• Corrosion Science and Technology
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• v.14 no.6
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• pp.296-300
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• 2015

ALDC8 (Al-Si-Cu) alloy has been often corroded with pattern of intergranular corrosion in corrosive environments. Thus, in order to improve its corrosion resistance, the effect of annealing heat treatment to corrosion resistance and hardness was investigated with parameters of heating temperatures such as $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$, $400^{\circ}C$ and $500^{\circ}C$ for 1hr. The hardness was varied with annealing temperature and slightly decreased with annealing heat treatment. However, the relation between annealing temperature and hardness agreed not well each other. Corrosion potential was shifted to noble direction and corrosion current density was also decreased with increasing annealing temperature. Moreover, both AC impedance at 10 mHz and polarization resistance on the cyclic voltammogram curve were also increased with increasing annealing temperature. Furthermore, intergranular corrosion was somewhat observed in non heat treatment as well as annealing temperatures at $100^{\circ}C$, $200^{\circ}C$ and $300^{\circ}C$, while, intergranular corrosion was not nearly observed at annealing temperature of $400^{\circ}C$, $500^{\circ}C$. Consequently, it is considered that the annealing heat treatment of ALDC8 alloy may be an available method not only to inhibit its intergranular corrosion but also to improve its corrosion resistance.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.8
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• pp.738-748
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• 2008

In this study, it has been investigated on the changing behavior of electrical properties in $ZnO-Bi_2O_3-Sb_2O_3$ (Sb/Bi=2.0, 1.0 and 0.5) ceramics. The samples were prepared by conventional ceramic process, and then characterized by I-V, C-V curve plots, impedance and modulus spectroscopy (IS & MS) measurement. The electrical properties of ZBS systems were strongly dependent on Sb/Bi. In ZBS systems, the varistor characteristics were deteriorated noticeably with increasing Sb/Bi and the donor density and interface state density were increased with increasing Sb/Bi. On the other hand, we observed that the grain boundary reacted actively with the ambient oxygen according to Sb/Bi ratio. Especially the grain boundaries of Sb/Bi=0.5 systems were divided into two types, i.e. sensitive to oxygen and thus electrically active one and electrically inactive intergranular one with temperature. Besides, the increased pyrochlore and $\beta$-spinel phase with Sb/Bi ratio caused the distributional inhomogeneity in the grain boundary barrier height and the temperature instability. To the contrary, the grain boundary layer was relatively homogeneous and more stable to temperature change and kept the system highly nonlinear at high Bi-rich phase contents.

• Journal of Hydrogen and New Energy
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• v.25 no.1
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• pp.28-38
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• 2014

The organic-inorganic composite membrane in polymer exchange membrane fuel cells (PEMFCs) have several fascinating technological advantages such as a proton conductivity, thermal stability and mechanical properties. As the inorganic filler, silicon carbide (SiC) fiber have been used in various fields due to its unique properties such as thermal stability, conductivity, and tensile strength. In this study, composite membrane was successfully fabricated by modified-silicon carbide fiber. Modified process, as a novel process in SiC, takes reaction by phosphoric acid after oxidation process (generated homogeniusly $SiO_2$ layer on SiC fiber). The mechanical property which was conducted by tensile test of the 5wt% modified-$SiO_2@SiCf$ composite membrane was better than that of Aquivion casting membrane as well as ion cxchange capacity(IEC) and proton conductivity. In addition, the single cell performance was observed that the 5wt% modified-$SiO_2@SiCf$ composite membrane was approximately $0.2A/cm^2$ higher than that of a Aquivion casting electrolyte membrane and electrochemical impedance was improved with the charge transfer resistance and membrane resistance.

• Corrosion Science and Technology
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• v.6 no.5
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• pp.227-232
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• 2007

The corrosion behavior of carbon steel (N80) in carbon dioxide saturated 1%NaCl solution with and without acetic acid or acetate was investigated by weight-loss test, electrochemical methods (polarization curve, Electrochemical impedance spectroscopy). The major objective is to make clear that the effect of acetic acid and acetate on the corrosion of carbon steel in $Co_2$ environments. The results indicate that either acetic acid or acetate accelerates cathodic reducing reaction, facilitates dissolution of corrosion products on carbon steel, and so promotes the corrosion rate of carbon steel in carbon dioxide saturated NaCl solution. All Nyquist Plots are consisting of a capacitive loop in high frequency region, an inductive loop in medial frequency region and a capacitive arc in low frequency region. The high frequency capacitive loop, medial frequency inductive loop and low frequency capacitive arc are corresponding to the electron transfer reaction, the formation/adsorption of intermediates and dissolution of corrosion products respectively. All arc of the measured impedance reduced with the increase of the concentration of Ac-, especially HAc. However, the same phenomenon is not notable after reducing pH value by adding HCl. HAc is a stronger proton donor and can be reduced directly by electrochemical reaction firstly. Ac- can't participate in electrochemistry reaction directly, but $Ac^-$ an hydrate easily to create HAc in carbon dioxide saturated environments. HAc is as catalyst in $Co_2$ corrosion. As a result, the corrosion rate was accelerated in the presence of acetate ion even pH value of solution increased.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.12
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• pp.87-94
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• 2008

This parer presents the soil ionization phenomena and parameters associated to characterize the transient performances of grounding system under lightning impulse Currents. Ionization properties in occurring some soil media were experimentally investigated. The cylindrical test cell was employed in order to facilitate the analysis of soil breakdown field intensity and ionized radius. The soil breakdown field intensity, dependence of impedance on the amplitude of impulse current, V-I curves and transient impedances were discussed based on the voltage and current oscillograms. It was found that the ionization process and dynamic behaviors were strongly dependent on the types of soil and two current peaks were not observed in highly water-saturated soils. The results presented in this paper will provide useful information on the improvement of transient performance of a grounding system subjected to lightning impulse Current considering the soil ionization.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.2
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• pp.273-280
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• 1999

This paper presents the design and implementation of circuit analyzer system for the convenient troubleshooting and diagnosis of the electronics appliance using the curve tracer technology of analog signature analysis. The circuit analyzer provides advanced troubleshooting capabilities to simplify testing newer technology components such as CMOS and MOS circuits, its built-in pulse generator lets thoroughly troubleshoot gate-fired devices such as SCRs, TRIACs and optocouplers. The circuit analyzer while the power to the circuitry testing is turned of, so that avoid an accidental short that could cause further damage, its allow to analyze the impedance state of a solid-state component, which makes it perfect for finding leakage or substrate damage that has brought a system or PCB down prematurely. Because it can compare suspect components to known-good equivalents, it's verified the ideal application for troubleshooting when documentation is missing or incomplete.

• Journal of Korean Academy of Fundamentals of Nursing
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• v.16 no.1
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• pp.14-20
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• 2009

Purpose: The purpose of this study was to identify how accurately body mass index (BMI) and waist circumference (WC) detect obesity in young adult women. Method: Measurements of height, weight, WC, and percent body fat (% BF) were obtained and bioelectrical impedance analysis was used to estimate body fat in 329 female college students. The sensitivity and specificity to screen obesity by BMI and WC were determined using SPSS. Received operating characteristic (ROC) curve analysis was used to assess the appropriate BMI and WC predicting % BF. Results: % BF-defined obesity $(\geq30%)$ had higher prevalence than BMI-defined obesity $(\geq25kg/m^2)$ and WC-defined obesity $(\geq80cm)$. BMI $\geq25kg/m^2$ and WC $\geq80cm$ had high specificity (both, 100%), but low sensitivity (respectively, 13.5% and 22.9%) in detecting % BF-defined obesity. The BMI and WC cutoff values corresponding to % BF-defined obesity were 21.2kg/$m^2$ and 73cm, which were lower than recommended reference values for Korean women. These values decreased specificity but increased sensitivity to detect obesity. The areas under the ROC curve were good (0.84, 0.86) for BMI and WC. Conclusion: BMI and WC have good specificity but miss more than $77\sim86%$ of people with excess fat. Therefore, BMI and WC cutoff values need to be revised and body fat should be considered when screening for obesity in young adult women.

• Applied Chemistry for Engineering
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• v.32 no.4
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• pp.442-448
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• 2021

Flow field is an important parameter for polymer electrolyte membrane fuel cell (PEMFC) performance to have an effect on the reactant supply, heat and water diffusion, and contact resistance. In this study, PEMFC performance was investigated using Cu foam flow field at the cathode of 25 cm² unit cell. Polarization curve and electrochemical impedance spectroscopy were performed at different pressure and relative humidity conditions. The Cu foam showed lower cell performance than that of serpentine type due to its high ohmic resistance, but lower activation and concentration loss due to the even reactant distribution of porous structure. Cu foam has the advantage of effective water transport because of its hydrophobicity. However, it showed low membrane hydration at low humidity condition. The metal foam flow field could improve fuel cell performance with a uniform pressure distribution and effective water management, so future research on the properties of metal foam should be conducted to reduce electrical resistance of bipolar plate.

• Applied Chemistry for Engineering
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• v.32 no.1
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• pp.68-74
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• 2021

Gas diffusion layer (GDL) compression is important parameter of polymer electrolyte membrane fuel cell (PEMFC) performance to have an effect on contact resistance, reactants transfer to electrode, water content in membrane and electrode assembly (MEA). In this study, the effect of GDL compression on fuel cell performance was investigated for commercial products, JNT20-A3. Polarization curve and electrochemical impedance spectroscopy was performed at different relative humidity and compression ratio using electrode area of 25 ㎠ unit cell. The contact resistance was reduced to 8, 30 mΩ·㎠ and membrane hydration was increased as GDL compression increase from 18.6% to 38.1% at relative humidity of 100 and 25%, respectively. It was identified through ohmic resistance change at relative humidity conditions that as GDL compression increased, water back-diffusion from cathode and electrolyte membrane hydration was increased because GDL porosity was decreased.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2003.10a
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• pp.119-119
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• 2003

Plasma polymerized organic thin films were deposited on Si(100) glass and Copper substrates at 25 ∼ 100 $^{\circ}C$ using cyclohexane and ethylcyclohexane precursors by PECVD method. In order to compare physical and electrochemical properties of the as-grown thin films, the effects of the RF plasma power in the range of 20∼50 W and deposition temperature on both corrosion protection efficiency and physical properties were studied. We found that the corrosion protection efficiency (P$\_$k/), which is one of the important factors for corrosion protection in the interlayer dielectrics of microelectronic devices application, was increased with increasing RF power. The highest P$\_$k/ value of plasma polymerized ethylcyclohexane film (92.1% at 50 W) was higher than that of the plasma polymerized cyclohexane film (85.26% at 50 W), indicating inhibition of oxygen reduction. Impedance analyzer was utilized for the determination of I-V curve for leakage current density and C-V for dielectric constants. To obtain C-V curve, we used a MIM structure of metal(Al)-insulator(plasma polymerized thin film)-metal(Pt) structure. Al as the electrode was evaporated on the ethylcyclohexane films that grew on Pt coated silicon substrates, and the dielectric constants of the as-grown films were then calculated from C-V data measured at 1㎒. From the electrical property measurements such as I-V ana C-V characteristics, the minimum dielectric constant and the best leakage current of ethylcyclohexane thin films were obtained to be about 3.11 and 5 ${\times}$ 10$\^$-12/ A/$\textrm{cm}^2$ and cyclohexane thin films were obtained to be about 2.3 and 8 ${\times}$ 10$\^$-12/ A/$\textrm{cm}^2$.