• Bulletin of the Korean Chemical Society
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• v.19 no.6
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• pp.661-666
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• 1998

Active reaction sites and electrochemical O2 reduction kinetics on La_{1-x}Sr_xMnO_{3+{\delta}} (x=0.1-0.4)/YSZ (yttria-stabilized zirconia) electrodes are investigated in the temperature range of 700-900 ℃ at $Po_2=10^{-3}$-0.21 atm. Results of the steady-state polarization measurements, which are formulated into the Butler-Volmer formalism to extract transfer coefficient values, lead us to conclude that the two-electron charge transfer step to atomically adsorbed oxygen is rate-limiting. The same conclusion is drawn from the $Po_2$-dependent ac impedance measurements, where the exponent m in the relationship of $I_o$ (exchange current density) ∝ $P_{o_{2}}^m$ is analyzed. Chemical analysis is performed on the quenched Mn perovskites to estimate their oxygen stoichiometry factors (δ) at the operating temperature (700-900 ℃). Here, the observed δ turns out to become smaller as both the Sr-doping contents (x) and the measured temperature increase. A comparison between the 8 values and cathodic activity of Mn perovskites reveals that the cathodic transfer coefficients $({\alpha}_c)$ for oxygen reduction reaction are inversely proportional to δ whereas the anodic ones $({\alpha}_a)$ show the opposite trend, reflecting that the surface oxygen vacancies on Mn perovskites actively participate in the $O_2$ reduction reaction. Among the samples of x= 0.1-0.4, the manganite with x=0.4 exhibits the smallest 8 value (even negative), and consistently this electrode shows the highest ${\alpha}_c$ and the best cathodic activity for the oxygen reduction reaction.

• Journal of Ocean Engineering and Technology
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• v.28 no.4
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• pp.356-362
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• 2014

Wear and corrosion of the engine parts surrounded with combustion chamber is more serious compared to the other parts of the engine because temperature of the exhaust gas in a combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality. Therefore, an optimum repair weldment as well as an available choice of the base metal for these parts are very important to prolong their lifetime in a economical point of view. It reported that there was an experimental result for repair weldment on the forged steel which would be generally used with piston crown material, however, it is considered that there is no study for the repair weldment on the cast steel of piston crown material. In this study, four types of electrodes such as 1.25Cr-0.5Mo, 0.5Mo Inconel 625 and 718 were welded with SMAW and GTAW methods on the cast steel which would be generally used with piston crown material. And the corrosion properties of weld metal, heat affected zone and base metal were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% $H_2SO_4$ solution. In the cases of Inconel 625, 718, the weld metals and base metals exhibited the best and worst corrosion resistance respectively, however, 1.25Cr-0.5Mo and 0.5Mo indicated that corrosion resistance of the base metal was better than the weld metal. And the weld metal welded with electrodes of Inconel 625 revealed the best corrosion resistance among the electrodes, and Inconel 718 followed the Inconel 625. Hardness relatively also indicated higher value in the weld metal compared to heat affected zone and base metal. In particular, Inconel 718 indicated the highest value of hardness compared to other electrodes in the heat affected zone.

• KSBB Journal
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• v.10 no.1
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• pp.63-70
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• 1995

The effect of operating conditions on separation of soybean proteins in a home-made free-flow electrophoresis apparatus was investigated. Measurement of the pH, conductivity, and UV-absorbance(280 nm) were carried out at each run and the purity of the sample was tested with SDS-PAGE analysis. The soybean extract pretreated with Tris and boric acid was mixed with the amino acids composed of glutamic acid, histidine, arginine, glycine(1 mM each) with glycyl-glycine(2mM) and KCl(1mM). When the cellulose acetate was used as a compartment between the electrode and the buffer solution in the cell, pH distribution in the separation cell varied from 3.0 at the anodic side to 8.0 at the cathodic side and had two inflection point. The applied voltage was from 300V to 1000V and the separation was better at a higher voltage but the voltage was limited by the capability of the cooling system due to Joule heat. The proteins focused near the middle of the channel. From the change of pH and conductivity it was found that the ions in the channel moved out to the electrodes through the membrane. In the case when the concentration of the buffer solution was increased 5 times, proteins were focused at 300V. We could not increase up to the ten times of the concentration since the temperature difference between inlet and outlet was more than $25^{\circ}C$ and denaturation of proteins was expected. When ion-exchange membranes were used U-type pH distribution was set up due to the ionic polarization near the membrane. The commercial ampholytes, instead of the mixed amino acids showed not much improvements in purity of the separated sample.

• Composites Research
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• v.27 no.4
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• pp.146-151
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• 2014

In this study, the experimental study has been performed by varying the polarization of the electric field and impact force to check the piezoelectric characteristics of piezoelectric paint sensor. Piezoelectric paint sensor used in this study is composed of epoxy resin with a hardener and PNN-PZT powder in 1:1 weight ratio. The dimensions of the paint sensor specimen are $40{\times}40{\times}1mm^3$ and regular specimens were made using a mold. The voids are removed from the specimen in the vacuum desiccator. Both upper side and bottom side of the paint sensor were coated with silver paste for making an electrode and then dried at room temperature for a day. The poling treatment has been carried out under controlled conditions of the electric field in order to check the effect of piezoelectric sensitivities, while the poling temperature was fixed at room temperature and the poling time was set to 30 min. The piezoelectric sensitivities have been measured by comparing output voltage from paint sensor with output force from impact hammer when the impact hammer hits the paint sensor. In result, the effect of the electric field has been evaluated for the sensitivity and describe the result.

• Journal of the Korean Electrochemical Society
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• v.11 no.2
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• pp.89-94
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• 2008

We synthesized and investigated $(La_{0.75}Sr_{0.25})_{1-x}FeO_{3-\delta}$ perovskite oxides having different stoichiomety (x = 0, 0.02, 0.04, 0.06, 0.08) as cathode materials. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The electrochemical performances of the synthesized powders were investigated by AC impedance spectroscopy. Both the electric conductivity and the electrochemical performance showed the highest properties at the stoichiometry x = 0.02. Finally, we concluded that the variation of A-site deficiency results in the variation of the amount of oxygen vacancy and micro structure, which leads to the variation of electric conductivity and polarization resistance.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.6
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• pp.24-33
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• 2000

Switching behaviour of the ferroelectric thin film and device characteristics of the MFSFET(Metal-Ferroelectric-Semiconductor FET) are simulated with taking into account the accumulation of oxygen vacancies near interface between the ferroelectric thin film and the bottom electrode caused by the progress of fatigue. In our switching model, relative switched charge is 0.74 nC before fatigue, but after the progress of fatigue it reduces to 0.15 nC with the generation of oxygen vacancies. It indicates that the generation of oxygen vacancies strongly suppresses polarization reversal. $C-V_G\;and\;I_D-V_G$ curves in our MFSFET device model exhibit the memory window of 2 V and show the accumulation, the depletion and the inversion regions in capacitance characteristic clearly. The difference of saturation drain current of the device before fatigue in shown by the dual threshold voltages in $I_D-V_G$ curve as 6nA/$cm^2$ and decreases as much as 50% after fatigue. Decrease of the difference of saturation drain currents by fatigue implies that the accumulation of oxygen vacancies with the fatigue should be avoided in the device application. Our simulation model is expected to play an important role in estimation of the behavior of MFSFET device with various ferroelectric thin films.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.8
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• pp.877-885
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• 2013

A seawater pipe of the engine room in the ships is being surrounded with severely corrosive environments caused by fast flowing of the seawater, containing aggressive chloride ion and high conductivity etc.. Therefore, the leakage of the seawater from its pipe have been often occurred due to its local corrosion by aggressive chloride ions. Subsequently, its leakage area is usually welded by AC shielded metal arc welding with various electrodes. In this study, when the sea water pipe is welded with several types of electrodes such as E4301, E4311, E4313 and E4316, a difference of the corrosion resistance on the welding metal zones was investigated using an electrochemical method, observing microstructure, measuring polarization behaviors and hardness. The weld metal zone welded with E4313 electrode exhibited the lowest value of hardness compared to other weld metal zones. In addition, its zone indicated also the best corrosion resistance than those of other weld metal zones. Furthermore, all of the weld metal zones revealed a relatively better corrosion resistance than those of the base metal zones. and also showed higher hardness than the base metal zones.

• Korean Journal of Materials Research
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• v.9 no.5
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• pp.484-490
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• 1999

$(Pb,La)TiO_3$(PLT) thin films were prepared on Pt/SiO$_2$/Si substrates by the sol-gel method and investigated the crystalline and electrical properties according to La concentration and post-annealing temperatures. The PLT films annealed at above $600^{\circ}C$ were exhibited the typical perovskite structures regardless of La contents. When the $(Pb,La)TiO_3$(PT) films were doped with La concentration up to 10mol%(PLT-10), the degree of z-axis orientation was greatly decreased from 63% to 26%. From AES depth profiles for the PLT-10 samples, no remarkable inter-reaction between PLT film and lower Pt electrode was found. The remanent polarization$(2Pr,Pr_+-Pr_-)$ were increased from $4\muC\textrm{cm}^2 to 16\muC\textrm{cm}^2$ as the annealing temperature increased from $600^{\circ}C to 700^{\circ}C$. This result may be ascribed to the improvement of crystallinity by the high temperature post-annealing. The dielectric constant$({\varepsilon}r)$ and tangent loss(tan$\delta$) of the PLT-10 films annealed at $650^{\circ}C$ were about 193 and 0.02, respectively with the pyroelectric coefficient($\gamma$) of around $4.0nC/\textrm{cm}^2{\cdot}^{\circ}C at 30^{\circ}C$.

• Applied Chemistry for Engineering
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• v.8 no.6
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• pp.1022-1028
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• 1997

This work was performed to study the characteristics of electrochemical intercalation reactions occurring at the interface between the organic electrolyte and tungsten trioxide thin film (thickness of $4000{\AA}$) prepared by e-beam evaporation method as cathodically coloring oxide with regard to the electrochromism by the intercalating reactions of the lithium cation in the 1M $LiClO_4/PC$ organic solution. The characteristics of electrochemical intercalation reactions were investigated by various DC electrochemical methods such as cathodic Tafel polarization test, multiple and the single sweep cyclic voltammetry and the coulomety titrations method. The surfaces of thin films were observed with the patterns of X ray diffraction after the coloring and bleaching reactions. In comparison with the previous results that $WO_3$ thin film intersely detached from the surface of electrode when the hydrogen cation was intercalated into $WO_3$ thin film in the o.1N $H_2SO_4$ aqueous solution, the intercalation reaction of lithium cation into $WO_3$ thin film in the 1M $LiClO_4/PC$ organic solution was shown that the stable bleaching and coloration was appeared within 1.0V of the applied overpotential. When the overpotential of electrochromic reaction for lithium cation in the 1M $LiClO_4/PC$ organic solution had been applied up to 1.5V, the accumulation phenomenon of lithium in amorphous $WO_3$ thin film layer occurred because the inserted lithium into amorphous $WO_3$ thin layer for coloring process was not fully removed from the thin layer to the electrolyte during bleaching process. It was found that there is a limitation of applied overpotential for coloring process by the reduction of the current densities of bleaching and coloration after few number of coloring and bleaching cycles.

• Applied Chemistry for Engineering
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• v.7 no.6
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• pp.1125-1131
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• 1996

Ca or Sr-doped $PrMnO_3$ were prepared for cathode material of solid oxide fuel cell. The characteristics such as the electrical conductivity and the cathodic overpotential were investigated as to doping contents. Also the reactivity with yttria stabilized zirconia of electrolyte, and the thermal expansion coefficient were studied. The prepared perovskite powder had the mean particle size of $2{\sim}5{\mu}m$, and the particle size and the surface area was out of relation to the doping content. When Ca doping amount of electrode material was 30mol%, the electrical conductivity was the highest value of $266S{\cdot}cm^{-1}$ at $1000^{\circ}C$, and also the polarization characteristics showed the best property. The reactivity between YSZ and Ca-doped $PrMnO_3$ at $1200^{\circ}C$ for 100hours was lower than that between YSZ and Sr-doped $PrMnO_3$. The thermal expansion coefficient of $Pr_{0.7}Ca_{0.3}MnO_3$ was $1.19{\times}10^{-5}K^{-1}$ in the temperature range of $300{\sim}1000^{\circ}C$, and this value was similar to that of YSZ, $1.15{\times}10^{-5}K^{-1}$.