• Journal of the Korean Electrochemical Society
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• v.14 no.2
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• pp.77-82
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• 2011

The surface of $Li[Ni_{0.35}Co_{0.3}Mn_{0.35}]O_2$ cathode was modified by $[Li,La]TiO_3$ coating using pH controlled coating solution. At low pH values (acidic solution), cathode powders, which is oxides, have a positive surface charge, whereas, they have a negative surface charge at high pH values. As a result, their charge could affect the formation of the coating layer on the surface of cathode powder. To determine the optimal pH value, the surface coating of the pristine powder was carried out at various pH values of the coating solution. The surface morphology of coated samples was characterization by SEM and TEM analyses. Impedance analysis and cyclic voltammogram presented that internal resistance of the cell was dependent upon the pH of coating solution.

• Corrosion Science and Technology
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• v.17 no.2
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• pp.45-53
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• 2018

A new 80Ti-15Ta-5Zr wt% alloy surface was protected by anodic oxidation in phosphoric acid solution. The protective oxide layer (TiO2, ZrO2 and Ta suboxides and thickness of 15.5 nm) incorporated $PO{_4}^{3-}$ ions from the solution, according to high resolution XPS spectra. The AFM analysis determined a high roughness with SEM detected pores (20 - 50 nm). The electrochemical studies of bare and anodically oxidized Ti-15Ta-5Zr alloy in Carter-Brugirard saliva of different pH values and saliva with 0.05M NaF, pointed to a nobler surface for the protected alloy, with a thicker electrodeposited oxide layer acting as a barrier against aggressive ions. The oxidized alloy significantly decreased corrosion current densities and total quantity of ions released into the oral environment in comparison with the bare one, at higher polarisation resistance and protective capacity of the electrodeposited layer. The impedance data revealed a bi-layered oxidation film formed by: a dense, compact, barrier layer in contact with the metallic substrate, decreasing the potential gradient across the metal/oxide layer/solution interface, reducing the anodic dissolution and a more permissive, porous layer in contact with the electrolyte. The open circuit potential for protected alloy shifted to nobler values, with thickening of the oxidation film signifying long-term protection.

• The Korean Journal of Ceramics
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• v.7 no.1
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• pp.6-10
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• 2001

Ultrafine $(CeO_2)_{0.9}(Gd_2O_3)_{0.1}$ solid solution powders synthesized by the glycine-nitrate process, with specific surface areas of $19-23\;\textrm{m}^2$/g were sintered at $1500^{\circ}C$ for various sintering times and then their electrical characteristics were investigated using AC impedance and four-point probe measurements. The electrical resistivity of the sintered $(CeO_2)_{0.9}(Gd_2O_3)_{0.1}$ bodies showed the minimum value at the sintering time of 10 hrs. The minimum total resistivity of the $(CeO_2)_{0.9}(Gd_2O_3)_{0.1}$ bodies sintered at $1500^{\circ}C$ for 10 hrs seems to result from the lowest activation energy for the electrical resistivity by the combination between the activation energies for the resistivities at the grain interior and grain boundary.

• Journal of Electrical Engineering and Technology
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• v.4 no.2
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• pp.277-281
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• 2009

The complex resonant frequency problem of a superconductor patch is formulated in terms of an integral equation which is the kernel of a dyadic Green's function. To include the effect of the superconductivity of the microstrip patch, the surface complex impedance of the superconductor film is introduced using the two fluids model of Gorter and Casimir. The Galerkin procedure is used in the resolution of the electric field integral equation. Numerical results concerning the effect of the operating temperature of a superconductor patch on the characteristics of the antenna are presented.

• Electrical & Electronic Materials
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• v.9 no.8
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• pp.831-835
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• 1996

The molten carbonate fuel cell has conspicuous features and high potential in being used as an energy converter of various fuels to electricity and heat. However, the MCFC which use strongly corrosive molten carbonate at 650[.deg. C] have many problem. Systematic investigation on corrosion behavior of Fe-based Cr has been done in ($62{\times}38$)mol % (Li+K)$CO_3$ melt at 923K by using steady state polarization and electrochemical impedance spectroscopy method. It was found that the corrosion current of these Fe-based alloys decreased with increasing Cr content, and this was attributed to the formation of $LiCrO_2$ layer at the surface .

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.6
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• pp.63-70
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• 2008

Conical horn is used in many high frequency ultrasonic horns, to achieve a longitudinal vibration mode across a wide ultrasonic tool horn output surface. Modal analysis is method for designing tuned ultrasonic tool horn and for the prediction natural frequency of ultrasonic tool horn vibration mode. The design of ultrasonic horn is based on prototype estimate obtained by FEM analysis. The FEM simulated ultrasonic tool horn is built and characterized experimentally through laser vibrometer and electrical impedance analysis. In this paper, FEM analysis is developed to predict the natural frequency of ultrasonic tool horn and use of in the optimal design of ultrasonic horn shape.

• Nuclear Engineering and Technology
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• v.35 no.5
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• pp.369-377
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• 2003

Since Zr-2.5Nb pressure tubes have a high risk for the formation of blisters during their operation in pressurized heavy water reactors, there has been a strong incentive to develop a method for the non-destructive detection of blisters grown on the tube surfaces. However, because there is little mismatch in acoustic impedance between the hydride blisters and zirconium matrix, it is not easy to distinguish the boundary between the blister and zirconium matrix with conventional ultrasonic methods. This study has focused on the development of a special ultrasonic method, so called ultrasonic velocity ratio method for a reliable detection of blisters formed on Zr-2.5Nb pressure tubes. Hydride blisters were grown on the outer surface of the Zr-2.5Nb pressure tube using a cold finger attached to a steady state thermal diffusion equipment. To maximize a difference in the ultrasonic velocity in hydride blisters and the zirconium matrix, the ultrasonic velocity ratio of longitudinal wave to shear wave, $V_L/V_S$, has been determined based on the flight time of the longitudinal echo and reflected shear echo from the outer surface of the tubes. The feasibility of the ultrasonic velocity ratio method is confirmed by comparing the contour plots reproduced by this method with those of the blisters grown on the Zr-2.5Nb pressure tubes.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.6
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• pp.460-464
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• 2003

The barium strontium titannate ((Ba,Sr)TiO$_3$:BST) thin films were etched in an inductively coupled plasma (ICP) as a function of CF$_4$/Ar gas mixing ratio. Under CF$_4$(20%)/Ar(80%), the maximum etch rate of the BST films was 400 $\AA$/min. Etching products were redeposited on the surface of BST and then the nature of crystallinity were varied. Therefore, we investigated the etched surface of BST by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The plasma damages were evaluated in terms of leakage current density by Agilent 4145C and dielectric constant by HP 4192 impedance analyzer. After the BST thin films exposed in the plasma, the leakage current density and roughness increases. After annealing at 600 $^{\circ}C$ for 10 min in $O_2$ ambient, the leakage current density, roughness and nonvolatile etch byproducts reduced. From this results, the plasma induced damages were recovered by annealing process owing to the relaxation of lattice mismatches by Ar ions and the desorption of metal fluorides in high temperature.

• Corrosion Science and Technology
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• v.20 no.4
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• pp.175-182
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• 2021

Magnesium alloy is limited in the industrial field because its standard electrode potential is -2.363 V vs. NHE (Normal Hydrogen Electrode) at 25 ℃. This high electrochemical activity causes magnesium to quickly corrode with oxygen in air; chemical conversion coating prevents corrosion but causes surface defects like cracks and pores. We have examined the anti-corrosion effect of sol-gel coating sealed on the defected conversion coating layer. Sol-gel coatings produced higher voltage current and smaller pore than the chemical conversion coating layer. The conversion coating on magnesium alloy AZ31 was prepared using phosphate-permanganate solution. The sol-gel coating was designed using trimethoxymethylsilane (MTMS) and (3-Glycidyloxypropyl) trimethoxysilane (GPTMS) as precursors, and aluminum acetylacetonate as a ring-opening agent. The thermal shock resistance was tested by exposing specimens at 140 ℃ in a convection oven; the results showed changes in the magnesium alloy AZ31 surface, such as oxidization and cracking. Scanning electron microscope (FE-SEM) analysis confirmed a sealed sol-gel coating layer on magnesium alloy AZ31. Electrochemical impedance spectroscopy (EIS) measured the differences in corrosion protection properties by sol-gel and conversion coatings in 0.35 wt% NaCl solution, and the potentiodynamic polarization test and confirmed conversion coating with the sol-gel coating show significantly improved resistance by crack sealing.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.6
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• pp.656-662
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• 2021

For the high efficiencies of quantum dot-sensitized solar cells (QDSCs), it is important to control the severe electron recombination at the interface of photoanode/electrolyte. In this work, we optimize the surface passivation process of ZnS/SiO₂ double overlayers for the enhanced photovoltaic performances of QDSCs. The overlayers of zinc sulfide (ZnS) and SiO₂ are coated on the surface of QD-sensitized photoanode by successive ionic layer adsorption and reaction (SILAR) method, and sol-gel reaction, respectively. In particular, for the sol-gel reaction of SiO₂, the influences of temperature of precursor solution are investigated. By application of SiO₂ overlayers on the ZnS-coated photoanode, the conversion efficiency of QDSCs is increased from 5.04% to 7.35%. The impedance analysis reveals that the electron recombination at the interface of photoanode/electrolyte is obviously reduced by the SiO₂ overlayers.