• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.211-211
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• 2011

Nanostructures, with a diversity of shapes, built on substrates have been developed within many research areas. Lithography is one powerful, but complex, technique to make structures at the nanometer scale, such as platinum nanowires for studying CO catalytic reactions [1], or aluminum nanodisks for studying the plasmon effect [2]. In this work, we approach a facile method to construct nanostructures using noble metals on a titania thin film by using self-assembled structures as a pattern. Here, a large-scale silica monolayer is transferred to the titania thin film substrates using a Langmuir-Blodgett trough, followed by the deposition of a thin transition metal layer. Owing to the hexagonal close-packed structure of the silica monolayer, we would obtain a metal nanostructure that includes separated metallic triangles (islands) after removing the patterning silica beads. This nanostructure can be employed to investigate the role of metal-oxide interfaces in CO catalytic reactions by changing the patterning silica particles with different sizes or by replacing the oxide support. The morphology and chemical composition of the structure can be characterized by scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. In addition, we modify these islands to a connected island structure by reducing the silica size of the patterning monolayer, which is utilized to generating hot electron flow based on the localized surface plasmon resonance effect of the metal nanostructures.

• Journal of Powder Materials
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• v.20 no.6
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• pp.411-424
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• 2013

In this study, the synthesis of nickel nanoparticles and copper nanospheres for the potential applications of MLCC electrode materials has been studied by plasma arc evaporation method. The change in the broad distribution of the size of nickel and copper nanopowders is successfully controlled by manifesting proper mixture of gas ambiance for plasma generation in the size range of 20 to 200 nm in diameter. The factors affecting the mean diameter of the nanopowder was studied by changing the composition of reactive gases, indicating that nitrogen enhances the formation of larger particles compared to hydrogen gas. The morphologies and particle sizes of the metal nanoparticles were observed by SEM, and ultrathin oxide layers on the powder surface generated during passivation step have been confirmed using TEM. The metallic FCC structure of the nanoparticles was confirmed using powder X-ray diffraction method.

• Korean Journal of Materials Research
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• v.20 no.10
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• pp.550-554
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• 2010

This work presents a fabrication procedure to make large-area, size-tunable, periodically different shape metal arrays using nanosphere lithography (NSL) combined with ashing and annealing. A polystyrene (PS, 580 ${\mu}m$) monolayer, which was used as a mask, was obtained with a mixed solution of PS in methanol by multi-step spin coating. The mask morphology was changed by oxygen RIE (Reactive Ion Etching) ashing and temperature processing by microwave heating. The Au or Pt deposition resulted in size tunable nano patterns with different morphologies such as hole and dots. These processes allow outstanding control of the size and morphology of the particles. Various sizes of hole patterns were obtained by reducing the size of the PS sphere through the ashing process, and by increasing the size of the PS sphere through annealing treatment, which resulted in tcontrolling the size of the metallic nanoparticles from 30 nm to 230 nm.

• Macromolecular Research
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• v.16 no.7
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• pp.626-630
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• 2008

Poly(vinyl pyrrolidone) was used successfully to control the size and distribution of silver nanoparticles generated on inorganic silica nanofibers. The inorganic nanofibers were electro spun using sol-gel chemistry of silicates, and the diameter of the prepared nanofibers was unaffected by adding up to 7% of poly(vinyl pyrrolidone). The silver ions, in the form of silver nitrate, were introduced into the silica nanofibers and reduced to metallic silver by ultraviolet irradiation with a subsequent thermal treatment. The size of the generated silver particles was decreased dramatically by adding poly(vinyl pyrrolidone). The size of the silver nanoparticles was 73 nm when no poly(vinyl pyrrolidone) was added but 23 nm with the addition of only 1% of poly(vinyl pyrrolidone). The extent of reduction could be checked by determining the concentration of silver ions leached into water from the silica nanofibers. After thermal treatment of the silica nanofibers, more than 99% of the silver remained in the nanofibers, indicating almost complete reduction of the silver ions to silver metal.

• Journal of the Korean Ceramic Society
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• v.28 no.5
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• pp.422-428
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• 1991

The reaction sintering of Al2O3-ZrO2-Nb composite has been investigated using Al2O3, and ZrAl2 powders. Two kinds of specimens, 78.3Al2O3-14.0Nb2O5-7.7ZrAl2 in wt.% (AZN-5) and 72.3Al2O3-13.8Nb2O5-7.5ZrAl2-6.4ZrO2(AZN-10), were prepared. Powder compacts were sintered at various temperatures between 1$600^{\circ}C$ and 1$700^{\circ}C$ for 30 min in Ar. DTA and X-ray analysis have showen that a reaction between Nb2O5 and ZrAl2 started at 149$0^{\circ}C$ to form Al2O3, ZrO2, and Nb. The sintered density increased with the sintering temperature. AZN-10 specimen showed higher density than AZN-5 specimen for almost all the experimental conditions. Al2O3-ZrO2-Nb composite hot pressed after reaction sintering showed higher toughness and lower hardness than hot pressed Al2O3-ZrO2. The crack propagated through many metallic Nb particles which showed plastic deformation, and this is the cause of the increase in toughness of Al2O3-ZrO2-Nb composite over Al2O3-ZrO2.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.518-522
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• 2013

This study investigatesthe coloration mechanism by identifying the factor that affects thered coloration of copper red glazesin traditional Korean ceramics. The characteristics of the reduction-fired copper red glaze's sections are analyzed using an optical microscope, Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX). The sections observed using an optical microscope are divided into domains of surface, red-bubble, and red band. According to the Raman micro spectroscopy analysis results, the major characteristic peak is identified as silicate in all three domains, and the intensity of $Cu_2O$ increases toward the red band. In addition, it is confirmed that the most abundant CuO exists in the glaze bubbles. Moreover, CuO and $Cu_2O$ exist as fine particles in a dispersed state in the surface domain. Thus, Cu combined with oxygen is distributed evenly throughout the copper red glaze, and $Cu_2O$ is more concentrated toward the interface between body and glaze. It is also confirmed that CuO is concentrated around the bubbles. Therefore, it is concluded that the red coloration of the copper red glaze is revealed not only through metallic Cu but also through $Cu_2O$ and CuO.

• Journal of the Korean Ceramic Society
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• v.55 no.1
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• pp.50-54
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• 2018

This study investigated the long-term durability of catalyst(Pd or Fe)-infiltrated solid oxide cells for $CO_2$/steam co-electrolysis. Fuel-electrode supported solid oxide cells with dimensions of $5{\times}5cm^2$ were fabricated, and palladium or iron was subsequently introduced via wet infiltration (as a form of PdO or FeO solution). The metallic catalysts were employed in the fuel-electrode to promote $CO_2$ reduction via reverse water gas shift reactions. The metal-precursor particles were well-dispersed on the fuel-electrode substrate, which formed a bimetallic alloy with Ni embedded on the substrate during high-temperature reduction processes. These planar cells were tested using a mixture of $H_2O$ and $CO_2$ to measure the electrochemical and gas-production stabilities during 350 h of co-electrolysis operations. The results confirmed that compared to the Fe-infiltrated cell, the Pd-infiltrated cell had higher stabilities for both electrochemical reactions and gas-production given its resistance to carbon deposition.

• Nuclear Engineering and Technology
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• v.36 no.6
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• pp.549-558
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• 2004

TTo comply with increasingly strict regulations for protection against radiation exposure, many nuclear power plants have been working ceaselessly to reduce and control both the radiation sources within power plants and the radiation exposure experienced by operational and maintenance personnel. Many research studies have shown that deposits of irradiated corrosion products on the surfaces of coolant systems are the main cause of occupational radiation exposure in nuclear power plant. These corrosion product deposits on the fuel-clad surface are also known to be main factors in the onset of axial offset anomaly (AOA). Hence, there is a great deal of ongoing research on water chermistry and corrosion processes. In this study, a magnetic filter with permanent magnets was devised to remove the corrosion products in the coolant stream by taking advantage of the magnetic properties of the corrosion products demonstrated a removal efficiency of over 90% for particles above 5${\mu}m$. This finding led to the construction of an electromagnetic device that causes the metallic particulates to flocculate into larger aggregates of about 5${\mu}m$ in diameter by using a novel application of electromagnetic flocculation on radioactive corrosion products.

• Journal of Powder Materials
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• v.17 no.1
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• pp.52-58
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• 2010

Bulk nanostructured metallic materials are generally synthesized by bottom-up processing which starts from powders for assembling bulk materials. In this study, the bottom-up powder metallurgy and High Pressure Torsion (HPT) approaches were combined to achieve both full density and grain refinement at the same time. After the HPT process at 473K, the disk samples reached a steady state condition when the microstructure and properties no longer evolve, and equilibrium boundaries with high angle grain boundaries (HAGBs) were dominant. The well dispersed alumina particles played important role of obstacles to dislocation glide and to grain growth, and thus, reduced the grain size at elevated temperature. The small grain size with HAGBs resulted in high strength and good ductility.

• Applied Chemistry for Engineering
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• v.35 no.2
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• pp.96-99
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• 2024

A sintering paste for bonding copper plates was synthesized using Cu formate nanofibers on Cu microparticles, mixed with formic acid. Copper oxide nanofibers of 10 ㎛ grown at 400 ℃ on Cu microparticles on the surface were transformed into copper formate nanofibers through the mixing of formic acid. Compared to Cu bulk particles or nanoparticles, Cu formate on Cu microparticles decomposed into metallic Cu at a lower temperature of 210 ℃, facilitating the sintering of copper paste. The growth of nanofiber on Cu microparticles allowed for an increase in the reaction rate of formation to copper formate, aggregating surface area, and decomposition rate of copper formate, resulting in fast sintering.