• 융복합기술연구소 논문집
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• 제2권2호
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• pp.25-29
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• 2012

Micro machining technologies have been required to satisfy various conditions in a high-technology industry. Micro electrochemical process is one of the most precision machining methods. Micro electrochemical process has been divided into electrochemical etching through protective layer and electrochemical machining using ultrashort voltage pulses. Micro shaft can be fabricated by electrochemical etching. The various protective layers such as photo-resist, oxide layer and oxidized recast layer have been used to protect metal surface during electrochemical etching. Micro patterning on metal surface can be machined by electrochemical etching through protective layer. Micro hole, groove and structures can be easily machined by electrochemical machining using ultrashort voltage pulses. Recently, the groove with subnanometer was machined using AFM.

• 한국전기전자재료학회논문지
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• 제28권3호
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• pp.180-184
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• 2015

Stainless steel (SS) mesh was used to fabricate photoelectrode for flexible dye-seisitzed solar cells (DSSCs) in order to evaluate them as replacements for more expensive transparent conductive oxide(TCO). We fabricated the DSSCs with new type of photoelectrode, which consisted of flexible SS mesh coated with 100 nm thickness titanium (Ti) protective layer deposited using electron-beam deposition system. SS mesh DSSCs with protective layer showed higher efficiency than those without a protective layer. The best cell property in the present study showed the open circuit voltage (Voc) of 0.608 V, short-circuit current density (Jsc) of $5.73mA\;cm^{-2}$, fill factor (FF) of 65.13%, and efficiency (${\eta}$) of 2.44%. Compared with SS mesh based on DSSCs (1.66%), solar conversion of SS mesh based on DSSCs with protective layer improved about 47%.

• 한국표면공학회지
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• 제32권1호
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• pp.49-60
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• 1999

The protective oxide scales and coatings formed on high temperature materials must be preserved in high temperature atmosphere. And the thermal stresses induced by thermal cycling and the growth stresses by the formation of oxide scales can cause the loss of adherence and spalling of the oxide scales and coated layers. Among the coating processes Al diffusion coating is favored due to thermochemical stability and superior adherence in an hostile atmosphere. In this study, protective oxide forming element, Al was coated on Ni, Inconel 600 and 690 by diffusion coating process varying coating temperature and time. And the surface stability and adherence of oxide scales formed on those Al diffusion coated materials were evaluated by thermal cycling test. Al diffusion coated specimens showed superior cyclic oxidation resistance compared to bare ones and specimens coated for longer period had better cyclic oxidation resistance, due to the abundant amount of Al in the coated layer. Meanwhile Al diffusion coated Inconel 600 and 690 showed improved cyclic oxidation resistance by the effect of Al in the coated layer and Cr in the substrate. Comparing both Al diffusion coated Inconel 600 and 690, Al diffusion coated Inconel 690 maintained better adhesion between coated layer and substrate by virtue of the bridging effect resulting from the segregation of Cr in the interdiffusion zone.

• 한국수소및신에너지학회논문집
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• 제20권2호
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• pp.116-124
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• 2009

We investigated the influences of cobalt coating deposited by DC electroplating on the ferritic stainless steel, STS 430, as a protective layer on a metallic interconnect for SOFC applications. Cobalt coated STS 430 revealed a uniform and denser-packing oxide surface and a reduced growth rate of $Cr_2O_3$ scales after oxidation at $800^{\circ}C$in air. Cobalt coating layer was oxidized to $CoCo_2O_4$ and Co containing mixed oxide spinels such as $Co_2CrO_4$, $CoCr_2O_4$, and $CoCrFeO_4$. The area specific resistance value of Co coated sample was $0.020\;{\Omega}cm^2$ lower than that of uncoated at $800^{\circ}C$ in air during 500 h. After 1000 h oxidation, cobalt oxide coating layer suppressed chromium outward diffusion.

• 한국세라믹학회지
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• 제37권3호
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• pp.263-270
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• 2000

The Pt/copper oxide/n-Si electrodes were fabricated by depositing copper oxide thin film of 500${\AA}$ and very thin Pt layer on the n-type (100) Si substrate. hotoelectrochemical properties and stability profiles of the electrodes were investigated as a function of deposition time of Pt layer. As the deposition time of Pt layer increased up to 10 seconds, the photocurrent and quantum efficiency were increased and then decreased with further depositing time. The better cell stability was observed for the electrode with longer deposition time. The improvements in above photoelectrochemical properties indicate that Pt layer acts as a catalyst layer at electrode/electrolyte interface as well as a protective layer. The decreasing tendency of the photocurrent and efficiency for the electrode with Pt layer deposited above 20 seconds was explained as an increases in probbility of electron-hole pair recombination and also the absorbing photon loss at electrode surface due to the excessive thickness of Pt layer. The results were confirmed by impedance spectroscopy, mutiple cycle voltammograms and microstructural analyses.

• 센서학회지
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• 제9권5호
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• pp.389-395
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• 2000

본 논문에서는 보호용 실리콘 산화층과 Al 층을 이용한 $Al_2O_3$ 예비층의 형성을 제안하였다. 실리콘 기판 위의 보호용 산화막 위에 알루미늄을 증착하고 이를 $800^{\circ}C$에서 열처리함으로써 에피텍시 $Al_2O_3$ 예비층 형성시킬 수 있었다. 그리고 형성된 $Al_2O_3$ 예비층위에 ${\gamma}-Al_2O_3$ 층을 형성하였다. ${\gamma}-Al_2O_3$막 성장시 공정의 초기 상태에서 발생하는 $N_2O$ 가스에 의한 Si 기판의 식각을 $Al_2O_3$ 예비층을 이용함으로써 방지할 수 있었다. $Al_2O_3$ 예비층이 초박막 ${\gamma}-Al_2O_3$의 표면의 형태를 개선하는데 많은 효과가 있었다.

• Tribology and Lubricants
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• 제33권6호
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• pp.275-281
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• 2017

In this work, we have fabricated anodic aluminum oxide (AAO) with ordered nanoscale porosity through an anodization process. We deposited gold and nano-organic thin films on the porous AAO surface to protect its structure and reduce friction. We investigated the tribological characteristics of the porous AAO with respect to the protective surface coatings using tribometers. While investigating the frictional characteristics of the samples by applying normal forces of the order of micro-Newton, we observed that AAO without a protective coating exhibits the highest friction coefficient. In the presence of protective surface coatings, the friction coefficient decreases significantly. We applied normal forces of the order of milli-Newton during the tribotests to investigate the wear characteristics of AAO, and observed that AAO without protective surface coatings experiences severe damage due to the brittle nature of the oxide layer. We observed the presence of several pieces of fractured particles in the wear track; these fractured particles lead to an increase in the friction. However, by using surface coatings such as gold thin films and nano-organic thin films, we confirmed that the thin films with nanoscale thickness protect the AAO surface without exhibiting significant wear tracks and maintain a stable friction coefficient for the duration of the tribotests.

• Corrosion Science and Technology
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• 제6권3호
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• pp.128-132
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• 2007

For a quantitative inspection on the performance of weathering steel bridges, we have investigated the relationship between the corrosion rate and the composition of the rust layers formed on weathering steel bridges located in various environments in Japan and applied a protective ability index (PAI) to the bridges. The corrosion rates were clearly classified by the PAI, ${\alpha}/{\gamma}*$ and sub index of $({\beta}+s)/{\gamma}*$, where $\alpha$, \gamma*, $\beta$ and s are the mass ratio of crystalline $\alpha-FeOOH$, the total of $\gamma$-FeOOH+ $\beta$-FeOOH + the spinel-type iron oxide (mainly $Fe_3O_4$), $\beta-FeOOH$ and spinel-type iron oxide, analyzed by powder X-ray diffraction, respectively. In the case of ${\alpha}/{\gamma}$*>1, the rust layer works protective enough to reduce the corrosion rate less than 0.01 mm/y. The sub index $({\beta}+s)/{\gamma}*$<0.5 or >0.5 classifies the corrosion rate of the non-protective rust layers, therefore the former state of the rust layer terms inactive and the latter terms active. The quantitative inspection of a weathering steel bridge requires a performance-inspection (PI) and periodical deteriorationinspections (DI). The PI can be completed by checking of the PAI, ${\alpha}/{\gamma}*$. The DI on the weathering steel bridges where deicing salt is sprinkled can be performed by checking the PAI, $({\beta}+s)/{\gamma}*$.

• 한국표면공학회지
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• 제47권1호
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• pp.7-12
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• 2014

The characteristics of oxidation for the Zry-4 was measured in the $800^{\circ}C$ and high steam pressure (50 bar, 75 bar, 100 bar) conditions, using an apparatus for high pressure steam oxidation. The effect of accelerated oxidation by high-pressure steam was increased more than 60% in hydrogen-charged cladding than normal cladding. This difference between hydrogen charged claddings and normal claddings tends to be larger as the higher pressure. The accelerated oxidation effect of hydrogen charging cladding is regarded as the hydrogen on the metal layer affects the formation of the protective oxide layer. The creation of the sound monoclinic phase in Zry-4 oxidation influences reinforcement of corrosion-resistance of the oxide layer. The oxidation is estimated to be accelerated due to the creation of equiaxial type oxide film with lower corrosion resistance than that of columnar type oxide film. When tetragonal oxide film transformed into the monoclinic oxide film, surface energy of the new monoclinic phase reduced by hydrogen in the metal layer.

• 한국표면공학회지
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• 제20권2호
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• pp.49-59
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• 1987

The properties of $Cr_2O_3-Al_2O_3-SiO_2$ composite oxide coatings on steel surface were investigated. The results obtained were as follows: The microhardness of oxide coating layer increased with increasing heat-treatment temperature and $Cr_2O_3$ content in coating layer. The hardness showed the highest value (850Hv) treated at 700$^{\circ}C$ for $SiO_2:Al_2O_3:Cr_2O_3$=1:1:4. Increasing heat-treatment temperature, corrosion current density became lower and coating layer became denser. The corrosion current density showed the lowest value $(6.5{\times}10^{-5}\;Acm^2)$ treated at 750$^{\circ}C\;for\;SiO_2:Al_2O_3:Cr_2O_3$=1:1:3. These results were explained by protective layer which was formed during heat-treatment. The bonding between matrix and coating layer is expected to be made mechanically and chemically by the inter diffusion of Ni and Fe. The composite oxide coating was formed by softening of the binder with increasing heat-treatment temperature. The strengthening of coating layer is to be resulted from the dispersion of major oxide particles.