• Journal of Electrochemical Science and Technology
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• 제2권2호
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• pp.76-84
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• 2011

Potentiostatic oxidation of Pb-1.7%Sb alloy used in the manufacture of grids of lead-acid batteries over the potential range from -1.0V to 2.3V in 5M $H_2SO_4$ in the absence and the presence of 0.4M $H_3PO_4$ and the self-discharge characteristics of the oxide layer formed is studied by electrochemical impedance spectroscopy (EIS). Depending on the potential value, sharp variations in resistance and capacitance of the alloy are recorded during the oxidation and they can be used for identification of the various substances involved in passive layer. Addition of $H_3PO_4$ is found to deteriorate the insulating properties of the passive layer by the retardation of the formation of $PbSO_4$. $H_3PO_4$ completely inhibits the current and impedance fluctuations recorded in $H_3PO_4$-free solutions in the potential range 0.5 V-1.7 V. These fluctuations are attributed to the occurrence of competitive redox processes that involve the formation of $PbSO_4$, $PbOSO_4$, PbO and $PbO_2$ and the repeated formation and breakdown of the passive layer. Self-discharge experiments indicate that the amount of $PbO_2$ formed in the presence of $H_3PO_4$ is lesser than in the $H_3PO_4$-free solutions. The start of transformation of $PbSO_4$ into $PbO_2$ is greatly shortened. $H_3PO_4$ facilitates the diffusion process of soluble species through the passive layer ($PbSO_4$ and basic $PbSO_4$) but impedes the diffusion process through $PbO_2$.

• 전기화학회지
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• 제3권4호
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• pp.211-218
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• 2000

마멸전극기법과 교류 임피던스법으로 스테인리스강의 합금원소, Cr, Mo, N가 합금의 재부동태 특성에 미치는 영향을 조사하였다. Fe-Cr, Fe-Cr-Mo, 304, 304LN, 316, 316LN등의 스테인리스강을 시편으로 사용하였으며 각 합금의 부동태 피막의 전기화학적 특성은 in-situ시험 기법인 d.c와 a.c전기화학적 기법을 각각 이용하였다 스테인리스강이 국부부식에 대하여 강한 저항성을 가지려면 부식 환경에서도 치밀한 부동태 피막을 유지해야 하고 피막의 파괴가 발생하더라도 재부동태 속도가 빨라야 하기 때문에 합금원소가 시간에 따른 재부동태 전류밀도와 재부동태 속도에 미치는 영향을 마멸 전극 시험법과 교류 임피던스 시험법으로 알아보았다. 부동태 피막의 안정성, 재부동태 속도 그리고 합금원소 사이의 관계를 규명하기 위하여 실험결과를 분석하였다.

• Advances in Energy Research
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• 제2권2호
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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.

• 전기학회논문지
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• 제56권10호
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• pp.1814-1819
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• 2007

A new active resonator using defected ground structure with islands (DGSI) is proposed. The proposed resonator is composed of the conventional microstrip line with DGSI and negative resistance of active devices. The negative resistance part is realized by field effect transistor (FET) series feedback circuits. The characteristic of the proposed resonator with DGSI is improved by combining the negative resistance part with the parallel microstrip line structure with islands, where the electric field is formed the most strongly. The measured improvement of the proposed active resonator with DGSI are 4.55dB and 0.32dB in S21 and S22, respectively, at the resonant frequency whorl it is compared to the existing passive resonator having DGSI only.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.467-472
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• 2000

It is known that chloride ion in concrete destroys the passive film of reinforcement inside concrete and accelerates corrosion which is the most influencing factor to durability of concrete structures. In this thesis, a chloride ion diffusion model for blast furnace slag(BFS) concrete, which has better resistance to both damage due to salt and chloride ion penetration than ordinary portland cement concrete, is proposed by modifying existing model of normal concrete. Proposed model is verified by comparing diffusion analysis results with both results by indoor chloride penetration test for specimens and field test results for actual RC bridge pier. Also, the optimum resistance condition to chloride penetration is obtained according to degrees of fineness and replacement ratios of BFS concrete. As a result, resistance to chloride ion penetration for BFS concrete is more affected by replacement ratio than degree of fineness.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 가을 학술발표회 논문집
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• pp.127-134
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• 2000

Soil nailing is in-situ ground improvement technique of reinforcing soils using passive inclusions for the purpose of slope stability. Also soil nailing, in general, was used and studied as a reinforcement technique at cut slope, but this paper presents the results of study for soil nailing application as a reinforcement technique at the banking over slided slope. In-situ pull-out tests of nails, instrumented with strain gauges, were performed to investigate the maximum pull-out load and to calculate the unit side resistance in each different layer. And the apparent average unit side resistance of this study was compared with that of other sites installed at cut slope.

• Journal of Welding and Joining
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• 제15권5호
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• pp.124-133
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• 1997

Corrosion behavior of welded SWS400 steel used for bridges was studied in a range of the acid-rain environment using immersion, potentiodynamic polartization, polarization resistance, and galvanic corrosion tests. The SWS400 steel exhibited active corrosion behavior in the range of acid-rain environment, i.e. no passivation. As the results of immersion corrosion test, Tafel extrapolation method, and polarization resistance measurement, the average corrosion rats of the steels were 0.31-0.72 mm/year in the pH of 4-5, and 0.17 mm/yera in the pH 6, respectively. The steel showed a resistance to corrosion in the pH 6. The observed active behavior of SWS400 steel in chloride-containing environment indicated that the chloride ions exerts a detrimental influence on the formation of passive films. Galvanic corrosion was observed between the weld and the base metals because the weld is anodic to the base metal.

• 한국표면공학회지
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• 제39권1호
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• pp.18-24
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• 2006

Although stainless steels have the excellent corrosion resistance by passive film, they are susceptible to pitting corrosion in the environment containing halogen elements such as chloride ions. The resistance to pitting corrosion can be evaluated by measuring the critical pitting temperature (CPT). CPT values can be obtained using immersion, potentiodynamic and potentiostatic polarization test methods. Results on duplex 2205 stainless steels showed that CPT values were measured as $50^{\circ}C,\;55^{\circ}C\;and\;61^{\circ}C$, respectively for immersion, potentiodynamic and potentiostatic polarization test methods, depending upon the different test methods, even though the difference between CPT values are not much.

• Steel and Composite Structures
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• 제2권5호
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• pp.379-396
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• 2002

The paper describes the mechanical behavior of short concrete-filled steel tube (CFT) columns with circular section. The efficiency of the steel tube in confining the concrete core depending on concrete strength and the steel tube thickness was examined. Fifteen columns were tested to failure under concentric axial loading. Furthermore, a mechanical model based on the interaction between the concrete core and the steel tube was developed. The model employs a volumetric strain history for the concrete, characterized by the level of applied confining stress. The situation of passive confinement is accounted for by an incremental procedure, which continuously updates the confining stress. The post-yield behavior of the columns is greatly influenced by the confinement level and is related to the efficiency of the steel tube in confining the concrete core. It is possible to classify the post-yield behavior into three categories: strain softening, perfectly plastic and strain hardening behavior. The softening behavior, which is due to a shear plane failure in the concrete core, was found for some of the CFT columns with high-strength concrete. Nevertheless, with a CFT column, it is possible to use high-strength concrete to obtain higher load resistance and still achieve a good ductile behavior.

• 대한기계학회논문집B
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• 제24권3호
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• pp.338-345
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• 2000

A model testing has been performed to investigate the flow characteristics of a vortex chamber, which plays a role of a flow switch and passively controls the discharge flow rate. This method of passive flow control is a matter of concern in the design of advanced nuclear reactor systems as an alternative to the active flow control to provide emergency water to the reactor core in case of postulated accidents like LOCA (Loss-Of-Coolant Accident). By changing the inflow direction in the vortex chamber and varying the flow resistance inside the chamber, the vortex chamber can control passively the injection flowrate. Fundamental characteristics such as discharge flow rate and pressure drop of the vortex chamber are measured, and its parametric effects on the performance of the vortex chamber are also systematically investigated.