• 한국분말재료학회지
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• 제20권6호
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• pp.405-410
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• 2013

During sintering of Ni-electrode multi-layer ceramic capacitors (MLCCs), the Ni electrode often becomes discontinuous because of its lower sintering temperature relative to that of $BaTiO_3$. In an attempt to retard the sintering of Ni, we introduced passivation of the Ni powder. To find the optimal passivation conditions, a thermogravimetric analysis (TGA) was conducted in air. After passivation at $250^{\circ}C$ for 11 h in air, a nickel oxide shell with a thickness of 4-5 nm was formed on nickel nanoparticles of 180 nm size. As anticipated, densification of the compacts of the passivated Ni/NiO core-shell powder was retarded: the starting temperature of densification increased from ${\sim}400^{\circ}C$ to ${\sim}600^{\circ}C$ in a $97N_2-3H_2$ (vol %) atmosphere. Grain growth was also retarded during sintering at temperatures of 750 and $1000^{\circ}C$. When the sintering atmosphere was changed from wet $99.93N_2-0.07H_2$ to wet $99.98N_2-0.02H_2$, the average grain size decreased at the same sintering temperature. The conductivity of the passivated powder sample sintered at $1150^{\circ}C$ for 8 h in wet $99.93N_2-0.07H_2$ was measured to be $3.9{\times}10^4S/cm$, which is comparable with that, $4.6{\times}10^4S/cm$, of the Ni powder compact without passivation. These results demonstrate that passivation of Ni is a viable means of retarding sintering of a Ni electrode and hence improving its continuity in the fabrication of $BaTiO_3$-based multi-layer ceramic capacitors.

• Journal of Ceramic Processing Research
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• 제20권5호
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• pp.484-489
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• 2019

VO2 is an attractive candidate as a transition metal oxide switching material as a selection device for reduction of sneak-path current. We demonstrate deposition of nanoscale VO2 thin films via thermal atomic layer deposition (ALD) with H2O reactant. Using this method, we demonstrate VO2 thin films with high-quality characteristics, including crystallinity, reproducibility using X-ray diffraction, and X-ray photoelectron spectroscopy measurement. We also present a method that can increase uniformity and thin film quality by splitting the pulse cycle into two using scanning electron microscope measurement. We demonstrate an ON / OFF ratio of about 40, which is caused by metal insulator transition (MIT) of VO2 thin film. ALD-deposited VO2 films with high film uniformity can be applied to next-generation nonvolatile memory devices with high density due to their metal-insulator transition characteristic with high current density, fast switching speed, and high ON / OFF ratio.

• The Korean Journal of Ceramics
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• 제4권2호
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• pp.122-127
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• 1998

Conductivities of polycrystalline ceria doped with several rare earth oxides were measured by AC admittance and DC four probe method. The conductions were separated into grain and grain boundary contributions using the complex admittance technique as well as grain size dependence of conductivity. The grain size dependence of polycrystalline conductivity, which can be adequately described by the so-called brick layer model, appears to give a more reliable measure of the grain conductivity compared to the complex admittance method. Polycrystalline resistivity(1/conductivity) increases linearly with the reciprocal of grain size. The intercept of resistivity vs. inverse grain size plot gives a measure of the grain resistivity and the slope gives a measure of the grain boundary resistivity. It was also noted that errors involved in the analysis of experimental data may be different between the complex admittance method and the impedance method. A greater resolution of the spectra was found in the complex admittance method, insofar as the present work is concerned, suggesting that the commonly used equivalent circuit may require re-evaluation.

• 세라미스트
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• 제22권3호
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• pp.243-255
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• 2019

Graphene, a two-dimensional material with a single atomic layer, has recently become a major research focus in various applications such as electronic devices, sensors, energy storage, catalysts, and adsorbents, because of its large theoretical surface area, excellent electrical conductivity, outstanding chemical stability, and good mechanical properties. Recently, 3D nanoporous graphene structures have received tremendous attention to expand the application of 2D graphene. Here, we overview the synthesis of 3D nanoporous graphene network structure with two-dimensional graphite oxide sheets, the control of porous parameters such as specific surface area, pore volume and pore size etc, and the modification of electronic structure by heteroatom doping along with its various applications. The 3D nanoporous graphene shows superior performance in diverse applications as a promising key material. Consequently, 3D nanoporous graphene can lead the future for advanced nanotechnology.

• 한국안전학회지
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• 제28권5호
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• pp.5-9
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• 2013

Recently, eco-friendly sources of energy by fuel cells that use hydrogen as an energy source has emerged as the next generation of energy to solve the problem of environmental issues and exhaustion of energy. A solid oxide fuel cell(SOFC) classified based on the type of ion transfer mediator electrolyte has actively being researched. However, the reliability according to the thermal cycle is low during the operation of the fuel cell, and deformation problem comes from the difference in thermal expansion coefficient between the electrode material, the components made of ceramic material is also brittle, which means disadvantages in terms of the strength. Therefore, in this study, considering the states of the manufacturing and operating of SOFC single cells, the stress analyses in the each of the interfacial layer between the anode, electrolyte and the cathode were performed to get the basic data for reliability assessment of SOFC. The obtained results show that von Mises stress according to the thickness direction on operating state occurred maximum stress value in the electrolyte layer. And also the stresses inside the active area on a distance of 1 ${\mu}m$ from the electrode interface were estimated. Futhermore the evaluation was done for the variation of the stress according to the stage of the operation divided into three stages of manufacturing, stack, and operating.

• 한국세라믹학회지
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• 제43권12호
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• pp.812-822
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• 2006

This study amis to investigate the functional analysis of anode and cathode materials in Anode supported Solid Oxide Fuel Cell. The concentration polarization of single cell was investigated with CFD (Computational Fluid Dynamics) method for the case of the different morphology by using four types of unit cell and discussed to reduce the concentration polarization. The concentration polarization at anode side effected the voltage loss in Anode supported Solid Oxide Fuel Cell and increased contact areas between fuel gas and anode side could reduce the concentration polarization. For intermediate temperature operation, Anode-supported single cells with thin electrolyte layer of YSZ (Yttria-Stabilized Zirconia) were fabricated and short stacks were built and evaluated. We also developed diesel and methane autothermal reforming (ATR) reactors in order to provide fuels to SOFC stacks. Influences of the $H_2O/C$ (steam to carbon ratio), $O_2/C$ (oxygen to carbon ratio) and GHSV (Gas Hourly Space Velocity) on performances of stacks have been investigated. Performance of the stack operated with a diesel reformer was lower than with using hydrogen as a fuel due to lower Nernst voltage and carbon formation at anode side. The stack operated with a natural gas reformer showed similar performances as with using hydrogen. Effects of various reformer parameters such as $H_2O/C$ and $O_2/C$ were carefully investigated. It is found that $O_2/C$ is a sensitive parameter to control stack performance.

• Korean Chemical Engineering Research
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• 제49권6호
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• pp.710-714
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• 2011

본 연구에서는 열 플라스마 용사 코팅 법을 사용하여 고체산화물 연료전지에서 사용되는 $La_{0.8}Ca_{0.2}CrO_{3}$(LCC), $La_{0.8}Sr_{0.2}CrO_{3}$(LSC), $La_{0.8}Ca_{0.2}CrO_{0.9}Co_{0.1}O_{3}$(LCCC) 세라믹 연결재를 코팅하여 코팅 층의 특성평가를 수행하였다. 열 플라즈마 코팅에 앞서 각 세라믹 연결재 입자의 특성평가를 위해 X선 회절, 미세 구조, 입자 측정 및 비표면적 분석을 수행하였다. 세라믹 연결재 입자의 특성평가 후, 열 플라스마 용사 코팅 법을 사용하여 연료극 지지체 위에 코팅하였으며, 코팅 층의 특성을 평가하기 위해 코팅 층의 표면, 파단면 분석, 가스 누출 속도 및 전기 전도도 측정을 수행하였다. 이러한 특성 평가 결과를 바탕으로 열 플라스마 용사 코팅 법을 통해 코팅된 LCCC 코팅 층이 고체산화물 연료전지의 세라믹 연결재로서 적합함을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.688-688
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• 2013

Al-doped ZnO (AZO) thin films have attracted a lot of attention as a cheap transparent conducting oxide (TCO) material that can replace the expensive Sn-doped In2O3. In particular, AZO thin films are widely used as a window layer of chalcogenide-based thin film solar cells such as Cu(In,Ga)Se2 and Cu2ZnSnS4 (CZTS). Mostly important requirements for the window layer material of the thin film solar cells are the high transparency and the low sheet resistance, because they influence the light absorption by the activelayer and the electron collection from the active layer, respectively. In this study, we prepared the AZO thin films by RF magnetron sputtering using a ZnO/Al2O3 (98：2wt%) ceramic target, and the effect of the sputtering condition such as the working pressure, RF power, and the working distance on the optical, electrical, and crystallographic properties of the AZO thin films was investigated. The AZO thin films with optimized properties were used as a window layer of CZTS thin film solar cells. The CZTS active layers were prepared by the electrochemical deposition and the subsequent sulfurization process, which is also one of the cost-effective synthetic approaches. In addition, the solar cell properties of the CZTS thin film solar cells, such as the photocurrent density-voltage (J-V) characteristics and the external quantum efficiency (EQE) were investigated.

• 한국세라믹학회지
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• 제34권2호
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• pp.181-187
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• 1997

다결정 BaTiO3 박막의 높은 유전상수와 비정질 BaTiO3 박막의 우수한 절연특성을 함께 지닌 적층구조 BaTiO3 박막을 제조하여 적층방법에 따른 전기적 특성을 비교, 평가하였다. BaTiO3 박막은 ITO 투명전전막이 입혀진 유리기판위에 rf=magnetron sputtering방법으로 형성하였으며 적층구조 BaTiO3박막의 제조에는 다결정 BaTiO3 박막의 상부에 기판의 자연 냉각과정중에 비정질층이 형성되는 새로운 적층방법을 사용하였다. 이와같이 제조된 적층박막은 다결정 BaTiO3 박막의 상부에 상온에서 비정질층을 형성시키는 일반적인 적층방법으로 제조한 적층박막에 비하여 높은 단위면적당 정전용량과 유전상수, 우수한 절연특성을 나타내었다. 일반적인 적층방법에 의하여 이중층 구조가 형성되는 반면, 새로운 적층방법으로 제조된 적층박막은 AES depth profile과 전기적 특성 분석을 통하여 비정질/microcrystalline/다결정 구조의 다층구조를 지닌 것으로 확인되었다.

• 폴리머
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• 제38권6호
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• pp.782-786
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• 2014

세라믹 방열 복합체의 특성 비교를 위해 casting method로 제작하였으며, 이들의 광학적 이미지와 단면 FE-SEM 분석을 실시하였다. 각각의 복합체의 열전도성 특성을 비교 분석하였으며, silicon carbide(SiC)의 분산도 문제를 해결하기 위해 wetting process를 도입하여 SiC/epoxy 복합체를 제작하였다. 기존의 방법에서 발견된 복합체 내공극과 분산도 문제가 wetting process를 통해 향상되었으며, 충전제 함량에 따른 열전도성 특성을 분석하였다. SiC 복합체의 함량에 따른 공극률 해석을 통해 70 wt% SiC 복합체에서 가장 높은 열전도도 값을 보였으며, 이들의 단면 FE-SEM 분석을 통해 복합체 내의 충전제 분산도를 확인하였다.