• Journal of the Korean Ceramic Society
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• 제47권2호
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• pp.195-198
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• 2010

It has been considered to apply GDC ($Gd_{0.1}Ce_{0.9}O_{1-X}$) for low-temperature SOFC electrolytes because it has higher ionic conductivity than YSZ at low temperature. However, open circuit voltage with using GDC ($Gd_{0.1}Ce_{0.9}O_{1-X}$) electrolyte in SOFCs, becomes lower than using YSZ (8 mol% Yttria stabilized Zirconia) electrolyte because GDC has electronic conductivity. In this work, the effect of changing GDC electrolyte thickness on the open circuit voltage has been investigated. Ni-GDC anode-supported unit cells were fabricated as follows. Mixed NiO-GDC powders were pressed and pre-sintered at $1200^{\circ}C$. And then, GDC electrolyte material was dip-coated on the anode and sintered at $1400^{\circ}C$. Finally the LSCF-GDC cathode material was screen-printed on the electrolyte and sintered at $1000^{\circ}C$. Electrolyte thickness was controlled by the number of dip-coating times. Open circuit voltage was measured depending on electrolyte thickness at $650^{\circ}C$ and found that the thicker GDC electrolyte was, the better OCV was.

• Journal of the Korean Ceramic Society
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• 제46권5호
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• pp.534-539
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• 2009

Reaction Bonded Silicon Carbide(RBSC) has been used for engineering ceramics due to low-temperature fabrication and near-net shape products with excellent structural properties such as thermal shock resistance, corrosion resistance and mechanical strength. Recently, attempts have been made to develop hot gas filter with gradient pore structure by RBSC to overcome weakness of commercial clay-bonded SiC filter such as low fracture toughness and low reliability. In this study a fabrication process of porous RBSC with multi-layer pore structure with gradient pore size was developed. The support layer of the RBSC with multi-layer pore structure was fabricated by conventional Si infiltration process. The intermediate and filter layers consisted of phenolic resin and fine SiC powder were prepared by dip-coating of the support RBSC in slurry of SiC and phenol resin. The temperature of $1550^{\circ}C$ to make Si left in RBSC support layer infiltrate into dip-coated layer to produce SiC by reacting with pyro-carbon from phenol resin.

• Corrosion Science and Technology
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• 제16권2호
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• pp.69-75
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• 2017

Zinc coating on carbon steels give the higher corrosion resistance in chloride containing environments and in carbonated concrete. However, hydrogen evolution accompanies the corrosion of zinc in the initial activity in fresh concrete, which can lead to the formation of a porous structure at the reinforcement -concrete interface, which can potentially reduce the bond-strength of the reinforcement with concrete. The present study examines the mechanism of the corrosion of hot-dip galvanized steel in detail, as in the model pore solutions and real concrete. Calcium ion plays an important role in the corrosion mechanism, as it prevents the formation of passive layers on zinc at an elevated alkalinity. The corrosion rate of galvanized steel decreases in accordance with the exposure time; however, the reason for this is not the zinc transition into passivity, but the consumption of the less corrosion-resistant phases of hot-dip galvanizing in the concrete environment. The results on the electrochemical tests have been confirmed by the bond-strength test for the reinforcement of concrete and by evaluating the porosity of the cement adjacent to the reinforcement.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제29권10호
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• pp.1156-1162
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• 2005

In this study, a noble method is proposed to prevent the edge overcoating (EOC) that may develop near the edge of the steel strip in the gas wiping process of continuous hot-dip galvanizing. In our past study (Trans. of the KSME (B), Vol. 27, No. 8, pp. $1105\~1113$), it was found that EOC is caused by the alternating vortices which are generated by the collision of two opposed jets in the region outside the steel strip. When the two opposed jets collide at an angle much less than $180^{o}$, non-alternating stable vortices are established symmetrically outside the steel strip, which lead to nearly uniform pressure on the strip surface. In order to deflect both jets downward by a certain angle, a cylinder with small diameter is installed tangentially to the exit of the lower lip of the two-dimensional jet. In order to find an optimum cylinder diameter, the three dimensional flow field is analysed numerically by using the commercial code, STAR-CD. And the coating thickness is calculated by using an integral analysis method to solve the boundary layer momentum equation. In order to compare the present noble method with the conventional baffle plate method to prevent the EOC, the flow field with a baffle plate is also calculated. The calculation results show that the tangentially installed cylinder at the bottom lip of the jet exit is more effective than the baffle plate to prevent EOC.

• Membrane Journal
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• 제29권6호
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• pp.362-376
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• 2019

In this study, hydrophilic coating characteristics of PVDF [poly(vinylidene fluoride)] hollow fiber membranes with flower type cross-section prepared by thermally induced phase separation were studied. The hollow fiber used in this study was provided from PureEnvitech Co. Ltd., and the hydrophilic coating experiment was performed with different concentration and number of coating of PEBAX 1657, 2533 and 3533 block copolymer solution using a dip coating method. The hydrophilic coated hollow fiber membrane was characterized to scanning microscope and contact angle measurements to determine the degree of hydrophilization. As a result of SEM characterization, it was confirmed that the thickness of the coating layer increased as the coating concentration increased and the number of coatings increased. Contact angle of surface of hollow fibers decreased as the concentration of the coating solution increased and the number of coatings increased. Gas permeance of oxygen gas was measured for the application of the hydrophilized hollow fiber to Membrane Areated Biofilm Reactor. As a result of gas permeation test, it was confirmed that gas permeance decreased with increasing coating concentration and number of coatings, and the more hydrophilized hollow fiber coated with PEBAX 1657 showed lower gas permeance than those coated with PEBAX 2533 and 3533.

• Journal of the Korean Ceramic Society
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• 제45권10호
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• pp.579-583
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• 2008

A porous $Al_2O_3$, scaffold coated with tricalcium phosphate(TCP) was fabricated by replica method using polyurethane(PU) foam as a fugitive material. Successive coatings of $Al_2O_3$ and hydroxyapatite(HAp) were applied via dip coating onto polyurethane foam, which has a slender and well interconnected network. A porous structure was obtained after sequentially burning out the foam and then sintering at $1500^{\circ}C$. The HAp phase was changed to TCP phase at high temperature. The scaffold showed excellent interconnected porosity with pore sizes ranging from $300{\sim}700{\mu}m$ in diameter. The inherent well interconnected structural feature of PU foam remained intact in the fabricated porous scaffold, where the PU foam material was entirely replaced by $Al_2O_3$ and TCP through a consecutive layering process. Thickness of the $Al_2O_3$ base and the TCP coating was about $7{\sim}10{\mu}m$ each. The TCP coating was homogeneously dispersed on the surface of the $Al_2O_3$ scaffold.

• Journal of the Korean Ceramic Society
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• 제42권3호
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• pp.165-170
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• 2005

Sol-gel methods offer many advantages over conventional slip-casting, including the ability to produce ceramic membranes. They are purer, more homogeneous, more reactive and contain a wider variety of compositions. We produced ormosil sol using sol-gel process under various molecular weight of polymer species[polyethylene glycol(PEG)] in total system [Tetraethyl ortho silicate(TEOS)-polyethylene glycol(PEG)]. The properties of as-prepared ormosil sol such as viscosity and gelation time are characterized. Also, the ceramic membrane was prepared by dip-coating with synthetic sol and its microstructure was observed by scanning electron microscopy. The permeability and rejection efficiency of membrane for oil/water emulsion were evaluated as cross­flow apparatus. The ormosil sol coated membrane was easily formed by steric effect of polymer and it improved flux efficiency because infiltration into porous support decreased. Its flux efficiency was elevated about $200\;l/m^2h$ compared with colloidal sol coated membrane at point of five minutes from starting test.

• Journal of Conservation Science
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• 제28권1호
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• pp.53-62
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• 2012

The archival objects are tangible evidence related to the public service. They are unique and offer information representing the specific events, time or person. The archival objects as modern cultural heritage do not have the guideline to classify, manage and conserve them. Especially, it is difficult to apply general conservation process for burial artifacts, because there are few study example of conservation for metal archival objects and they have complex administrative value. We tried to find suitable material and application method for consolidation of copper alloy archival object. We choose three kinds of wax and acrylic resin for burial artifacts and had done comparative analysis of their characterizations following kinds and coating methods. As a result of evaluation by several surface analysis such as optical microscope, measuring film thickness, adhesive strength, contact angle and yellowing test, acrylic resin can use to archival objects of copper alloy, effectively but the method of heating after dip-coating with Wax B used before can get best effect of consolidation.

• Bulletin of the Korean Chemical Society
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• 제31권2호
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• pp.360-364
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• 2010

$Li_4Ti_5O_{12}$ thin film with inverse hemispheric structure was fabricated on a Pt/Ti/$SiO_2$/Si substrate by the sol-gel and dip coating method for use as an anode for 3-dimensional (3D) thin-film batteries. Polystyrene (PS) beads of 400 nm diameter were used to prepare the template for the inverse hemispheric structure. A coating solution prepared using precursor sources was dropped on the template-deposited substrates, which were then calcinated at $400^{\circ}C$. The template was removed by calcination, and the inverse hemispheric structure was successfully formed by an annealing process. The cyclic performance during high-rate charge/discharge processes of the $Li_4Ti_5O_{12}$ film with inverse hemispheric structure was superior to that of the flat $Li_4Ti_5O_{12}$ film.

• Journal of the Korean Ceramic Society
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• 제32권4호
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• pp.516-524
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• 1995

In this study, to prepare the dielectric (Ba, Sr)TiO3 thin films by the sol-gel process, Titaminum (IV) sio-propoxide (Ti[OCH(CH3)2]4), Ba and Sr acetate were used for sol and thin films were prepared by dip-coating process. Stability of sol decreased with the increase of Sr, and thickness of thin films were obtained 0.13~0.17${\mu}{\textrm}{m}$ by 1 coating cycle. Transmittance of amorphous thin films heated at 500 and 55$0^{\circ}C$ was very good, and crystallization tendency of thin films according to heat-treatment temperature and crystallization characteristics of thin films heated at 11$0^{\circ}C$ for 3 hrs were analysed. As a result, good perovskite structure was obtained higher than 100$0^{\circ}C$, and tetragonality of thin film was decreased but pyrochlore was formed with increasing Sr. In case of addition to substitute 0.4mol% Sr for Ba, dielectric constant was 288 and loss factor (tan $\delta$) was 0.04.