mechanism was analyzed. The weld defects were successfully eliminated by laser-TIG hybrid welding. This is because the leading TIG arc partially melted the upper sheet and vaporized/oxidized the coated zinc on the lapped surfaces prior to the trailing laser illuminating the specimen.
아연도금 강판의 $CO_2$ 레이저-TIG 하이브리드 용접에 관한 연구 Part 2 : 공정변수와 용접성과의 관계
김철희,최웅용,채현병,김정한,이세헌,Kim, Cheol-Hee,Choi, Woong-Yong,Chae, Hyun-Byung,Kim, Jeong-Han,Rhee, Se-Hun 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.4
Optimization of process parameters for laser-arc hybrid welding process is intrinsically sophisticated because the process has three kinds of parameters-arc, laser and hybrid welding parameters. In this paper, the relationship between weldability and several process parameters such as laser beam-arc distance, electrode height, welding current and welding speed, were investigated by the full factorial experimental design. Weld quality was evaluated by using weight of spatters which is related with the pore area. It was found that the weld quality was increased with the increases in laser beam-arc distance and welding current, and decreased with the increases in electrode height and welding speed.
김철희,Kim, Cheol-Hui 한국천문학회 1996 天文學論叢 Vol.11 No.1
In order to discover the candidates of emission-line galaxies towards Hydra Void, objective-prism observations using U.K. Schmidt Telescope were carried out. To search the emission feature of [0III]${\lambda}{\lambda}4959,5007$ for all objects on the plate, all observed prism plates were scanned with APM at the Royal Observatory and the copied direct R plates were scanned with PDS Microdensitometer operating in the Inter- University Center for National Science Research Facilities. By utilizing the "XIMTOOL" package, both spectral and direct images for the same field were displayed simultaneously on up and down windows separately. In case of distinct emission features for a certain object, corresponding direct object on the other window was examined through eyeballing to see whether this object is a galaxy. Through this procedure, we discovered in total 33 candidates of emission-line galaxies in a single field.