• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1825-1828
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• 2008

A simple method for the fabrication of porous nano-master for antireflective surface is presented. In conventional fabrication methods for antireflective surface, coating method with low refractive index has usually been used. However, it is required to have high cost and long times for mass production. In this paper, we suggested the fabrication method of antireflective surface by the hot embossing process using the porous nano patterned master on silicon wafer fabricated by low-temperature anodic aluminum oxidation. Through multi-AAO and etching processes, nano patterned master with high aspect ratio was fabricated at the large area. Pore diameter and inter-pore distance are about 150nm and from 150 to 200nm. In order to replicate anti-reflective structure, hot embossing process was performed by varying the processing parameters such as temperature, pressure and embossing time etc. Finally, antireflective surface can be successfully obtained after etching process to remove selectively silicon layer of AAO master.

• 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.

• 한국자동차공학회논문집
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• 제16권5호
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• pp.60-67
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• 2008

The catalytic filter of Cu-ZSM5/alumina beads was considered to reduce NOx in the urea SCR system. Catalytic support of porous alumina beads with mean pore size $130{\mu}m$ and porosity $75{\sim}83%$ were prepared using foaming and gel-casting method. The Cu-ZSM5 catalysts were coated on the supporting alumina beads using $Cu(NO_3)_2$ by ion exchange method. After a washcoating process was applied to coat 10w% Cu-ZSM5 on porous alumina bead, coating layer was estimated $20{\mu}m$ in thickness. The characterization and the feasibility as a catalytic supports were investigated. And the NOx conversion test in Cu-ZSM5/Alumina Beads filter system was conducted by using Urea as reductants under laboratory test. The NOx conversion was increased as size and porosity of beads and observed more than 95% excellent NOx conversion above $300^{\circ}C$.

• 한국생산제조학회지
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• 제18권6호
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• pp.697-701
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• 2009

A simple method for the fabrication of porous nano-master for the anti-reflection effect on the transparent substrates is presented. In the conventional fabrication methods for antireflective surface, coating method using materials with low refractive index has usually been used. However, it is required to have a high cost and long processing time for mass production. In this paper, we developed a porous nano-master with anti-reflective surface for the molding stamper of the injection mold, hot embossing and UV imprinting by using the aluminum anodizing process. Through two-step anodizing and etching processes, a porous nano-master with anti-reflective surface was fabricated at the large area. Pattern size Pore diameter and inter-pore distance are about 130nm and 200nm, respectively. In order to replicate anti-reflective structure, hot embossing process was performed by varying the processing parameters such as temperature, pressure and embossing time etc. Finally, antireflective surface can be successfully obtained after etching process to remove selectively silicon layer of AAO master.

• 한국결정성장학회지
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• 제6권4호
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• pp.571-583
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• 1996

1 mM의 $[Fe(CN)_{6}]^{3-}/[Fe(CN)_{6}]^{4-}$ 이온이 첨가된 0.5 M $K_{2}SO_{4}$용액에서 Impedance spectroscopy를 통하여 비교적 porous한 표면조직을 갖는 흑연재료인 electrographite와 graphite foil의 계면의 전기화학적 거동을 조사하였다. 이들 두 흑연재료의 변전위 전류 전압곡선의 경우 전극표면의 구조로 인하여 비교적 높은 전류가 나타났으며, graphite foil의 경우 높은 이중층 용량이 나타났다. 또한 두 재료 모두 field transport의 작용에 의해 분극증가에 따른 임피던스 스펙트럼의 변화와 Faraday-임피던스의 변화가 크게 나타나지 않았다. 특히 electrographite의 경우 전극계면에서 흡착현상이 나타났으며, 양극분극의 증가에 의해 흡착현상은 현저하게 증가하였다.

• 한국표면공학회지
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• 제48권1호
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• pp.11-22
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• 2015

Pd alloy hydrogen membranes for hydrogen purification and separation need thermal stability at high temperature for commercial applications. Intermetallic diffusion between the Pd alloy film and the porous metal support gives rise to serious problems in long-term stability of Pd alloy membranes. Ceramic barriers are widely used to prevent the intermetallic diffusion from the porous metal support. However, these layers result in poor adhesion at the interface between film and barrier because of the fundamentally poor chemical affinity and a large thermal stress. In this study, we developed Pd alloy membranes having a dense microstructure and saturated composition on modified metal supports by advanced DC magnetron sputtering and heat treatment for enhanced thermal stability. Experimental results showed that Pd-Cu and Pd-Ag alloy membranes had considerably enhanced long-term stability owing to stable, dense alloy film microstructure and saturated composition, effective diffusion barrier, and good adhesive interface layer.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.315-316
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• 2006

The paper presents some results regarding the obtaining of some copper heat pipes with a porous copper internal layer for electronic components cooling. The heat pipes were realized by sintering of spherical copper powders of $90{\div}125\;{\mu}m$ size directly on the internal side of a copper pipe of 18 mm in diameter. The obtained pipes were then brazed in order to obtain a heat pipe of 0.5 m in length. After that, the heat pipe was sealed and filled with a small quantity of distilled water as working fluid. To establish the total heat transport coefficient and the thermal flow transferred at the evaporator, some external devices were realized to allow the heating of the evaporator and the cooling of the condenser. Water heat pipes are explored in the intermediate temperature range of 303 up to 500 K. Test data are reported for copper water heat pipe, which was tested under different orientations. The obtained results show that the water heat pipe has a good thermal transfer performance in the temperatures range between 345 and 463 K.

• Advances in nano research
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• 제12권6호
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• pp.593-603
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• 2022

The critical buckling temperature rise of a newly proposed piezoelectrically active sandwich plate (ASP) has been investigated in this work. This structure includes a porous polymeric layer integrated between two piezoelectric nanocomposite layers. The piezoelectric material is made of a passive polymeric material that is activated by lead-free nanowires (NWs) of zinc oxide (ZnO) embedded inside the matrix. In both nanocomposite layers and porous core, functional graded (FG) patterns have been considered for the distributions of ZnO NWs and voids, respectively. By adopting a higher-order theory of plates, the governing equations of thermal buckling are obtained. This set of equations is then treated using an extended mesh-free solution. The effects of plate dimensions, porosity states, and the nanowire parameters have been investigated on the critical buckling temperature rises of the proposed lightweight ASPs with different boundary conditions. The results disclose that the use of porosities in the core and/or mixing ZnO NWs in the face sheets substantially arise the critical buckling temperatures of the newly proposed active sandwich plates.

• Steel and Composite Structures
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• 제48권3호
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• pp.335-351
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• 2023

This research studies the primary resonance and nonlinear vibratory responses of multilayer functionally graded shallow (MFGS) shells under external excitations. The shells considered with functionally graded porous (FGP) core and resting on two types of nonlinear viscoelastic foundations (NVEF) governed by either a linear model with two parameters of Winkler and Pasternak foundations or a nonlinear model of hardening/softening cubic stiffness augmented by a Kelvin-Voigt viscoelastic model. The shells considered have three layers, sandwiched by functionally graded (FG), FGP, and FG materials. To investigate the influence of various porosity distributions, two types of FGP middle layer cores are considered. With the first-order shear deformation theory (FSDT), Hooke's law, and von-Kármán equation, the stress-strain relations for the MFGS shells with FGP core are developed. The governing equations of the shells are consequently derived. For the sake of higher accuracy and reliability, the P-T method is implemented in numerically analyzing the vibration, and the method of multiple scales (MMS) as one of the perturbation methods is used to investigate the primary resonance. The results of the present research are verified with the results available in the literature. The analytical results are compared with the P-T method. The influences of material, geometry, and nonlinear viscoelastic foundation parameters on the responses of the shells are illustrated.

• 한국도로학회논문집
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• 제13권3호
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• pp.39-49
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• 2011

도시부 도로에서 투수성포장의 효용성은 널리 인식되고 있으나, 빗물침투로 인한 노상의 약화를 고려한 포장 두께 설계는 아직 제시되지 못하고 있다. 도시에서 빗물을 도로포장의 표면에서 바로 배수시키지 않고, 표면을 투과해서 노상으로 침투시키는 구조를 갖는 투수성포장은 도시홍수의 억제, 배수시설의 부하 경감, 지중생태계 개선, 열섬현상 억제 등 기존 불투수성 포장으로 인해 발생되는 여러 가지 문제를 저감시킬 수 있을 것으로 기대되고 있다. 그러나 투수성포장의 구조설계는 빗물 침투로 노상이 약화되는 현상을 적절히 고려할 수 없어, 투수성포장에 대한 구조설계방법은 아직 제시되지 못하고 있다. 본 연구에서는 빗물에 의한 노상의 약화 정도에 대한 문헌적 정보와 역학적 분석을 통해 잠정적으로 적용할 수 있는 투수성 아스팔트포장의 구조설계방법을 제시하였다. 문헌적 정보는 노상함수비가 최적함수비에서 2% 증가에 따라 탄성계수가 20% 감소한다는 조건을 적용하였다. 실제 현장을 대상으로 투수성포장을 적용할 경우 유한요소 해석결과와 기존 설계방법에 노상의 강도저하를 고려한 결과 기존두께에 30cm 정도 보조기층을 보강해야 하는 것으로 분석되었다. 이것은 일본에서 투수성 아스팔트포장의 구조설계에 적용하고 있는 증가두께와 유사한 것으로 나타났다.