• Journal of Korea Multimedia Society
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• v.20 no.2
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• pp.115-125
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• 2017

For many stroke patients undergoing rehabilitation therapy, there is a need for indicator for evaluating the body function in paretic and non-paretic regions of stroke patients quantitatively. In this paper, the function of muscles and cells in paretic and non-paretic regions of severe and mild hemiplegic stroke patients was evaluated using multi-channel bioelectrical impedance spectroscopy. The paretic and non-paretic regions of severe and mild stroke patients were quantitatively assessed by using bioelectrical impedance parameters such as prediction marker (PM), phase angle (${\theta}$), characteristic frequency ($f_c$), and bioelectrical impedance vector analysis (BIVA). The mean values of impedance vector were significantly discriminated in all comparisons (severe-paretic, severe-non-paretic, mild-paretic, and mild-non-paretic). The bioelectrical impedance parameters were proved to be a very valuable tool for quantitatively evaluating the paretic and non-paretic regions of hemiplegic stroke patients.

• Journal of the Korean Electrochemical Society
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• v.2 no.1
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• pp.38-45
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• 1999

Electrochemical lithium intercalation into a PECVD (plasma enhanced chemical vapour deposited) carbon film electrode was investigated in 1 M $LiPF_6-EC$ (ethylene carbonate) and DEC (diethyl carbonate) solution during lithium intercalation and deintercalation, by using cyclic voltammetry supplemented with ac-impedance spectroscopy. The size of the graphitic crystallite in the a- and c-axis directions obtained from the carbon film electrode was much smaller than those of the graphite one, indicating less-developed crystalline structure with hydrogen bonded to carbon, from the results of AES (Auger electron spectroscopy), powder XRD (X-ray diffraction) method, and FTIR(Fourier transform infra-red) spectroscopy. It was shown from the cyclic voltammograms and ac-impedance spectra of carbon film electrode that a threshold overpotential was needed to overcome an activation barrier to entrance of lithium into the carbon film electrode, such as the poor crystalline structure of the carbon film electrode showing disordered carbon and the presence of residual hydrogen in its structure. The experimental results were discussed in terms of the effect of host carbon structure on the lithium intercalation capability.

• Journal of the Korean Ceramic Society
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• v.45 no.1
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• pp.69-74
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• 2008

The effects of $SiO_2$ impurity on the high temperature resistivities of AIN ceramics have been investigated. When $SiO_2$ was added into 1 wt% $Y_2O_3$-doped AIN, DC resistivities have decreased and electrode polarizations disappeared. Impedance spectroscopy showed two semi-circles at $600^{\circ}C$, which were attributed to grain and grain boundary, respectively. $SiO_2$ doping had more significant effects on the grain resistivity than grain boundary resistivity, implying that doped Si acted as a donor in AIN lattice. In addition, voltage dependency of DC resistivity was observed, which might be related to dependency of size of grain boundary semi-circle on the bias voltage in impedance spectroscopy.

• Journal of the Korean Electrochemical Society
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• v.10 no.1
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• pp.7-13
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• 2007

We synthesized and investigated $La_{0.75}Sr_{0.25}FeO_3$ by Glycine Nitrate Process(GNP) method used as cathode materials for SOFC(solid oxide fuel cell). Optimized amount of glycine is 3.17 mol. ICP elemental composition analysis indicated that the stoichiometry of the synthesized powders have nearly nominal values. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The sample powders were isostatically pressed to form a pellet. The green body was sintered at $1200^{\circ}C$ and the relative density of the sintered specimens were measured by Archimedes mettled. We measured electrochemical performance of LSF by AC impedance spectroscopy. Resistance of LSF shows lower value than that of LSM throughout all temperature region. The anode-supported solid oxide fuel cell showed a performance of $342mW/cm^2(0.7V,\;488mA/cm^2)$ at $750^{\circ}C$. The electrochemical characteristics of the single cell were examined by at impedance method.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.192-193
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• 2005

Magnesium thin films were prepared on cold-rolled steel substrates by RF(Radio Frequency) magnetron sputtering technique.$^{1)}$ The crystal orientation and monitoring of the deposited films were investigated by using XRD(X-ray Diffraction) and EIS(Electrochemical Impedance Spectroscopy), respectively. The corrosion rates of Mg thin films deposited with different argon gas pressure and substrate bias voltage were monitored by AC impedance method under a cyclic wet-dry condition, which was conducted by exposure to alternate conditions of 1h immersion in 3%NaCl solution and 5h drying at 60% RH and 25$^{\circ}C$. The result of corrosion rate of Mg thin films deposited at various Ar gas pressures and substrate bias voltage under wet-dry cyclic exposure in chloride-containing solutions was showed the following conclusions. At the region I during the onset of the wet cycle, corrosion rate showed relatively low value. The increase in the Corrosion rate of region II is due to the increase in the chloride concentration. Corrosion rate of region III during the onset of the cycle zero and salt crystals remain on the metal surface.$^{2)}$

• Corrosion Science and Technology
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• v.6 no.1
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• pp.18-23
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• 2007

DLC coatings have been deposited onto substrate of STS 316L and Ti alloy using r.f. PACVD (plasma-assisted chemical vapor deposition) with a mixture of $C_{6}H_{6}$ and $SiH_{4}$ as the process gases. Corrosion performance of DLC coatings was investigated by electrochemical techniques (potentiodynamic polarization test and electrochemical impedance spectroscopy) and surface analysis (scanning electron microscopy). The electrolyte used in this test was a 0.89% NaCl solution of pH 7.4 at temperature $37^{\circ}C$. The porosity and protective efficiency of DLC coatings were obtained using potentiodynamic polarization test. Moreover, the delamination area and volume fraction of water uptake of DLC coatings as a function of immersion time were calculated using electrochemical impedance spectroscopy. This study provides the reliable and quantitative data for assessment of the effect of substrate on corrosion performance of Si-DLC coatings. The results showed that Si-DLC coating on Ti alloy could improve corrosion resistance more than that on STS 316L in the simulated body fluid environment. This could be attributed to the formation of a dense and low-porosity coating, which impedes the penetration of water and ions.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.157-159
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• 2001

The molten carbonate fuel cell has conspicuous feature and high potential in being used as an energy converter of various fuel to electricity and heat. However, the MCFC which use strongly corrosive molten carbonate at 650$^{\circ}C$ have many problem. Systematic investigation on corrosion behavior of Fe/20Cr/Ti alloys has been done in (62+38)mol% (Li+K)CO$_3$ melt at 923K by using steady state polarization and electrochemical impedance spectroscopy method. And, The research and development for the solid oxide fuel cell have been promoted rapidly and extensively in recent years, because of their high efficiency and future potential. Therefore this paper describes the manufacturing method and characteristics of anode electrode for SOFC, by the way, Ni-YSZ materials are used as anode of SOFC widely. So in this experiments, we investigated the optimum content of Ni, by the impedance characteristics, overvoltage. As a result, the performance of Ni-YSZ anode(47vo1%) was bettor excellent than the others.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.927-933
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• 2000

The molten carbonate fuel cell has conspicuous feature and high potential in being used as an energy converter of various fuel to electricity and heat. However, the MCFC which use strongly corrosive molten carbonate at 650$^{\circ}C$ have many problem. Systematic investigation on corrosion behavior of Fe/20Cr/Ti alloys has been done in (62+38)mol% (Li+K)CO3 melt at 923K by using steady state polarization and electrochemical impedance spectroscopy method. And, The research and development for the solid oxide fuel cell have been promoted rapidly and extensively in recent years, because of their high efficiency and future potential. Therefore this paper describes the manufacturing method and characteristics of anode electrode for SOFC, by the way , Ni-YSZ materials are used as anode of SOFC widely. So in this experiments, we investigated the optimum content of Ni, by the impedance characteristics, overvoltage. As a results, the performance of Ni-YSZ anode(40vo1%) was better excellent than the others.

• Journal of the Korea Institute of Building Construction
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• v.22 no.6
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• pp.651-662
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• 2022

The electrochemical impedance spectroscopy(EIS) method was used to evaluate the concrete deterioration process related to chloride-induced steel corrosion with various corrosion levels(initiation, rust propagation and acceleration periods). The impressed current technique, with four total current levels of 0C, 13C, 65C and 130C, was used to accelerate steel corrosion in concrete cylinder samples with w/c ratio of 0.4, 0.5, and 0.6, immersed in a 0.5M NaCl solution. A series of EIS measurements was performed to monitor concrete deterioration during the accelerated corrosion test in this study. Some critical parameters of the equivalent circuit were obtained through the EIS analysis. It was observed that the charge transfer resistance(R_c) dropped sharply as the impressed current increased from 0C to 13C, indicating a value of approximately 10kΩcm². However, the sensitivity of R_c significantly decreased when the impressed current was further increased from 13C to 130C after corrosion of steel had been initiated. Meanwhile, the double-layer capacitance value(C_dl) linearly increased from 50×10^-6μF/cm² to 250×10^-6μF/cm² as the impressed current in creased from 0C to 130C. The results in this study showed that monitoring C_dl is an effective measurement parameter for evaluating the progress of internal concrete damages(de-bonding between steel and concrete, micro-cracks, and surface-breaking cracks) induced by steel corrosion. The findings of this study provide a fundamental basis for developing an embedded sensor and signal interpretation method for monitoring concrete deterioration due to steel corrosion at various corrosion levels.

• Bulletin of the Korean Chemical Society
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• v.32 no.3
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• pp.836-840
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• 2011

This study examines the effects of a carbon coating on the electrochemical performances of $LiFePO_4$. The results show that the capacity of bare $LiFePO_4$ decreased sharply, whereas the $LiFePO_4$/C shows a well maintained initial capacity. The Li ion diffusivity of the bare and carbon coated $LiFePO_4$ is calculated using cyclic voltammetry (CV) to determine the correlation between the electrochemical performance of $LiFePO_4$ and Li diffusion. The diffusion constants for $LiFePO_4$ and $LiFePO_4$/C measured from CV are $6.56{\times}10^{-16}$ and $2.48{\times}10^{-15}\;cm^2\;s^{-1}$, respectively, indicating considerable increases in diffusivity after modifications. The Li ion diffusivity (DLi) values as a function of the lithium content in the cathode are estimated by electrochemical impedance spectroscopy (EIS). The effects of the carbon coating as well as the mechanisms for the improved electrochemical performances after modification are discussed based on the diffusivity data.