• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.204.2-204.2
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• 2014

Among various metal oxides, ZrO2 is of particular interests and has received widespread attention thanks to its ideal mechanical and chemical stability. As a cheap metal, Ag nanoparticles are also widely used as catalysts in ethylene epoxidation and methanol oxidation. However, the nature of Ag-ZrO2 interfaces is still unknown. In this work, the growth, interfacial interaction and thermal stability of Ag nanoparticles on ZrO2(111) film surfaces were studied by low-energy electron diffraction (LEED), synchrotron radiation photoemission spectroscopy (SRPES), and X-ray photoelectron spectroscopy (XPS). The ZrO2(111) films were epitaxially grown on Pt(111). Three-dimensional (3D) growth model of Ag on the ZrO2(111) surface at 300 K was observed with a density of ${\sim}2.0{\times}1012particles/cm2$. The binding energy of Ag 3d shifts to low BE from very low to high Ag coverages by 0.5 eV. The Auger parameters shows the primary contribution to the Ag core level BE shift is final state effect, indicating a very weak interaction between Ag clusters and ZrO2(111) film. Thermal stability experiments demonstrate that Ag particles underwent serious sintering before they desorb from the zirconia film surface. In addition, large Ag particles have stronger ability of inhibiting sintering.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.2
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• pp.365-372
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• 1997

This study was executed to measure the shear bond strength of Panavia EX and Panavia 21 when the Ni-Cr-Be alloy castings were cemented to the enamel surfaces with these cements. The cast metal plates of Ni-Cr-Be alloy were sandblasted and cemented to acid etched enamel surface with Panavia EX or Panavia 21. Their shear bond strength were measured with Instron Universal Testing machine. Within the limits of this study, following conclusions were withdrawn. 1. The mean shear bond strength were 26.85.7MPa, in Panavia EX and 28.35.2MPa, in Panavia 21. 2. t-Test revealed no statistical significance between two groups(.05 level) 3. Macroscopically, bond failures were revealed compound fracture at metal and enamel interfaces, in cases of both cements, as the cement attached partly on both metal and enamel surface.

• Smart Structures and Systems
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• v.6 no.8
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• pp.921-938
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• 2010

Most of studies on control of beams containing piezoelectric sensors and actuators have been based on linear quadratic regulator (LQR) with state feedback or output feedback law. The aim of this study is to develop velocity-acceleration feedback law in the optimal control of smart piezoelectric beams. A new controller which is an optimal control system with velocity-acceleration feedback is presented. In finite element modeling of the beam, the variation of mechanical displacement through the thickness is modeled by a sinus model that ensures inter-laminar continuity of shear stress at the layer interfaces as well as the boundary conditions on the upper and lower surfaces of the beam. In addition to mechanical degrees of freedom, one electric potential degree of freedom is considered for each piezoelectric element layer. The efficiency of this control strategy is evaluated by applying to an aluminum cantilever beam under different loading conditions. Numerical simulations show that this new control scheme is almost as efficient as an optimal control system with state feedback. However, inclusion of the acceleration in the control algorithm increases practical value of a system due to easier and more accurate measurement of accelerations.

• Journal of the Korean Chemical Society
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• v.57 no.3
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• pp.365-369
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• 2013

With the wide application of ASP (alkaline-surfactant-polymer) flooding, the scaling becomes more and more serious, which is harmful to the oilfield and environment. In order to investigate the effects of HPAM on calcium carbonate crystallization, the crystallization behaviors of $CaCO_3$ in HPAM (Hydrolyzed polyacrylamide) solutions were studied and the composition and morphology of $CaCO_3$ crystal were investigated in different concentrations of polyacrylamide solutions. The crystal forms and morphologies of $CaCO_3$ were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The results show that the crystallization of $CaCO_3$ is strongly influenced by the HPAM. The paper analyzed the internal cause, and the results show: The reasons leading to the change of morphology are carboxyl groups in polyacrylamide molecule and $Ca^{2+}$ in solution form chelates by coordination bond. And the chelates are adsorbed on the calcium hydroxide surfaces of solid-liquid interfaces so as to change the formation rate of calcium carbonate crystal nucleus. The research provides a reliable basis for the mechanism research of the scaling problem in the oil extraction process of ASP flooding and the adoption of scale inhibition and scale inhibitor.

• Journal of Korea Foundry Society
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• v.10 no.5
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• pp.417-425
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• 1990

The purpose of this study is to investigate the effect of Be addition on the microstructure and mechanical properties of as-cast and homogenization treated Al-Li-(Be)alloys. The ductility of as-cast Al-Li alloy was increased by the addition of Be and the fracture morphology was changed from brittle to ductile mode. Also, hardness and strength have been decreased by homogenization treatment. The morphology of eutectic structure which consists of ${\alpha}(Al)$ and ${\alpha}(Be)$ was changed from lammellae to spherical type by homogenization treatment. The shape of ${\alpha}(Be)$ phase has been revealed as hollow type by TEM observation. It consists of outer surfaces with well defined crystal facets and the core filled with ${\alpha}(Al)$. The microstructure of as-cast Al-Li-Be alloys showed coarse ${\delta}'$, fine ${\delta}'$, and coarse ${\delta}$ phases. The coarse and fine ${\delta}'$ phases were formed at Be-rich phase /matrix interfaces and in matrix, respectively. By homogenization treatment, the ${\delta}$ phase in Al-Li and Al-Li-Be alloys dissolved and the size of ${\delta}$ phase in Al-Li-Be alloys was finer than that of Al-Li alloy.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1382-1387
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• 2004

From the viewpoint of a macro state, there is no thermal boundary resistance (TBR) at an interface if both surfaces at an interface are perfectly contacted. However, recent molecular dynamics (MD) studies reported that there still exists the TDR at the interface in an ideal epitaxial superlttice. Our previous studies suggested the model to predict the TBR not only quantitatively also qualitatively in superlattices. The suggested model was based on the classical theory of a wave reflection, and provided highly satisfactory results for an engineering purpose. However, it was not the complete model because our previous model was derived by considering only the effects from a mass ratio and a potential ratio of two species. The interaction of two species presented by the Lennard-Jones (L-J) potential is governed by the mutual ratio of the masses, the potential well depths, and the diameters. In this study, we performed the preliminary simulations to investigate the effect resulting from the diameter ratio of two species for the completion of our model and confirmed that it was also a ruling factor to the TBR at an interface in superlattices.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.158-162
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• 2001

The effects of chemical treatment on Kevlar-29 fibers have been studied in a composite system. The surface characteristics of the Kevlar-29 fibers were characterized by pH, acid-base value and X-ray photoelectron spectroscopy (XPS). The mechanical interfacial properties of final composites were studied by interlaminar shear strength (ILSS) and critical stress intensity factor ($K_{IC}$). Also, the impact properties of the composites were investigated in the differentiating studies between initiation and propagation energies, and ductile index (DI) along with maximum farce and total energy. It was found that the chemical treatment with phosphoric acid ($H_3PO_4$) solution significantly affected the degree of adhesion at interfaces between fibers and resin matrix, resulting in improving the mechanical interfacial strength of the composites. This was probably due to the presence of chemical polar groups on Kevlar surfaces, leading to an increment of interfacial binding force in a composite system.

• Korean Journal of Materials Research
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• v.15 no.7
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• pp.458-464
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• 2005

In microelectronics packaging, the reliability of the metal/polymer interfaces is an important issue because the adhesion strength between dissimilar materials is often inherently poor. The modification of polymer surfaces by ion beam irradiation and rf plasma is commonly used to enhance the adhesion strength of the interface. T-peel strengths were measured using a Cu/polyimide system under varying $N_2^+$ ion beam irradiation conditions for pretreatment. The measured T-peel strength showed reversed camel back shape regarding the fixed metal-layer thickness, which was quite different from the results of the 90° peel test. The elementary analysis suggests that the variation of the T-peel strength is a combined outcome of the plastic bending work of the metal and polymer strips. The results indicate that the peel strength increases with $N_2^+$ ion beam irradiation energy at the fixed metal-layer thickness.

• Nuclear Engineering and Technology
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• v.50 no.8
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• pp.1330-1338
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• 2018

High-density UMo/Zr monolithic nuclear fuel plates have a promising application prospect in high flux research and test reactors. The solid state welding method called co-rolling is used for their fabrication. Hot co-rolling simulations for the composite blanks of UMo/Zr monolithic nuclear fuel plates are performed. The effects of coupon sizes and mechanical property parameters on the contact pressures between the to-be-bonded surfaces are investigated and analyzed. The numerical simulation results indicate that 1) the maximum contact pressures between the fuel coupon and the Zircaloy cover exist near the central line along the plate length direction; as a whole the contact pressures decrease toward the edges in the plate width direction; and lower contact pressures appear at a large zone near the coupon corner, where de-bonding is easy to take place in the in-pile irradiation environments; 2) the maximum contact pressures between the fuel coupon and the Zircaloy parts increase with the initial coupon thickness; after reaching a certain thickness value, the contact pressures hardly change, which was mainly induced by the complex deformation mechanism and special mechanical constitutive relation of fuel coupon; 3) softer fuel coupon will result in lower contact pressures and form interfaces being more out-of-flatness.

• Steel and Composite Structures
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• v.49 no.5
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• pp.547-570
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• 2023

In the present work, a comparative study has been carried out between power, exponential, and sigmoidal sandwich FGM plates for free vibration conditions under hygro-thermal conditions. Rules of mixture is used to determine effective material properties across the thickness for power-law and sigmoid sandwich FGM plates. Exponential law is used to plot effective material properties for exponentially graded sandwich FGM plates. Temperature and moisture dependent material properties were used during the analysis. Free vibration analysis is carried out using recently proposed finite element based HOZT. Present formulation satisfies interlayer transverse stress continuity conditions at interfaces and transverse shear stress-free conditions at the plate's top and bottom surfaces. The present model is free from any penalty or post-processing requirements. Several new results are reported in the present work, especially for unsymmetric sandwich FGM plates and exponential and sigmoidal sandwich FGM plates.