• Nano
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• v.13 no.11
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• pp.1850127.1-1850127.13
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• 2018

Bi metal deposited on $Bi_2MoO_6$ composite photocatalysts have been successfully synthesized via a simple reduction method at room temperature with using $NaBH_4$ as the reducing agent. The photocatalytic activity of the composite was evaluated by degradation of rhodamine B (RhB) and bisphenol A (BPA) solution under visible light. The rate constant of $Bi/Bi_2MoO_6$ composite to RhB is 10.8 times that of $Bi_2MoO_6$, and the degradation rate constant of BPA is 6.9 times of that of $Bi_2MoO_6$. Nitrogen absorption-desorption isotherm proved that the increase of specific surface area is one of the reasons for the improvement of photocatalytic degradation activity of $Bi/Bi_2MoO_6$ composites. The higher charge transfer efficiency of $Bi/Bi_2MoO_6$ is found through the characterization of the photocurrent and impedance, which are attributed to the surface plasmon resonance (SPR) effect produced by the introduction of the metal Bi monomer in the composite. Free radical capture experiments proved that cavitation is the main active species. Based on the above conclusions, a possible mechanism of photocatalytic degradation is proposed.

• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.5-10
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• 2019

In this study, electrochemical characteristics of artificial graphite coated with petroleum pitch using solvent method as anode material of lithium ion battery were investigated. As the solvent, n-hexane, toluene, tetrahydrofuran and quinoline were used. The surface of the prepared anode material was analyzed by SEM and TEM. Also the electrochemical performances of the prepared anode materials were performed by constant current first charge/discharge, cycle, cyclic voltammetry and impedance tests in the electrolyte of $LiPF_6$ dissolved inorganic solvents (EC:DEC=1:1 vol%). The coating thickness of the prepared graphite was about 100-500 nm and the graphite coated with THF solvent had a smoother surface than that using other solvents. It was found that pitch-coated graphite (THF) show the low initial irreversible capacity (51 mAh/g), the high discharge capacity (360 mAh/g) and coulombic efficiency (99%).

• Corrosion Science and Technology
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• v.11 no.3
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• pp.96-102
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• 2012

Outer diameter stress corrosion cracking (ODSCC) has occurred for Alloy 600 (Ni 75 wt%, Cr 15 wt%, Fe 10 wt%) as a heat exchanger tube of the steam generator (SG) in nuclear power plants (NPP) during long term operation. Among many causes for SCC, lead (Pb) is known to be one of the most deleterious species in the secondary system. In the present work, the oxide formed on Alloy 600 was characterized as a function of the PbO content in 0.1 M NaOH at $315^{\circ}C$ by using an electrochemical impedance spectroscopy (EIS), a transmission electron microscopy (TEM), equipped with an energy dispersive x-ray spectroscopy (EDS). The oxide property was analyzed in view of SCC susceptibility.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.2
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• pp.416-422
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• 2017

The robot control with safety consideration is required since robots and human work together in the same space more frequently in these days. For safety, robots must have compliance to human force and robust tracking performance with high impednace for the nonhuman disturbances. The novel idea is proposed to achieve the compliance and high impedance with one controller structure. For the compliance, the ISMC(Integral Sliding Mode Control) and HDOB(Human Disturbance Observer) The human force is identified by using the human band pass filter and its output is sent to the sliding surface. The sliding mode dynamic is affected by human disturbance and the compliance for human is achieved. The disturbances besides human frequencies are decoupled by the ISMC and the robust tracking is achieved. The additional LDOB(Low Frequency Disturbance Observer) decreases the maxim nonlinear gain and leads low chattering. The introduction of human disturbance into the sliding mode dynamic is the main novel idea of this paper.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.45-45
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• 2007

Capacitors among the embedded passive components are most widely studied because they are the major components in terms of size and number and hard to embed compared with resistors and inductors due to the more complicated structure. To fabricate a capacitor-embedded PCB for in-line process, it is essential to adopt a low temperature process (<$200^{\circ}C$). However, high dielectric materials such as ferroelectrics show a low permittivity and a high dielectric loss when they are processed at low temperatures. To solve these contradicting problems, we studied BMN materials as a candidate for dielectric capacitors. processed at PCB-compatible temperatures. The morphologies of BMN thin films were investigated by AFM and SEM equipment. The electric properties (C-F, I-V) of Pt/BMN/Cu/polymer were evaluated using an impedance analysis (HP 4194A) and semiconductor parameter analyzer (HP4156A). $Bi_2Mg_{2/3}Nb_{4/3}O_7$(BMN) thin films deposited on copper clad laminate substrates by sputtering system as a function of Ar/$O_2$ flow rate at room temperature showed smooth surface morphologies having root mean square roughness of approximately 5.0 nm. 200-nm-thick films deposited at RT exhibit a dielectric constant of 40, a capacitance density of approximately $150\;nF/cm^2$, and breakdown voltage above 6 V. The crystallinity of the BMN thin films was studied by TEM and XRD. BMN thin film capacitors are expected to be promising candidates as embedded capacitors for printed circuit board (PCB).

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.348-351
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• 2006

Bipolar plate, which forms about 50% of the stack cost, is an important core part with polymer electrolyte membrane in PEMFC. Bipolar plates have been commonly fabricated from graphite meterial having high electrical conductivity and corrosion resistance. Lately, many researchers have concentrated their efforts on the development of metallic bipolar plate and stainless steel has been considered as a potential material for metallic bipolar plate because of its high strength, chemical stability, low gas permeability and applicability to mass production. However, it has been reported that its inadequate corrosion behavior under PEMFC environment lead to a deterioration of membrane by dissolved metal ions and an increase in contact resistance by the growth of passive film therefore, its corrosion resistance as well as contact resistance must be improved for bipolar plate application. In this work, several types of coating were applied to 316L and their electrical conductivity and corrosion resistance were evaluated In the simulated PEMFC environment. Application of coating gave rise to low interfacial contact resistances below $19m{\Omega}cm^2$ under the compress force of $150N/cm^2$. It also made the corrosion potential to shift in the posit ive direct ion by 0.3V or above and decreased the corrosion current from ca. $9{\mu}A/cm^2$ to ca. $0.5{\mu}A/cm^2$ in the mixed solution of $0.1N\;N_2SO_4$ and 2ppm HF A coat ing layer under potentiostatic control of 0.6V and $0.75V_{SCE}$ for 500 hours or longer showed some instabilities, however, no significant change in coat Ing layer were observed from Impedance data. In addition, the corrosion current maintained less than $1{\mu}A/cm^2$ for most of time for potentiostatic tests. It indicates that high electrical conductivity and corrosion resistance can be obtained by application of coatings in the present work.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.8
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• pp.930-936
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• 2007

In this paper, the high gain and broadband antenna operating for SDMB(Satellite Digital Multimedia Broadcasting) system is realized, The proposed antenna consists of the SAP(Shorted Annular Patch) structure, which inhibits surface-wave and the parasitic SAP element with spacing of $0.25 {\lambda}_0$ in order to improve gain, bandwidth and directivity. The RHCP(Right Hand Circular Polarization) is generated by two slits, which are made along the periphery of the circular patch at the diametrically opposite points, The simulated maximum gain of the proposed antenna is 12.6 dBi, which is better 5.22 dBi than maximum gain of the conventional microstrip patch antenna. The measured maximum gain is 10.5dBi at operating frequency 2.63GHz. Also, the measured impedance bandwidth$(VSWR{\leq}2)$ of the proposed antenna is $360MHz(2.488{\sim}2.848 GHz)$, which is better 300 MHz than the bandwidth of the conventional microstrip patch antenna. The measured HPBW(Half Power Beam Width) of the proposed antenna is $45.8^{\circ}$, and the measured FBR(Front to Back Ratio) is 15.49 dBi, The 3dB axial ratio bandwidth is 220 MHz$(2.54{\sim}2.76 GHz)$.

• Korean Chemical Engineering Research
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• v.60 no.1
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• pp.1-6
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• 2022

As the demand for wearable devices increases, many studies have been studied on the development of flexible electrode materials recently. In particular, the development of high-performance flexible electrode materials is very important for wearable sensors for healthcare because it is necessary to continuously monitor and accurately detect body information such as body temperature, heart rate, blood glucose, and oxygen concentration in real time. In this study, we fabricated the nonenzymatic glucose sensor based on polyaniline/carbon nanotube fiber (PANI/CNT fiber) electrode. PANI layer was synthesized on the flexible CNT fiber electrode through electrochemical polymerization process in order to improve the performance of a flexible CNT fiber based electrode material. Surface morphology of the PANI/CNT fiber electrode was observed by scanning electron microscopy. And its electrochemical characteristics were investigated by chronoamperometry, cyclic voltammetry, electrochemical impedance spectroscopy. Compared to bare CNT fiber electrode, this PANI/CNT fiber electrode exhibited small electron transfer resistance, low peak separation potential and large surface area, resulting in enhanced sensing properties for glucose such as wide linear range (0.024~0.39 and 1.56~50 mM), high sensitivity (52.91 and 2.24 ㎂/mM·cm²), low detection limit (2 μM) and good selectivity. Therefore, it is expected that it will be possible to develop high performance CNT fiber based flexible electrode materials using various nanomaterials.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.457-465
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• 2013

We integrated and correlated datasets from surface and subsurface geophysics, drilling cores, and engineering geology to identify geological interfaces and characterize the joints and fracture zones within the rock mass. The regional geometry of a geologically weak zone was investigated via a fence projection of electrical resistivity data and a borehole image-processing system. Subsurface discontinuities and intensive fracture zones within the rock mass are delineated by cross-hole seismic tomography and analyses of dip directions in rose diagrams. The dynamic elastic modulus is studied in terms of the P-wave velocity and Poisson's ratio. Subsurface discontinuities, which are conventionally identified using the N value and from core samples, can now be identified from anomalous reflection coefficients (i.e., acoustic impedance contrast) calculated using a pair of well logs, comprising seismic velocity from suspension-PS logging and density from logging. Intensive fracture zones identified in the synthetic seismogram are matched to core loss zones in the drilling core data and to a high concentration of joints in the borehole imaging system. The upper boundaries of fracture zones are correlated to strongly negative amplitude in the synthetic trace, which is constructed by convolution of the optimal Ricker wavelet with a reflection coefficient. The standard deviations of dynamic elastic moduli are higher for fracture zones than for acompact rock mass, due to the wide range of velocities resulting from the large numbers of joints and fractures within the zone.

• Journal of the Korean Electrochemical Society
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• v.10 no.3
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• pp.207-212
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• 2007

[ $PSCF3737(Pr_{0.3}Sr_{0.7}Co_{0.3}Fe_{0.7}O_3)$ ] is a good candidate cathode material for IT-SOFC(intermediate temperature solid oxide fuel cell) because of high MIEC(mixed ionic electronic conductor) conductivity. In this study, the characteristics of PSCF3737 was investigated and optimizations of sintering temperature and thickness for $PSCF3737(Pr_{0.3}Sr_{0.7}Co_{0.3}Fe_{0.7}O_3)$ was carried out. Impedance responses were divided into two parts by frequency region. Middle frequency part (${\sim}10^2\;Hz$) was concerned with oxygen reduction reaction on surface and low frequency part (${\sim}10^{-1}\;Hz$) was related with oxygen diffusion. The reasonable sintering temperature and thickness of cathode were $1200^{\circ}C$ and about $27\;{\mu}m$ with regard to EIS(electrochemical impedance spectroscopy). ASR(areas specific resistance) of optimized cathode is $0.115\;{\Omega}\;cm^2$ at $700^{\circ}C$.