• Title, Summary, Keyword: Polarization resistance

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The Effect of particle size and ratio of LSM-YSZ powders on SOFC cathod properties (LSM과 YSZ의 분말크기 및 분말크기비가 SOFC의 양극특성에 미치는 영향)

  • 김재동;김구대;박지애
    • Journal of the Korean Ceramic Society
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    • v.37 no.3
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    • pp.227-232
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    • 2000
  • The LSM-YSZ composite electrode as a mixture of LSM and YSZ shows percolation characteristics. It was identified that the polarization resistance of LSM-YSZ composite electrode depend on YSZ connectivity by changing powder size ratio of the DLSM/DYSZ. That is, YSZ in composite electrode showed low electrochemical activity without YSZ connectivity. However, the polarization resistance decreased abruptly with YSZ connectivity due to high electrochemical activity of YSZ in composite electrode. Because the amount of three phase boundary is dependent on LSM and YSZ particle size, the polarization resistance of cathode decreases as LSM and YSZ particle size decreases.

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A Quantitative Evaluation on Steel Corrosion by Polarization Resistance Method (분극저항법에 의한 철근부식의 정량적 평가)

  • 정우용;손영무;윤영수;변근주
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.688-693
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    • 2000
  • Recently great efforts and investment have been made in order to evaluate concrete durability by steel corrosion. But most of study is relatively or qualitatively estimated, therefore it has a great limitation in evaluating a remaining service life of concrete. In this research, steel corrosion rate was measured quantitatively by polarization resistance method and multi-regressed considering chloride, carbonation, coverage depth, relative humidity, W/C, and the use of deicing salts. And a half cell potential method was used at th same time for the purpose of comparing with polarization resistance method.

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Permeation Behavior of Surfactant through Membrane (계면활성제의 분리막에 대한 투과거동)

  • Ahn, Soon-Cheol;Lee, Kwang-Rae;Kim, Ki-Chang
    • Journal of Industrial Technology
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    • v.18
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    • pp.259-265
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    • 1998
  • The molecular weights of surfactant SDS(M.W. 288) and SLS(M.W. 420) are smaller than the molecular weigh cut-off of cellulose acetate membrane used in this study. However, 20% of SDS and 67% of SLS were rejected by cellulose aectate membrane. The higher rejection rate of SLS than that of SDS is due to the longer hydrophobic chain and greater molecular weight. There was no resistance to permeation rate by membrane fouling. Most of permeation resistance was due to the concentration polarization. Permeation rate was declined with operating time and with increase in concentration of surfactant due to concentration polarization.

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Influence of the cathode catalyst layer thickness on the behaviour of an air breathing PEM fuel cell

  • Ferreira-Aparicio, Paloma;Chaparro, Antonio M.
    • Advances in Energy Research
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    • v.2 no.2
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    • pp.73-84
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    • 2014
  • Fuel cells of proton exchange membrane type (PEMFC) working with hydrogen in the anode and ambient air in the cathode ('air breathing') have been prepared and characterized. The cells have been studied with variable thickness of the cathode catalyst layer ($L_{CL}$), maintaining constant the platinum and ionomer loads. Polarization curves and electrochemical active area measurements have been carried out. The polarization curves are analyzed in terms of a model for a flooded passive air breathing cathode. The analysis shows that $L_{CL}$ affects to electrochemical kinetics and mass transport processes inside the electrode, as reflected by two parameters of the polarization curves: the Tafel slope and the internal resistance. The observed decrease in Tafel slope with decreasing $L_{CL}$ shows improvements in the oxygen reduction kinetics which we attribute to changes in the catalyst layer structure. A decrease in the internal resistance with $L_{CL}$ is attributed to lower protonic resistance of thinner catalyst layers, although the observed decrease is lower than expected probably because the electronic conduction starts to be hindered by more hydrophilic character and thicker ionomer film.

Effect of Concentration Polarization on The Pervaporation of Aqueous Chlorinated-Organic Solution (유기염화물 수용액의 투과증발에 미치는 농도분극의 영향)

  • Cho, Min-Suk;Kim, Seung-Jai;Kim, Jin-Hwan
    • Applied Chemistry for Engineering
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    • v.9 no.5
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    • pp.698-703
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    • 1998
  • The pervaporation experiments of aqueous solutions of trichloroethylene (TCE) and chlorobenzene (CB) through the silicone rubber (polydimethylsiloxane, PDMS) membrane were carried out and the effect of concentration polarization on the separation characteristics was investigated. The resistance-in-series model was used to explain the boundary layer resistance. It was clear that the concentration polarization phenomenon had a significant effect on the permeation behavior in the pervaporation separation of the trace organic chlorides from aqueous solutions. With the same membrane thickness, the permeation of TCE, which has a stronger affinity for the PDMS, appeared to be more influenced by the boundary layer resistance than that of CB. The effect of boundary layer resistance was reduced and the membrane resistance became dominant with increasing membrane thickness at a given hydrodynamic condition. The separation factor was increased to approach the intrinsic separation factor of the membrane with its thickness.

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Evaluation of Corrosion Resistance of Ti-Zr-Nb-Pd Based Alloys for Biomedical applications by electron Theory (전자론에 의한 생체용 Ti-Zr-Nb-Pd계 합금의 내식성 평가)

  • Jung, Jong-Hyun;Sun, Gum-Ju
    • The Journal of Korean Academy of Dental Technology
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    • v.26 no.1
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    • pp.35-40
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    • 2004
  • In order to understand alloying effects on the corrosion resistance of Ti-(10$\sim$20)%Zr-(2$\sim$8%)Nb-0.2%Pd alloys, Polarization curves were measured at 5%HCI solution. The results were interpreted in terms of two parameters obtained by the molecular orbital calculation ; one is the bond order($B_{\circ}$) and the other is the metal d-orbital level($M_{d}$). $B_{\circ}$ is a measure of the strength of covalent bonds between titanium and alloying elements. $M_{d}$ is correlative with the electronegativity of elements. It was found that increasing of Zr and Nb with higher $B_{\circ}$ values showed a lower critical anodic current density in the polarization curve and hence higher corrosion resistance. On the other hand, increasing of Zr and Nb with higher $M_{d}$ values showed a higher corrosion resistance.

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Evaluation on Resistance to Pitting Corrosion of Fe-Cr Alloys via Measurement of the Critical Pitting Temperature (CPT) and Potentiodynamic Polarization According to KS D 0238 (wet, dry), ASTM G 61 and ISO 17475 Standards (Fe-Cr합금의 공식저항성 평가를 위하여 다양한 규격(KS D 0238, ASTM G 61, ISO 17475)에 따라 실시한 동전위 분극 시험과 임계공식온도 측정시험)

  • Kang, Su-Yeon;Lee, Jae-Bong;Kim, Yeong-Ho
    • Korean Journal of Metals and Materials
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    • v.47 no.10
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    • pp.635-643
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    • 2009
  • The resistance to pitting corrosion of Fe-Cr alloys was evaluated by performing potentiodynamic polarization and critical pitting temperature (CPT) tests. For the potentiodynamic polarization tests, various standards were applied, i.e., KS D 0238 (wet, dry), ASTM G 61, and ISO 17475, showing different potentiodynamic polarization results including pitting potentials. ASTM G 61 and ISO 17475 standards presented relatively higher pitting potential while KS D 0238 (dry) indicated lower values than the others. Effects of surface roughness, scan rates, and exposure time to air before tests were also investigated. CPT tests were performed under two different applied potentials, 300 m$V_{SCE}$ and 200 m$V_{SCE}$ in deaerated 1 M NaCl aqueous solution. CPT values and the polarization test results showed a linear relationship.

A Study on the Corrosion of Al-Alloy Propeller Used for a Coasting Vessel (연안 선박용 Al합금 프로펠러의 부식에 관한 연구)

  • LIM, Uh-Joh;PARK, Hee-Ok;YUN, Byoung-Du
    • Journal of Fisheries and Marine Sciences Education
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    • v.15 no.2
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    • pp.176-183
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    • 2003
  • Recently, with the tendency of lightening, high-strength and high-speed in the marine industries such as marine structures, ships and propellers, it is rapidly enlarged the use of the aluminium alloy. Therefore, there occurs much interest in the study on corrosion characteristics of aluminium alloy. This paper was studied on the corrosion characteristics of Al-Mg alloy propeller used for a coasting vessel. Under the various pH of marine environment, the corrosion test of Al-Mg alloy was carried out. And thus polarization resistance, corrosion potential, and current density behavior of Al-Mg alloy and galvanic corrosion behavior of Al-brass and Al-Mg alloy coupled Al 5086 and SS 400 for hull were investigated. The main results are as following: 1. The corrosion potential of Al-brass propeller is more nobel than materials for hull, but that of Al-Mg alloy propeller is low or similar to materials for hull. Therefore, the galvanic corrosion of hull due to Al-Mg propeller don't occur. 2. The polarization resistance of Al-Mg alloy in sea water of pH 4 is highest, and corrosion current density of Al-Mg propeller is the most controlled. 3. As pH value decreases, potential showed Evans polarization diagram approaches cathodic potential. The corrosion current density of Al-Mg alloy is controlled to anodic reaction rate, therefore, the corrosion reaction of Al-Mg alloy is anodic control.

Electroplating on the Lead Frames Fabricated from Domestic Copper Plate (국산동판을 사용한 리드프레임 도금기술에 관한 연구)

  • Jang, Hyeon-Gu;Lee, Dae-Seung
    • Journal of the Korean institute of surface engineering
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    • v.19 no.3
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    • pp.92-108
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    • 1986
  • An electroplating on the lead frame fabricated from domestic copper plate was studied experimentally. In this study, nickel was plated on the thin copper lead frame and silver layer was coated on the nickel film in the cyanide electrolyte. The effect of process variables such as current density, plating time, coating thickness and flow rate of electrolytic solution on the properties of coating was investigated. Some samples on each step were fabricated during electroplating. The results obtained from polarization measurement, observation of SEM photograph, adhesion test of coating and microhardness test are as follows. On silver plating, polarization resistance of potentiostatic cathodic polarization curve is reduced as the flow rate of Ag electrolytic solution increases. And above resistance is also reduced when the minor chemicals of sodium cyanide and sodium carbonate are added in potassium silver cyanide bath. The reduced polarization resistance makes silver deposition on the cathode easy. An increase in the current density and the coating thickness causes the particle size of deposit to coarsen, and consequently the Knoop microhardness of the coating decreases. On selective plating an increase in the flow rate of plating solution lead to do high speed plating with high current density. In this case, the surface morphology of deposit is of fine microstructure with high Knoop hardness. An increasing trend of the adhesion of coating was shown with increasing the current density and flow rate of electrolytic solution.

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A Study on the Concentration Polarization Layer Resistance in Ultrafiltration of Macromolecular Solutions (고분자 용액의 한외여과에서 농도분극층 저항에 관한 연구)

  • 염경호
    • Membrane Journal
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    • v.2 no.1
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    • pp.59-66
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    • 1992
  • The experimental studies were carried out on ultrafiltration of PEG #6000 and dextran 70T macromole¬cules. using an asymmetric cellulose acetate membrane in a cross flow plane type cell. Effects of pressure difference. feed concentration were studied on permeate flux and observed rejection for both the macromole¬cules. and the concentration polarization layer resistance $R_{b1}$ on permeate flux was analysed. The concentration polarization layer resistance $R_{b1}$ was correlated with the average macromolecule concen¬tration $C_{b1}$ in polarization layer. The resulting dimensionless correlation was expressed as : $\frac{R_{b1}}{{R_m}}=\alpha[\frac{\rho_{b1}}{C_{b1}}]^\beta$

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