• Applied Chemistry for Engineering
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• v.26 no.6
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• pp.666-673
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• 2015

In this paper the selective reduction catalyst (SCR) for controlling the NOx at high temperature range was studied. XRD and FT-IR BET analysis was also performed to determine the structural properties and adsorption/desorption characteristics of the catalyst. In the case of anatase $TiO_2$ support, a negligible NOx conversion was observed, but the $W/TiO_2$ catalyst made using W as a active metal showed an excellent ability to remove NOx. In particular, the $W/TiO_2$ exhibited a rapid increase in the catalytic activity due to the presence of W for the NOx conversion compared to that of using the pure $TiO_2$ at a high temperature range over $400^{\circ}C$. In addition, the phenomenon of reduced reaction activity due to the heat shock for a long time was found to be suppressed.

• Journal of Energy Engineering
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• v.7 no.1
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• pp.73-80
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• 1998

Zinc titanate sorbents were prepared and regeneration of used sorbents for high temperature desulfurization of fuel gases was studied. Zn/Ti molar ratio of prepared sorbents was 1.5 and quartz fixed-bed reactors with 1 cm and 3 cm diameters were used. Regeneration of zinc titanate sorbents at high temperature is exothermic reaction; that brings about deterioration of sorbents. Therefore, we experimented regeneration reaction of zinc titanate sorbents for the purpose of obtaining the most suitable regeneration conditions by changing experimental parameters such as reaction temperature, oxygen concentration, flow rate and steam content. $H_2S$ and $SO_2$ breakthrough curves were obtained during desulfurization-regeneration. Also, properties of the sorbents before and after regeneration were analyzed using SEM, XRD, Hg-porosimetry and BET method. From such results, we obtained the most suitable regeneration conditions including regeneration temperature of 650$^{\circ}$C, $O_2$ content of 5% and steam content of 10% in the gas stream.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.4
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• pp.1-8
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• 2012

The aim of this study is to evaluate fire-induced damage for shield tunnel linings. Full-scale fire test was conducted to evaluate fire-induced damage. Residual compressive strength was measured on the core samples of shield tunnel lining subjected to high temperatures. Heating temperature was predicted by XRD and TG analysis. As a result, Strength degradation of concrete with temperatures can be evaluated by residual compressive strength of core samples. In addition, residual compressive strength can be estimated by previous studies if heating temperature is exactly predicted. It is possible that heating temperature is predicted by XRD and TG analysis at $450^{\circ}C$. For more accurate prediction of heating temperature it should be performed both instrumental analysis and analytical methods with temperatures ranging from $400{\sim}600^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.38 no.12
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• pp.1104-1109
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• 2001

Samples with the nominal composition, B $i_{1.84}$P $b_{0.34}$S $r_{1.91}$C $a_{2.03}$C $u_{3.06}$ $O_{10+}$$\delta$/ high $T_{c}$ superconductors containing As as an additive were fabricated by a solid-state reaction method. Samples with Ag of 10wt%, 30 wt% and 50 wt% each were sintered at 86$0^{\circ}C$~875$^{\circ}C$ for 24 hours. The structural characteristics, critical temperature and grain size with respect to Ag contents were analyzed by XRD(X-ray Diffraction) and SEM(Scanning Electron Microscope), respectively. As Ag contents increased, XRD peaks of g in Bi-2223 phase superconductors intensified and the proportion of the phase transition from Bi-2223 to Bi-2212 was increased.increased.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.3
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• pp.239-244
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• 2000

Synthesis and high temperature phase stability of $_{1+x}$ Co$_{y}$ Mn$_{2-y}$ $O_4$(0$\leq$x$\leq$0.2,y=0,1/9,1/6) spinel, both the excess lithium and cobalt added, have been studied. The spinel was prepared by oxalate precipitation method as the wet chemical process. Oxalate derived spinel was synthesized by heating of precipitates at temperature lower than $600^{\circ}C$. As a result of the TG-DTA and XRD analysis of prepared and quenched powders, it was found that reversible phase transitions started at temperatures $T_1$, $T_2$및 $T_{2'}$. The transitions involved weight (oxygen) loss and gain during heating and cooling. The effects of Li excess and Co doping on the spinel lattice constant, phase stability and transition temperatures of the prepared powders are investigated. This study would provide important data for determining the spinel preparation process such as synthesis temperature and cooling speed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.3
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• pp.143-147
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• 2017

To evaluate surface characteristics and improve crystalline quality of AlN single crystal grown by physical vapor transport (PVT) method, wet chemical etching process using $KOH/H_2O_2$ mixture in a low temperature condition and thermal annealing process was proceeded respectively. Conventional etching process using strong base etchant at a high temperature (above $300^{\circ}C$) had formed over etching phenomenon according to crystalline quality of materials. When it occurred to over etching phenomenon, it had a low reliability of dislocation density because it cannot show correct number of etch pits per estimated area. Therefore, it was proceeded to etching process in a low temperature (below $100^{\circ}C$) using $H_2O_2$ as an oxidizer in KOH aqueous solution and to be determined optimum etching condition and dislocation density via scanning electron microscope (SEM). For improving crystalline quality of AlN single crystal, thermal annealing process was proceeded. When compared with specimens as-prepared and as-annealed, full width at half maximum (FWHM) of the specimen as-annealed was decreased exponentially, and we analyzed the mechanism of this process via double crystal X-ray diffraction (DC-XRD).

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.135.1-135.1
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• 2010

최근 고온에서 사용 가능한 PEMFC용 고분자전해질 막 개발에 대한 연구가 활발히 진행되고 있다. PEMFC가 고온에서 작동하게 되면 높은 성능과 많은 장점을 갖게 된다. PEMFC를 $100^{\circ}C$ 이상에서 운전하게 될 경우 백금 전극 반응을 향상시켜 고가의 백금 촉매 양을 줄일 수 있게 되고, 수소연료 속에 미량 포함된 CO에 의한 촉매표면 피독현상에 대한 내구성을 높일 수 있어 저 순도 수소연료 사용이 가능해 진다. 또한 가습장치와 수소 연료 개질장치의 부피를 줄일 수 있게 되어 전체적인 PEMFC 시스템이 단순화 된다. 현재 연료전지용 고분자 전해질막으로 DuPont사의 과-불소계 고분자 전해질막인 Nafion$^{(R)}$이 가장 널리 사용되고 있다. Nafion$^{(R)}$은 유연한 분자구조 안에 소수성이 강한 주사슬과 친수성을 나타내는 술폰산이 결합된 곁사슬이 존재하여 술폰화 곁사슬의 클러스터 둘레에는 친수성 영역이 형성이 되기때문에 소수/친수 상 분리가 잘되어 이온 클러스터 형성이 용이하지만 제조비용이 높은 단점을 갖고 있다. 특히, 전해질 막내에서 Bronsted base 역할을 하는 물에 의해 이온전도가 이루어지기 때문에 고온에서는 수분증발로 인해 성능이 급격히 감소된다. 따라서, 본 연구에서는 고온 저가습 조건에서 운전이 가능하고 Nafion이 갖는 문제점을 해결하고자, 내열특성이 뛰어나며 높은 수소이온 전도도 학보가 용이한 Sulfonated Poly(aryl ether)sulfone(SPAES) 고분자 전해질에, 고온에서도 수화성이 유지될 수 있도록 지르코니아를 황산화한 sulfated zirconia(s-$ZrO_2$)를 함침하여 복합 고분자전해질막을 제조하여 고온 저가습 조건에서의 수소이온 전도 특성에 관한 연구를 수행하였다. 개발된 막의 물리/화학적 특성은 water content(Wup%), 이온교환 용량(IEC, meq $g^{-1}$), 수소이온전도도(s $cm^{-1}$) 열 중량 분석(TGA), X선 회절분석(XRD) 등을 통하여 분석 및 관찰하였다. 내화학 및 열적 특성분석 결과, 황산화 반응공정으로 $ZrO_2$에 술폰산기가 안정적으로 결합하고 있음이 관찰되었으며, 본 연구에서 개발된 유 무기 복합막이 $250^{\circ}C$이상 열적안정성을 확보하고 있는 것으로 판단되었다. $100^{\circ}C$ 이하의 저온 영역에서, 일정 비율의 s-$ZrO_2$/SPAES막에서 이온교환용량(IEC)이 순수 SPAES 막보다 낮음에도 불구하고, water uptake가 증가함과 동시에 수소이온 전도도가 향상된 것을 관찰하였다. 또한, 고온에서는 수소이온이 자유롭게 이동할 수 있는 water channel을 형성하는 free water는 증발 하지만 s-$ZrO_2$와 SPAES의 술폰산기 사이에 강력하게 결합하고 있는 bound Water는 $100^{\circ}C$ 이상의 고온 영역에서도 존재하여, 비록 무가습 조건에서도 일정 비율의 s-$ZrO_2$/SPAES50 전해질 막의 경우, 높은 전도도를 나타냄을 관찰할 수 있었다. 따라서 본 연구를 통해 저가습 고온 적용을 목적으로 개발된 s-$ZrO_2$/SPAES50막은 우수한 내열 특성을 나타냄과 동시에 저가습 고온 영역($120^{\circ}C$, $50RH{\downarrow}$)에서 높은 수소이온 전도도를 유지하여, 고온 저가습 연료전지 운전에 적합할 것으로 사료된다.

• Proceedings of the KAIS Fall Conference
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• 2005.05a
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• pp.45-47
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• 2005

전기, 전자, 우주, 자동차, 무기 등의 여러 분야에서 응용되고 있는 고정밀, 고저항체 박막인 TaNx 다층박막을 반응성 마그네트론 스퍼터링법으로 제조하여 질소분압에 따른 TCR 특성 변화를 조사하고, XRD와 SEM 관찰을 통하여 미세조직이 전기적 성질에 미치는 영향을 알아보았다. 제조된 TaNx 박막의 전기저항은 질소분율이 증가함에 따라 저온보다 고온에서 전기저항이 감소함을 보여 뚜렷한 (-)TCR 특성을 나타내었다. XRD 분석 결과, $Ar/N_2$ 비가 0.05에서 TaN 상이 형성되고 0.1에서 우수한 결정성을 나타내었으며, $N_2$의 양이 증가할수록 비정질이 형성되었다. 박막의 표면 형상은 미세하고 불연속 아일랜드 형태로 변화하였다.

• Journal of Powder Materials
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• v.6 no.1
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• pp.49-55
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• 1999

Al-Cr-Zr nanocomposite metal powders were prepared by mechnical alloying (MA) in order to develop aircraft structure materials with lighter weight and lower cost than the conventional Ti and Ni alloys. The morphological changes and microstrutural evolution of Al-6wt.%Cr-3wt.%Zr nanocomposite metal powders during MA were investigated by SEM, XRD and TEM. The approximately 50$\mu$m sized Al-Cr-Zr nanocomposite metal powders has been formed after 20 h of MA. The individual X-ray diffraction peaks of Al, Cr and Zr were broadened and peak intensitied were decreased as a function of MA time. The observed Al crystallite size by TEM was in the range of 20 nm, which is a simliar value calculated by Scherrer equation. The microhardness of Al-Cr-Zr nanocomposite metal powders increases alomost linearly with increase of the processing time, reaching a saturation hardness value of 127 kg/$mm^2$ after 20 h of processing. The intermetallic compound phase of $Al_3Zr_4$ in the matrix was identifed by XRD and TEM.

• Journal of Applied Reliability
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• v.16 no.1
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• pp.41-47
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• 2016

Purpose: The purpose of this study was to evaluate electrical and structural degradation of flexible CIGS sollar cell exposed to high temperature and humid atmosphere. Method: Accelerated degradation was performed for various time under $85^{\circ}C/85%RH$ and then electrical and structural properties were analyzed by 4-point probe method, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Results: Sheet resistance of the top ITO layer increased with exposure time to the high temperature and humid atmosphere. Blunting of the protrusion morphology of ITO layer was observed for the degraded specimen, while no phase change was detected by XRD. Oxygen was detected at the edge area after 300 hours of exposure. Conclusion: Increase in electrical resistance of the degraded CIGS solar cell under high temperature and humid environment was attribute to the oxygen or water absorption.