• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.690-695
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• 2007

Scandia stabilized zirconia (ScSZ) is adapted for electrolyte material of solid oxide fuel cell (SOFC) because of its high ionic conductivity and chemical stability. ScMnSZ1 powder having a composition of $((ZrO_2)_{0.89}(Sc_2O_3)_{0.1}(MnO_2)_{0.01})$ is synthesized by ultrasonic spray pyrolysis (USP) method. Porous ScMnSZ1 powder is obtained by using a pore forming agent. Microstructure and morphology, particle size distribution of porous powder synthesized with 3wt% pore forming agent are investigated. Sintered ScMnSZ1 sample with ground fine powder are also investigated their microstructure and electrical conductivity. The electrical conductivity of sintered ScMnSZ1 samples with ground fine powder was 0.082 S/cm, 0.127 S/cm and 0.249 S/cm at $750^{\circ}C$, $800^{\circ}C$ and $900^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
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• v.54 no.4
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• pp.285-291
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• 2017

This study investigated the effects of grain size and phase constitution on the mechanical properties of $3Y-ZrO_2$ by varying the sintering conditions. The raw powder prepared by a low-cost wet milling using the coarse solid oxide powders was sintered by both pressureless sintering and hot-pressing, respectively. As increasing holding time at $1450^{\circ}C$ for pressureless sintering, it promoted the microstructural coarsening of matrix grains and the phase transformation to tetragonal phase, whereas the bimodal microstructure embedded with abnormal $cubic-ZrO_2$ grains was observed regardless of sintering time. On the other hand, the specimens hot-pressed at $1300^{\circ}C$ for 2 h reached ~ 97% of relative density with homogeneous fine microstructure and mixed phase constitution. It was found that the proportion of untransformed monoclinic zirconia had the most adverse effect on the biaxial strength compared to the impacts of grain size and density. The pressureless sintering of the low-cost powder for prolonged sintering time to 8 h led to a decent combination of mechanical properties ($H_V=13.2GPa$, $K_{IC}=8.16MPa{\cdot}m^{1/2}$, ${\sigma}=981MPa$).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.232-235
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• 2002

An 150 kV gas cluster ion accelerator was fabricated and assessed. The change of surface morphology and surface roughness were examined by an atom force microscope (AFM) after irradiation of $CO_2$ gas clusters on Si (100) surfaces at the acceleration voltages of 50 kV. The density of hillocks induced by cluster ion impact was gradually increased with the dosage up to 5$\times$10$^{11}$ ions/$\textrm{cm}^2$. At the boundary of the ion dosage of 10$^{12}$ ions/$\textrm{cm}^2$, the density of the induced hillocks was decreased and RMS (root mean square) surface roughness was not deteriorated further. At the dosage of 5x10$^{13}$ ions/$\textrm{cm}^2$, the induced hillocks completely disappeared and the surface became very flat. In addition, the irradiated region was sputtered. $CO_2$ cluster ions are irradiated at the acceleration voltage of 25 kV to remove hillocks on indium tin oxide (ITO) surface and thus to attain highly smooth surfaces. $CO_2$ monomer ions are also bombarded on the ITO surface at the same acceleration voltage to compare sputtering phenomena. From the AFM results, the irradiation of monomer ions make the hillocks sharper and the surfaces rougher On the other hand, the irradiation of $CO_2$ cluster ions reduces the hight of hillocks and planarize the ITO surfaces. From the experiment of isolated cluster ion impact on the Si surfaces, the induced hillocks m high had the surfaces embossed at the lower ion dosages. The surface roughness was slightly increased with the hillock density and the ion dosage. At higher than a critical ion dosage, the induced hillocks were sputtered and the sputtered particles migrated in order to fill valleys among the hillocks. After prolonged irradiation of cluster ions, the irradiated region was very flat and etched.

• Journal of the Korean Ceramic Society
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• v.41 no.2
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• pp.151-157
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• 2004

Because of the excellent thermal and chemical properties of mullite and cordierite as the stable oxide ceramic materials, they were widely used from engineering materials to electronic materials. Notwithstanding of their high demands, mullite was synthesised because it is not existed in nature. It is also difficult to produce cordierite of fine powder with high purity due to the narrow range of synthetic temperature. Mullite was synthesised by solid state reaction. However, synthesized mullite has been inhomogeneous. Because of the facts, various synthetic methods have been studied so far including sol-gel method. The purpose of this study is to synthesis mullite and cordierite of fine powder with high purity at the lower temperature by solution-polymerization route using PVA as a polymer carrier, which is an economical method by using low cost materials. As a result, mullite and cordierite were produced with mono crystal phase at 1200$^{\circ}C$ and 1250$^{\circ}C$, respectively, and their surface area over 20 ㎡/g.

• Journal of Electrochemical Science and Technology
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• v.8 no.3
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• pp.183-196
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• 2017

The research efforts directed at advancing water electrolysis technology continue to intensify together with the increasing interest in hydrogen as an alternative source of energy to fossil fuels. Among the various water electrolysis systems reported to date, systems employing a solid polymer electrolyte membrane are known to display both improved safety and efficiency as a result of enhanced separation of products: hydrogen and oxygen. Conducting water electrolysis in an alkaline medium lowers the system cost by allowing non-platinum group metals to be used as catalysts for the complex multi-electron transfer reactions involved in water electrolysis, namely the hydrogen and oxygen evolution reactions (HER and OER, respectively). We briefly review the anion exchange membranes (AEMs) and electrocatalysts developed and applied thus far in alkaline AEM water electrolysis (AEMWE) devices. Testing the developed components in AEMWE cells is a key step in maximizing the device performance since cell performance depends strongly on the structure of the electrodes containing the HER and OER catalysts and the polymer membrane under specific cell operating conditions. In this review, we discuss the properties of reported AEMs that have been used to fabricate membrane-electrode assemblies for AEMWE cells, including membranes based on polysulfone, poly(2,6-dimethyl-p-phylene) oxide, polybenzimidazole, and inorganic composite materials. The activities and stabilities of tertiary metal oxides, metal carbon composites, and ultra-low Pt-loading electrodes toward OER and HER in AEMWE cells are also described.

• Journal of Electrochemical Science and Technology
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• v.8 no.3
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• pp.250-256
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• 2017

A graphene electrode with a novel in-plane structure is proposed and successfully adopted for use in supercapacitor applications. The in-plane structure allows electrolyte ions to interact with all the graphene layers in the electrode, thereby maximizing the utilization of the electrochemical surface area. This novel structure contrasts with the conventional out-of-plane stacked structure of such supercapacitors. We herein compare the volumetric capacitances of in-plane- and out-of-plane-structured devices with reduced multi-layer graphene oxide films as electrodes. The in-plane-structured device exhibits a capacitance 2.5 times higher (i.e., $327F\;cm^{-3}$) than that of the out-of-plane-structured device, in addition to an energy density of $11.4mWh\;cm^{-3}$, which is higher than that of lithium-ion thin-film batteries and is the highest among in-plane-structured ultra-small graphene-based supercapacitors reported to date. Therefore, this study demonstrates the potential of in-plane-structured supercapacitors with high volumetric performances as ultra-small energy storage devices.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.4
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• pp.399-407
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• 2011

This study analyzes the performance of hybrid power systems combining a solid oxide fuel cell (SOFC) and a gas turbine (GT). Research focus is given to the influence of the size-dependent gas turbine performance on hybrid system performance. Three hybrid systems adopting different gas turbines (kW, sub-MW, multi-MW classes) are designed. As the gas turbine power increases (i.e. as the gas turbine performance enhances), the gas turbine power portion increases and the hybrid system efficiency increases. The hybrid system shows efficiency improvement over the SOFC only system even in the case where the gas turbine net power is nearly zero. The increase of gas turbine pressure ratio contributes to the net hybrid system power output in all of the three cases, while system efficiency is almost independent on the pressure ratio.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.1
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• pp.40-50
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• 2012

The electrification of the waste heat of stack is necessary to enhance the efficiency of fuel cell system. For this purpose, the hybrid SOFC/GT/ST system is suitable. The purpose of this work is to predict the performance of methane fueled SOFC/GT/ST hybrid power system and to analyze the influence of operating temperature of stack, current density of stack, and gas turbine pressure ratio. According to the analysis, it is proved that the SOFC/GT/ST hybrid system suppress the rapid decrease in efficiency and lead to the significant improvement of efficiency as compared with SOFC system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.2
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• pp.139-148
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• 2013

In this study, an ejector was designed to recirculate the anodic off-gas of SOFC, and a parametric study of the system performance was conducted at various ejector entrainment ratios. Aspen Plus, a chemical engineering program, was used to calculate the operational conditions of the ejector. To minimize the calculation load of the CFD and to ensure the global optimum, a genetic algorithm and Kriging model were used for the optimization. The optimization results showed that the dominant design variables of the sonic ejector are the throat diameter and the first flow nozzle position. The designed ejector has enough flexibility for different operating conditions of a 1-kW SOFC system. When the ejector was applied to the SOFC, it reduced 56% of the steam and 8.4% of the fuel compared to the reference case.

• Applied Chemistry for Engineering
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• v.26 no.6
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• pp.725-729
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• 2015

Organic light emitting diodes (OLEDs) are regarded as the next generation display and solid-state lighting due to their superb achievements from extensive research efforts on improving the efficiency and stability of OLEDs in addition to developing new materials. Herein, efficient green phosphorescent OLEDs were obtained by using hexaazatrinaphthylene (HAT) derivatives as a hole injection layer. External quantum and current efficiencies of OLEDs were enhanced from 8.8% and 30.8 cd/A to 13.6% and 47.7 cd/A, respectively by inserting a thin layer of HAT derivatives between the ITO and hole transporting layer. The enhancement of OLEDs was found to be originated from the inserted HAT derivatives, which resulted in the optimized hole-electron balance inside the emission layer.