• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.130-131
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• 2013

Nanostructured oxides are widely used in heterogeneous catalysis where their catalytic properties are closely associated with the size and morphology at nanometer level. The effect of particle size has been well decumented in the past two decades, but the shape of the nanoparticles has rarely been concerned. Here we illustrate that the redox and acidic-basic properties of oxides are largely dependent on their shapes by taking $Co_3O_4$, $Fe_2O_3$, $CeO_2$ and $La_2O_3$ nanorods as typical examples. The catalytic activities of these rod-shaped oxides are mainly governed by the nature of the exposed crystal planes. For instance, the predominant presence of {110} planes which are rich in active $Co^{3+}$ on $Co_3O_4$ nanorods led to a much higher activity for CO oxidation than the nanoparticles that mainly exposed the {111} planes. The simultaneous exposure of iron and oxygen ions on the surface of $Fe_2O_3$ nanorods have significantly enhanced the adsorption and activation of NO and thereby promoted the efficiency of DeNOx process. Moreover, the exposed surface planes of these rod-shaped oxides mediated the reaction performance of the integrated metal-oxide catalysts. Au/$CeO_2$ catalysts exhibited outstanding stability under water-gas shift conditions owing to the strong bonding of gold particle on the $CeO_2$ nanorods where the formed gold-ceria interface was resistant towards sintering. Cu nanoparticles dispersed on $La_2O_3$ nanorods efficiently catalyzed transfer dehydrogenation of primary aliphatic alcohols based on the uniue role of the exposed {110} planes on the support. Morphology control at nanometer level allows preferential exposure of the catalytically active sites, providing a new stragegy for the design of highly efficient nanostructured catalysts.

• 한국분말재료학회지
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• 제13권5호
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• pp.321-326
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• 2006

Electronic packaging involves interconnecting, powering, protecting, and cooling of semiconductor circuits fur the use in a variety of microelectronic applications. For microelectronic circuits, the main type of failure is thermal fatigue, owing to the different thermal expansion coefficients of semiconductor chips and packaging materials. Therefore, the search for matched coefficients of thermal expansion (CTE) of packaging materials in combination with a high thermal conductivity is the main task for developments of heat sink materials electronics, and good mechanical properties are also required. The aim of this work is to develop copper matrix composites reinforced with carbon nanofibers. The advantages of carbon nanofibers, especially the good thermal conductivity, are utlized to obtain a composite material having a thermal conductivity higher than 400 W/mK. The main challenge is to obtain a homogeneous dispersion of carbon nanofibers in copper. In this paper, a technology for obtaining a homogeneous mixture of copper and nanofibers will be presented and the microstructure and properties of consolidated samples will be discussed. In order to improve the bonding strength between copper and nanofibers, different alloying elements were added. The microstructure and the properties will be presented and the influence of interface modification will be discussed.

• Steel and Composite Structures
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• 제27권5호
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• pp.577-598
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• 2018

The imperfect steel-concrete interface bonding is an important deficiency of the concrete-filled double skin tubular (CFDST) columns that led to separating concrete and steel surfaces under lateral loads and triggering buckling failure of the columns. To improve this issue, it is proposed in this study to use longitudinal and transverse steel stiffeners in CFDST columns. CFDST columns with different patterns of stiffeners embedded in the interior or exterior surfaces of the inner or outer tubes were analyzed under constant axial force and reversed cyclic loading. In the finite element modeling, the confinement effects of both inner and outer tubes on the compressive strength of concrete as well as the effect of discrete crack for concrete fracture were incorporated which give a realistic prediction of the seismic behavior of CFDST columns. Lateral strength, stiffness, ductility and energy absorption are evaluated based on the hysteresis loops. The results indicated that the stiffeners had determinant role on improving pinching behavior resulting from the outer tube's local buckling and opening/closing of the major tensile crack of concrete. The lateral strength, initial stiffness and energy absorption capacity of longitudinally stiffened columns with fixed-free end condition were increased by as much as 17%, 20% and 70%, respectively. The energy dissipation was accentuated up to 107% for fixed-guided end condition. The use of transverse stiffeners at the base of columns increased energy dissipation up to 35%. Axial load ratio, hollow ratio and concrete strength affecting the initial stiffness and lateral strength, had negligible effect of the energy dissipation of the columns. It was also found that the longitudinal stiffeners and transverse stiffeners have, respectively, negative and positive effects on ductility of CFDST columns. The conclusions, drawn from this study, can in turn, lead to the suggestion of some guidelines for the design of CFDST columns.

• 한국분말재료학회지
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• 제27권1호
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• pp.25-30
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• 2020

Recently, the amount of heat generated in devices has been increasing due to the miniaturization and high performance of electronic devices. Cu-graphite composites are emerging as a heat sink material, but its capability is limited due to the weak interface bonding between the two materials. To overcome these problems, Cu nanoparticles were deposited on a graphite flake surface by electroless plating to increase the interfacial bonds between Cu and graphite, and then composite materials were consolidated by spark plasma sintering. The Cu content was varied from 20 wt.% to 60 wt.% to investigate the effect of the graphite fraction and microstructure on thermal conductivity of the Cu-graphite composites. The highest thermal conductivity of 692 W m^-1K^-1 was achieved for the composite with 40 wt.% Cu. The measured coefficients of thermal expansion of the composites ranged from 5.36 × 10^-6 to 3.06 × 10^-6K^-1. We anticipate that the Cu-graphite composites have remarkable potential for heat dissipation applications in energy storage and electronics owing to their high thermal conductivity and low thermal expansion coefficient.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.314-323
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• 2010

Recently, granular soils having a large particle size are frequently used as a filling material in the construction of foundation, harbor, dam, and so on. The shear behavior of this granular soil plays a key role in the stability of structures. For example, soil particle crushing occurring at the interface between structure and soil and/or within soil mass can cause the disturbance of ground characteristics and consequently induce an issues in respect of stability of structures. In order to investigate the shear behavior according to an existence and nonexistence of particle crushing, numerical analyses were conducted by using the DEM(Discrete Element Method)-based software program PFC(Particle Flow Code). Using the crushing model and non-crushing model which were created in this study, numerical analyses of ring shear test were conducted and their results were analyzed and compared. In general, landslide and slope stability are accompanied by a large displacement and consequently not only a peak strength but also a residual strength are very important in the analysis of landslide and slope stability. However the direct shear test which has been commonly used in the determination of shear strength parameters has a limitation on displacement therefore the residual strength parameters can not be obtained. The characteristics of residual shear behavior were investigated through the numerical analyses in this study.

• Korean Chemical Engineering Research
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• 제54권6호
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• pp.830-837
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• 2016

그라파이트 폼의 압축강도를 향상시키기 위하여 메조페이스 핏치를 공기분위기에서 산화안정화 한 후 다양한 불소 부분압으로 처리하였다. 불소화 처리된 메조페이스 핏치의 불소/탄소 표면화학 조성은 불소 부분압에 따라서 약 23.75%~61.48%의 범위를 가진다. 불소화 메조페이스 핏치기반 그라파이트 폼의 압축강도는 겉보기 밀도의 증가에 비례하여 증가되었다. 불소/탄소 표면화학 조성이 35.93%의 값을 갖는 메조페이스 핏치로부터 제조된 그라파이트 폼의 압축강도는 최대 $2.93{\pm}0.06MPa$의 값을 보여 주었으며, 이 값은 미처리된 메조페이스 핏치로부터 제조된 그라파이트 폼과 비교하여 27.95% 증가되었다. 이러한 결과는 표면에너지가 큰 불소 작용기로 인한 메조페이스 핏치간의 계면결합력이 그 압축강도를 증가시켰기 때문으로 여겨진다.

• The Korean Journal of Ceramics
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• 제5권4호
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• pp.336-340
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• 1999

Glasses in the system $CaO-TiO_2-SiO_2-Al_2O_3-ZrO_2-B_2O_3$ were investigated to find the glass seal compositions suitable for use in the planar solid oxide fuel cell (SOFC). Glass-ceramics prepared from the glasses by one-stage heat treatment at $1,000^{\circ}C$ showed various thermal expansion coefficients (i,e., $8.6\times10^{-6^{\circ}}C^{-1}$ to $42.7\times10^{-6^{\circ}}C^{-1}$ in the range 25-$1,000^{\circ}C$) due to the viscoelastic response of glass phase. The average values of contact angles between the zirconia substrate and the glass particles heated at 1,000-$1,200^{\circ}C$ were in the range of $131^{\circ}\pm4^{\circ}$~$137^{\circ}\pm9^{\circ}$, indicating that the glass-ceramic was in partial non-wetting condition with the zirconia substrate. With increasing heat treatment time of glass samples from 0.5 to 24 h at $1,100^{\circ}C$, the DC electrical conductivity of the resultant glass-ceramics decreased from at $800^{\circ}C$. Isothermal hold of the glass sample at $1100^{\circ}C$ for 48h resulted in diffusion of Ca, Si, and Al ions from glass phase into the zirconia substrate through the glass/zirconia bonding interface. Glass phase and diffusion of the moving ion such as $Ca^{2+}$ in glass phase is responsible for the electrical conduction in the glass-ceramics.

• 콘크리트학회논문집
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• 제16권2호
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• pp.213-220
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• 2004

본 논문은 신공법인 carbon fiber rod로 보강된 교량 바닥판의 정적 및 피로성능개선 효과에 대한 것이다. 이 연구의 실험에서 적용된 보강변수는 등방성 및 이방성 보강이며, 보강성능을 평가하기 위하여 보강된 바닥판 시험체에 대해 정적 및 피로실험을 실시하여 그에 따른 내하성능, 균열 및 파괴양상 등을 분석하였다. 실험결과, 보강된 모든 시험체가 증설된 모르타르와 콘크리트와의 계면이 조기에 탈락하여 펀칭전단 파괴되는 양상을 보였다. 보강성능을 살펴보면, CFR로 보강된 바닥판은 무보강 시험체에 비해 극한강도, 강성, 피로수명 등에서 우수한 것으로 나타났다 또한 보강형식 측면에서는, 이방성 보강(CR-UE)이 등방성 보강(CR-E)보다 우수한 것으로 나타났다.

• 구강회복응용과학지
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• 제21권1호
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• pp.69-81
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• 2005

The objective of this study was to evaluate the toothbrush abrasion characteristics of class V restorations. Thirty extracted human premolars, which were collected from oral surgery clinics were used. We mounted five teeth in a metal ring mold of 50 mm in diameter and 15 mm in height using chemically cured acrylic resin. Class V cavities were prepared in lingual cervical root surfaces and restored using one of following restorative materials : Dentin Conditioner/Fuji II LC (Group FL), All Bond II/Z-250 (Group ZT), One-up Bond F/Palfigue Estelite (Group PE), F2000 Primer/Adhesive (Group FT), and Prime & Bond 2.1/Dyract AP (Group DR). They were stored under distilled water at $37^{\circ}C$ for seven days. The toothbrush abrasion test was conducted using a wear testing machine of pin-on disk type under a load of 1.5 N for 100,000 cycles. We have examined the bonded interfaces, the changes of surface roughness and color of abraded surfaces. From this experiment, the following results were obtained. 1. The change of surface roughness showed high degree: RMGIC>compomer>composite resin (p<0.05). 2. Because of the protrusion and missing of filler particles, SEM observation of abraded surfaces of RMGIC and compomers revealed the increase of surface roughness due to the selective removal of matrix resin. 3. The color change by toothbrush abrasion was affected in large part by the change of $L^*$ and $b^*$ of resin composites (p<0.05). 4. The color change by toothbrush abrasion was so small to detect by human eyes. 5. SEM observation of abraded surfaces revealed the interface bonding was the best in the FT group.

• Composites Research
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• 제25권6호
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• pp.205-210
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• 2012

전기저항 측정법을 이용하여 단일 탄소섬유의 인장 실험을 실시하였다. 탄소섬유의 전도성을 이용하여 인장하중에 따른 신율과 전기저항 변화도간의 관계를 연구하였다. 섬유 인장 과정동안에 일정 신율 거리상 응력과 전기저항 변화율간의 상관관계를 통계적으로 정리하였다. 결과에 대해 추세선을 그어 섬유의 변형에 따른 거동 모델을 구성하였다. 프레그먼테이션 시편을 이용하여 인장 실험에 따른 인장 응력이 재료 내부로 전달되면서, 시편 내부 탄소섬유에도 인장 응력이 가해져 기지보다 섬유가 먼저 파괴되었다. 이 경우 탄소섬유의 전기저항 변화도를 측정한 결과 값을 탄소섬유의 거동 모델에 대입하여 프레그먼테이션 시편 내부에 있었던 탄소섬유의 거동을 분석할 수 있었다. 탄소섬유의 인장 신율을 예측하고 프레그먼테이션 시편의 실제 신율을 비교하여 섬유와 기지 사이에 발생된 섬유 미끌림 정도를 확인하였다. 섬유 미끌림 정도의 수치가 클 경우, 기지와 섬유 간 계면 상태가 약한 접합의 상태였다. 이러한 결과를 확인하기 위해서 접착일 평가법을 이용하였으며, 두 실험법의 결과, 동일한 경향임을 확인하였다.