• Corrosion Science and Technology
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• v.20 no.2
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• pp.45-51
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• 2021

In this work, we describe the effect of pulse anodizing duty ratio on the corrosion resistance of anodic films in magnesium AZ31B. The process involves the application of square pulse potential for a constant period with a duty ratio varying from 40, 60 and 80%. In several samples, a sealing treatment for 30 minutes was conducted after anodization in order to seal the pores available in the anodic layer. After anodizing, the surface morphology of the anodic layer was examined using a scanning electron microscope (SEM Hitachi SU3500). The corrosion characteristics of the sample were evaluated through an open circuit potential (OCP) and potentiodynamic polarization test using potentiogalvanostat. SEM observation shows that the increase of anodization duty ratio (α) results in a more uniform anodic layer, with fewer pores and cracks. The increase of duty ratio (α) decreases the OCP value from approximately -1.475 to about -1.6 Volt, and significantly improves the corrosion resistance of the anodic coating by 68%. The combination of anodization and sealing treatment produces an anodic coating with a very low corrosion rate of 4.4 mpy.

• Journal of the Korean institute of surface engineering
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• v.30 no.4
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• pp.262-271
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• 1997

Nickel-matal hydride(Ni-MH) batteries are receiving attention as non-pollunting. high performance rehargeable energy stoage system. The performance of Ni-Mh is significantly influenced by the hydrogen storage alloy materiels used as an anode material. Recently, having discharge capacities higher than the $AB_5$-type hydrogen storage alloys, the Zr-based $AB_2$-Type hydrogen storage alloys has remaining problems regarding cycle life and self-dischareg. These problems need to be solved by improvements in the alloy design and/or surface treatment. This work investiggates the effects the effects of surface property by fluorination on $Zr_{0.7}Ti_{0.3}V_{0.4}Mn_{0.4}Ni{1.2}$ composittion $AB_2$-Type hydrogen storage alloys. EPMA, SEM and AES techniques were used for surface analysis, and the crystal structure was characterized by constant current cycling test and potential sweep methods. Fluorination was found to be effective when La-was incorporated into the alloy, and has unique morphology, higher reactivity, and at the same time formed a protective film. Through, fluorination, the cycle life of an electrode was found to increase significantly, charge/discharge characteristics of the electrode the potential difference between the charge/discharge plateau, i.e polarization(overpotential)were improved.

• Journal of the Korean Ceramic Society
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• v.42 no.12 s.283
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• pp.793-799
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• 2005

A composite cathode of LSCF$(La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_3)\;and\;GDC\; (Gd_2O_3-doped\;CeO_2:Ce_{0.9}Gd_{0.1}O_{1.95_})$ was characterized in terms of an electrode response, using a point contact in an Yttria-Stabilized Zirconia (YSZ) electrolyte incorporated into AC two-point impedance spectroscopy. The point-contacted configuration amplifies the responses occurring near the YSZ/cathode interface through the aligned point contact on the planar LSCF/GDC electrode. The point contact interface increases the bulk resistance allowing the estimation of the point contact geometry and resolving the electrode-related responses. The resultant impedance spectra are analyzed through an equivalent circuit model constructed by resistors and constant phase elements. The bulk responses can be resolved from the electrode-related portions in terms of spreading resistance. The electrode-related polarizations are measured in terms of temperature and oxygen partial pressure. The modified impedance spectroscopy is discussed in terms of methodology and analytical aspects, toward resolving the electrode-polarization issues in solid oxide fuel cells.

• Membrane and Water Treatment
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• v.1 no.2
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• pp.139-158
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• 2010

This work focuses on the application of nanofiltration (NF) to the concentration of a pharmaceutical product, Clavulanate ($CA^-$), from clarified fermentation broths, which show a complex composition with six main identified ions ($K^+$, $Cl^-$, ${NH_4}^+$, $H_2{PO_4}^-$, ${SO_4}^{2-}$ and $CA^-$), glucose and glycerol. The solutes transport through the NF membrane pores was investigated using the SEDE (Steric, Electric and Dielectric Exclusion) model. This model was applied to predict the rejection rates of the initial feed solution and the final concentrated solution (10-fold concentrated solution). The best results were achieved with a single fitted parameter, ${\varepsilon}_p$ (the dielectric constant of the solution inside pores) and considering that the membrane selectivity is governed by steric, electric (Donnan) and Born dielectric exclusion mechanisms. While the predicted intrinsic rejections of solutions comprising up to six ions and uncharged solutes were in good agreement with the experimental values, the deviations were much larger for the 10-fold concentrated solution.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.2
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• pp.98-102
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• 2000

Ferroelectric PZT heterolayered thin films were fabricated by spin coating method on the Pt/Ti/SiO2/Si substrate using PZT(10/90) and PZT(90/10) m7etal alkoxide solutions. All PZT heterolayered films showed a homogeneous grain structures without presence of rosette structure. It can be assumed that the lower PZT layers played a role of nucleation site for the formation of the upper PZT layer. Pb-deficient PZT phase was formed at PZT/Pt interface due to the diffusion of Pb element into a Pt bottom electrode. The relative dielectric constant and the dielectric loss of the PZT-6 film were 567 and 3.6%, respectively. Increasing the number of coatings, remanent polarization and coercive field were decreased and the values of the PZT-6 heterolayered film were $7.18\muC/cm^2$ and 68.5kV/cm, respectively. Leakage current densities were increased with increasing the number of coatings, and the value of the PZT-4 film was about $7\times10-8A/cm^2$ at 0.05MV/cm.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1301-1302
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• 2007

The multilayered $Pb_{1.1}(Zr_{0.4}Ti_{0.6})O_{3}$/$Pb_{1.1}(Zr_{0.6}Ti_{0.4})O_{3}/Pb_{1.1}(Zr_{0.4}Ti_{0.6})O_{3}$[PZT(4060)/(6040)/(4060)] thin films were deposited by RF sputtering method on the Pt/TiO2/SiO2/Si substrate. We investigated the effects of deposition conditions on the structural and electrical properties of the multilayered PZT thin films. All the multilayered PZT thin films showed dense and homogeneous structure without the presence of the rosette structure. The dielectric properties such as dielectric constant, loss, remanent polarization of the multilayered PZT thin film were superior to those of single composition PZT(4060) and PZT(6040) films, and those values for the multilayered PZT(10/20/10) thin film were 903, 1.01% and $25.60{\mu}C/cm^2$. This study suggests that the design of the multilayered PZT thin films capacitor with tetragonal and rhombohedral phase should be an effective method to enhance the dielectric and ferroelectric performance in devices.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1324_1325
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• 2009

The heterolayered $BaTiO_3/(Bi_{0.5}Na_{0.5})TiO_3$ thick films were fabricated by screen printing techniques on alumina substrates electrodes with Pt. We report the improved ferroelectric properties in the heterolayered teteragonal/rhombohedral structure composed of the $BaTiO_3$ and the $(Bi_{0.5}Na_{0.5})TiO_3$ thick films. We investigated the effects of deposition conditions on the structural and electrical properties of the heterolayered BNT/BT thick films. The structural and electrical properties of the heterolayered BNT/BT thick films were studied. All PZT heterolayered thin films show dense and homogeneous structure without the presence of the rosette structure. The dielectric constant, loss and remanent polarization oft heheterolayered BNT/BT thick films were superior to those of single composition $BaTiO_3$ and $(Bi_{1/2}Na_{1/2})TiO_3$, and those values for the heterolayered BNT/BT thick films sintered at $1100^{\circ}C$ were 916, 0.79 and $12.63{\mu}C/cm^2$.

• Transactions on Electrical and Electronic Materials
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• v.7 no.3
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• pp.129-133
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• 2006

Ferroelectric PZT heterolayered thick films were fabricated by the alkoxide-based sol-gel method. PZT(20/80) and PZT(80/20) paste were made and alternately screen-printed on the alumina substrates. The coating and drying procedure was repeated 4 times to form the heterolayered thick films. The thickness of the PZT heterolayered thick films was approximately $60{\mu}m$. All PZT thick films showed the typical XRD patterns of a polycrystalline rhombohedral structure. And in the PZT thick films sintered at $1100^{\circ}C$, the pyrochlore phase was observed due to the evaporation of PbO. The relative dielectric constant and the dielectric loss of the PZT thick films sintered at $1050^{\circ}C$ were 445.2 and 1.90 % at 1 kHz, respectively. The remanent polarization and coercive field of the PZT thick films sintered at $1050^{\circ}C$ were $14.15{\mu}C/cm^2$ and 19.13 kV/cm, respectively.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.6
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• pp.799-803
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• 2018

We demonstrated memory thin-film transistors (MTFTs) with organic ferroelectric polymer poly(vinylidene fluoride-co-trifluoroethylene) and an amorphous oxide semiconducting indium gallium zinc oxide channel on the elastomeric substrate. The dielectric constant for the P(VDF-TrFE) thin film prepared on the elastomeric substrate was calculated to be 10 at a high frequency of 1 MHz. The voltage-dependent capacitance variations showed typical butterfly-shaped hysteresis behaviors owing to the polarization reversal in the film. The carrier mobility and memory on/off ratio of the MTFTs showed $15cm^2V^{-1}s^{-1}$ and $10^6$, respectively. This result indicates that the P(VDF-TrFE) film prepared on the elastomeric substrate exhibits ferroelectric natures. The fabricated MTFTs exhibited sufficiently encouraging device characteristics even on the elastomeric substrate to realize mechanically stretchable nonvolatile memory devices.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.137-146
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• 2006

Shear wave velocity of uncemented soil can be expressed as the function of effective stresses when capillary phenomenons are negligible. However, the terms of effective stresses are divided to the direction of wave propagation and polarization because stress states are generally anisotropy. The shear wave velocities are affected by parameters and exponents that are experimentally determined. The exponents are controlled contact effects of particulate materials(sizes, shapes, and structures of particles) and the parameters are changed contact behaviors between particles, material properties of particles, and type of packing(i.e., void ratio and coordination number). In this study, consolidation tests are performed by using clay, mica and sand specimens. Shear wave velocities are measured during consolidation tests to investigate the stress-induced and inherent anisotropies through bender elements. Results show the shear wave velocities depends on the stress-induced anisotropy for round particles. Furthermore the shear wave velocity is dependent on particle alignment under the constant effective stress. This study suggests that the shear wave velocity and the shear modulus should be carefully calculated and used for the design and construction of geotechnical structures.