• Ceramist
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• v.9 no.6
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• pp.24-29
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• 2006

Electron beam physical vapor deposition (EB-PVD) process has currently been applied to thermal barrier coatings (TBCs) for aircraft engines. Due to unique columnar structure, EB-PVD TBCs have advantages in resistances to thermal shock and thermal cycle for their applications, compared to films prepared by plasma spray By the EB-PVD equipment, we successfully obtained yttria-stabilized zirconia (YSZ) layer which has columnar and feather like structure including a large amount of nano size pores and gaps. The EB-PVD technique has been developed for coating functional perovskite type oxides such as (La, Sr)MnO3. Electrode properties have been improved by interface and structural control.

• Vacuum Magazine
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• v.3 no.1
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• pp.22-31
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• 2016

Although graphene has been considered as one of the promise materials for future logic devices due to extremely high mobility, its applications in electronics have been limited to a few cases such as a flexible interconnect, and RF devices. Furthermore, most of the studies on graphene devices reported unstable operations, claimed to be due to the poor quality of graphene. Nevertheless, recent studies showed that the electrical performance of graphene field effect transistor could be stabilized even with CVD graphene when well-established integration processes to control the interface of graphene were used. These results indicate that as in the case of silicon devices, a proper control of graphene interface is very important for the stable operation of graphene device as well as other 2D material based devices.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1122-1125
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• 2006

The TFT performances were enhanced and stabilized by plasma oxidation of the polycrystalline Si surface prior to the plasma enhanced atomic layer deposition of $Al_2O_3$ gate dielectric film. We attribute the improvement to the formation of a high quality oxide interface layer between the gate dielectric film and the poly-Si film. The interface oxide has a predominant effect on the TFT's characteristics, and is regulated by the gap distance between the electrode and the polycrystalline Si surface.

• Journal of the Korean Ceramic Society
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• v.35 no.12
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• pp.1257-1265
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• 1998

Hertzian contact tests were used to investigate the evolution of fracturedamage in the coating layer as functions of contact load and coating thickness by studying crack patterns in porcelain on glass-infiltrated alumina bilayer system conceived to simulate the crown structure of a tooth. Cone cracks initiated at the coating top surface without delamination at interface and crack propagation to substrate. Preferentially the cracks made multi-cracks at the coating top surface rather than proceeding to interface. The cracks were highly stabilized with wide ranges between the loads to initiate first cracking and to cause final failure im-plying damage-tolerant capability. Finite element modelling was used to evaluate the stress distribution. Maximum tensile stress were responsible for the cracking at the coating layer and had a profound influence on the crack pattern and fracture damage in the layered structure materials.

• Journal of the Korean Ceramic Society
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• v.55 no.6
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• pp.576-580
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• 2018

In this study, a small amount of CoO was added to commercial Gd-doped $CeO_2$ (GDC) powder. The CoO addition greatly enhanced sinterability at low temperatures, i.e., more than 98% of relative density was achieved at $1,000^{\circ}C$. When GDC/8YSZ (8 mol% yttrium stabilized zirconia) bilayers were sintered, Co-doped GDC showed excellent adhesion to the YSZ electrolyte. Transmission electron microscope (TEM) analysis showed that there were no traces of liquid films at the grain boundaries of GDC, whereas liquid films were observed in the Co-doped GDC sample. Because liquid films facilitate particle rearrangement and migration during sintering, mechanical stresses at the interface of a bilayer, which are developed based on different densification rates between the layers, might be reduced. In spite of $Co^{2+}$ doping in GDC, the electrical conductivity was not significantly changed, relative to GDC.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.8
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• pp.2611-2625
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• 1996

A numerical method on multi-block technique by Bi-CGSTAB(Bi-Conjugate Gradient STABilized) solver has been proposed. The present multi-block technique can reduce the numerical manipulation greatly because the common regions at the interface of each block are not necessary. In order to test the computational performance of present multi-block technique, the flow characteristics in a T type duct system and a N type duct system have been investigated by three kinds of methods such as the single-block method, the previous multi-block technique and the multi-block technique with Bi-CGSTAB solver. The results indicated that the required CPU time by present multi block technique was shorter than that of other two numerical methods and the convergency history was shown very stable at the present multi-block technique.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.78.1-78.1
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• 2014

An ionization front (IF) surrounding an H II region is a sharp interface through which a cold neutral gas makes transition to a warm ionized phase by absorbing UV photons from central massive stars. We investigate the structure and instability of a plane-parallel D-type IF threaded by magnetic fields parallel to the front. We find that magnetic fields increase the maximum propagation speed of the IFs, while reducing the expansion factor, defined as the density ratio of neutral to ionized phases. IFs become unstable to distortional perturbations due to gas expansion across the fronts, exactly analogous to the Darrieus-Landau instability of ablation fronts in terrestrial flames. The growth rate of the IF instability is proportional linearly to the perturbation wavenumber as well as the upstream flow speed. The IF instability is stabilized by gas compressibility and becomes completely quenched when the front is D-critical. The instability is also stabilized by magnetic pressure when the perturbations propagate in the direction perpendicular to the fields. When the perturbations propagate in the direction parallel to the fields, on the other hand, it is magnetic tension that reduces the growth rate, completely suppressing the instability when ${\beta}$ < 1.5, with ${\beta}$ denoting the square of the ratio of the sound speed to the Alfven speed in the pre-IF region. When the front experiences an acceleration, the IF instability cooperates with the Rayleigh-Taylor instability to make the front more unstable. We discuss potential effects of IF instability on the evolution and dynamics of IFs in the interstellar medium.

• Journal of the Korean Geosynthetics Society
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• v.17 no.2
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• pp.33-40
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• 2018

Characteristics of interface friction between cohesionless soils and geotechnical structure surfaces play an important role in the analysis of earth load and resistance on the structure. In general, geotechnical structures are mainly composed of either steel or concrete, and their surface roughnesses with respect to soil particle sizes influence the interface characteristics between soils and the structures. Accurate assessment of the interface friction characteristics between soils and structures is important to ensure the safety of geotechnical structures, such as mechanically stabilized earth walls reinforced with inextensible reinforcements, piles embedded into soils, retaining wall backfilled with soils. In this study, based on the database of high quality interface friction tests between frictional soils and solid surfaces from literature, equation representing peak interface friction angle is proposed. The influential factors of the peak interface friction angle are relative roughness between soil and solid surface, relative density of frictional soil, and residual (constant volume) interface friction angle. Futhermore, for the developed equation of the interface friction angle, its uncertainty was assessed statistically based on Goodness-of-fit test results.

• Journal of Sensor Science and Technology
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• v.23 no.3
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• pp.170-172
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• 2014

$CO_2$ sensor was used only one solid electrolyte in many cases. To improve the sensing characteristics of $CO_2$ sensors, solid electrolyte $CO_2$ sensor has been developed by bi-electrolyte type sensor using Na-Beta-alumina and YSZ. However, in many further studies, bi-electrolyte type sensor was made by pellet pressed by press machine and additional treatment for formation of interface. In the aspect of mass production, using thick film and additional treatment is not suitable. In this study, $CO_2$ sensor was fabricated by bi-electrolyte structure which was made by an NBA paste layer deposited on YSZ pellet and fired at $1650^{\circ}C$ for 2 hour. The formation of stable interface between YSZ and NBA were confirmed by SEM image. When the type IV electrochemical cell arrangement represented by $CO_2,O_2,Pt{\mid}Li_2CO_3-CaCO_3{\parallel}NBA{\parallel}YSZ{\mid}O_2,Pt$ is used to measure the $CO_2$ concentration in air. This sensor EMF should depend only on the concentration of $CO_2$ by logarithmic. Also, sensor shows $P_{CO_2}$ and EMF relationship like nerstian reaction at a temperature of $450^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.42 no.12 s.283
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• pp.793-799
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• 2005

A composite cathode of LSCF$(La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_3)\;and\;GDC\; (Gd_2O_3-doped\;CeO_2:Ce_{0.9}Gd_{0.1}O_{1.95_})$ was characterized in terms of an electrode response, using a point contact in an Yttria-Stabilized Zirconia (YSZ) electrolyte incorporated into AC two-point impedance spectroscopy. The point-contacted configuration amplifies the responses occurring near the YSZ/cathode interface through the aligned point contact on the planar LSCF/GDC electrode. The point contact interface increases the bulk resistance allowing the estimation of the point contact geometry and resolving the electrode-related responses. The resultant impedance spectra are analyzed through an equivalent circuit model constructed by resistors and constant phase elements. The bulk responses can be resolved from the electrode-related portions in terms of spreading resistance. The electrode-related polarizations are measured in terms of temperature and oxygen partial pressure. The modified impedance spectroscopy is discussed in terms of methodology and analytical aspects, toward resolving the electrode-polarization issues in solid oxide fuel cells.