• Korean Chemical Engineering Research
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• v.53 no.5
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• pp.603-608
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• 2015

Alumina powder have been expanded its application in industry and required to control its morphology such as powder size and aspect ratio of single particle. It can be synthesized by molten - salt method which is possible to obtain various shapes of ceramic particles by controlling the growth direction because each crystal face has different growth rate. In this study, various combinations of salts such as NaCl, $Na_2SO_4$, $Na_3PO_4$ and their mixture were used for control the growth of plate like alumina particle from the initial stage of synthesis because salt having different ionic strength can control the growth direction of ceramic particle under its melting condition around $800{\sim}900^{\circ}C$, and growth behavior of plate-like alumina particle with different reaction conditions such as temperature and concentration on the crystal size and shape was studied.

• The Journal of the Petrological Society of Korea
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• v.13 no.4
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• pp.179-190
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• 2004

Precambrian metamorphic rocks of Yeongyang-Uljin area, which is located in the eastern part of Sobaegsan Massif, Korea, are composed of Pyeonghae, Giseong, Wonnam Formations and Hada leuco granite gneisses. These show a zonal distribution of WNW-ESE trend, and are intruded by Mesozoic igneous rocks and are unconformably overlain by Mesozoic sedimentary rocks. This study clarifies the deformation history of Precambrian metamorphic rocks after the formation of gneissosity or schistosity on the basis of the geometric and kinematic features and the forming sequence of multi-deformed rock structures, and suggests that the geological structures of this area experienced at least four phases of deformation i.e. ductile shear deformation, one deformation before that, at least two deformations after that. (1) The first phase of deformation formed regional foliations and WNW-trending isoclinal folds with subhorizontal axes and steep axial planes dipping to the north. (2) The second phase of deformation occurred by dextral ductile shear deformation of top-to-the east movement, forming stretching lineations of E-W trend, S-C mylonitic structure foliations, and Z-shaped asymmetric folds. (3) The third phase deformation formed I-W trending open- or kink-type recumbent folds with subhorizontal axes and gently dipping axial planes. (4) The fourth phase deformation took place under compression of NNW-SSE direction, forming ENE-WSW trending symmetric open upright folds and asymmetric conjugate kink folds with subhorizontal axes, and conjugate faults thrusting to the both NNW and SSE with drag folds related to it. These four phases of deformation are closely connected with the orientation of regional foliation in the Yeongyang-Uljin area. 1st deformation produced regional foliation striking WNW and steeply dipping to the north, 2nd deformation locally change the strike of regional foliation into N-S direction, and 3rd and 4th deformations locally change dip-angle and dip-direction of regional foliation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.375-381
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• 2010

In this paper, the heat-transfer characteristics of steam reforming in an annular reactor are presented. Heat is supplied by the catalytic combustion of syn-gas. The thermal behaviors of exothermic and endothermic reactions in a directly coupled concentric-tube packed-bed reactor were investigated experimentally. The gas mixture supplied for catalytic combustion consisted of the off-gas emitted from MCFC anode. Methane in steam at a suitable S/C (steam-to-carbon) ratio was used in the reforming reactions. On the basis of the experimental results, a simple simulation was performed to predict the temperature profile required in the reforming side of the reactor to achieve optimum hydrogen yield. The results of this study may be utilized as reference data in future studies for further development of coupled reactors.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.223.2-223.2
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• 2010

용융탄산염 연료전지(MCFC)는 $650^{\circ}C$에서 작동하는 고온형 연료전지 시스템이다. 이 시스템은 천연가스 등을 개질하여 생산된 수소를 바로 전기로 생산할 수 있는 시스템으로 열효율이 높으며, 현재 대체 발전시스템으로 각광을 받고 있다. MCFC는 개질방식에 따라 내부개질 방식과 외부개질 방식이 있다. 내부개질 방식은 수소를 생산하는 개질기가 스택내부에 장착된 형식으로 천연가스를 스택내부에서 개질하여 바로 전기를 생산하는 방식이다. 이 내부개질반응에 사용되는 촉매로는 알루미나에 담지된 니켈(Ni) 계열촉매이 주로 쓰이고 있다. 또한 내부개질촉매의 형태는 작은 원주형의 촉매형태로 성형되어 사용된다. 이 성형된 촉매의 크기가 바로 내부개질 스택의 크기를 결정하는 중요한 요소이다. 그래서 촉매의 크기는 되도록이면 작게 성형하는 것이 중요하다. 그러나 촉매의 크기가 너무 작으면 촉매를 성형하는데 큰 어려움이 생기게 된다. 본 연구에서는 니켈 촉매를 공침법이 아닌 균일용액침전법을 이용하여 제조하였으며, 이 촉매를 이용하여 지름이 약 2 mm 이하로 촉매를 압출성형하는 방법을 연구하였다. 먼저 요소(urea)를 이용한 균일용액침전법으로 촉매를 제조하였다. 최적의 촉매 합성조건을 살펴보기 위해서, 반응 온도를 80, 85, 90, 95, $100^{\circ}C$로 변화 시키면서 제조된 촉매의 특성을 살펴보았다. 그리고 촉매의 적절한 니켈 양을 알아보기 위해서 니켈의 양을 30, 40, 50, 60, 70 wt%로 변화 시켰으며, 조촉매로 사용되는 MgO 양을 5, 10, 15, 20 wt%로 변화 시켜서 제조된 촉매의 특성을 살펴보았다. 물성을 비교하기 위해서, X-선 회절분석(XRD) 및 TPR, 물리화학흡착을 하였다. 그 결과 침전반응온도가 $80^{\circ}C$에서 촉매가 가장 좋은 물성을 보였으며, 우수한 개질성능을 보였다. 그리고 촉매 활성물질인 니켈의 함량은 50 wt% 정도가 가장 적절한 함량이었으며, MgO의 함량이 15 wt%일 때 가장 우수한 물성과 개질 성능을 보여주었다. 이 촉매들은 공침법으로 제조된 상용촉매와 비교하였을 때, 보다 우수한 물성과 개질성능 보였다. 그래서 이 촉매를 균일침전법을 이용하여 대량으로 제조한 다음 압출성형 방법을 이용하여 촉매를 원주형으로 제조하였다. 먼저 제조된 촉매는 별도의 분쇄작업(볼밀 혹은 제트밀)을 거치지 않아도 입자사이즈가 약 $4{\mu}m$ 수준이 나오도록 촉매 제조조건을 조절 하였다. 그리고 소량의 Methyl cellulose(MC) 바이더와 물만 사용하여 촉매를 혼합한 다음 스크류 압출기를 이용하여 촉매를 성형하였다. 이 촉매는 지름이 약 2 mm 이하로 제조할 수 있었으며, 기계적 강도는 타정기로 성형한 상용촉매보다 우수하였다. 그리고 촉매 성능 또한 상용촉매와 비교하였을 때, 우수한 성능 보였다. MCFC용 내부개질 촉매로 균일용액침전법을 사용한 촉매가 적합하다고 판단되며, 압출성형에도 적합하다고 판단되었다.

• Journal of Sensor Science and Technology
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• v.6 no.4
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• pp.316-327
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• 1997

Polycrystalline $Sr_{2}Nb_{2}O_{7}$ and $La_{2}Ti_{2}O_{7}$ ceramics with very high Curie temperatures were synthesized by the chemical coprecipitation method (CCP). The powders synthesized were identified by XRD and their sintering behavior and physical properties were studied. The grain-orientation and electrical properties of sintered ceramics were investigated as a function of firing temperature. Single phase could be obtained by CCP method at temperature lower than that of the conventional method by 100 - $150^{\circ}C$. Strontium niobate, $Sr_{2}Nb_{2}O_{7}$, powder was Prepared by CCP method at temperatures as low as $800^{\circ}C$ via intermediate phase of $Sr_{5}Nb_{4}O_{15}$ formed at $700^{\circ}C$. The resulting CCP-derived powder was observed to have finer and more uniform particle size distribution than those obtained through the conventional or the molten salt synthesis method. Sintering of CCP-derived $Sr_{2}Nb_{2}O_{7}$ powder at $1500^{\circ}C$ yielded a highly dense ceramics with 97% theoretical density. Very high grain-orientation developed along the (0k0) direction was observed by SEM, which resulted in anisotropic dielectric properties of the sintered samples, with the dielectric constant values approaching those for single crystal.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.1
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• pp.45-53
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• 2012

The metal chloride wastes from a pyrochemical process to recover uranium and transuranic elements has been considered as a problematic waste difficult to apply to a conventional solidification method due to the high volatility and low compatibility with silicate glass. In this study, a dechlorination approach to treat LiCl-KCl waste for final disposal was adapted. In this study, a $SiO_2-Al_2O_3-P_2O_5$ (SAP) inorganic composite as a dechlorination agent was prepared by a conventional sol-gel process. By using a series of SAPs, the dechlorination behavior and consolidation of reaction products were investigated. Different from LiCl waste, the dechlorination reaction occurred mainly at two temperature ranges. The thermogravimetric test indicated that the first reaction range was about $400^{\circ}C$ for LiCl and the second was about $700^{\circ}C$ for KCl. The SAP 1071 (Si/Al/P=1/0.75/1 in molar) was found to be the most favorable SAP as a dechlorination agent under given conditions. The consolidation test revealed that the bulk shape and the densification of consolidated forms depended on the SAP/Salt ratios. The leaching test by PCT-A method was performed to evaluate the durability of consolidated forms. This study provided the basic information on the dechlorination approach. Based on the experimental results, the dechlorination method using a $SiO_2-Al_2O_3-P_2O_5$ (SAP) could be considered as one of alternatives for the immobilization of waste salt.