• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.352-358
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• 2019

In recent years, printing paper with a function of information delivery and aesthetic value has attracted a great attention with increasing market demand for coated paper that is capable of high quality printing. The coated paper for inkjet printing with high-quality of photorealistic grades requires the coating layer with a good wettability and porous surface structure in order to improve the printability of ink. In this study, the coated paper was prepared using polyvinyl alcohol (PVA) and surface treated nano silica sol with silane coupling agent. It was confirmed that the coating layer with surface treated nano silica sol showed a uniform pore distribution and flat surface roughness. Glossiness of the prepared printing paper was similar to that of commercial high quality photo paper. Especially, the coated paper with surface treated nano silica sol showed improved printability with excellent roundness of the printed dot of ink. These results indicates that the coating layer with excellent wettability and uniform pore distribution can be formed by using the nano-silica particles with improved dispersibility through the surface treatment of the silane coupling agent.

• Journal of Hydrogen and New Energy
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• v.17 no.2
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• pp.204-211
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• 2006

The electrolyte in the solid oxide fuel cell must be dense enough to avoid gas leakage and thin enough to reduce the ohmic resistance. In order to manufacture the thin and dense electrolyte layer, 8 mol% $Y_2O_3$ stabilized-$ZrO_2$ (8YSZ) electrolyte layers were coated on the porous tubular substrate by the novel vacuum slurry dip-coating process. The effects of the slurry concentration, presintering temperature, and vacuum pressure on the thickness and the gas permeability of the coated electrolyte layers have been examined in the vacuum slurry coating process. The vacuum-coated electrolyte layers showed very low gas permeabilities and had thin thicknesses. The single cell with the vacuum-coated electrolyte layer indicated a good performance of $495\;mW/cm^2$, 0.7 V at $700^{\circ}C$. The experimental results show that the vacuum dip-coating process is an effective method to fabricate dense thin film on the porous tubular substrate.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.21-27
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• 2014

Recently, various biochip environments have been presented. In this study, a novel transparent film with porous membrane windows, which is an essential component in a co-cultured biochip environment, is fabricated using spin-coating, 3D printing, and electrospinning processes. In detail, a transparent polystyrene film was fabricated by means of the spin-coating process followed bywindow cutting, after which apolycaprolactone-chloroform solution was deposited along the window edge to introduce an adhesion layer between the PS film and the PCL nanofibers. Nanofibers were electrospun into the window region using a direct-write electrospinning method. Consequently, it was demonstrated that the fabricated window film could be used in a co-culture biochip environment.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.152-153
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• 2006

본 연구에서는 태양전지 표면에 입사된 광자의 반사손실을 최소화하기 위한 방법으로써 기판 표면에 다공성 실리콘층을 이용한 반사방지막 (Anti-Reflection Coating, ARC)을 형성하는 실험을 하였다. 다공성 실리콘(Porous silicon, PSi)은 실온에서 일정 비율로 만든 전해질 용액($HF-C_2H_5OH-H_2O$)을 사용하여 실리콘 표면을 양극산화처리 함으로써 단순 공정만으로 실리콘 기판의 반사율을 높일 수 있다. 또한 새로운 레이어(layer)없이 기존 기판을 식각시켜 만들기 때문에 박막형 태양전지를 제작시 적용이 용이하다. 저비용, 단순공정의 이점을 살려 전류밀도에 따른 PSi의 반사방지막으로써의 특성을 비교 분석하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.8
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• pp.617-623
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• 2008

The membrane filter adhered with nanostructured porous layer was made by heat treatment after deposition of nanoparticle-agglomerates sintered in aerosol phase onto a conventional micron-fibrous metal filter as a substrate filter. The Sintered-Nanoparticle-Agglomerates-coated NanoStructured porous layer Membrane Filter (SNA-NSMF), whose the filtration performance was improved compared with the conventional metal membrane filters, was developed by adhesion of nanoparticle-agglomerates of dendrite structure sintered onto the micron-fibrous metal filter. The size of nanoparticle-agglomerates of dendrite structure decreased with increasing the sintering temperature because nanoparticle-agglomerates shrank. When shrinking nanoparticle-agglomerates were deposited and treated with heat onto the conventional micron-fibrous metal filter, pore size of nanostructured porous layer decreased. Therefore, pressure drops of SNA-NSMFs increased from 0.3 to 0.516 kPa and filtration efficiencies remarkably increased from 95.612 to 99.9993%.

• Tribology and Lubricants
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• v.36 no.3
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• pp.124-132
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• 2020

The effect of the stoichiometry on the sliding wear properties of NiAl coatings has been investigated. Three different powder mixtures with the compositions of Ni-50at%Al, Ni-54at%Al and Ni-42at%Al were diepressed respectively, and which were subsequently coated on mild steel through combustion synthesis in an induction heating system. Sliding wear behavior of the coatings was examined against an alloyed tool steel using a pin-on-disc type sliding wear test machine. As results, it could be seen that powder mixture(Ni-54at%Al) with displaying Al-rich deviations from the stoichiometry of NiAl(Ni-50at%Al) was promoted the most the synthetic reactivity. The microstructure of the coating layer with the compositions of Ni-54at%Al exhibits the porous NiAl single phase structure. However, the microstructure of the coating layer of the compositions of Ni-42at%Al exhibits the denser multi-phase structure containing several intermediate phases in addition to NiAl. Densification of the coating layer was enhanced by increasing the reacting temperature. On the other hand, the wear properties of the coating layers showed that the wear mode at speeds of around 1 m/s was severe wear, regardless of the stoichiometry and reacting temperature. However, wear properties of coating layer with the compositions of Ni-42at%Al were superior to those of coating layer with the compositions of Ni-54at%Al. This would be attributed by the fact that coating layer with the compositions of Ni-42at%Al develops little void and much intermediate phases with high strength.

• Journal of Surface Science and Engineering
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• v.52 no.3
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• pp.111-116
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• 2019

Chromium was coated on a steel substrate by the Cr(III) electroplating method, and corroded at $500-900^{\circ}C$ for 5 h in $N_2/0.1%H_2S-mixed$ gas to study the high-temperature corrosion behavior of the Cr(III) coating in the highly corrosive $H_2S-environment$. The coating consisted of (C, O)-supersaturated, nodular chromium grains with microcracks. Corrosion was dominated by oxidation owing to thermodynamic stability of oxides compared to sulfides and nitrides. Corrosion initially led to formation of the thin $Cr_2O_3$ layer, below which (S, O)-dissolved, thin, porous region developed. As corrosion progressed, a $Fe_2Cr_2O_4$ layer formed below the $Cr_2O_3$ layer. The coating displayed relatively good corrosion resistance due to formation of the $Cr_2O_3$ scale and progressive sealing of microcracks.

• Journal of Powder Materials
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• v.24 no.2
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• pp.102-107
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• 2017

Porous polytetrafluoroethylene (PTFE) thin films are fabricated by spin-coating using a dispersion solution containing PTFE powders, and their crystalline properties are investigated after thermal annealing at various temperatures ranging from 300 to $500^{\circ}C$. Before thermal annealing, the film is densely packed and consists of many granular particles 200-300 nm in diameter. However, after thermal annealing, the film contains many voids and fibrous grains on the surface. In addition, the film thickness decreases after thermal annealing owing to evaporation of the surfactant, binder, and solvent composing the PTFE dispersion solution. The film thickness is systematically controlled from 2 to $6.5{\mu}m$ by decreasing the spin speed from 1,500 to 500 rpm. A triboelectric nanogenerator is fabricated by spin-coating PTFE thin films onto polished Cu foils, where they act as an active layer to convert mechanical energy to electrical energy. A triboelectric nanogenerator consisting of a PTFE layer and Al metal foil pair shows typical output characteristics, exhibiting positive and negative peaks during applied strain and relief cycles due to charging and discharging of electrical charge carriers. Further, the voltage and current outputs increase with increasing strain cycle owing to accumulation of electrical charge carriers during charge-discharge.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.367-370
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• 2009

It is important to reduce a reflection of light as a solar cell is device that directly converts the energy of solar radiation to electrical energy in oder to improve efficiency of solar cells. The antireflection coating has proven effective in providing substantial increase in solar cell efficiency. This paper investigates the formation of thin film PSi(porous silicon) layer on the surface of crystalline silicon substrates without other ARC(antirefiection coating) layers. On the other hand the formation of $SO_{2}/SiN_x$ ARC layers on the surface of crystalline silicon substrates. After that, the structure of PSi and $SO_2/SiN_x$ ARC was investigated by SEM and reflectance. The formation of PSi layer and $SO_{2}/SiN_x$ ARC layers on the textured silicon wafer result about 5% in the wavelength region from 0.4 to $1.0{\mu}m$. It is achieved on the textured crystalline silicon solar cell that each efficiency is 14.43%, 16.01%.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.2
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• pp.99-106
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• 2005

Falling film heat transfer has been widely used in many applications in which heat and mass transfer occur simultaneously, such as evaporative coolers, cooling towers, absorption chillers, etc. In such cases, it is desirable that the falling film spreads widely on the surface to form a thin liquid film to enlarge contact surface and to reduce the thermal resistance across the film and/or the flow resistance to the vapor stream over the film. In this respect, hydrophilic treatment of the surface has been tried to improve the surface wettability by decreasing the contact angle between the liquid and the surface. However, the hydrophilic treatment was found not very effective to increase the surface wettedness of inclined surfaces, since the liquid flow forms rivulet patterns instead of a thin film as it flows down the inclined surface and accelerates gradually by the gravity. In this work, a novel method is suggested to improve the surface wettedness enormously. In this work, the surface is treated to have a thin hydrophilic porous layer on the surface. With this treatment, the liquid can spread widely on the surface by the capillary force resulting from the porous structure. In addition to this, the liquid can be held within the porous structure to improve surface wettedness regardless of the surface inclination. The experiment on the evaporative cooling of inclined surfaces has been conducted to verify the effectiveness of the surface treatment. It is measured that the latent heat transfer increases almost by $80\%$ at the hydrophilic porous layer coated surface as compared with the untreated surface.