• 한국표면공학회지
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• 제46권2호
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• pp.68-74
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• 2013

For the coating of diamond films on WC-Co tools, a buffer interlayer is needed because Co catalyzes diamond into graphite. W and Ti were chosen as candidate interlayer materials to prevent the diffusion of Co during diamond deposition. W or Ti interlayer of $1{\mu}m$ thickness was deposited on WC-Co substrate under Ar in a DC magnetron sputter. After seeding treatment of the interlayer-deposited specimens in an ultrasonic bath containing nanometer diamond powders, $2{\mu}m$ thick nanocrystalline diamond (NCD) films were deposited at $600^{\circ}C$ over the metal layers in a 2.45 GHz microwave plasma CVD system. The cross-sectional morphology of films was observed by FESEM. X-ray diffraction and visual Raman spectroscopy were used to confirm the NCD crystal structure. Micro hardness was measured by nano-indenter. The coefficient of friction (COF) was measured by tribology test using ball on disk method. After tribology test, wear tracks were examined by optical microscope and alpha step profiler. Rockwell C indentation test was performed to characterize the adhesion between films and substrate. Ti and W were found good interlayer materials to act as Co diffusion barriers and diamond nucleation layers. The COFs on NCD films with W or Ti interlayer were measured as less than 0.1 whereas that on bare WC-Co was 0.6~1.0. However, W interlayer exhibited better results than Ti in terms of the adhesion to WC-Co substrate and to NCD film. This result is believed to be due to smaller difference in the coefficients of thermal expansion of the related films in the case of W interlayer than Ti one. By varying the thickness of W interlayer as 1, 2, and $4{\mu}m$ with a fixed $2{\mu}m$ thick NCD film, no difference in COF and wear behavior but a significant change in adhesion was observed. It was shown that the thicker the interlayer, the stronger the adhesion. It is suggested that thicker W interlayer is more effective in relieving the residual stress of NCD film during cooling after deposition and results in stronger adhesion.

• Corrosion Science and Technology
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• 제6권4호
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• pp.206-210
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• 2007

Aerospace aluminum alloys such as Al alloy 2024-T3 and 7075-T6 are subject to localized corrosion due the existence of intermetallics containing Cu, Mg or Zn. Chromate is currently widely used in the aerospace industry as the corrosion inhibitor for these alloys. However, chromate needs to be replaced due to its strong carcinogenicity. In this study, an extensive pigment screening has been performed to find replacements for chromates. Different categories of inhibitors were evaluated by immersion tests, DC polarization tests and other methods. Phosphates, zinc salts, cerium salts, vanadates and benzotriazole were found to be effective inhibitors for AA7075. Among those inhibitors, zinc phosphate was found to be the most effective in our novel, silane-based, one-step aqueous primer system. The performance of this primer is comparable to that of currently used chromate primers in accelerated corrosion tests, while it is completely chromate-free and its VOC is about 80% less than that of current primers. Studies by SEM/EDS showed that the unique structure of the superprimer accounts for the strong anti-corrosion performance of the zinc phosphate pigment. The self-assembled stratified double-layer structure of the superprimer is characterized by a less-penetrable hydrophobic layer at the top and a hydrophilic layer accommodating the inhibitors underneath. The top layer functions as the physical barrier against water ingress, while the lower layer functions as a reservoirfor the inhibitor, which is leached out only if the coating is damaged by a scratch or scribe. The presence of a silane in the primer further improves the adhesion and anti-corrosion performance of the primer.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.90.1-90.1
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• 2010

Due to the rapidly diminishing energy sources and higher energy production cost, the interest in dye-sensitized solar cells (DSSCs) has been increasing dramatically in recent years. A typical DSSC is constructed of wide band gap semiconductor electrode such as $TiO_2$ or ZnO that are anchored by light-harvesting sensitizer dyes and surrounded by a liquid electrolyte with a iodide ion/triiodide ion redox couple. DSSCs based on one-dimensional nano-structures, such as ZnO nanorods, have been recently attracting increasing attention due to their excellent electrical conductivity, high optical transmittance, diverse and abundant configurations, direct band gap, absence of toxicity, large exiton binding energy, etc. However, solar-to-electrical conversion performances of DSSCs composed of ZnO n-type photo electrode compared with that of $TiO_2$ are not satisfactory. An important reason for the low photovoltaic performance is the dissolution of $Zn^{2+}$ by the adsorption of acidic dye followed by the formation of agglomerates with dye molecules which could block the I-diffusion pathway into the dye molecule on the ZnO surface. In this paper, we prepared the DSSC with the ZnO electrode using the chemical bath deposition (CBD) method under low temperature condition (< $100^{\circ}C$). It was demonstrated that the ZnO seed layers played an important role on the formation of the ZnO nanostructures using CBD. To achieve truly low-temperature growth of the ZnO nanostructures on the substrates, a two-step method was developed and optimized in the present work. Firstly, ZnO seed layer was prepared on the FTO substrate through the spin-coating method. Secondly, the deposited ZnO seed substrate was immersed into an aqueous solution of 0.25M zinc nitrate hexahydrate and 0.25M hexamethylenetetramine at $90^{\circ}C$ for hydrothermal reaction several times.

• Korean Chemical Engineering Research
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• 제59권4호
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• pp.639-643
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• 2021

본 연구에서는 3차원 다층 미세유체 디바이스를 제작하기 위한 접착제로서 불소화 에틸렌 프로필렌(fluorinated ethylene propylene, FEP) 나노입자를 연구하였다. FEP 분산 용액을 1500 rpm에서 30초 동안 단순 스핀 코팅하여 기판에 3 ㎛ 두께의 균일하게 분포된 FEP 나노 입자 층을 형성하였다. FEP 나노입자는 300 ℃에서 1시간 동안 열처리 후 소수성 박막으로 변형되었으며, FEP 나노입자를 이용하여 제작된 폴리이미드 필름 기반 미세유체 디바이스는 최대 2250 psi의 압력을 견디는 것을 확인하였다. 마지막으로 기존의 포토리소그래피로 제작하기 어려운 16개의 마이크로 반응기로 구성된 3차원 다층 미세유체 디바이스를 FEP가 코팅된 9개의 폴리이미드 필름을 간단한 1단계 정렬로 성공적으로 구현하였다. 개발된 3차원 다층 미세유체 디바이스는 화학 및 생물학의 다양한 응용을 위한 고속대량 스크리닝, 대량 생산, 병렬화 및 대규모 미세유체 통합과 같은 강력한 도구가 될 가능성이 있습니다.

• The Plant Pathology Journal
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• 제37권6호
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• pp.555-565
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• 2021

Bacteriophages infecting Acidovorax citrulli, the causal agent of bacterial fruit blotch, have been proven to be effective for the prevention and control of this disease. However, the occurrence of bacteriophage-resistant bacteria is one of hurdles in phage biocontrol and the understanding of phage resistance in this bacterium is an essential step. In this study, we aim to investigate possible phage resistance of A. citrulli and relationship between phage resistance and pathogenicity, and to isolate and characterize the genes involved in these phenomena. A phage-resistant and less-virulent mutant named as AC-17-G1 was isolated among 3,264 A. citrulli Tn5 mutants through serial spot assays and plaque assays followed by pathogenicity test using seed coating method. The mutant has the integrated Tn5 in the middle of a cupin protein gene. This mutant recovered its pathogenicity and phage sensitivity by complementation with corresponding wild-type gene. Site-directed mutation of this gene from wild-type by CRISPR/Cas9 system resulted in the loss of pathogenicity and acquisition of phage resistance. The growth of AC-17-G1 in King's B medium was much less than the wild-type, but the growth turned into normal in the medium supplemented with D-mannose 6-phosphate or D-fructose 6-phosphate indicating the cupin protein functions as a phosphomannos isomerase. Sodium dodecyl sulfa analysis of lipopolysaccharide (LPS) extracted from the mutant was smaller than that from wild-type. All these data suggest that the cupin protein is a phosphomannos isomerase involved in LPS synthesis, and LPS is an important determinant of pathogenicity and phage susceptibility of A. citrulli.

• 한국발생생물학회지:발생과생식
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• 제10권1호
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• pp.63-73
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• 2006

간질환 환자의 대부분은 간 조직 손상으로 인해 간세포의 재생 능력이 감소한다. 간세포 이식은 이러한 간질환을 치료하는데 있어 혁신적인 방법으로 대두되고 있으나, 여전히 많은 의문과 문제점이 제기되고 있다. 사람의 양막으로부터 얻은 줄기 세포를 이용하여 간세포 분화를 위한 최적의 조건을 알아 보고자 하였다. 세포내 알부민에 대한 면역 화학적 방법, 세포내 글리코겐의 특이 염색법, 세포의 형태적 변화 연구 방법 등을 이용하여 여러가지 배양 조건을 조사한 결과, 배양 접시를 fibronectin으로 coating하고 배양액내에 insulin/transferrin/selenium(ITS)을 첨가하는 것이 양막 줄기세포의 간세포로의 분화에 효과적이었다. 또한 배양액내에 fibroblast growth factor(FGF)-1과 FGF-2를 함께 첨가하는 것이 둘 중 하나만 첨가하거나 첨가하지 않는 것보다 효과적이었다. 한편 분화 배양은 한가지 배양액을 사용한 지속적인 배양법(continuous culture method)보다 배양 조건을 달리하여 두 단계로 배양하는 2단계 배양법(two-step culture method)가 훨씬 효과적이었다. 마지막으로, 기본 배양액에 FGF-2와 FGF-4를 첨가한 조건과 FGF-4와 $TGF-{\alpha}$를 첨가한 조건이 다른 조건 보다 알부민 분비를 많이 하는 것으로 보아 FGF-4가 간세포 분화 과정에 중요한 역할을 하는 것으로 여겨지며 FGF-2 및 $TGF-{\alpha}$ 첨가는 더욱 효과적인 배양 조건으로 관찰되었다. 따라서, 양막에서 유래한 성체 줄기 세포는 적절한 배양 조건이 주어질 때, 간세포로 분화가 가능하며, 분화 과정에서 FGF-4가 주도적인 역할을 하며 FGF-2와 $TGF-{\alpha}$는 상승 효과를 갖는 것으로 사료된다.