• Title/Summary/Keyword: Impedance Reduction Rate

Search Result 39, Processing Time 0.021 seconds

Workpiece Horizontality and Reference Positioning of Cutting Tool by Measuring Impedance in Ultra-Precision-Machining (초정밀가공 시 임피던스 측정을 통한 시편 수평맞춤 및 공구의 기준위치 설정)

  • Lee, Ho-Cheol;Kim, Gi-Dae
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.28 no.12
    • /
    • pp.1366-1371
    • /
    • 2011
  • In ultra precision machining, it is necessary to adjust the horizontality and reference position of a workpiece in a noncontact manner. For this, a simple process by measuring impedance between a tool tip and a workpiece which are connected to impedance analyzer is proposed. As the distance between the tool and the workpiece gets closer, the reduction rate of impedance becomes higher over all frequency ranges. By setting threshold value of impedance reduction rate at specific frequencies through preliminary experiments, the distance between the tool and the workpiece can be predicted and it directly enables us to horizontalize the workpiece and to set the tool to the desired reference position.

A Review of Ac-impedance Models for the Analysis of the Oxygen Reduction Reaction on the Porous Cathode Electrode for Solid Oxide Fuel Cell

  • Kim, Ju-Sik;Pyun, Su-Il
    • Journal of the Korean Electrochemical Society
    • /
    • v.8 no.2
    • /
    • pp.106-114
    • /
    • 2005
  • This article covers the theoretical ac-impedance models for the analysis of oxygen reduction on the porous cathode electrode f3r solid oxide fuel cell (SOFC). Firstly, ac-impedance models were explained on the basis of the mechanism of oxygen reduction, which were classified into the rate-determining steps; (i) adsorption of oxygen atom on the electrode surface, (ii) diffusion of adsorbed oxygen atom along the electrode surface towards the three-phase (electrode/electrolyte/gas) boundaries, (iii) surface diffusion of adsorbed oxygen atom m ixed with the adsorption reaction of oxygen atom on the electrode surface and (iv) diffusion of oxygen vacancy through the electrode coupled with the charge transfer reaction at the electrode/gas interface. In each section for ac-impedance model, the representative impedance plots and the interpretation of important parameters attributed to the oxygen reduction reaction were explained. Finally, we discussed in detail the applications of the proposed theoretical ac-impedance models to the real electrode of SOFC system.

AC Impedance Study of Hydrogen Oxidation and Reduction at Pd/Nafion Interface

  • Song, Seong-Min;Koo, Il-Gyo;Lee, Woong-Moo
    • Journal of Hydrogen and New Energy
    • /
    • v.12 no.3
    • /
    • pp.231-238
    • /
    • 2001
  • Electrocatalytic activity of palladium for hydrogen oxidation and reduction was studied using AC impedance method. The system under study was arranged in electrolytic mode consisting of Pd electrode under study, Pt counter electrode and Nafion electrolyte between them. Two types of Pd electrodes were used - carbon-supported Pd (Pd/C) and Pd foil electrode. Pd/C anode contacting pure hydrogen showed a steady decrease of charge transfer resistance with the increase of anodic overpotential, which is an opposite trend to that found with Pd foil anode. But Pd foil cathode also exhibited a decrease of the resistance with the increase of cathodic overpotential. The relationship between imposition of overpotential and subsequent change of the charge transfer resistance is determined by the ratio of the rate of faradaic process to the rate of mass transportation; if mass transfer limitation holds, increase of overpotential accompanies the increase of charge transfer resistance. Regardless of the physical type of Pd electrode, the anode contacting hydrogen/oxygen gas mixture did not reveal any independent arc originated from local anodic oxygen reduction.

  • PDF

Corrosion Resistance Properties of Rice Husk Ash Blended Concrete

  • Ganesan, K.;Rajagopal, K.;Thangavel, K.
    • Corrosion Science and Technology
    • /
    • v.6 no.1
    • /
    • pp.12-17
    • /
    • 2007
  • Portland cement incorporating supplementary cementing material develops excellent mechanical properties and long term durability characteristics. India is a leading rice producing country and rice husk is considered as waste in the rice milling industries. In this present work, the rice husk ash (RHA) was added to concrete as cement replacement from 0 to 30%. Corrosion performance of reinforcing steel embedded in RHA blended concretes was studied using linear polarization, AC impedance and gravimetric methods. The corrosion rate of steel bars embedded in RHA concretes were compared with control concrete. The results clearly indicate that the corrosion rate of reinforcing steel embedded in concrete is significantly reduced with the incorporation of RHA. A good correlation among gravimetric method and electrochemical methods was observed. Electrochemical impedance study showed 98 percentage reduction in corrosion rate to the RHA blended concrete with 15% replacement than control concrete.

Electrode of Low Impedance by Polypyrrole Addition for Supercapacitor (폴리피롤 첨가에 의한 supercapacitor용 저 임피던스 전극)

  • 김경민;장인영;강안수
    • Proceedings of the Safety Management and Science Conference
    • /
    • 2003.11a
    • /
    • pp.343-350
    • /
    • 2003
  • The best Ppy weight ratio was 7 wt% and the optimal electrode composition ratio was 78 : 17 : 5 wt.% of (MSP-20 : BP-20 =1 : 1), (Super P : Ppy =10 : 7) and P(VdF-co-HFP). Implantation of Ppy as the conducting agents have led to superior electrochemical characteristics because of the low of internal resistance and faradaic capacitance. The result of unit cell with Ppy 7 wt% were as follows: 28.02 Fig of specific capacitance, 1.34 Ω of DC-ESR and 0.36 Ω of AC-ESR. Unit cell showed a good stability up to 200 charge-discharge cycles, retaining 82% of their original capacity at 200 cycles. From the analysis of impedance, the electrodes with Ppy 7 wt% showed low ESR, low charge transfer resistance and quick reaction rate. It was inferred that quick charge-discharge was possible. As compared with the specific capacitance (rectangular shape) of CV, it was also concluded that the specific capacitance originated from thecompound phenomena of the faradaic capacitance by oxidation and reduction of Ppy and the non-faradaic capacitance by adsorption-desorption of activated carbon.

  • PDF

Realization of High Impedance Surface Characteristics Using a Periodically Transformed Artificial Magnetic Conductor Structure and Reduction Technique of Specific Absorption Rate

  • Lee, Seungwoo;Rhee, Seung-Yeop;Kim, Pan-Yeol;Kim, Nam
    • Journal of electromagnetic engineering and science
    • /
    • v.13 no.2
    • /
    • pp.113-119
    • /
    • 2013
  • We developed a transformed, symmetrical, mushroom-like surface without via holes in cells focused on a 2.4-GHz WLAN band. Each slot in the novel type structure plays a key role in modeling at the desired frequencies. The designed artificial magnetic conductor (AMC) has several advantages, including a small size, a wider bandwidth, a short reflecting distance to the antenna, and easy fabrication because there are no via holes. Overall dimensions of the AMC cell are 21 mm $(Width){\times}21mm$ $(Height){\times}2.6mm$ (Thickness), and the bandwidth is about three times wider (11.7%) compared to that of a conventional AMC (4.0%). For evaluating the performance of the proposed structure, a reflector, which periodically consists of the designed AMC cells, was developed. The antenna with the investigated AMC reflector not only works within a quarter of the wavelength because of the extremely high wave impedance generated by the AMC cells on the surface of the structure but also reduces the specific absorption rate (SAR). Electromagnetic field (EMF) exposure to a human phantom was analyzed by applying the designed reflector to the 2.4-GHz dipole antenna in a tablet PC. The calculated peak SAR averaged over 1 g was 0.125 W/kg when the input power was 1 W and the antenna was located at 20 cm from the human phantom. However, the SAR value was only 0.002 W/kg (i.e., 98.4% blocked) when the designed reflector was inserted in front of the antenna.

Assessment on Recovery of Cesium, Strontium, and Barium From Eutectic LiCl-KCl Salt With Liquid Bismuth System

  • Woods, Michael E.;Phongikaroon, Supathorn
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
    • /
    • v.18 no.4
    • /
    • pp.421-437
    • /
    • 2020
  • This study provides an assessment on a proposed method for separation of cesium, strontium, and barium using electrochemical reduction at a liquid bismuth cathode in LiCl-KCl eutectic salt, investigated via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS). CV studies were performed at temperatures of 723-823 K and concentrations of the target species up to 4.0wt%. Redox reactions occurring during potential sweeps were observed. Concentration of BaCl2 in the salt did not seem to influence the diffusivity in the studied concentration range up to 4.0wt%. The presence of strontium in the system affected the redox reaction of lithium; however, there were no distinguishable redox peaks that could be measured. Impedance spectra obtained from EIS methods were used to calculate the exchange current densities of the electroactive active redox couple at the bismuth cathode. Results show the rate-controlling step in deposition to be the mass transport of Cs+ ions from the bulk salt to the cathode surface layer. Results from SEM-EDS suggest that Cs-Bi and Sr-Bi intermetallics from LiCl-KCl salt are not thermodynamically favorable.

Corrosion Behavior of High Pressure Die Cast Al-Ni and Al-Ni-Ca Alloys in 3.5% NaCl Solution

  • Arthanari, Srinivasan;Jang, Jae Cheol;Shin, Kwang Seon
    • Corrosion Science and Technology
    • /
    • v.16 no.3
    • /
    • pp.100-108
    • /
    • 2017
  • In this investigation corrosion behavior of newly developed high-pressure die cast Al-Ni (N15) and Al-Ni-Ca (NX1503) alloys was studied in 3.5% NaCl solution. The electrochemical corrosion behavior was evaluated using open circuit potential (OCP) measurement, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. Potentiodynamic polarization results validated that NX1503 alloy exhibited lower corrosion current density ($i_{corr}$) value ($5.969{\mu}A/cm^2$) compared to N15 ($7.387{\mu}A/cm^2$). EIS-Bode plots revealed a higher impedance (${\mid}Z{\mid}$) value and maximum phase angle value for NX1503 than N15 alloy. Equivalent circuit curve fitting analysis revealed that surface layer ($R_1$) and charge transfer resistance ($R_{ct}$) values of NX1503 alloy was higher compared to N15 alloy. Immersion corrosion studies were also conducted for alloys using fishing line specimen arrangement to simultaneously measure corrosion rates from weight loss ($P_W$) and hydrogen volume ($P_H$) after 72 hours and NX1503 alloy had lower corrosion rate compared to N15 alloy. The addition of Ca to N15 alloy significantly reduced the Al3Ni intermetallic phase and further grain refinement may be attributed for reduction in the corrosion rate.

Cathodic Polarization Measurements on La0.9Sr0.1MnO3 Electrode for Solid Oxide Fuel Cells

  • Lee, H.Y.;Oh, S.M.
    • Applied Chemistry for Engineering
    • /
    • v.4 no.1
    • /
    • pp.153-161
    • /
    • 1993
  • Cathodic oxygen reduction kinetics on $La_{0.9}Sr_{0.1}MnO_3$ electrode have been examined at $700-900^{\circ}C$ under various oxygen partial pressures. AC impedance and current interruption techniques were employed for the determination of charge transfer resistances for electrochemical oxygen reduction. The $R_{ct}$ values obtained from two different methods were very close each other for $La_{0.9}Sr_{0.1}MnO_3$ electrode. Activation energy for the electrochemical oxygen reduction was found to be 174kJ/mol under atmospheric oxygen pressure. $R_{ct}$ measurements as a function of oxygen partial pressure indicate that the rate-determining step for the electrochemical oxygen reduction on $La_{0.9}Sr_{0.1}MnO_3$ electrode is the charge transfer process.

  • PDF

Development of $YSZ/La_0.85S_r0.15MnO_3$ Composite Electrodes for Solid Oxide Fuel Cells (고체산화물 연료전지용 $YSZ/La_0.85S_r0.15MnO_3$계 복합전극의 개발)

  • 윤성필;현상훈;김승구;남석우;홍성안
    • Journal of the Korean Ceramic Society
    • /
    • v.36 no.9
    • /
    • pp.982-990
    • /
    • 1999
  • YSZ/LSM composite cathode was fabricated by dip-coating of YSZ sol on the internal pore surface of a LSM cathode followed by sintering at low temperature (800-100$0^{\circ}C$) The YSZ coating significantly increased the TPB(Triple Phase Boundary) where the gas the electrode and the electrolyte were in contact with each other. Sinter the formation of resistive materials such as La2Zr2O7 or SrZrO3 was prevented due to the low processing temperature and TPB was increased due to the YSZ film coating the electrode resistance (Rel) was reduced about 100 times compared to non-modified cathode. From the analysis of a.c impedance it was shown that microstructural change of the cathode caused by YSZ film coating affected the oxygen reduction reaction. In the case of non-modified cathode the RDS (rate determining step) was electrode reactions rather than mass transfer or the oxygen gas diffusion in the experimental conditions employed in this study ($600^{\circ}C$-100$0^{\circ}C$ and 0,01-1 atm of Po2) for the YSZ film coated cathode however the RDS involved the oxygen diffusion through micropores of YSZ film at high temperature of 950-100$0^{\circ}C$ and low oxygen partial pressure of 0.01-0.03 atm.

  • PDF