• 한국전산유체공학회지
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• 제13권4호
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• pp.1-7
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• 2008

In the process of continuous hot-dip galvanizing, it is well known that the gas wiping through an air knife system is most effective because of its uniformity in coating thickness, possibility of thin coating, workability in high speed, and simplicity of control. However, gas wiping used in the galvanizing process brings about a problem of splashing at the strip edge above a certain high speed of process. It is also known that the problem of edge splashing is more harmful than that at the mid strip surface. For a given liquid(of a certain viscosity and surface tension), the onset of splashing mainly depends upon the strip velocity, the gas-jet pressure, and the nozzle's stand-off distance. In these connections in the present study, we proposed three kinds of air knife system having nozzles of constant expansion rate, and compared the jet structures issuing from newly proposed nozzle systems with the result by a conventional one. In numerical analysis, the governing equations are consisted of two-dimensional time dependent Navier-Stokes equations, and the standard k-${\varepsilon}$ turbulence model is employed to solve turbulence stress and so on. As the result, it is found that we had better use the constant expansion-rate nozzle which can be interpreted from the point view of the energy saving for the same coating thickness. Also, we better reduce the size of separation bubble and enhance the cutting ability at the strip surface, by using an air-knife having constant expansion-rate nozzle.

• Progress in Superconductivity
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• 제9권1호
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• pp.85-90
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• 2007

Lanthanum aluminate($LaAlO_3$) film has been prepared on single crystal and metal substrates by dip coating method. Lanthanum acetate and aluminum were prepared via ligand exchange starting from lanthanum nitrate hexahydrate and aluminum nitrate hexahydrate in acetate glacial acetic acid solution after being refluxed. Coating solution was obtained by diluting the gel with methanol and 2-methoxyethanol to adjust the total cation concentration to 0.67 M. Precursor coated film was prepared by dip-coating with a speed of 25 mm/min on various substrates such as $LaAlO_3$ (001), MgO(001), $SrTiO_3$(001) single crystal, LMO/MgO/Ni-alloy. Thin films have been obtained by heat treating the precursor film at various temperatures from $600^{\circ}C{\sim}900^{\circ}C$ and various heating rate from $0.83^{\circ}C/min{\sim}1.25^{\circ}C/min$ under $Ar/O_2$ mixture containing 1000ppm oxygen. The films have been characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). XRD analysis for the prepared film showed that $LaAlO_3$ thin films with a preferred orientation of (100) plane parallel to substrate surface were obtained at $800^{\circ}C(1.11\;^{\circ}C/min)$ on LMO/MgO/Ni-alloy substrate, but the intensity decreased with the increase of heat treatment temperature.

• 한국세라믹학회지
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• 제39권12호
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• pp.1153-1157
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• 2002

입도가 다른 두 가지 고순도 ${\alpha}-Al_2O_3$ 분말을 이용하여 slip casting법과 담금코팅(dip coating)법으로 다공질 알루미나 지지체와 중간층을 각각 제조하였으며, 그 위에 분리막인 산화티탄($Tio_2$)층을 Ti-naphthenate용액으로 screen printing한 후 열분해시켜 형성시킴으로써, 3층 구조의 비대칭성 세라믹 분리막을 제조하였다. 알루미나 지지체의 곡강도, 기공율 및 평균 기공크기는 각각 231 Kg/$cm^2$, 30.26%, 0.19 ${mu}m$였으며, 중간층은 두께가 약 30 ${mu}m$, 평균 기공크기가 0.063 ${mu}m$였다. 또한 최상층 $Tio_2$ 분리막은 그 두께가 약 0.5 ${mu}m$였으며 평균 약 20 nm 정도의 미세 기공들이 매우 균일하게 형성되어 있었다.

• 한국재료학회지
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• 제24권5호
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• pp.259-265
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• 2014

$ZrO_2$ films were coated on aluminum etching foil by the sol-gel method to apply $ZrO_2$ as a dielectric material in an aluminum(Al) electrolytic capacitor. $ZrO_2$ films annealed above $450^{\circ}C$ appeared to have a tetragonal structure. The withdrawal speed during dip-coating, and the annealing temperature, influenced crack-growth in the films. The $ZrO_2$ films annealed at $500^{\circ}C$ exhibited a dielectric constant of 33 at 1 kHz. Also, uniform $ZrO_2$ tunnels formed in Al etch-pits $1{\mu}m$ in diameter. However, $ZrO_2$ film of 100-200 nm thickness showed the withstanding voltage of 15 V, which was unsuitable for a high-voltage capacitor. In order to improve the withstanding voltage, $ZrO_2$-coated Al etching foils were anodized at 300 V. After being anodized, the $Al_2O_3$ film grew in the directions of both the Al-metal matrix and the $ZrO_2$ film, and the $ZrO_2$-coated Al foil showed a withstanding voltage of 300 V. However, the capacitance of the $ZrO_2$-coated Al foil exhibited only a small increase because the thickness of the $Al_2O_3$ film was 4-5 times thicker than that of $ZrO_2$ film.

• 한국재료학회지
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• 제22권8호
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• pp.416-420
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• 2012

Recently nanoscience and nanotechnology have been studied intensively, and many plants, insects, and animals in nature have been found to have nanostructures in their bodies. Among them, lotus leaves have a unique nanostructure and microstructure in combination and show superhydrophobicity and a self-cleaning function to wipe and clean impurities on their surfaces. Coating films with combined nanostructures and microstructures resembling those of lotus leaves may also have superhydrophobicity and self-cleaning functions; as a result, they could be used in various applications, such as in outfits, tents, building walls, or exterior surfaces of transportation vehicles like cars, ships, or airplanes. In this study, coating films were prepared by dip coating method using polypropylene polymers dissolved in a mixture of solvent, xylene and non-solvent, methylethylketon, and ethanol. Additionally, attempts were made to prepare nanostructures on top of microstructures by coating with the same coating solution with an addition of carbon nanotubes, or by applying a carbon nanotube over-coat on polymer coating films. Coating films prepared without carbon nanotubes were found to have superhydrophobicity, with a water contact angle of $152^{\circ}$ and sliding angle less than $2^{\circ}$. Coating films prepared with carbon nanotubes were also found to have a similar degree of superhydrophobicity, with a water contact angle of 150 degrees and a sliding angle of 3 degrees.

• Korean Chemical Engineering Research
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• 제55권2호
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• pp.247-252
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• 2017

실란커플링제인 아미노실란을 15~20 nm의 직경을 갖는 콜로이드 실리카와 반응시킴에 의해 친수성 코팅 용액을 제조하였다. 또한 친수성 코팅 용액을 폴리카보네이트 기재 위에 담금 코팅 시킨 후 $120^{\circ}C$에서 열경화 시킴에 의해 친수성 코팅 도막이 제조되었다. 이 과정 중 아미노실란의 종류 변화가 코팅 도막의 물성에 미치는 영향을 연구하였다. 그 결과 아미노실란으로서 3-aminopropyltriethoxysilane (APTES)을 사용하여 제조된 코팅 도막은 $25{\sim}44^{\circ}$의 접촉각과 B의 좋지 못한 연필경도를 나타내었다. 반면에 아미노실란으로서 3-aminopropyltrimethoxysilane (APTMS)을 사용하여 제조된 코팅 도막은 $26{\sim}37^{\circ}$의 접촉각과 2H의 우수한 연필경도를 나타내었다.

• 한국세라믹학회지
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• 제52권4호
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• pp.234-236
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• 2015

$Y_2O_3$-SiC composite membrane was dip-coated using $Y_2O_3$ sol solution; this membrane was compared with a non- coated one. Each membrane was characterized by XRD, FE-SEM and BET techniques. Hydrogen and CO permeation were tested with self-manufactured Sievert's type equipment. $Y_2O_3$ coating was enhanced for the selectivity of the membrane ($H_2$ versus CO). The hydrogen permeation was measured at 1 bar with increasing temperatures. In case of the coated membrane, hydrogen permeation was found to be $1.24{\times}10^{-7}mol/m^2sPa$ with perm-selectivity of 4.26 at 323 K.

• 한국초전도ㆍ저온공학회논문지
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• 제4권1호
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• pp.13-16
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• 2002

$SrZrO_3 $resistive oxide barriers on Ag sheathed Bi2223 tapes were prepared by the sol-gel and dip coating method to reduce AC coupling loss. The performance of the dip-coated $SrZrO_3 $ thin films was evaluated in terms of bond strength by varying the Sr/Zr mol ratio and the amount of organic vehicle (ethyl cellulose and a-terpineol) additives. The bond strength of the coatings increased as the Sr/Zr ratio decreased and the amount of organic vehicle rose, respectively. It was found that the effect of organic vehicle addition was more pronounced, suggesting that the adherence of the $SrZrO_3 $ films on Bi2223 tapes was governed primarily by the amount of organic vehicle additive.

• 한국안전학회지
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• 제13권1호
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• pp.85-91
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• 1998

Sol-gel derived silica films were prepared by dip-coating onto polymethylmethacylate with Tetraethoxysilane(TEOS) as starting materials. Film properties such as viscosity and thickness were investigated as a function of dip speed, waterprecursor ratio, sol aging time. IR spectra of the gel films prepared from TEOS at various R are given. At small values of R the absorption peaks assignable to C-H vibration in $-OC_2H_5$ groups are observed around 3000 and 1500-1300 $cm^{-1}$. These bands indicate that the -$-OC_2H_5$ groups are retained in the gel at small values of R because of incomplete hydrolysis of TEOS. Film behaviour was interpreted in terms of the dependence of hydrolysis and condensation rates on the interplay between sol pH and waterprecursor ratio. Film thickness was found to increase by approximately a factor of two as waterprecursor ratio increased from two to six. Film thickness also increased with sol prepolymerization time. Surface quality was correlated with processing conditions.

• 한국표면공학회지
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• 제35권5호
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• pp.279-288
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• 2002

Zinc phosphating for cold forming of steel was studied with emphasis on decreasing phosphating temperature. To lower phosphating temperature, some techniques, such as adding Cu ion into bath, using activator in the form of pre-dip, and aeration in bath, instead of using conventional accelerator, namely oxidizing agent, have been tried. It was revealed that phosphating, leading to coatings of Improved uniformity and fine crystal size, can be carried out using above techniques at lower temperature ($55^{\circ}C$) compared to conventional phosphating temperature ($80 ~ 90^{\circ}C$ ). Under present condition, it was seen that optimum concentrations of Cu ion in phosphating bath and activator in pre-dip are 0.015% (w/w) and 2.0 g/1, respectively. The coating weight was within the range of 15 ~ 20 g/$\m^2$. When lubricant was applied into phosphating coatings, the amount of lubricating component (total soap) was found to be 6 ~ 10 g/$\m^2$ and the lubricated panel revealed excellent lubricating properties.