• 한국환경과학회:학술대회논문집
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• 한국환경과학회 2019년도 정기학술대회 발표논문집
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• pp.223-223
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• 2019

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.274-274
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• 2014

금속칼코게나이드 화합물중 하나인 $MoS_2$는 초저 마찰계수의 금속성 윤활제로 널리 사용되고 있으며 흑연과 비슷한 판상 구조를 지니고 있어 기계적 박리법을 통한 그래핀의 발견 이후 2차원 박막 합성법에 대한 활발한 연구가 진행되고 있다. 최근 다양한 응용이 진행 중인 그래핀의 경우 높은 전자이동도, 기계적 강도, 유연성, 열전도도 등 뛰어난 물리적 특성을 지니고 있으나 zero-bandgap으로 인한 낮은 on/off ratio는 thin film transistor (TFT), 논리회로(logic circuit) 등 반도체 소자 응용에 한계가 있다. 하지만 $MoS_2$는 벌크상태에서 약 1.2 eV의 indirect band-gap을 지닌 반면 단일층의 경우 1.8 eV의 direct-bandgap을 나타내고 있다. 또한 단일층 $MoS_2$를 이용하여 $HfO_2/MoS_2/SiO_2$ 구조의 트랜지스터를 제작하였을 때 $200cm^2/v^{-1}s^{-1}$의 높은 mobility와 $10^8$ 이상의 on/off ratio 나타낸다는 연구가 보고되어 있어 박막형 트랜지스터 응용을 위한 신소재로 주목을 받고 있다. 한편 2차원 $MoS_2$ 박막을 합성하기 위한 대표적인 방법인 기계적 박리법의 경우 고품질의 단일층 $MoS_2$ 성장이 가능하지만 대면적 합성에 한계를 지니고 있으며 화학기상증착법(CVD)의 경우 공정 gas의 분해를 위한 높은 온도가 요구되므로 박막형 투명 트랜지스터 응용을 위한 플라스틱 기판으로의 in-situ 성장이 어렵기 때문에 이를 보완할 수 있는 $MoS_2$ 박막 합성 공정 개발이 필요하다. 특히 Plasma enhanced chemical vapor deposition (PECVD) 방법은 공정 gas가 전기적 에너지로 분해되어 chamber 내부에서 cold-plasma 형태로 존 재하기 때문에 박막의 저온성장 및 대면적 합성이 가능하며 고진공을 바탕으로 합성 중 발생하는 오염 요소를 효과적으로 제어할 수 있다. 본 연구에서는PECVD를 이용하여 plasma power, 공정압력, 공정 gas의 유량 등 다양한 공정 변수를 조절함으로써 저온, 저압 조건하에서의 $MoS_2$ 박막 성장 가능성을 확인하였으며 전구체로는 Mo 금속과 $H_2S$ gas를 사용하였다. 또한 향후 flexible 소자 응용을 위한 플라스틱 기판의 녹는점을 고려하여 공정 온도는 $300^{\circ}C$ 이하로 설정하였으며 합성된 $MoS_2$ 박막의 두께 및 화학적 구성은 Raman spectroscopy를 이용하여 확인 하였다. 공정온도 $200^{\circ}C$와 $150^{\circ}C$에서 성장한 $MoS_2$ 박막의 Raman peak의 경우 상대적으로 낮은 공정온도로 인하여 Mo와 H2S의 화학적 결합이 감소된 것을 관찰할 수 있었고 $300^{\circ}C$의 경우 약 $26{\sim}27cm^{-1}$의 Raman peak 간격을 통해 5~6층의 $MoS_2$ 박막이 형성 된 것을 확인할 수 있었다.

• 공업화학
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• 제5권2호
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• pp.327-336
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• 1994

본 연구는 아크롤레인의 선택산화반응에서 Mo-V-O와 금속산화물의 기계적 혼합촉매에 대한 synergy 효과를 고찰한 것으로 금속산화물로는 $SnO_2$, ${\alpha}-Sb_2O_4$, $WO_3$, ${\alpha}-Al_2O_3$, CuO, $MnO_2$, $Cu_2O$, MgO, CoO 그리고 ZnO 등을 사용하였다. $SnO_2$나 ${\alpha}-Sb_2O_4$와 Mo-V-O의 혼합물 촉매는 Mo-V-O보다 높은 전화율과 수율을 나타내었는데 이것은 이들이 산소 빈자리에 해리 홉착된 산소를 형성하여 Mo-V-O에 전달하는 상간협동에 의한 것으로 판단된다 그러나 $Cu_2O$, MgO, CuO, $MnO_2$와 Mo-V-O의 혼합물 촉매의 경우 전화율은 증가하였으나 수율은 감소하였고, CoO와 ZnO는 Mo-V-O의 촉매성능을 억제하였다. 각 금속산화물의 역할이 서로 다른 점을 그들의 산화-환원 특성으로 설명하였다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제3권1호
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• pp.44-47
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• 1998

Maximum cellulase production was sought by comparing the activities of the cellulases produced by different Trichoderma reesei strains and Aspergillus niger. Trichoderma reesei Rut-C30 showed higher cellulase activity than other Trichoderma reesei stains and Aspergillus niger that was isolated from soil. By optimizing the cultivation conditions during shake flask culture, higher cellulase production could be achieved. The FP(filter paper) activity of 3.7U/ml and CMCase (Carboxymethylcellulase) activity of 60U/ml were obtained from shake flask culture. When it was grown in 2.5L fermentor, where pH and DO levels are controlled, the enzyme activities were 133.35U/ml (CMCase) and 11.67U/ml(FP), respectively. Ammonium sulfate precipitation method was used to recover enzymes from fermentation broth. The dried cellulase powder showed 3074.9U/g of CMCase activity and 166.7U/g of FP activity with 83.5% CMCase recovery.

• 자원환경지질
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• 제24권3호
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• pp.245-260
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• 1991

Surficial dispersion patterns of heavy metals and toxic elements (U, Mo, Cu, Zn, Fe, Mn, Co, Cr, V, Ni, Pb, and Cd) were investigated in the Dukpyungri, Goesan area covered with low grade uranium-bearing black shales. Maximum abundance of U in the black shale was 455ppm. Radioactivity was counted at a maximum of 7cps in black shales, and was less than 0.5cps in shales, slates, and oil shales of the control areas. Enrichment of Mo, V, Cu, Zn, Cd, and Pb in black shales is particularly characteristic compared with shales, slates, and oil shales of the control areas, whereas contents of Mn, Cr, Co, and Th in all rock samples tend to be almost similar. Residual top soils (0~15cm depth) over black shales show high contents of Mo, Cu, Zn, Ni, Cd, and V in comparison with the control areas. Contents of trace elements in subsoils (15~30cm depth) were higher about one and half times than those in topsoils. Average contents of Mo, Cu, Pb, Zn, Cd and V in garden soil and playground soil of an elementary school in Dukpyungri, Goesan area, were high about two to fifteen times compared with the control areas. Contents of trace elements in stream sediments were higher from two to eight times than those in residual soils. Sodium, AI, K, V, Cr, and Fe were more enriched in the roots of pine than in the twigs of pine. Contents of Li, AI, V, Ni, Cd, Fe, and Co were higher in the roots of azalea than in the twigs of azalea. Enrichment of P, Ca, and Mg was remarkable in the twigs of both pine and azalea. Biological absorption coefficients for essential elements (Zn, P, Mn, Ca and K)tend to be high, whereas those for the non-essential elements.(Ba, Ti, V, and Mo) and toxic elements(Cr, Co, Pb and Ni) be low. Less mobile elements (Pd, Cd, and Co) tend to show anomalies with higher contrast than more mobile elements(Mo, V, Zn, Cu and Ni) in the area covered with black shales.

• Nuclear Engineering and Technology
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• 제52권4호
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• pp.802-810
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• 2020

Three-dimensional finite element simulations are implemented for the in-pile thermo-mechanical behavior in U-Mo/Al monolithic fuel plates with different thermal creep rates of cladding involved. The numerical results indicate that the thickness increment of fuel foil rises with the thermal creep coefficient of cladding. The maximum Mises stress of cladding is reduced by ~85% from 344 MPa on the 98.0^th day when the creep coefficient of cladding increases from 0.01 to 10.0, due to its equivalent thermal creep strain enlarged by 3.5 times. When the thermal creep coefficient of Aluminum cladding increases from 0 to 1.0, the maximum mesoscale stress of fuel foil varies slightly. At the same time, the peak mesoscale normal stress of fuel foil can reach 51 MPa on the 98.0^th day for the thermal creep coefficient of 10, which increases by 60.3% of that with the thermal creep un-occurred in the cladding. The maximum through-thickness creep strain components of fuel foil differ slightly for different thermal creep coefficients of cladding. The dangerous region of fuel foil becomes much closer to the heavily irradiated side when the creep coefficient of cladding becomes 10.0. The creep performance of Aluminum cladding should be optimized for the integrity of monolithic fuel plates.

• Nuclear Engineering and Technology
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• 제55권9호
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• pp.3464-3471
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• 2023

The Uranium/Molybdenum metallic fuel has been proposed as promising advanced fuel concept especially in the dispersed fuel geometry. The fuel is manufactured in the form of small fuel droplets (particles) placed in a fuel pin covered by a matrix. In addition to fuel particles, the pin contains voids necessary to compensate material swelling and release of fission gases from the fuel particles. When investigating this advanced fuel design, two important questions were raised. Can the dispersed fuel performance be analyzed using homogenization without significant inaccuracy and what size of fuel drops should be used for the fuel design to achieve optimal utilization? To answer, 2D burnup calculations of fuel assemblies with different fuel particle sizes were performed. The analysis was supported by an additional 3D fuel pin calculation with the dispersed fuel particle size variations. The results show a significant difference in the multiplication factor between the homogenized calculation and the detailed calculation with precise fuel particle geometry. The recommended fuel particle size depends on the final burnup to be achieved. As shown in the results, for lower burnup levels, larger fuel drops offer better multiplication factor. However, when higher burnup levels are required, then smaller fuel drops perform better.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.2195-2205
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• 2023

One of the salient nuclear fuel performance parameters for new fuel types under development is changes in fuel thickness. To test the new commercially fabricated U-10Mo monolithic plate-type fuel, an irradiation experiment was designed that consisted of multiple mini-plate capsules distributed within the Advanced Test Reactor (ATR) core, the mini-plate 1 (MP-1) experiment. Each capsule contains eight mini-plates that were either fueled or "dummy" plates. Fuel thickness changes within a fuel assembly can be characterized by measuring the gaps between the plates ultrasonically. The channel gap probe (CGP) system is designed to measure the gaps between the plates and will provide information that supports qualification of U-10Mo monolithic fuel. This study will discuss the design and the results from the use of a custom-designed CGP system for characterizing the gaps between mini-plates within the MP-1 capsules. To ensure accurate and repeatable data, acceptance and calibration procedures have been developed. Unfortunately, there is no "gold" standard measurement to compare to CGP measurements. An effort was made to use plate thickness obtained from post-irradiation measurements to derive channel gap estimates for comparison with the CGP characterization.

• 한국전자파학회논문지
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• 제20권5호
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• pp.428-434
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• 2009

본 논문에서는 U-형태의 기생 패치를 가지는 U-슬롯 마이크로스트립 안테나를 제안하였다. U-슬롯에 의해 발생하는 2개의 공진에 기생 패치에 의한 공진을 추가하여 더 넓은 대역폭을 가지도록 설계하였다. 유전체를 포함한 안테나 복사 소자의 크기는 $64{\times}53\;mm^2$이며, 접지면과 유전체를 포함한 안테나의 전체 크기는 $150{\times}150{\times}11.5\;mm^3$이다. 제안된 안테나는 VSWR<2를 기준으로 $1.85{\sim}2.40\;GHz$의 대역폭을 가져 DCS 1900, WCDMA, WiMax 등의 서비스 대역을 모두 만족하도록 설계하였다. 안테나의 복사 특성은 대역폭 내에서 비교적 일정한 형태를 유지하고, 빔 폭은 $60^{\circ}$ 정도이며, 7 dBi 이상의 이득을 갖는다.

• Bulletin of the Korean Chemical Society
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• 제20권1호
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• pp.59-64
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• 1999

Based on the study of hydrolysis behaviour of U(Ⅵ) ion and major fission product metal ions such as Cs(Ⅰ), Ce(Ⅲ), Nd(Ⅲ), Mo(Ⅵ), Ru(Ⅱ), and ZR(Ⅳ) in the titration media, the performance of noncomplexing-alkalimetric titration method for the determination of free acid in the presence of these metal ions was investigated and its results were compared to those from the completing methods. The free acidities could be determined as low as 0.05 meq in uranium solutions in which the molar ratio of U(Ⅵ)/H+ was less than 5, when the end-point of titration was estimated by Gran plot. The biases in the determinations were less than 1% and about +3% respectively for 0.4 meq and 0.05 meq of free acid at the U(Vl)/H+ molar ratio of up to 5. Applicability of this method to the determination of free acid in spent fuel solutions was confirmed by the analysis of nitric acid content in simulated spent fuel solutions and in a real spent fuel solution.