• 한국재료학회지
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• 제23권5호
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• pp.281-285
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• 2013

In the present work, ZnO nanofibers were applied to electrode materials for the detection of cholesterol. ZnO nanofibers were synthesized using the electrospinning technique with zinc acetate as a precursor. Electrospinning-synthesized ZnO nanofibers were uniformly distributed by properly controlling the electrospinning parameters. After the calcination treatment, nanofibers of pure ZnO phase were synthesized. Then, these fibers were successfully placed on Au-coated glass substrates by dispersion of ZnO nanofibers in ethanol, dropping, and drying, in sequence. Cholesterol oxidase was then immobilized onto the surface of the ZnO nanofibers. To enhance the immobilization, Nafion was additionally applied. The sensing performances of the fabricated ZnO nanofibers-based sensors were analyzed by cyclic voltammetry in terms of cholesterol concentration ranging from 100 to 400 mg/dl. In the I-V curves, measured by cyclic voltammetry, the ZnO nanofiber-based sensor showed a proportional current behavior with cholesterol concentrations in phosphate buffered saline solution. The sensitivity was measured and found to be $30.7nA/mM{\cdot}cm^2$, which is comparable to the values reported in the literature. After not only optimizing the shape of the ZnO nanofibers but also improving the adhesion nature between the ZnO nanofibers and the Au conducting layer, these fibers can be a good candidate for electrode materials in devices used to detect low concentrations of cholesterol in blood.

• 한국분말재료학회지
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• 제14권6호
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• pp.372-379
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• 2007

The microstructure, mechanical and electrochemical properties of plasma electrolytic coatings (PEO) coatings on Mg-4.3 wt%Zn-1.0 wt%Y and Mg-1.0 wt%Zn-2.0 wt%Y alloys prepared by gas atomization, followed by compaction at 320 for 10 min under the pressure of 700 MPa and sintering at 380 and 420 respectively for 24 h, were investigated, which was compared with the cast Mg-1.0 wt%Zn alloy. All coatings consisting of MgO and $Mg_2SiO_4$ oxides showed porous and coarse surface features with some volcano top-like pores distributed disorderly and cracks between pores. In particular, the surface of coatings on Mg-1.0 wt%Zn-2.0 wt%Y alloy showed smaller area of pores and cracks compared to the Mg-4.3 wt%Zn-1.0 wt%Y and Mg-1.0 wt%Zn alloys. The cross section micro-hardness of coatings on the gas atomized Mg-Zn-Y alloys was higher than that on the cast Mg-1.0 wt%Zn alloy. Additionally, the coated Mg-1.0 wt%Zn-2.0 wt%Y alloy exhibited the best corrosion resistance in 3.5%NaCl solution. It could be concluded that the addition of Y has a beneficial effect on the formation of protective and hard coatings on Mg alloys by plasma electrolytic oxidation treatment.

• 전기전자학회논문지
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• 제23권2호
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• pp.594-598
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• 2019

HfZnO 박막 위 패턴 전사 기법을 이용하여 기존의 러빙법을 대체하는 배향 공정에 대하여 연구하였다. 정렬 패턴은 레이저 간섭 리소그래피를 이용하여 실리콘 웨이퍼 위에 제작하였다. 졸겔 공정을 이용하여 HfZnO 용액을 제작하였고, 유리기판 위에 스핀코팅하였다. 미리 제작한 정렬패턴을 스핀코팅된 HfZnO 위에 올려놓고, $100^{\circ}C$에서 30분간 소성하였다. HfZnO 박막에 평행한 그루브가 형성되었음을 atomic force microscopy 와 scanning electron microscopy로부터 확인할 수 있었다. HfZnO 박막을 이용하여 액정 셀을 제작하였으며, POM 분석으로부터 액정이 균일하게 정렬되었음을 확인할 수 있었다. 액정은 $0.25^{\circ}$의 프리틸트 각을 가졌으며, 수평배향 특성을 보여주었다. 액정 분자는 평행한 그루브에 의한 HfZnO 박막 표면 이방성에 의하여 균일하게 정렬되었음을 확인할 수 있었다.

• 한국자기학회지
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• 제15권3호
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• pp.202-206
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• 2005

무전해 도금법에 의해 제조된 은 피복 Ni-Zn 페라이트 분말의 전파흡수특성을 조사하였다. 분무건조법 및 소결 고정에 의해 평균입경이 $50{\mu}m$ 정도인 페라이트 구형 분말을 제조하고, 이 분말 위에 은 피막을 무전해 도금법에 의해 코팅하였다. 페라이트 표면에 형성되는 은 피막의 미세조직은 도금욕의 $AgNO_3$의 농도에 따라 민감히 변화하였다. 균일한 은 피막을 얻기 위해 페라이트 분말 20g당 10g/L $AgNO_3$가 필요하였다. 페라이트 분말 표면에 은 피막이 형성됨에 따라 전기저항은 $10^{-2}\~10^{-3}\;\Omega$ 정도까지 감소하였다. 도금 처리되지 않은 순수 페라이트 분말은 400 MHz에서 자기공명을 나타내는 전형적인 자성재료의 특성을 나타내었고, 복소유전율은 실수 항이 35, 허수 항은 거의 0에 가까운 값을 나타내었다. 반면 균일한 은 도금이 이루어진 페라이트 분말은 투자율의 큰 변화 없이 복소유전율 실수항이 35, 허수항이 8 이상으로 매우 크게 증가하였다. 이에 따라 전파흡수체의 두께를 현저히 줄일 수 있었다. 임피던스 정합두께는 C-band대역에서 도금되지 않은 페라이트 분말의 경우 5mm로부터 도금 후 2mm 수준으로 감소하였다.

• Journal of Welding and Joining
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• 제13권1호
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• pp.145-155
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• 1995

Continuous wave C $O_{2}$ laser beam welding and formability of zinc coated steel plates were investigated. First, the optimal welding condition could be obtained in lap configuration by using the data for heat input, gap size and fracture behaviour. The gap size for fully-penetrated bead could be predicted by the gap model by Akhter et al. AIso, it was found that the joining efficiency was constant. Secondly, the butt welding of dissimilar materials (zinc coated steel plate and cold rolled steel plate) with different thicknesses was investigated. In the thickness range of 0.8-2.0 mm, the maximum welding speed of 10m/min was obtained. In the butt welding of two plates with thickness 2.0 mm and l.6mm, the maximum, welding speed of 6m/min was obtained, Finally. the forming results of butt-welded plates showed that the joining design was important to apply the laser welded blank in the automotive production.

• 한국기계가공학회지
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• 제1권1호
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• pp.71-78
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• 2002

Since the early 1980's the use of zinc-aluminum alloy-coated steel sheet(Galvalume) for vehicular corrosion protection has increased drastically. It is consisting of 55%Al-43.4% Zn-1.6%Si. Galvalume has a good corrosion resistance, heat reflectivity and shiny appearance, which has a dendritic structure of alloy layer. It has a good corrosion resistance due to dendritic structure. But, this also has a weak point against moisture during long period of transportation as sheeted and or coiled without any relation of chromating on the surface of steel sheet or not because of high humidity and temperature. Here, We studied the corrosion mechanism by the moisture.

• 한국재료학회지
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• 제19권11호
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• pp.631-636
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• 2009

We investigated the NO gas sensing characteristics of ZnO-carbon nanotube (ZnO-CNT) layered composites fabricated by coaxial coating of single-walled CNTs with a thin layer of 1 wt% Al-doped ZnO using rf magnetron sputtering deposition. Morphological studies clearly revealed that the ZnO appeared to form beadshaped crystalline nanoparticles with an average diameter as small as 30 nm, attaching to the surface of the nanotubes. It was found that the NO gas sensing properties of the ZnO-CNT layered composites were dramatically improved over Al-doped ZnO thin films. It is reasoned from these observations that an increase in the surface-to-volume ratio associated with the numerous ZnO “nanobeads” on the surface of the CNTs results in the enhancement of the NO gas sensing properties. The ZnO-CNT layered composite sensors exhibited a maximum sensitivity of 13.7 to 2 ppm NO gas at a temperature of 200${^{\circ}C}$ and a low NO gas detection limit of 0.2 ppm in dry air.

• Journal of Electrical Engineering and Technology
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• 제5권4호
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• pp.640-645
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• 2010

This paper describes the power generating property of hydrothermally grown ZnO nanorods on a flexible polyethersulfone (PES) substrate. The piezoelectric currents generated by the ZnO nanorods were measured when bending the ZnO nanorod by using I-AFM, and the measured piezoelectric currents ranged from 60 to 100 pA. When the PtIr coated tip bends a ZnO nanorod, piezoelectrical asymmetric potential is created on the nanorod surface. The Schottky barrier at the ZnO-metal interface accumulates elecntrons and then release very quickly generating the currents when the tip moves from tensile to compressed part of ZnO nanorod. These ZnO nanorods were grown almost vertically with the length of 300-500 nm and the diameter of 30-60 nm on the Ag/Ti/PES substrate at $90^{\circ}C$ for 6 hours by hydrothermal method. The metal-semiconductor interface property was evaluated by using a HP 4145B Semiconductor Parameter Analyzer and the piezoelectric effect of the ZnO nanorods were evaluated by using an I-AFM. From the measured I-V characteristics, it was observed that ZnO-Ag and ZnO-Au metal-semiconductor interfaces showed an ohmic and a Schottky contact characteristics, respectively. ANSYS finite element simulation was performed in order to understand the power generation mechanism of the ZnO nanorods under applied external stress theoretically.

• 한국재료학회지
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• 제22권5호
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• pp.237-242
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• 2012

We report on the NO gas sensing properties of Al-doped zinc oxide-carbon nanotube (ZnO-CNT) wire-like layered composites fabricated by coaxially coating Al-doped ZnO thin films on randomly oriented single-walled carbon nanotubes. We were able to wrap thin ZnO layers around the CNTs using the pulsed laser deposition method, forming wire-like nanostructures of ZnO-CNT. Microstructural observations revealed an ultrathin wire-like structure with a diameter of several tens of nm. Gas sensors based on ZnO-CNT wire-like layered composites were found to exhibit a novel sensing capability that originated from the genuine characteristics of the composites. Specifically, it was observed by measured gas sensing characteristics that the gas sensors based on ZnO-CNT layered composites showed a very high sensitivity of above 1,500% for NO gas in dry air at an optimal operating temperature of $200^{\circ}C$; the sensors also showed a low NO gas detection limit at a sub-ppm level in dry air. The enhanced gas sensing properties of the ZnO-CNT wire-like layered composites are ascribed to a catalytic effect of Al elements on the surface reaction and an increase in the effective surface reaction area of the active ZnO layer due to the coating of CNT templates with a higher surface-to-volume ratio structure. These results suggest that ZnO-CNT composites made of ultrathin Al-doped ZnO layers uniformly coated around carbon nanotubes can be promising materials for use in practical high-performance NO gas sensors.

• 대한환경공학회지
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• 제36권11호
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• pp.771-780
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• 2014

본 연구에서는 광촉매 nano-ZnO 분말을 수질정화에 사용 후 회수 공정을 생략하기 위해 지지체에 고정화/안정화 시 발생하는 효율 저하를 유기오염물의 수착(sorption)으로 극복하고 복합체로부터 nano-ZnO의 탈리(detachment) 현상을 방지 하고자 실리콘(silicone), ABS (acrylonitrile-butadiene-styrene), 에폭시(epoxy), 부타디엔 고무(butadiene rubber)를 선정하여 nano-ZnO/Organic composites (NZOCs)를 제조하였다. 또한, 개발된 다양한 NZOCs의 수중 안정성을 규명 하고, 지하수 내 대표적인 난분해성 유기오염물인 1,1,2-trichloroethylene (TCE)를 대상으로 액상에서 제거 실험을 통해 NZOCs의 활용 타당성을 검증하였다. 연구 결과, 내수성실험을 통해 개발된 NZOCs는 수질정화 용도로 장기간 사용이 타당함을 확인하였다. 또한, FE-SEM, EDX, imaging 분석을 통해 Nano-ZnO/Butadiene rubber Composite (NZBC)는 다양한 공극과 균열에 nano-ZnO 분말이 비교적 균질하게 부착된 반면, Nano-ZnO/Silicone Composite (NZSC), Nano-ZnO/ABS Composite (NZAC), Nano-ZnO/Epoxy Composite (NZEC)는 표면에 공극과 균열이 발달되지 않아 불균질한 부착이 이뤄졌음을 확인할 수 있었다. 또한, NZBC는 초기농도 대비 60%의 TCE 수착 능을 보였는데 이는 다른 유기계 지지체와 달리 비결정성 고분자이며, TCE 분자의 소수성 분배가 활발히 발생하였기 때문으로 판단된다. 액상에서 TCE의 제거효율(수착+광분해)은 NZBC가 99% 제거 효율로 가장 우수했으며, 복합체 주입량이 증가할수록 TCE 제거효율이 크게 증가하였다. 이러한 결과는 butadiene rubber의 우수한 수착능과 nano-ZnO의 광촉매 기작이 동시에 발생하였기 때문인 것으로 판단된다. 마지막으로 액상에서 TCE 제거는 선형모델을 활용해서 비교적 잘 모사할 수 있었으며($R^2{\geq}0.936$), NZBC의 총 반응상수($K_{app}$)는 UV에 의한 TCE 분해상수($K_{photolysis}$) 대비 2.64~3.85배로 높은 값으로 확인되어 butadiene rubber가 TCE 수착 효율이 우수하며, 광분해 기작을 억제하지 않는 지지체로 활용 가능한 것으로 판단하였다.