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L1₂ 기 Al-Ti-Cr 합금의 상안정성에 미치는 Zr 첨가효과
천동현,이재경,오명훈,위당문 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.1
Interest in the L1₂ phase in the Al-Ti-Cr system has increased with respect to the demand for light weight materials at elevated temperature because of its enhanced mechanical properties that arise through the substitution of Cr for Al in Al₃Ti intermetallic compounds. Additionally, recent work has indicated that the application of L1₂- based alloys was extended to oxidation resistance coating materials for γ-based TiAl alloy because the L12 phase could form a protective Al₂O₃ scale under oxidizing environments. However, L1₂ phase decomposes partially or completely to a more brittle phase when exposed to temperatures in the range of 800~1000℃, resulting a serious degradation of the cracking resistance in L1₂-based alloys. In this study, Zr was substituted for Ti in Al-21Ti-23Cr alloys to improve the phase stability around 800℃. As a result of Zr addition in L12-based Al-Ti-Cr alloys, the fraction of L12 phase decomposition at 800℃ was decreased. Furthermore, temperature range, in which L1₂ phase was decomposed to other brittle phase, was shrunken when Zr was added in the Al-Ti-Cr alloys. These phenomena resulted from the fact that the L1₂ phase field was less shifted in the direction of the Al-rich corner at 800oC in the Al-Ti-Cr system and that atomic diffusion for the L1₂ phase decomposition was reduced. Therefore, the addition of Zr is required to increase the possibility for potential usage of L1₂-based Al-Ti-Cr alloys at elevated temperatures around 800℃ because of the improvement of phase stability.
FT 합성반응용 철촉매에 미치는 촉매특성에 미치는SiO<sub>2</sub> 첨가효과
천동현(Chun, Dong-Hyun),김학주(Kim, Hak-Joo),현순택(Hyun, Sun-Taek),양정훈(Yang, Jung-Hoon),이호태(Lee, Ho-Tae),양정일(Yang, Jung-Il),정헌(Jung, Heon) 한국신재생에너지학회 2009 한국신재생에너지학회 학술대회논문집 Vol.2009 No.06
Precipitated iron-based catalysts are highly promising for the Fischer-Tropsch synthesis (FTS), in particular for the low temperature FTS below 280?C, because of their high activity and low cost. SiO₂ is an essential promoter for the precipitated iron-based catalysts to improve the attrition strength and physical stability. In this study, we carried out FTS over precipitated iron-based catalysts with and without SiO₂ in a fixed-bed reactor. The catalysts were prepared by a conventional co-precipitation method. In case of the catalysts with SiO₂, we used two comparative preparation methods, i.e., incorporation of SiO₂ before precipitation (denoted as precipitated SiO₂) and after precipitation (denoted as binder SiO₂), respectively. The addition of SiO₂ crucially affects both physico-chemical properties and catalytic peformance of precipitated iron-based catalysts.
SiO<sub>2</sub> 원료물질에 따른 Fischer-Tropsch 합성반응용 Fe계 촉매의 성능변화
천동현(Chun, Dong Hyun),김학주(Kim, Hak-Joo),현순택(Hyun, Sun-Taek),이호태(Lee, Ho-Tae),양정일(Yang, Jung-Il),양정훈(Yang, Jung Hoon),정헌(Jung, Heon) 한국신재생에너지학회 2010 한국신재생에너지학회 학술대회논문집 Vol.2010 No.06
Fe계 촉매는 FT(Fischer-Tropsch) 합성반응에 매우 유망한 촉매로 주목받고 있으며, 280?C 미만의 저온 FT 합성반응의 경우, 침전법이 Fe계 촉매의 가장 전형적인 제조방법으로 알려져 있다. Fe계 촉매에 첨가되는 조촉매로는 Cu, K, SiO₂ 등이 가장 대표적이며, 이 중에서 특히 구조 조촉매로 첨가되는 SiO₂는 Fe계 촉매의 기계적 강도를 향상시킬 뿐만 아니라, 촉매의 성능에도 크게 영향을 미치는 것으로 보고되고 있다. 본 연구에서는 침전법을 이용하여 저온 FT 합성반응용 Fe계 촉매를 제조하였고, 구조 조촉매로 첨가한 SiO₂의 원료물질에 따른 Fe계 촉매의 성능변화를 조사하였다. SiO₂의 원료물질로는 콜로이드 SiO₂와 분말 SiO₂를 이용하였으며, 분말 SiO₂를 이용한 촉매가 콜로이드 SiO₂를 이용한 촉매보다 다소 높은 CO 전환율 및 중질탄화수소 선택도를 나타내는 것을 확인하였다.