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자기펄스 성형 및 방전 플라즈마 소결 공정으로 제조한 텅스텐 소결체의 특성
이의선,변종민,정영근,오승탁,Lee, Eui Seon,Byun, Jongmin,Jeong, Young-Keun,Oh, Sung-Tag 한국재료학회 2020 한국재료학회지 Vol.30 No.6
The present study demonstrates the effect of magnetic pulse compaction and spark plasma sintering on the microstructure and mechanical property of a sintered W body. The relative density of green specimens prepared by magnetic pulse compaction increases with increase in applied pressure, but when the applied pressure is 3.4 GPa or more, some cracks in the specimen are observed. The pressureless-sintered W shows neck growth between W particles, but there are still many pores. The sintered body fabricated by spark plasma sintering exhibits a relative density of above 90 %, and the specimen sintered at 1,600 ℃ after magnetic pulse compaction shows the highest density, with a relative density of 93.6 %. Compared to the specimen for which the W powder is directly sintered, the specimen sintered after magnetic pulse compaction shows a smaller crystal grain size, which is explained by the reduced W particle size and microstructure homogenization during the magnetic pulse compaction process. Sintering at 1,600 ℃ led to the largest Vickers hardness value, but the value is slightly lower than that of the conventional W sintered body, which is attributed mainly to the increased grain size and low sintering density.
이의선,문정숙 한국소비자정책교육학회 2008 소비자정책교육연구 Vol.4 No.1
본 연구는 약관규제에 관한 연구로서 약관의 규제는 사업자보호의 목적과 소비자의 경제적권익보호의 목적을 모두 지니고 있는 정부규제의 영역이다. 따라서 약관규제를 첫째, 정부규제의 특성에 맞추어 제 과정을 분석함으로써 규제의 근거가 효과적으로 해결이 되고 있는지 규명해 보고, 둘째, 정부규제를 목적에 따라 분류하여 소비자의 경제적 권익보호를 위한 사회적규제로의 분류 가능성을 알아보고자 한다. 또한 공정거래위원회의 불공정약관 심결례를 분석하여 약관규제가 소비자적 의의 탐구의 가치가 있는지 타진해보고, 향후 소비자정책 제언의 근거로 제시하고자 한다. This paper is about the government regulation of general clauses. Its characteristic purposes are to protect businesses and to protect consumer’s properties. Since the study of general clause is usually conducted with a business viewpoint, the writers reviewed the basic theory this regulation with the consumer’s viewpoint. As a result of the review, writers suggested three study points. First, as a study of the general clause process from a part of government regulation process, the writers could find out whether the problems which suggested causes of government regulation solved or not. Second, the writers classified the regulation of general clause as purposes to find out a possibility that they could classify a social regulation for consumer’s properties protection. As a last point, the writers reviewed determined unfair clause cases by FTC to learn the significance of the consumer’s view.
동결건조 공정에서 Tert-butyl alcohol 기공형성제가 텅스텐 다공체의 기공구조에 미치는 영향
이의선,허연지,고윤택,박진경,좌용호,오승탁,Lee, Eui Seon,Heo, Youn Ji,Ko, Yun Taek,Park, Jin Gyeong,Cho, Yong-Ho,Oh, Sung-Tag 한국분말재료학회 (*구 분말야금학회) 2021 한국분말재료학회지 (KPMI) Vol.28 No.3
The effect of tert-butyl alcohol (TBA) as a freezing solvent on the pore structure of a porous tungsten body prepared by freeze-drying is analyzed. TBA slurries with a WO3 content of 10 vol% are prepared by mixing with a small amount of dispersant and binder at 30℃. The slurries are frozen at -25℃, and pores are formed in the frozen specimens by the sublimation of TBA during drying in air. After hydrogen reduction at 800℃ and sintering at 1000℃, the green body of WO<sub>3</sub> is completely converted to porous W with various pore structures. Directional pores from the center of the specimen to the outside are observed in the sintered bodies because of the columnar growth of TBA. A decrease in pore directionality and porosity is observed in the specimens prepared by long-duration drying and sintering. The change in pore structure is explained by the growth of the freezing solvent and densification.
WO<sub>3</sub>/tert-butyl alcohol 슬러리의 동결건조 조건이 다공체의 미세구조 특성에 미치는 영향
이의선,허연지,석명진,오승탁,Lee, Eui Seon,Heo, Youn Ji,Suk, Myung-Jin,Oh, Sung-Tag 한국분말재료학회 (*구 분말야금학회) 2021 한국분말재료학회지 (KPMI) Vol.28 No.4
The effects of drying temperature on the microstructure of porous W fabricated by the freeze-casting process of tert-butyl alcohol slurry with WO<sub>3</sub> powder was investigated. Green bodies were hydrogen-reduced at 800℃ for 1 h and sintered at 1000℃ for 6 h. X-ray diffraction analysis revealed that WO<sub>3</sub> powders were completely converted to W without any reaction phases by hydrogen reduction. The sintered body showed pores aligned in the direction of tert-butyl alcohol growth, and the porosity and pore size decreased as the amount of WO<sub>3</sub> increased from 5 to 10vol%. As the drying temperature of the frozen body increased from -25℃ to -10℃, the pore size and thickness of the struts increased. The change in microstructural characteristics based on the amount of powder added and the drying temperature was explained by the growth behavior of the freezing agent and the degree of rearrangement of the solid powder during the solidification of the slurry.