• 열처리공학회지
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• 제31권3호
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• pp.126-134
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• 2018

In this research, we produced polycrystalline n-type $Bi_2Te_{2.7}Se_{0.3}$ powder using water atomization. To obtain full benefit through water atomized powder, we have implemented spark plasma sintering and hot extrusion for powder compaction. The microstructure and thermoelectric properties were investigated and compared. The average grain size of SPS and extruded bulks were 3.08 and $3.86{\mu}m$ respectively. The extruded material microstructure contains layered grains with less grain boundaries and its counter-part SPS displays dense packed grains with high grain boundaries. Among both bulks, extrusion sample exhibited high power factor (PF) of $2.96{\times}10^{-3}Wm^{-1}K^{-2}$ which is 38% higher than SPS ($2.14{\times}10^{-3}$) bulk sample. Due to variations in grain size and grain boundaries, the SPS bulk shows low thermal conductivity than extruded bulk. However, the extruded bulk sample exhibited a peak ZT of 0.69 at 400 K, which is 19% higher than SPS bulk sample, due to its higher power factor.

• 한국입자에어로졸학회지
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• 제8권4호
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• pp.173-180
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• 2012

SiC particles, 8.3 ${\mu}m$ in volume average diameter, were chlorinated in an alumina tubular reactor, 2.4 cm in diameter and 32 cm in length, with reactor temperature varied from 100 to $1200^{\circ}C$. The flow rate of the gas admitted to the reactor was held constant at 300 cc/min, the mole fraction of chlorine in the gas at 0.1 and the reaction time at 4 h. The chlorination was negligibly small up to the temperature of $500^{\circ}C$. Thereafter, the degree of chlorination increased remarkably with increasing temperature until $900^{\circ}C$. As the temperature was increased further from 900 to $1200^{\circ}C$, the increments in chlorination degree were rather small. At $1200^{\circ}C$, the chlorination has nearly been completed. The surface area of the residual carbon varied with chlorination temperature in a manner similar to that with the variation of chlorination degree with temperature. The surface area at $1200^{\circ}C$ was 912 $m^{2}/g$. A simple model was developed to predict the conversion of a SiC under various conditions. A Langmuir-Hinshelwood type rate law with two rate constants was employed in the model. Assuming that the two rate constants, $k_{1}$ and $k_{2}$, can be expressed as $A_{1e}^{-E_{1}/RT}$ and $A_{2e}^{-E_{2}/RT}$, the four parameters, $A_{1}$, $E_{1}$, $A_{2}$, and $E_{2}$ were determined to be 32.0 m/min, 103,071 J/mol, 2.24 $m^{3}/mol$ and 39,526 J/mol, respectively, through regression to best fit experimental data.

• 한국광물학회지
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• 제24권2호
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• pp.133-143
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• 2011

무주군 적상면 사산리에는 선캠브리아기 화강암질 편마암 복합체가 분포하고 이를 쥬라기 편암질 화강암과 페그마타이트가 관입하고 있으며, 페그마타이브 내 Nb-Ta 광화대가 발달하고 있다. 페그마타이트의 구성광물은 거정질의 석영, 장석류, 및 백운모가 우세하며 장석류는 정장석과 알바이트의 탄종성분을 보여준다. Nb-Ta 광물로는 콜럼바이트가 우세하며 백운모는 후기 마그마 기원으로 콜럼바이트와 밀접히 수반되어 산출한다. 조립의 콜럼바이트는 석영, 장석과 함께 산출하는 반면, 미립의 콜럼바이트는 백운모와 함께 산출하는데 조립질에 비해 미립의 콜럼바이트는 상대적으로 낮은 Nb 함량을 보여준다. 조사지역에 발달한 페그마트이트 맥은 폭 4~15 m, 길이가 각각 120 및 250 m인데, 5개 공 총 600 m 시추 결과 맥의 지하 연장은 별로 좋지 못하며 콜럼바이트는 미량으로 산출하고 있다. 따라서 조사지역에서 희유금속에 대한 광산개발가능성은 적다고 판단된다.

• 한국분말재료학회지
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• 제23권2호
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• pp.143-148
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• 2016

A microfluidic reactor with computer-controlled programmable isocratic pumps and online detectors is employed as a combinatorial synthesis system to synthesize and analyze materials for fabricating CdSe quantum dots for various applications. Four reaction condition parameters, namely, the reaction temperature, reaction time, Cd/Se compositional ratio, and precursor concentration, are combined in synthesis condition sets, and the size of the synthesized CdSe quantum dots is determined for each condition. The average time corresponding to each reaction condition for obtaining the ultraviolet-visible absorbance and photoluminescence spectra is approximately 10 min. Using the data from the combinatorial synthesis system, the effects of the reaction conditions on the synthesized CdSe quantum dots are determined. Further, the data is used to determine the relationships between the reaction conditions and the CdSe particle size. This method should aid in determining and selecting the optimal conditions for synthesizing nanoparticles for diverse applications.

• 한국분말재료학회지
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• 제27권5호
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• pp.381-387
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• 2020

In this work, TiO₂ 3D nanostructures (TF30) were prepared via a facile wet chemical process using ammonium hexafluorotitanate. The synthesized 3D TiO₂ nanostructures exhibited well-defined crystalline and hierarchical structures assembled from TiO₂ nanorods with different thicknesses and diameters, which comprised numerous small beads. Moreover, the maximum specific surface area of TiO₂ 3D nanostructures was observed to be 191 ㎡g^-1, with concentration of F ions on the surface being 2 at%. The TiO₂ 3D nanostructures were tested as photocatalysts under UV irradiation using Rhodamine B solution in order to determine their photocatalytic performance. The TiO₂ 3D nanostructures showed a higher photocatalytic activity than that of the other TiO₂ samples, which was likely associated with the combined effects of a high crystallinity, unique features of the hierarchical structure, a high specific surface area, and the advantage of adsorbing F ions.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2003년도 가을 학술논문집
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• pp.363-367
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• 2003

우라늄 산화물의 금속전환을 위해 고온 용융염 중에서 전기화학적 환원공정에 대한 관심이 고조되고 있다. 본 공정은 우라늄 산화물뿐만 아니라 다른 악틴족 원소 산화물 및 일부 희토류원소 산화물 역시 금속으로 환원되는 장점을 가지고 있다. 이러한 금속산화물들은 독창적으로 고안된 일체형 음극 및 불활성 양극을 이용하여 금속으로 환원되며, 음극에서 발생된 산소 이온은 양극으로 전달되어 산화됨으로서 산소기체를 발생시킨다. 용융염 중에서 알칼리 및 알칼리토류 산화물에 대한 전기화학적 거동은 아직 완전히 밝혀지지 않았으며, 후행핵연료주기의 단위공정으로서 개발중에 있다. 사용후핵연료의 열 부하는 주로 세슘 및 스트론슘에 의한 것으로, LiC1 용융염 중에서 세슘, 스트론슘 및 바륨 산화물에 대한 용해 속도 및 환원전위를 고찰하였다.

• 공업화학
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• 제25권4호
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• pp.414-417
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• 2014

습식제련 기술을 통한 Ga의 재활용을 위해 고결정성 GaN으로 구성되어 있는 LED 공정스크랩의 침출 거동을 연구하였다. 고결정성 GaN은 산성 및 염기성 조건에서 매우 안정하여 침출이 어려운 물질로 알려져 있다. 따라서, 본 연구에서는 볼밀링을 통해 원료와 $Na_2CO_3$를 1:1 비율로 섞은 후 관상로를 이용해 $1000-1200^{\circ}C$에서 열처리 하여 산화물로의 상변화를 유도하였다. 열처리 결과로써, $1100^{\circ}C$에서 GaN은 약 73 wt%의 Ga을 포함하는 산화물로 상변화 되었다. 이러한 열처리 샘플은 $100^{\circ}C$ 4 M HCl에서 96%의 높은 침출률을 나타냈다.

• 한국재료학회지
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• 제30권1호
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• pp.31-37
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• 2020

In this study, the effects of Sm addition (0, 0.05, 0.2, 0.5 wt%) on the microstructure, hardness, and electrical and thermal conductivity of Al-11Si-1.5Cu aluminum alloy were investigated. As a result of Sm addition, increment in the amount of α-Al and refinement of primary Si from 70 to 10 ㎛ were observed due to eutectic temperature depression. On the other hand, Sm was less effective at refining eutectic Si because of insufficient addition. The phase analysis results indicated that Sm-rich intermetallic phases such as Al-Fe-Mg-Si and Al-Si-Cu formed and led to decrements in the amount of primary Si and eutectic Si. These microstructure changes affected not only the hardness but also the electrical and thermal conductivity. When 0.5 wt% Sm was added to the alloy, hardness increased from 84.4 to 91.3 Hv, and electric conductivity increased from 15.14 to 16.97 MS/m. Thermal conductivity greatly increased from 133 to 157 W/m·K.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.70.1-70.1
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• 2012

In-situ X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy studies of SOFC cathode materials will be discussed in this presentation. The mixed conducting perovskites (ABO3) containing rare and alkaline earth metals on the A-site and a transition metal on the B-site are commonly used as cathodes for solid oxide fuel cells (SOFC). However, the details of the oxygen reduction reaction are still not clearly understood. The information about the type of adsorbed oxygen species and their concentration is important for a mechanistic understanding of the oxygen incorporation into these cathode materials. XPS has been widely used for the analysis of adsorbed species and surface structure. However, the conventional XPS experiments have the severe drawback to operate at room temperature and with the sample under ultrahigh vacuum (UHV) conditions, which is far from the relevant conditions of SOFC operation. The disadvantages of conventional XPS can be overcome to a large extent with a "high pressure" XPS setup installed at the BESSY II synchrotron. It allows sample depth profiling over 2 nm without sputtering by variation of the excitation energy, and most importantly measurements under a residual gas pressure in the mbar range. It is also well known that the catalytic activity for the oxygen reduction is very sensitive to their electrical conductivity and oxygen nonstoichiometry. Although the electrical conductivity of perovskite oxides has been intensively studied as a function of temperature or oxygen partial pressure (Po2), in-situ measurements of the conductivity of these materials in contact with the electrolyte as a SOFC configuration have little been reported. In order to measure the in-plane conductivity of an electrode film on the electrolyte, a substrate with high resistance is required for excluding the leakage current of the substrate. It is also hardly possible to measure the conductivity of cracked thin film by electrical methods. In this study, we report the electrical conductivity of perovskite $La_{0.6}Sr_{0.4}CoO_{3-{\delta}}$ (LSC) thin films on yttria-stabilized zirconia (YSZ) electrolyte quantitatively obtained by in-situ IR spectroscopy. This method enables a reliable measurement of the electronic conductivity of the electrodes as part of the SOFC configuration regardless of leakage current to the substrate and cracks in the film.

• 한국실내디자인학회논문집
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• 제18권6호
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• pp.150-157
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• 2009

In the 1970's the Interior Design Associations was established and the activity of youth designers who werecalled the "first generation of Korean interior designers" were created. This study is aimed to analyze characteristics and trends of commercial interior design in the 1970's. The design methods include the documentary research and the actual proof research conducted. The frames of analysis were made by the background theories about Korean interior design, and the annual case studies were analyzed and estimated according to the design types. The design types were analyzed by the geometrical simplicity research, the romantic emotional expression, the Korean identity expression, the machine technical asthetic expression and the eclectic style with western classics. In the early 1970's, the abstract, brief, and simple expression were presented most frequently by the geometrical form and the repetition of the pattern. From the mid-1970's the romantic and emotional atmosphere of the youth culture that was popular at that time were expressed as vernacular design by the rough finishing of the natural materials such as plaster, brick, and wood floorings etc. The space such as a Korean food restaurant relates to the Korean traditional culture aims to be different through the expression by the Korean traditional patterns, furniture, and materials. In the late 1970's the metals and glass were used for the expression of the machine aesthetic form but was not popular because of the rare application. The type that revived the past western traditional form was presented by using the arch, dome, and the curved and luxurious moldings.