• Advances in nano research
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• 제6권4호
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• pp.357-375
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• 2018

Two dimensional (2D) atomic layered nanomaterials exhibit some of the most striking phenomena in modern materials research and hold promise for a wide range of applications including energy and biomedical technologies. Graphene has received much attention for having extremely high surface area to mass ratio and excellent electric conductivity. Graphene has also been shown to maximize the activity of surface-assembled metal nanoparticle catalysts due to its unique characteristics of enhancing mass transport of reactants to catalysts. This paper specifically investigates the strategy of pre-formed nanoparticle self-assembly used for the formation of various metal nanoparticles supported on graphene families such as graphene, graphene oxide, and reduced graphene oxide and aims at understanding the interactions between ligand-capped metal nanoparticles and 2D nanomaterials. By varying the functional groups on the ligands between alkyl, aromatic, amine, and alcohol groups, different interactions such as van der Waals, ${\pi}-{\pi}$ stacking, dipole-dipole, and hydrogen bonding are formed as the 2D hybrids produced.

• Journal of Welding and Joining
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• 제23권6호
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• pp.99-105
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• 2005

The mixing ratio effect of the GTD-111(base metal) powder and the GNI-3 (Ni-l4Cr-9.5Co-3.5Al-2.5B) powder on TLP(Transient Liquid Phase) bonding phenomena and mechanism was investigated. At the mixing ratio of the base metal powder under $50wt\%$, the base metal powders fully melted at the initial time and a large amount of the base metal near the bonded interlayer was dissolved by liquid inter metal. Liquid insert metal was eliminated by isothermal solidification which was controlled by the diffusion of B into the base metal. The solid phases in the bonded interlayer grew epitaxially from the base metal near the bonded interlayer inward the insert metal during the isothermal solidification. The number of grain boundaries farmed at the bonded interlayer corresponded with those of base metal. At the mixing ratio above $60wt\%$, the base metal powder melted only at the surface of the powder and the amount of the base metal dissolution was also less at the initial time. Nuclear of solids firmed not only from the base metal near the bonded interlayer but also from the remained base metal powder in the bonded interlayer. Finally, the polycrystal in the bonded interlayer was formed when the isothermal solidification finished. When the isothermal solidification was finished, the contents of the elements in the boned interlayer were approximately equal to those of the base metal. Cr-W borides and Cr-W-Ta-Ti borides formed in the base metal near the bonded interlayer. And these borides decreased with the increasing of holding time.

• 폴리머
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• 제24권6호
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• pp.829-836
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• 2000

SMC 욕조 생산 시 발생하는 폐 FRP와 석재 가공공정에서 발생되는 석분슬러지를 재활용하기 위하여 불포화에스테르 매트릭스 수지에 분말 충전하여 복합재를 제조하였다. 또한 충전제와 매트릭스 간의 계면결합력을 향상시키기 위해 석분을 실란 커플링제 ${\gamma}$-methacryloxypropyltrimethoxysiiane (${\gamma}$-MPS)로 전처리하여 복합재를 제조하고 기계적 물성 및 계면현상을 관찰하였다. 복합재의 굴곡탄성율은 석분함량이 10 wt%, 실란커플링제의 농도가 3 wt%일 때 가장 우수하였으며 석분 충전량이 증가함에 따라 감소하는 경향을 보였다. 또한 복합재의 초기 열분해온도는 352~359$^{\circ}C$이었으며 이 온도에서 중량감소율은 약 3%로 충전제의 양에 관계없이 거의 일정한 경향을 보였다. ${\gamma}$-MPS 처리에 따른 복합재의 물성변화를 관찰한 결과 충전제와 매트릭스 수지간 계면결합력이 증진되어 물리 화학적으로 안정한 결합을 이루고 있고 pull out현상이 발생하지 않음을 확인할 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.361-361
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• 2012

PZT (Pb(Zr,Ti)O3) thin films have been used widely in the MEMS application, due to their inherent ferroelectric and piezoelectric properties. Such ferroelectricity induces much higher dielectric constants compared to those of the nonperovskite materials. In this work, the PZT thin films were deposited onto Indium-Tin-oxide (ITO) substrates through the spin-coating of PZT sols. The deposited PZT thin films were characterized in terms of the electrical and optical properties with special emphases on conductivity and optical constants. The detailed analysis techniques incorporate the dc-based current-voltage characteristics for the electrical properties, spectroscopic ellipsometry for optical characterization, atomic force microscopy for surface morphology, X-ray Photoelectron Spectroscopy for chemical bonding, Energy-dispersive X-ray Spectrometry for chemical analyses and X-ray diffraction for crystallinity. The ferroelectric phenomena were confirmed using capacitance-voltage measurements. The integrated physical/chemical features are attempted towards energy-oriented applications applicable to next-generation high-efficiency power generation systems.

• 대한기계학회논문집A
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• 제27권5호
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• pp.840-847
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• 2003

The bonding of adhesive joints of adhesive joints is influenced by the surface roughness of the joining Parts. However, the magnitude of the influence has not yet been clarified because of the complexity of the phenomena. In this study, it is shown that surface treatment affects adhesive strength and durability of alumina/polycarbonate single-lap .joints, and leading speed affects tensile-shea strength of adhesive Joints. To evaluate effect of surface treatments on the adhesive strength, several surface treatment methods are used, that is, cleaning, grinding, SiC polishing and sand blasting. It is shown that an optimum value of the surface roughness exists with respect to the tensile-shea strength of adhesive joints. The adhesive strength shows linear relationship with the surface roughness and loading speed. And the mechanical removal of disturbing films of lubricants, impurities and oxides make adhesive strength increase significantly.

• 설비공학논문집
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• 제13권3호
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• pp.194-199
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• 2001

The turbulent flow resistance of water solution with polymer is reduced as compared with that of pure water. This effects is named th drag reduction and offers the significant reduction of the pumping power and the energy consumption. But the intense shear forces and the high temperature experienced by the polymer solution when passing through the pipes cause the degradation a loss of drag reduction effectiveness. Especially, the degradation behavior is found to be strongly dependent on temperature. This mechanical and thermal degradation can be avoided by adding materials such as surfactant to the polymer solution, which enhance the bonding force between molecules. In the present study, Copolymer and SDS were utilized and they were mixed in 10 different mixture ratios, while total concentration was fixed as 100wppm. Degradation of Copolymer-SDS mixture solutions was investigated experimentally in closed loop at the temperature of $10^{\circ}C\; and\; 80^{\circ}C$ with various flow average velocities of 1.5 m/sec, 3.0m/sec, and 4.5m/sec. Degradation characteristics of polymer solution without surfactant show a radical loss of drag reduction effectiveness at high temperature. Degradation alleviation ability of surfactant is especially effective at high temperature. Consequently, this results show that the addition of surfactant to the polymer solution can control unfavorable degradation phenomena for high temperature systems.

• Interaction and multiscale mechanics
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• 제2권2호
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• pp.129-151
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• 2009

This paper presents a meshfree procedure using a convex generalized meshfree (GMF) approximation for the large deformation analysis of particle-reinforced rubber compounds on microscopic level. The convex GMF approximation possesses the weak-Kronecker-delta property that guarantees the continuity of displacement across the material interface in the rubber compounds. The convex approximation also ensures the positive mass in the discrete system and is less sensitive to the meshfree nodal support size and integration order effects. In this study, the convex approximation is generated in the GMF method by choosing the positive and monotonic increasing basis function. In order to impose the periodic boundary condition in the unit cell method for the microscopic analysis, a singular kernel is introduced on the periodic boundary nodes in the construction of GMF approximation. The periodic boundary condition is solved by the transformation method in both explicit and implicit analyses. To simulate the interface de-bonding phenomena in the rubber compound, the cohesive interface element method is employed in corporation with meshfree method in this study. Several numerical examples are presented to demonstrate the effectiveness of the proposed numerical procedure in the large deformation analysis.

• 대한치과기공학회지
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• 제25권1호
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• pp.21-28
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• 2003

The purpose of this study was to process bio-active glass ceramic composite, reinforced with sapphire fibers, by hot press. Also to study the interface of the matrix and the sapphire fiber, and the mechanical properties. Glass raw materials melted in Pt crucible at 1300$^{\circ}C$ during 3.5 hours. The melt was crushed in ball mill and then crushed material, ground and sieved to $<40{\beta}{\mu}m$. Sapphire fibers cut (30mm) and aligned. Powder and fibers hot pressed. The micrographs show good bonding between the matrix and the fiber and no porosity in the glass matrix. This means ideal fracture phenomena. Glass is fractured before the fiber. This is indication of good fracture strength. EDXS showing aluminum rich phase and crystalline phase. Bright field image of the matrix showing crystalline phase. Also diffraction pattern of TEM showing the crystalline phase and more than one phase. Strength of the samples was determined by 3 point bend testing. Strength of the 10vol% sample was approximately 69MPa, while strength of the control sample is 35MPa. Conclusions through this study as follow: 1. Micrographs show no porosity in the glass matrix and the interface. 2. The interface between the fiber and the glass matrix show no gaps. 3. Fracture of the glass indicates characteristic fiber-matrix separation. 4. Presence of crystalline phase at high processing temperature. 5. Sapphire is compatible with bioactive glass.

• 한국지반공학회논문집
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• 제18권6호
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• pp.83-101
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• 2002

탄성파는 지표면에 가까운 흙에 관한 중요한 정보를 공급한다. 흙특성 파악에 물리탐사기법의 원활한 적용을 위하여 탄성파인자와 흙특성과의 관계를 고찰하였다. 적용 예로서, 비포화토의 거동 및 특성을 전단파 시험을 통하여 알아보았다. 포화시료를 건조하면서 밴더엘리먼트를 사용하여 미소변형률 전단강성을 연속적으로 측정하였다. 비포화토에서는 모세관현상, 이온공유에 의한 접착, 세립자 이동에 의한 강화효과, 염 침전에 의한 시멘트결합과 같은 입자간 힘의 변화가 강성의 변화에 직접적으로 영향을 끼치는 것으로 나타났다. 비포화토의 시료를 교란함으로써 메니스커스의 회복에 대한 연구를 수행하였고, 비포화토에서 일어나는 여러 가지 현상들을 제시하였다.

• 한국재료학회지
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• 제8권12호
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• pp.1077-1081
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• 1998

목분 충진제의 함량을 달리 하여 PE수지를 매트릭스로 하여 Wood Plastic Composites (WPC)를 제조하였다. 또한 매트릭스와 충진제간의 결합력을 증가시키기 위하여 커플링제를 사용하였으며, 보강재의 보강률과 커플링제 처리가 복합재의 기계적 물성에 미치는 영향과 계면현상을 관찰하였다. 커플링제로 MA를 사용하였을 경우에 tensile strength는 3wt%의 농도에서 25.91MPa의 최대값을 나타내었으며. MAOMS커플링제의 경우, 3wt%의 처리 농도에서 22.48MPa로 MA로 처리한 것보다 낮았다. 충격강도는 MA의 경우에는 3wt%일 때 44.38J/m의 최대값을 나타냈으며, MAOMS의 처리에서는 36.09J/m로 MA처리한 것보다 낮게 나타났다.