• 한국수소및신에너지학회논문집
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• 제23권5호
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• pp.493-502
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• 2012

Syngas laminar burning velocity measurements were carried out at atmospheric pressure and ambient temperature using the Bunsen flame configuration with nozzle burner as a fundamental study on flame stability of syngas fuel. Representative syngas mixture compositions ($H_2$:CO) such as 25:75%, 50:50% and 75:25% and equivalence ratios from 0.5 to 1.4 have been conducted. Average laminar burning velocities have been determined by the stabilized nozzle burner flames using the angle method, radical surface area method and compared with the data obtained from the other literatures. And the results of each experimental methodologies in the various composition ratios and equivalence ratios were coincided with the result of numerical simulation. Especially, it was confirmed that there was necessary to choice a more accurate measurement methodology even the same static flame method for the various composition ratios of syngas fuel including hydrogen. Also, it was reconfirmed that the laminar burning velocities gradually increased with the increasing of hydrogen content in a fuel mixture.

• 대한기계학회논문집B
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• 제38권8호
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• pp.677-685
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• 2014

직접 탄소 연료전지(DCFC)는 석탄을 비롯한 탄소계 연료의 화학에너지를 직접 전기로 변환시킨다. 특히, 약 10 년 전에 고체산화물 전해질을 사용하고 연료극 매개체로 용융탄산염을 사용하는 고성능 직접탄소 연료전지 시스템이 제안되었다. 이 시스템의 경우, 운전 온도가 증가할수록 고체산화물 전해질의 이온 전도도가 향상되고 전기화학 반응이 활성화되어 성능이 향상되나, 연료극 매개체의 화학적인 안정성 문제발생이 우려된다. 본 연구에서는 탄소-탄산염 혼합 매개체의 고온 안정성을 이해하기 위한 일련의 실험을 수행하였다. 질소 또는 이산화탄소 분위기에서 카본블랙과 혼합된 $Li_2CO_3$와 $K_2CO_3$의 TGA 분석을 수행하였으며, 가열 과정에서 시료로부터 생성되는 가스 성분을 분석하였다. 이러한 결과를 해석하기 위하여, 탄산염의 열분해와 탄산염 등에 의하여 가속화되는 탄소 가스화 반응을 고려한 화학반응 모델을 제시하였으며, 실험 결과로부터 구한 매개체의 중량 손실과 가스 생성을 정성적으로 설명하였다.

• 한국해양공학회지
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• 제31권3호
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• pp.241-247
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• 2017

Plywood, which is created by bonding an odd number of thin veneers perpendicular to the grain orientation of an adjacent layer, was developed to supplement the weak points such as contraction and expansion of conventional wood materials. With structural merits such as strength, durability, and good absorption against impact loads, plywood has been adopted as a structural material in the insulation system of a membrane type liquefied natural gas (LNG) carrier. In the present study, as an attempt to resolve recent failure problems with plywood in an LNG insulation system, conventional PF (phenolic-formaldehyde) resin plywood and its alternative MUF (melamine-urea-formaldehyde) resin bonded plywood were investigated by performing material bending tests at ambient ($20^{\circ}C$) and cryogenic ($-163^{\circ}C$) temperatures to understand the resin and grain effects on the mechanical behavior of the plywood. In addition, the failure characteristics of the plywood were investigated with regard to the grain orientation and testing temperature.

• 자원리싸이클링
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• 제16권1호
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• pp.37-43
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• 2007

본 연구에서는 함수염화마그네슘 탈수를 통하여 마그네슘 용융염전해의 원료 물질인 무수염화마그네슘을 제조하였으며, 탈수는 관상로를 이용하여 $350{\sim}580^{\circ}C$ 범위에서 수행하였다. 함수염화마그네슘을 대기중에서 탈수할 경우 모두 산화마그네슘으로 산화되는 것을 알 수 있었으며, 염화수소가스 분위기에서 탈수시켜 무수염화마그네슘을 제조할 수 있음을 확인하였다. 그리고 탈수 온도와 시간이 증가함에 따라 탈수된 무수염화마그네슘의 결정성이 증가하였다. 염화수소가스 분위기에서 탈수가 일어나는 동안 발생되는 미반응 염화수소가스는 모두 염산으로 회수할 수 있었으며, 회수한 염산은 산화마그네슘으로부터 함수염화마그네슘을 제조하는 데에 재사용 가능할 것으로 판단된다.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1671-1678
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• 1996

In external chemical vapor deposition processes including VAD and OVD the distribution of flame-synthesized silica particles is determined by heat and mass transfer limitations to particle formation. Combustion gas flow velocities are such that the particle diffusion time scale is longer than that of gas flow convection in the zone of particle formation. The consequence of these effects is that the particles formed tend to remain along straight smooth flow stream lines. Silica particles are formed due to oxidation and hydrolysis. In the hydrolysis, the particles are formed in diffuse bands and particle formation thus requires the diffusion of SiCl$\_$4/ toward CH$\_$4//O$\_$2/ combustion zone to react with H$\_$2/O diffusing away from these same zones on the torch face. The conversion kinetics of hydrolysis is fast compared to diffusion and the rate of conversion is thus diffusion-limited. In the language of combustion, the hydrolysis occurs as a Burke-Schumann process. In selected conditions, reaction zone shape and temperature distributions predicted by the Burke-Schumann analysis are introduced and compared with experimental data available. The calculated centerline temperatures inside the reaction zone agree well with the data, but the calculated values outside the reaction zone are a little higher than the data since the analysis does not consider diffusion in the axial direction and mixing of the combustion products with ambient air. The temperatures along the radial direction agree with the data near the centerline, but gradually diverge from the data as the distance is away from the centerline. This is caused by the convection in the radial direction, which is not considered in the analysis. Spatial distribution of silica particles are affected by convection and diffusion, resulting in a Gaussian form in the radial direction.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.185-185
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• 2011

ZnTe semiconductor is very attractive materials for optoelectronic devices in the visible green spectral region because of it has direct bandgap of 2.26 eV. The prototypes of ZnTe light emitting diodes (LEDs) have been reported [1], showing that their green emission peak closely matches the most sensitive region of the human eye. Another application to photovoltaics proved that ZnTe is useful for the production of high-efficiency multi-junction solar cells [2,3]. By using the pulse laser deposition system, ZnTe thin films were deposited on ZnO thin layer, which is grown on (0001) Al2O3substrates. To produce the plasma plume from an ablated ZnO and ZnTe target, a pulsed (10 Hz) YGA:Nd laser with energy density of 95 mJ/$cm^2$ and wavelength of 266 nm by a nonlinear fourth harmonic generator was used. The laser spot focused on the surface of the ZnO and ZnTe target by using an optical lens was approximately 1 mm2. The base pressure of the chamber was kept at a pressure around $10^{-6}$ Torr by using a turbo molecular pump. The oxygen gas flow was controlled around 3 sccm by using a mass flow controller system. During the ZnTe deposition, the substrate temperature was $400^{\circ}C$ and the ambient gas pressure was $10^{-2}$ Torr. The structural properties of the samples were analyzed by XRD measurement. The optical properties were investigated by using the photoluminescence spectra obtained with a 325 nm wavelength He-Cd laser. The film surface and carrier concentration were analyzed by an atomic force microscope and Hall measurement system.

• Biotechnology and Bioprocess Engineering:BBE
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• 제11권6호
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• pp.484-488
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• 2006

Alteration of illumination with optimum carbon dioxide fixation-based curve in this research successfully enhanced the $CO_{2}-fixation\;(q_CO_{2}$ capability of Chlorella vulgaris Buitenzorg cultivated in a bubble column photo bioreactor. The level of $CO_{2}$ fixation was up to 1.91 times that observed from cultivation with intensification of illumination on an optimum growth-based curve. During 144 h of cultivation, alteration of light intensity on an optimum $CO_{2}-fixation-based$ curve produced a $q_CO_{2}$ of $12.8\;h^{-1}$. Meanwhile, alteration of light intensity with a growth-based curve only produced a $q_CO_{2}$ of $6.68\;h^{-1}$. Increases in light intensity based on a curve of optimum $CO_{2}-fixation$ produced a final cell concentration of about 5.78 g/L. Both cultivation methods were carried out under ambient pressure at a temperature of $29^{\circ}C$ with a superficial gas velocity of $2.4\;m/h(U_{G}$. Cells were grown on Beneck medium in a 1.0 L Bubble Column Photo bioreactor illuminated by a Phillips Halogen Lamp (20 W/12 V/50 Hz). The inlet gas had a carbon dioxide content of 10%.

• 분석과학
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• 제26권4호
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• pp.235-244
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• 2013

할로겐족 원소들의 강한 원자 방출선들은 진공자외선 영역에 존재하여, 공기 중에서 레이저 펄스를 시료에 집속하여 플라즈마 방출 스펙트럼을 얻어 원소 분석을 수행하기 매우 어렵다. 또한 근적외선 영역에 할로겐족 원소들의 들뜬 전자 상태들 사이의 전이에 의한 원자 방출선들이 존재하는데, 이들은 스타크 효과에 의한 선폭 넓어짐 현상이 매우 커서, 공기 중에서 원소 분석에 충분한 신호 대 잡음비를 얻기 어렵다. 헬륨 가스 플로우를 이용하여 근적외선 영역의 할로겐족 원소들의 원자 방출선들은 레이저유도 플라즈마로부터 관측하였다. 특히, 804.374 nm와 905.833 nm의 아이오딘 원자 방출선들은 레이저유도 플라즈마에서 처음으로 관찰된 것이다. 헬륨 분위기에서 스타크 효과에 의한 선폭 넓어짐 현상과 연속 배경복사의 세기는 현저히 억제되었다. 헬륨 가스 플로우의 유량에 따른 원자 방출선의 세기, 플라즈마 온도, 전자 밀도의 변화를 조사하였다. 이 방법을 이용하여 고무의 난연제 성분에 포함된 염소와 불소를 레이저유도 플라즈마 분광법을 이용하여 검출하였다. 마지막으로 레이저유도 플라즈마 분광법을 이용하여 할로젠 원소들을 검출하는데 헬륨 가스 소모량을 줄일 수 있는 가스 펄스 젯 장치를 제안한다.

• 한국진공학회지
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• 제21권5호
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• pp.273-278
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• 2012

현재 Hf (Hafnium)을 기반으로한 게이트 유전체의 연구는 여러 분야에서 다양하게 진행되어져 왔다. 이는 기존의 $SiO_2$보다 유전상수 값이 크고, 또한 계속되는 scaling-down 공정에서도 양자역학적인 터널링을 차단하는 특성이 뛰어나기 때문이다. MOSFET 구조에서 유전체 박막의 두께 감소로 인한 전기적 특성 저하를 보완하기 위해서 high-K 재료가 대두되었고 현재 주를 이루고 있다. 그러나 현재까지 $HfO_2$에 대한 nano-mechanical 특성 연구는 부족한 상태이므로 본 연구에서는 게이트 절연층으로 최적화하기 위하여 $HfO_2$ 박막의 nano-mechanical properties를 자세히 조사하였다. 시료는 rf magnetron sputter를 이용하여 Si (silicon) 기판 위에 Hafnium target으로 산소유량(4, 8 sccm)을 달리하여 증착하였고, 이후 furnace에서 400에서 $800^{\circ}C$까지 질소분위기에서 20분간 열처리를 실시하였다. 실험결과 산소 유량을 8 sccm으로 증착한 시료가 열처리 온도가 증가할수록 누설전류 특성 성능이 우수 해졌다. Nano-indenter로 측정하고 Weibull distribution으로 정량적 계산을 한 결과, $HfO_2$ 박막의 stress는 as-deposited 시료를 기준으로 $400^{\circ}C$에서는 tensile stress로 변화되었다. 그러나 온도가 증가(600, $800^{\circ}C$)할수록 compressive stress로 변화 되었다. 특히, $400^{\circ}C$ 열처리한 시료에서 hardness 값이 (산소유량 4 sccm : 5.35 GPa, 8 sccm : 5.54 GPa) 가장 감소되었다. 반면에 $800^{\circ}C$ 열처리한 시료에서는(산소유량 4 sccm : 8.09 GPa, 8 sccm : 8.17 GPa) 크게 증가된 것을 확인하였다. 이를 통해 온도에 따른 $HfO_2$ 박막의 stress 변화를 해석하였다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.42.2-42.2
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• 2010

Transparent conducting oxides (TCOs) are of significant importance for their applications in various devices, such as light-emitting diodes, thin-film solar cells, organic light-emitting diodes, liquid crystal displays, and so on. In order for TCOs to contribute to the performance improvement of these devices, TCOs should have high transmittance and good electrical properties simultaneously. Sn-doped $In_2O_3$ (ITO) is the most commonly used TCO. However, indium is toxic and scarce in nature. Thus, ZnO has attracted a lot of attention because of the possibility for replacing ITO. In particular, group III impurity-doped ZnO showed the optoelectronic properties comparable to those of ITO electrodes. Al-doped ZnO exhibited the best performance among various doped ZnO films because of the high substitutional doping efficiency. However, in order for the Al-doped ZnO to replace ITO in electronic devices, their electrical and optical properties should further significantly be improved. In this connection, different ways such as a variation of deposition conditions, different deposition techniques, and post-deposition annealing processes have been investigated so far. Among the deposition methods, RF magnetron sputtering has been extensively used because of the easiness in controlling deposition parameters and its fast deposition rate. In addition, when combined with post-deposition annealing in a reducing ambient, the optoelectronic properties of Al-doped ZnO films were found to be further improved. In this presentation, we deposited Al-doped ZnO (ZnO:$Al_2O_3$ = 98:2 wt%) thin films on the glass and sapphire substrates using RF magnetron sputtering as a function of substrate temperature. In addition, the ZnO samples were annealed in different conditions, e.g., rapid thermal annealing (RTA) at $900^{\circ}C$ in $N_2$ ambient for 1 min, tube-furnace annealing at $500^{\circ}C$ in $N_2:H_2$=9:1 gas flow for 1 hour, or RTA combined with tube-furnace annealing. It is found that the mobilities and carrier concentrations of the samples are dependent on growth temperature followed by one of three subsequent post-deposition annealing conditions.