• KSBB Journal
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• 제11권1호
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• pp.100-106
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• 1996

300bar와 313K에서 초임계 이산화탄소와 에틸아세테이트와 메탄올을 보조용매로 사용하여 주목나무로부터 taxol과 baccatin III를 추출하는 실험을 한 결과 추출되어지는 taxol의 추출량은 보조용매로 사용된 에틸아세테이트의 농도에는 영향을 받지 않았으며 3wt%의 메탄올을 사용했을 때 가장 많은 양이 추출되었고 taxol의 선택성은 보조용매로 에틸아세테이트를 사용했을 때 0.117mass%로 가장 높게 나타났다. Baccatin III는 보조용매로 에틸아세테이트를 사용하면 유기용매 추출량과 거의 같은 양이 추출되어지며 이 때의 선택성은 0.7wt% 에틸아세테이트에서 1.245wt%, 3.0wt% 에틸아세테이트에서 1.115wt%로 유기용매 추출에 비해 19배까지 크게 증가하였으며 3wt%의 메탄올을 사용했을 때에는 약 6.4배 증가하였다. 여기서 에틸아세테이트는 baccatin III를 추출하는데 있어 수율과 선택성면에서 가장 효과적인 보조용매라는 것을 알 수 있다. 또한 시료를 n-hexane으로 처리하면 비극성 물질은 상당히 제거되나 그 과정에서 많은 양의 taxol 과 baccatin III가 손실될 뿐만 아니라 선택성도 증가하지 않으므로 공정상 불필요하며 보조용매를 사용한 초임계유체 추출이 주목나무로부터 특정성분을 추출하는데 아주 효과적이라는 것을 알 수있다.

• 에너지공학
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• 제6권2호
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• pp.198-202
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• 1997

The oxidation behavior of UO$_2$pellets was studied using a thermogravimetric analyzer and an XRD in the temperature range of 300 to 550$^{\circ}C$ in air. From XRD studies it is found that UO$_2$is converted to U$_3$O$\_$8/ and the weight gains of UO$_2$specimen are characterized by S-shape curves. After complete oxidation the specimens broke into fine powder and the average weight gain was about 3.93 wt%. The activation energy of 50% conversion of UO$_2$to U$_3$O$\_$8/ is 81.6 kJ/mol and the oxidation rate per unit time was found to be as follows dw/dt=6.54${\times}$10$\^$6/ e (equation omitted), wt%/h : at 50% conversion of UO$_2$into U$_3$O$\_$8/ where w, t and T were wt% gain, conversion time and temperature, respectively.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 춘계학술대회논문집
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• pp.183-186
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• 2000

The high temperature deformation behavior of spray-formed Al-19wt%Si-1.87wt%Mg-0.085wt.%Fe alloy was studied by torsion testing in the strain rate range of 0.001-1 sec-1 and in the temperature range of 300-500 $^{\circ}C$. The relationship between stress temperature and strain rate is expressed using the Power law. the behavior of dynamic recrystallization is showed in 300-35$0^{\circ}C$, 1-0.1sec-1 and the behavior of dynamic recovery is showed in 450-50$0^{\circ}C$, 0.01-0.001sec-1 The size of Si particles is mall when the temperature is low and the strain rate is high. The strain rate sensitivity(m) and the apparent activation energy(Q) indicate the dependence on strain rate and temperature for flow stress respectively. The hot ductility is high when m is high and Q is low. The maps of strain rate sensitivity and apparent activation energy suggest the optimum processing conditions.

• 한국환경과학회지
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• 제25권3호
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• pp.373-383
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• 2016

The aim of this study is to determine the exposure concentration of tetrabromobisphenol A(TBBPA) in southwestern coast and their photodecomposition rate. Also, it is to identify the radical species of the photodecomposition of TBBPA and their reactive byproducts using the electron spin resonance(ESR) method. TBBPA was not detected in any of the sea water samples from Mokpo, Gunsan, or Goheung. The sediment samples from Mokpo contained not detection(N.D)~50.0 ng/g dry wt., while those from Gunsan contained N.D~28.5 ng/g dry wt. and those from Goheung contained N.D~7.3 ng/g dry wt. The photodecomposition rates were $2.56{\times}10^{-6}/hr$ by visible light(400 nm), $7.98{\times}10^{-6}/hr$ by ultraviolet light(300 nm <), and $6.78{\times}10^{-6}/hr$ by sunlight. Also, we confirmed that singlet oxygen and hydroxyl radicals are the key reactive oxygen species at wavelengths greater than 400 and 300 nm, respectively. This study shows that the main byproducts formed during irradiation at wavelengths above 300 nm are 2,6-dibromobenzosemiquinone radical(2,6-$DBSQ{\cdot}^-$) and g-value 2.0048 doublet spectrum.

• 한국분말재료학회지
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• 제1권1호
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• pp.4-14
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• 1994

The effects of Ce on the mechanical alloying behavior and the thermal stability of Al-8wt.%Fe were investigated. The steady states of Al-8wt.%Fe and Al-8wt.%Fe-4wt.%Ce powders with 1.5 wt.% stearic acid as a process control agent were reached after mechanical alloying for 1000 minuties and 1300 minuties respectively at the conditions of the impeller revolving velocity of 300 rpm and the ball to powder input ratio of 50 : 1. The hardness of Al-8wt.%Fe specimen hot extruded and isothermally aged at various temperatures for up to 1000 hours decreased rapidly at 50$0^{\circ}C$ and its high temperature ultimate tensile strength began to decrease at 40$0^{\circ}C$ with increasing aging time. The decrease in the hardness and ultimate tensile strength of the specimen were reduced substantially by addition of Ce. It was thought to be due to the formation of thermally stable A14Ce and All3Fe3Ce intermetallic compounds.

• 한국환경과학회지
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• 제20권2호
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• pp.223-229
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• 2011

Toluene desorption of modified activated carbon for microwave irradiation was evaluated. As a virgin GAC reacted from microwave energy, it created an "arcing" between GAC particles in desorption process. The arcing became more and more vigorous and achieved a red flame of GAC. The silica coated GAC(Si/GAC) was developed to prevent arcing phenomenon and temperature control problem. The result shows virgin GAC with 5wt%, 10wt% and 20wt% silica had no arcing and could control temperature very well. However, the adsorption rate of Si/GAC was decreased by coated silica amount due to decreasing surface area of GAC. The 5wt% Si/GAC adsorption rate was quite similar to virgin GAC adsorption rate. After adsorption, the toluene-loaded GAC and Si/GAC was reactivated by 2450MHz MW irradiation with 300W for 5 min. Quantitative desorption of the toluene was achieved at MW irradiation at 300W with desorption efficiencies as high as 98.59% to 84.65%% after four cycles.

• Corrosion Science and Technology
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• 제11권5호
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• pp.191-195
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• 2012

The aim of this study was to investigate effects of hafnium content on the corrosion behavior of Ti alloys in electrolyte containing chloride ion. For this study, Ti-Hf binary alloys contained 10 wt%, 20 wt% and 30 wt% Hf were manufactured in a vacuum arc-melting furnace and subjected to heat treatment for 12h at $1000^{\circ}C$ in an argon atmosphere. The pitting corrosion behavior of the specimens was examined through potentiodynamic and potentiostatic tests in 0.9 wt% NaCl electrolyte at $36.5{\pm}1^{\circ}C$. The corrosion morphology of Ti-xHf alloys was investigated using optical microscopy (OM) and X-ray diffractometer (XRD). From the optical microstructures and XRD results, needle-like martensite ($\alpha$') phases of the Ti-xHf alloys increased with an increase of Hf addition. Corrosion current density $(I_{corr})$ and current density $(I_{300mV})$ in passive region decreased, whereas, corrosion potential increased with Hf content. At the constant potential ($300mV_{SCE}$), current density decreased as time increased.

• 한국산학기술학회논문지
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• 제14권9호
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• pp.4185-4190
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• 2013

본 연구에서는 불순물 첨가에 따른 MgO의 소결에 대한 물성변화를 확인하고자 99.9%순도, 300nm크기의 MgO 파우더에 고순도의 CaO를 0wt%, 0.25wt%, 0.50wt% 첨가하여 7GPa의 초고압 하에서 각각 $600^{\circ}C$~$800^{\circ}C$로 5분간 소결을 진행하였다. MgO(-CaO) 소결체의 미세구조와 기계적 물성 변화 확인을 위해 scanning electron microscopy(SEM), X-ray diffractometry(XRD), Vickers 경도, 밀도 측정을 진행하였다. SEM 분석 결과 처리전 300nm 의 MgO 응집체는 $800^{\circ}C$ 고압소결 후 CaO첨가와 관련 없이 모두 약 520nm 입도의 소결체가 되었다. XRD 분석결과 CaO상 자체는 확인할 수 없었으나 CaO고용에 따른 MgO 피크의 쉬프트에 의해 CaO의 존재를 확인할 수 있었다. 비커스 경도치 확인결과 CaO를 첨가하지 않은 MgO 소결체에 비해 동일 온도조건에서 약 12% 증가하였으며 비슷한 경도치를 얻기 위해 소결온도를 약 $100^{\circ}C$이상 낮출 수 있었음을 확인할 수 있었다. 밀도 측정결과 $600^{\circ}C$의 낮은 온도조건 하에서도 CaO를 첨가하지 않은 MgO 소결체에 비해 약 5%이상 증가한 98%이상의 효과적인 소결밀도를 얻을 수 있었다.

• 한국전자통신학회논문지
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• 제18권5호
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• pp.797-802
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• 2023

본 연구에서는 펄스 레이저 증착법으로 기판 온도에 따른 GZO(Ga₂O₃ : 5 wt %, ZnO : 95 wt %) 박막을 유리 기판에 증착하여 전기적 및 광학적 특성을 조사하였다. XRD측정을 통해 기판 온도에 무관하게 모든 GZO 박막이 c 축으로 우선 성장함을 확인할 수 있었고, 300℃ 에서 증착한 GZO 박막이 반가폭 0.38° 로 가장 우수한 결정성을 나타내었다. 기판 온도가 150에서 300℃ 로 증가함에 따라 GZO 박막의 비저항은 감소하는 경향을 보인 반면에 가시광 영역에서의 평균 투과도는 크게 영향을 받지 않는 것으로 조사되었다. 300℃ 에서 증착한 GZO 박막의 재료 평가 지수가 2.05×10⁴ Ω^-1·cm^-1 로 가장 우수한 값을 나타내었고, 이때 비저항과 가시광 영역에서의 평균 투과도는 각각 3.72 × 10^-4 Ω·cm 과 87.71 % 이었다. 본 연구를 통해 GZO 박막이 매우 유망한 투명 전도막 재료라는 것을 알 수 있었다.

• 대한금속재료학회지
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• 제50권12호
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• pp.955-959
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• 2012

To increase the hydrogen storage capacity of Mg-based materials, a sample with a composition of 69.7 wt% $MgH_2$ + 30.3 wt% $LiBH_4$ was prepared by planetary ball milling under hydrogen. The absorption and desorption properties of unmilled $MgH_2$, unmilled $LiBH_4$, and 69.7 wt% $MgH_2$ + 30.3 wt% $LiBH_4$ were examined. At 648 K the unmilled $MgH_2$ desorbed 5.70 wt% for 60 min. The unmilled $LiBH_4$ desorbed 6.40 wt% H for 780 min at 673 K. The 69.7 wt% $MgH_2$ + 30.3 wt% $LiBH_4$ sample desorbed 3.10 wt% H for 50 min, and 3.32 wt% H for 300 min at 623 K at the second cycle.