• Transactions of the Korean hydrogen and new energy society
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• v.7 no.2
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• pp.173-180
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• 1996

4-probe resistivity measurement technique was used to study kinetics of hydrogen absorption-desorption on Pd film($520{\AA}$ thick) at room temperature upto 1 bar. Kinetics data are fitted well to 1st order kinetics equation in ${\alpha}$ and ${\alpha}^{\prime}$ phases. In ${\alpha}+{\alpha}^{\prime}$ phase, absorption kinetics was very complicated, but it could be explained partially with nucleation and growth process. Ln(dR/dt) vs. time plot gives rate constant k value(R is resistance of sample, t is time). k value for absorption is $4^{-6}{\times}10^{-4}/sec$ in ${\alpha}$ phase. k is increasing upto $4^{\times}10^{-2}/sec$ as hydrogen pressure increasing in ${\alpha}^{\prime}$ phase. k is proportional to ln(Pop/Peq), where Peq is equilibrium plateau pressure and Pop is the opposing pressure. In contrast to bulk sample k value was decreasing with increasing number of A-D cycling in ${\alpha}^{\prime}$ phase absorption.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.44 no.7
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• pp.914-918
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• 1995

In this study, Pb(Zr$_{x}$ Ti$_{1-x}$ )O$_{3}$ (x=0.65, 0.52, 0.35) thin films were fabricated by Sol-Gel method. A stock solution with excess Pb 10[mol%] of Pb(Zr$_{x}$ Ti$_{1-x}$ )O$_{3}$ was made and spin-coated on the Pt/SiO$_{2}$/Si substrate at 4000[rpm] for 30[sec.]. Coated specimens were dried on the hot-plate at 400[.deg. C] for 10[min.]. Sintering temperature and time were 500~800[.deg. C] and 1~60[min.]. The coating process was repeated 6 times and the final thickness of the thin films were about 4800[A]. To investigate crystallization condition, PZT thin films were analyzed with sintering temperature, time and composition by the XRD. The microstructure of thin fulms were investigated by SEM. The ferroelectric perovskite phases precipitated under the sintering of 700[.deg. C] for 1 hours. In the PZT(52/48) composition, dielectric constant and dielectric loss were 2133, 2.2[%] at room temperature, respectively.ively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.11
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• pp.1003-1008
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• 2002

In this paper, the estimation of lifetime with the various conditions of the interface between toughened epoxy and rubber which are consisting materials of underground power delivery system has been studied. After the measurement of the short time AC interfacial breakdown strength on macro interfaces at room temperature, the breakdown time at several voltages were measured under the constant voltages lower than the short time breakdown voltage. The long time breakdown voltage was calculated by using Inverse Power Law. Two types of interfaces was studied. One was the interface between toughened epoxy and EPDM(Ethylene Prorylene Diene Terpolymer). The other was the interface between toughened epoxy and silicon rubber. Interfacial pressure and roughness of interfaces was determined through the characteristic of short time AC interfacial breakdown strength. Oil condition was no oiled, low viscosity oiled and high viscosity oiled. High viscosity oiled interface between Toughened epoxy and silicon rubber had the best lifetime exponent, 20.69. and the breakdown voltage of this interface after 30 years was evaluated 19.27㎸.

• Electrical & Electronic Materials
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• v.8 no.3
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• pp.291-297
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• 1995

The InP crystals have been grown by modified synthesis solute diffusion (SSD) method and its properties have been investigated. The crystals have been grown by lowering the crucible quartz for growth in the furnace and crystal growth rate is 1.8mm/day. The lattice constant a. of the grown crystals is 5.867.angs.. Etch pits density along growth direction of crystal changes from 3.0*10.sup 3/cm$\^$-2/ of first freeze part to 6.7*10$\^$4/cm$\^$-2/ of last freeze part and the radial direction of wafer shows nearly uniform distribution. The resistivity and the carrier concentration of the grown crystals are 1.43*10$\^$-1/.ohm.-cm, 7.7*10$\^$15/cm$\^$-3/ at room temperature, respectively. In the photolurninescence at 10K, the radiation transitions are observed by the near band edge recombination, a pair recombination due to Si donor - Zn acceptor and its phonon replica in the InP. The activation energy by Zn diffusion in undoped n-InP crystals is 1.22eV.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.12
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• pp.1283-1288
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• 2004

Metal-ferroelectric-insulator-semiconductor(WFIS) capacitors using rapid thermal annealed LiNbO$_3$/AlN/Si(100) structure were fabricated and demonstrated nonvolatile memory operations. The capacitors on highly doped Si wafer showed hysteresis behavior like a butterfly shape due to the ferroelectric nature of the LiNbO$_3$ films. The typical dielectric constant value of LiNbO$_3$ film in the MFIS device was about 27, The gate leakage current density of the MFIS capacitor was 10$^{-9}$ A/cm$^2$ order at the electric field of 500 kV/cm. The typical measured remnant polarization(2P$_{r}$) and coercive filed(Ec) values were about 1.2 $\mu$C/cm$^2$ and 120 kV/cm, respectively The ferroelectric capacitors showed no polarization degradation up to 10$^{11}$ switching cycles when subjected to symmetric bipolar voltage pulses of 1 MHz. The switching charges degraded only by 10 % of their initial values after 4 days at room temperature.e.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.900-903
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• 2003

Using $DV-X{\alpha}$ method, it is calculated that nickel reduces the energy band gap of manganese oxide in 3 additives of titanium, nickel and tin. Therefore, it is estimated that the electrical conductivity of manganese-nickel oxide has the lowest value in 3 kinds of manganese oxide. The manganese oxide and manganese-nickel oxide which were produced by anodic deposition under $30mA/cm^2$ at room temperature in manganese sulfate and manganese-nickel sulfate solution were thermal-analyzed by DTA and TGA. The weight change of manganese oxide continuously decreased below $508^{\circ}C$ and kept constant at $518{\sim}600^{\circ}C$. However, the manganeses-nickel oxide transformed at the temperature range of $510{\sim}537^{\circ}C$. It is observed that the nickel addition to manganese oxide increases transformation temperature and its range.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.48-48
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• 2010

In this paper, we have investigated temperature dependence of dielectric breakdown voltage at epoxy with added nano-filler(MgO), which is used as a filler of epoxy additives for HVDC(high voltage direct current) submarine cable insulating material with high thermal conductivity and restraining tree to improve electrical properties of epoxy resin in high temperature region. In order to find dispersion of the specimen, the cross sectional area of nano-composite material is observed by using the SEM(Scanning Electron Microscope) and it is conformed that each specimen is evenly distributed without the cohesion. As a result, it is confirmed that the strength of breakdown of all specimen at 50 [$^{\circ}C$] decreased more than that of the dielectric breakdown strength at room temperature. When temperature increases from 50 [$^{\circ}C$] to 100 [$^{\circ}C$], we have confirmed that breakdown strength of virgin specimen decreases, but specimens with added MgO show constant dielectric breakdown strength.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.1
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• pp.76-81
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• 2012

Ultrasonic metal welding is one of the welding methods which welds metal by applying high frequency vibrational energy into specific area at constant pressure, avaliable in room temperature and low temperature. Ultrasonic metal welder is consisted of power supply, transducer, booster, and horn. Precise designing is required since each parts' shape, length and mass can affect driving frequency and vibration mode. This paper focused to horn design, its length L was set to 62mm by calculating vibration equation. By performing modal analysis with various shape variable b times integer, when length of b is 30mm the output was 39,599Hz at 10th mode. Also by performing harmonic response analysis, the frequency response result was 39,533Hz, which was similar to modal analysis result. In order to observe the designed horn's performance, about 4,000 voltage data was obtained from a light sensor and was analyzed by FFT analysis using Origin Tool. The result RMS amplitude was approximately 8.5${\mu}m$ at 40,000Hz, and maximum amplitude was 12.3${\mu}m$. Therefore, it was verified that the ultrasonic metal welding horn was optimally designed.

• Journal of Power System Engineering
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• v.18 no.1
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• pp.91-98
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• 2014

In this investigation, the effect of crack orientation on spatial randomness of fatigue crack growth rate (FCGR) in friction stir welded (FSWed) 7075-T651 aluminum alloy joints has been statistically analyzed by Weibull distribution. The fatigue crack growth tests are conducted under three different constant stress intensity factor range (SIFR) control at room temperature with R = 0.1 and frequency 10Hz on compact tension (CT) specimen machined at base metal (BM) and weld metal (WM). The experimental fatigue crack growth rate data were obtained for two types of specimens having LT and TL orientations. LT specimens both base metal and weld metal showed higher fatigue crack growth rate as compared to TL specimens. In the lower SIFR region, FCGR were found to be almost 3 times higher in higher SIFR region. The shape parameter of Weibull both LT and TL orientation for FCGR was increased with increasing SIFR, the scale parameter was also increased with increasing SIFR. The smallest value of the shape parameter was shown in weld metal specimens having LT orientation at lower SIFR region.

• Journal of the Korean Vacuum Society
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• v.5 no.1
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• pp.62-66
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• 1996

$(Ba_{1-x}Sr_xTiO_3$ (BST) thin films have been grown on Pt-coated MgO by metal -organic chemical vapor deposition. X-ray diffraction results showed that BST films were grown on a Pt/MgO substrate with (100) preferred orientation perpendicular to the surface. The lineawr relationship of P-E curve obtained form hysteresis loop measurement indicated that the BST films had a Curie transitions below room temperature . Films deposited at $900^{\circ}C$ exhibited a smooth and dense microstructure, a dielectric constant of 202, and a dissipation facotr of 0.02 at 100kHz. The leakage current density of the BST films is about $2\times10^{-10} \;A/\textrm{cm}^2$$ at an applied electric field of 0.2 MV/cm. The electrical behavior on the current-voltage characteristics is well explained by the bulk-limited Pool-Frenkel emission.