• Microbiology and Biotechnology Letters
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• v.39 no.1
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• pp.77-85
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• 2011

The antibacterial activities of silver nanoparticles (Ag-NPs) were studied with respect to Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli by observing the bacterial cells treated or not with Ag-NPs by FE-SEM as well as measuring the growth curves, formation of bactericidal ROS, protein leakage, and lactate dehydrogenase activity involved in the respiratory chain. Bacterial cells were treated with Ag-NPs powder, and the growth rates were investigated under varying concentrations of Ag-NPs, incubation times, incubation temperatures, and pHs. As a result, S. aureus and E. coli were shown to be substantially inhibited by Ag-NPs, and the antibacterial activity of Ag-NPs did not fluctuate with temperature or pH. These results suggest that Ag-NPs could be used as an effective antibacterial material.

• Korean Journal of Materials Research
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• v.24 no.9
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• pp.502-507
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• 2014

Recently, improvement in the conversion efficiency of silicon-based solar cells has been achieved by decreasing emitter doping concentration, because the lightly doped emitter can effectively prevent the recombination of electrons and holes generated by solar light irradiation. This type of emitter is very thin due to the low doping concentration, thus conductive materials (i.e., silver) used for front electrodes can easily penetrate the emitter during a firing process because of their large diffusivity in silicon. This results in junction leakage currents which might reduce cell efficiencies. In this study, $Al_2O_3$-coated Ag powders were synthesized by an ultrasonic spray pyrolysis method and applied to the conductive materials of the front electrode to control the junction leakage current. The $Al_2O_3$ shell obstructs the Ag diffusion into the emitter during the firing process. The powder is spherical with a core-shell structure and the thickness of the $Al_2O_3$ shell is tens of nanometers. Solar cells were fabricated using pure Ag powders or the $Al_2O_3$-coated Ag powder as front electrode materials, and the conversion efficiency and junction leakage current were compared to investigate the role of the $Al_2O_3$ shell during the firing processes.

• Conservation Science in Museum
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• v.5
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• pp.23-30
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• 2004

Buddhist image engraved on the bronze mirror in the Goryo period were conserved in 1986 and 1996, respectively. As the time passed, re-conservation was required that powdered copper corrosion product on the mirror image occurred. Accordingly, additional conservation including stabilization and consolidation were carried out to prevent further corrosion. The powder filled in the line of the buddhist image and the chasing techniques were examined using microscope and portable X-ray fluorescence analyzer. The result showed that composition of powder were gold, silver and calcium(calcite or gypsum). The main chasing techniques used to engrave pattern seemed to be dotted-line, hairline and the kicking-line engraving.

• Journal of the Microelectronics and Packaging Society
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• v.19 no.4
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• pp.79-83
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• 2012

LTCC (Low temperature co-fired ceramic) package have been paid much attention due its good reliability, miniaturization, and application of silver paste with complex wiring and printing. Therefore, LTCC package has been expected to replace vulnerable plastic package in the field of high power LED device. Currently, LTCC ceramic package is mainly made up of aluminum oxide powder. In this study, zinc oxide powder is added or replaced for the fabrication of LTCC ceramic body. By adding small amount of ZnO, thermal conductivity of the LTCC ceramic body could be remarkably increased by 25% leading to the extension of LED life time. The LTCC package structure with composition including ZnO has an increased thermal flux by 56% as a result of ANSYS simulation. Actually, the fabricated LED package with the addition of ZnO exhibits a decreased thermal resistivity by 14.9%.

• Journal of Korea Foundry Society
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• v.22 no.5
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• pp.265-270
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• 2002

A novel jewelry master pattern manufacturing process which reduce manufacturing steps by employing a Duraform rapid prototyping mold and a low melting alloy has been suggested. The novel process follows the steps of 'jewelry 3D CAD design ${\rightarrow}$ Durafrom RP mold ${\rightarrow}$ low melting alloy master pattern' while the previous process follows more complicated steps of 'jewelry idea sketch ${\rightarrow}$ detailed drawing ${\rightarrow}$ wax carving ${\rightarrow}$ flask ${\rightarrow}$ silver master pattern.' An upper and a lower part of molds have been manufactured of Duraform powder, of which melting point is $190^{\circ}C$. A maser pattern was manufactured by pouring a low melting alloy of Pb-Sn-Bi-Cd, so called Woods Metal, of which melting point is $70^{\circ}C$, into the mold. The master pattern is a shape of a disk of 20mm diameter that contains various design factors. The variations of dimensions, surface roughness, surface pore ratio were measured by an optical microscope, a surface roughness profilometer, and a Rockwell hardness tester. The pattern made of were maeasured by an optical microscope, a surface roughness profilometer, and a Rockwell hardness tester. The pattern made of low melting alloy has sufficient surface hardness, and surface pore ratio to be used as the jewelry master pattern.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.10
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• pp.966-970
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• 2006

We reported on characteristics of the piezoelectric ceramic-polymer composite for the application of the thick-film speaker. The PVDF-PZT composites were fabricated to incorporate the advantages of both ceramic and polymer with various mixing ratios by 3-roll mill mixer. The composite solutions were coated by the conventional screen-printing method on ITO electrode coated PET (Polyethylene terephthalate) polymer film. After depositing the top-electrode of silver-paste, 4 kV/mm of DC field was applied at $120^{\circ}C$ for 30 min to poling the composite films. The value of $d_{33}$ (piezoelectric charge constant) was increased when the PZT weight percent was increased. The maximum value of the $d_{33}$ was 24 pC/N at 70 wt% PZT. But the $g{33}$ (piezoelectric voltage constant) showed the maximum value of $32mV{\cdot}m/N$ at 65 wt% of PZT powder. The SPL (sound pressure level) of the speaker fabricated with the 65:35 composite film was about 68 dB at 1 kHz.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1331-1334
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• 2004

The research on electromagnetic shielding has been advanced for military applications as well as for commercial products. Utilizing the reflective properties and absorptive properties of shielding material, the replied signal measured at the rear surface or at the signal source can be minimized. The shielding effect was obtained from materials having special absorptive properties or from structural characteristics such as stacking sequence. Recently researchers studied the electromagnetic properties of nano size particles. In this research {glass fiber}/{epoxy}/{nano particle} composites(GFR-Nano composites), was fabricated using various nano particles, and their properties in electromagnetic shielding were compared. For the visual observation of the nano composite materials, SEM(Scanning Electron Microscope) and TEM(Transmission Electron Microscope) were used. For the measurement of electromagnetic shielding, HP8719ES S-parameter Vector Network Analyser System was used on the frequency range of 8 GHz～12GHz. Among the nano particles, carbon black and Multi-Walled Carbon Nano-Tube (MWCNT) revealed outstanding electromagnetic shielding. Although silver nano particles (flake and powder) were expected to have effective electromagnetic shielding due to their excellent electric conductivities, test showed little shielding effect.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.735-738
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• 2003

Downsizing electronics requires precision position control with an accuracy of sub-micron order, which demands development of ultra-fine displacive devices. Piezoelectric transducer is one of devices transferring electric field energy into mechanical energy and being capable for fine displacement control. The transducer has been widely used as fine Position control device Multilayer piezoelectric actuator, one of typical piezo-transducer, is fabricated by stacking alternatively ceramic and electrode layers several hundred times followed by cofiring process. Electrode material should be tolerable in the firing process maintaining at ceramic-sintering temperatures up to $1100{\sim}1300^{\circ}C$. Ag-Pd can be used as stable electrode material in heat treatment above $960^{\circ}C$. Besides, adding small quantity ceramic powder allow the actuator to be fabricated in a good shape by diminishing shrinkage difference between ceramic and electrode layers, resulting in avoidance of crack and delamination at and/or nearby interface between ceramic an electrode layers. This study presents synthesis of nano-oxide-added Ag/Pd powders and its feasibility to candidate material tolerable at high temperature. The powders were formed in a co-precipitation process of Ag and Pd in nano-oxide-dispersed solution where Ag and Pd precursors are melted in $HNO_3$ acid.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.597-600
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• 2003

Bi-2223/Ag HTS wires have been fabricated by the PIT(powder in tube)process. Intermediate annealing was carried out to increase the homogenization and uniformity of the superconducting filaments embedded in the silver matrix during the deformation process that is important to sustain the engineering critical current density in long superconducting wire. Intermediate annealing act to release the deformation hardening of the superconducting wires during drawing process. Rolling parameters were investigated to roll the superconducting tapes with uniform thickness, width and winding tensions. Critical current of 60 m long superconducting tapes was measured 54.3 A continuously after final sintering heat treatment. The phase analysis of Bi-2223/Ag superconducting tapes are examined by the XRD.

• Tribology and Lubricants
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• v.11 no.5
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• pp.40-46
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• 1995

This study concerns the design and development of the non-vibrating capacitance probe which could be used as a non-contact sensor for tribological wear. This device detects surface charge through temporal variation in the work function of a material. Experiments are performed to demonstrate the operation of the probe on a roating aluminum shaft. The reference electrode of the probe, made of lead, is placed adjacent (< 1.25-mm distance) to the shaft. Both surfaces which are electrically connected, form a capacitor. An artificial spatial variation in the work function is imposed on the shaft surface by coating a segment along the shaft circumference with a colloidal silver paint. As the shaft rotates, the reference electode senses changing contact potential difference with the shaft surface, owing to compositional variation. Temporal variation in the contact potential difference induces a current through the electrical connection. This current is amplified and converted to a voltage signal by an electoronic circuit with an operational amplifier. The magnitude of the signal decreases asymptotically with the electrode-shaft distance and increases linearly with the rotational frequency. These results are consistent with the theoretical model. Potential applications of the probe on wear monitoring are proposed.