• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.8
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• pp.694-699
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• 2000

S $r_{0.9}$/B $i_{2.1}$/T $a_{2}$/ $O_{9}$ solutions was synthesized by MOD (metalorganic decomposition) method. SBT thin films with 2000$\AA$ thickness were prepared on Ir $O_2$/ $SiO_2$/Si and Pt/Ti/ $SiO_2$/Si substrates using the spin coating process and then investigated the dielectric and electrical properties of them. In the case of using Ir $O_2$bottom electrode the hysteresis loop was saturated at lower temperature than Pt/Ti electrode but the breakdown phenomenon was occurred at low voltage because of the rough surface morphology and porous microstructure of SBT thin films. As the results of the fatigue and imprint characteristics related to the lifetime and reliability of devices after 10$^{10}$ cycles the fatigue rates were about 10% at the Ir $O_2$and Pt/Ti bottom electrodes. Both SBT thin films with Ir $O_2$ and with Pt/Ti bottom electrodes show a slight tendency to imprint after 10$^{9}$ cycles but do not lead to a failure.e.e.

• Corrosion Science and Technology
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• v.17 no.4
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• pp.193-201
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• 2018

In order to suppress $CO_2$ emission and protect passengers in case of vehicle collision, continuous efforts are being made to increase the application ratio and tensile strength of advanced high strength steels used in the manufacturing of automotive body. Simultaneously, hydrogen embrittlement which was not a concern in the past has currently become a major issue due to microstructure that is sensitive to hydrogen uptake. The sensitivity increases with residual stress and hydrogen uptake content. Many automotive OEM companies and mill makers are setting specifications to control hydrogen embrittlement. The factors which lead to hydrogen embrittlement are material sensitivity, residual stress, and hydrogen concentration; researches are in progress to develop countermeasures. To reduce material sensitivity, mill makers add high energy trap elements or microstructure refinement elements. Automotive OEM companies design the car parts not to concentrate local stress. And they manage the levels to not to exceed critical hydrogen concentration. In this article, we have reviewed hydrogen embrittlement evaluation methods and corresponding solutions that are being studied in automobile manufacturing industries and mill makers.

• Nuclear Engineering and Technology
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• v.43 no.3
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• pp.195-204
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• 2011

The effects on pool boiling heat transfer of aqueous solutions of boric acid ($H_3BO_3$) and sodium chloride (NaCl) as working fluids have been studied. Borated and NaCl water were prepared by dissolving 0.5~5% volume concentration of boric acid and NaCl in distilled-deionized water. The pool boiling tests were conducted using $1{\times}1\;cm^2$ flat heaters at 1 atm. The critical heat flux (CHF) dramatically increased compared to boiling pure water. At the end of boiling tests it was observed that particles of boric acid and NaCl had deposited and formed a coating on the heater surface. The CHF enhancement and surface modification during boiling tests were very similar to those obtained from boiling with nanofluids. Additional experiments were carried out to investigate the reliability of the additives deposition in pure water. The boric acid and NaCl coatings disappeared after repeated boiling tests on the same surface due to the soluble nature of the coatings, thus CHF enhancement no longer existed. These results demonstrate that not only insoluble nanoparticles but also soluble salts can be deposited during boiling process and the deposited layer is solely responsible for significant CHF enhancement.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.804-805
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• 2006

Electric scroll-compressor drives are commonly used for e.g. home appliance cooling units. The recent development of hybrid cars with internal combustion engine in combination with electrical propulsion requires new solutions to be able to cool the passenger compartment of cars at stand-still. Both application areas demand efficient motor drives to reach good economy and efficient use of limited battery power as well as competitive volume/weight for a given output. The BLDC motor is a controllable and efficient solution. A major part of the motor is the soft-magnetic core. The powder based $Somaloy^{(R)}$ material shows high resistivity and induction as the result of engineered iron particles with in-organic coating. The unique features of compacted $Somaloy^{(R)}$ components can be utilized to enhance the shape and total volume of the BLDC motor with at least maintained efficiency compared to the use of traditional laminated steel sheet cores. A careful design of the $Somaloy^{(R)}$ components can also simplify assembly and positively influence the coil configuration. This study shows a comparison between a typical laminated BLDC motor and a redesigned, $Somaloy^{(R)}$ based version adapted for a scroll-compressor application.

• Journal of the Korean Ceramic Society
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• v.37 no.3
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• pp.233-239
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• 2000

Sr0.9Bi2+xTa2O9(x=0, 0.1, 0.2, 0.3) thin films on IrO2/SiO2/Si or Pt/Ti/SiO2/Si substrate were prepared by spin coating method using SBT stock solutions synthesized by MOD process. SBT thin films on IrO2 transformed to layered perovskite phase at $700^{\circ}C$, but showed low breakdown voltage due to their porous microstructure. The smaple of Sr0.9Bi2+xTa2O9 composition showed the best dielectric and electrical properties. When the sample of the same composition was annealed at 80$0^{\circ}C$, the dielectric and electric properties were improved due to the grian growth and dense surface. the remanent polarization values(2Pr) at $\pm$3 V for IrO2 and Pt electrodes were 10.5, 7.15$\mu$C/$\textrm{cm}^2$, respectively. The SBT thin film with IrO2 electrode showed the lower coercive field. The leakage current density and breakdown voltage of SBT thin films on IrO2 were higher than those on Pt.

• Korean Chemical Engineering Research
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• v.49 no.4
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• pp.411-416
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• 2011

NCO terminated polyurethane prepolymers were synthesized from isophorone diisocyanate(IPDI), polycarbonate diol(PCD) and dimethylol propionic acid(DMPA). Subsequently, acrylic terminated prepolymers were prepared by capping the NCO groups of polyurethane prepolymers with different moles of pentaerythritol triacrylate (0~0.024 moles) as a acrylate monomer. The average particle size of the acrylic terminated polyurethane solutions was increased with increasing PETA contents. Also, the prepared coating films showed better abrasion resistance and pencil hardness than pure waterborne polyurethane.

• Clean Technology
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• v.20 no.2
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• pp.136-140
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• 2014

The quaternary alloy (Co/Ni/P/Mn) coatings were prepared using electroless plating on the polypropylene. Compositions of the quaternary alloys (Co/Ni/P/Mn) were controlled by the amount of agents. The composition by EDS, morphology with SEM, film thickness, and surface electrical resistance of the samples were measured. Higher phosphorous content samples give larger electric resistance, thus a relationship is admitted between P content and electric resistance. The corrosivity of the coatings were evaluated by electrochemical methods in the 3.5 wt% NaCl and 5.0 wt% $H_2SO_4$ solutions, respectively. It was concluded that phosphorous addition enhances resistivity in the corrosion.

• Corrosion Science and Technology
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• v.16 no.2
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• pp.69-75
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• 2017

Zinc coating on carbon steels give the higher corrosion resistance in chloride containing environments and in carbonated concrete. However, hydrogen evolution accompanies the corrosion of zinc in the initial activity in fresh concrete, which can lead to the formation of a porous structure at the reinforcement -concrete interface, which can potentially reduce the bond-strength of the reinforcement with concrete. The present study examines the mechanism of the corrosion of hot-dip galvanized steel in detail, as in the model pore solutions and real concrete. Calcium ion plays an important role in the corrosion mechanism, as it prevents the formation of passive layers on zinc at an elevated alkalinity. The corrosion rate of galvanized steel decreases in accordance with the exposure time; however, the reason for this is not the zinc transition into passivity, but the consumption of the less corrosion-resistant phases of hot-dip galvanizing in the concrete environment. The results on the electrochemical tests have been confirmed by the bond-strength test for the reinforcement of concrete and by evaluating the porosity of the cement adjacent to the reinforcement.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.394-394
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• 2007

Transparent conductive films can serve as a critical component in displays, solar cells, lasers, optical communication devices, and solid state lighting. Carbon nanotube (CNT) based transparent conductive films are fabricated on glass and polymer substrates. CNTs typically exist in form of quasi-crystalline bundles or highly entangled bundles containing tens of individual nanotubes. To achieve full potential, CNTs must be dispersed in a solvent or other organic media. CNTs are acid treated with nitric acid then the stable dispersion of CNTs in polar solvent such as alcohols, DMF, etc. is achieved by sonication. The solubility of CNTs correlates well with the area ratio of the D and G bands from Raman spectrum. Thin films are formed from well dispersed CNT solutions using spray coating method. CNT thin films exhibit a sheet resistance ($R_s$) of nearby $10^3\;{\Omega}/sq$ with a transmittance of around 80% on the visible light range, which is attributed by excellent dispersion and interaction among CNTs, solvents and polymeric binders.