Papers by Author: Eun Hee Lee

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Authors: Eun Hee Lee, Min Ku Lee, Chang Kyu Rhee
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Authors: Eun Hee Lee, Min Ku Lee, Chang Kyu Rhee
Abstract: The stability of nanosized Ni dispersions with varying concentrations of poly (1-vinyl-2- pyrrolidone) (PVP) was investigated by means of a visual inspection, transmission profile measured by Turbiscan, zeta potential, and transmission electron microscopy. For dispersions with PVP, the ζ potential values varied from positive charge to negative charge. For dispersion with a 0.04 weight percentage of PVP, the ζ potential value showed 31.71 mV, which was the highest value, and the flocculation of Ni nanoparticles was not observed. Stable dispersions of Ni nanoparticles were produced by electrostatic, steric interactions, and the formation of bridging aggregation.
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Authors: Eun Hee Lee, Kyung Mo Kim, Hong Po Kim, Uh Chul Kim, Jang Ho Bae, Chang Wan Won
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Authors: C.H Lee, Eun Hee Lee
Abstract: We have studied the effect of pH on the dispersion stability of aqueous suspensions of Fe2O3 powders over a wide pH range in the presence of the poly (acrylic acid) (PAA). In order to investigate the ionization behavior of the PAA, pH of PAA solutions was measured. Sedimentation and zeta-potential measurements were conducted on aqueous Fe2O3 suspensions to characterize the dispersion stability of the suspensions. The PAA was ionized over a wide pH range and the quantity of ionization was abruptly increased at pH > 10. Thus, the dispersion of the Fe2O3 powders was observed even in acidic solutions and the dispersion stability of the suspensions increased as pH of the solutions increased. The magnitude of zeta-potential values increased with increasing pH.
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Authors: Eun Hee Lee, Min Ku Lee, Chang Kyu Rhee
Abstract: In order to select the most suitable solvent for the stable dispersion of Alloy 625 nanoparticles, we investigated the effects of several organic solvents on the dispersion stability. After preparing suspensions with a dispersant, we characterized the dispersion stability of the suspensions by means of visual inspection and Turbiscan transmission profiles. The dispersion stability of the solvents increased in the following order: ethyl acetate, xylene, toluene, 2-propanol, and ethanol. The polarity of the solvent affected the dispersion stability. The Alloy 625 nanoparticles were optimally dispersed in ethanol with the dispersant, Hypermer KD-2, which was stabilized by the steric effect of the dispersant.
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Authors: Eun Hee Lee, Min Ku Lee, Chang Kyu Rhee
Abstract: Colloid stability of the suspensions of Ni nanoparticles has been investigated with adding polymeric dispersant in various organic media. We characterized the dispersion stability of Ni nanoparticles by means of visual inspection, transmission profiles measured by Turbiscan, the particle size distribution, and the zeta potential. 0.01 wt% of Ni nanoparticles were found to be optimally dispersed in ethanol among various organic media employed in this study with adding the dispersant (0.6 wt%-2 wt%). As the concentration of the dispersant increased, the particle size decreased in size from 300 nm to 200 nm due to less coalescence. The zeta potential values of the Ni nanoparticles in suspensions with the dispersant were greater than -40mV. Such stable Ni nanoparticle suspensions are attributed to the electrosteric effect of the polymeric dispersant.
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Authors: Kyung Mo Kim, Eun Hee Lee, Uh Chul Kim
Abstract: Several chemicals were studied to suppress the damage due to stress corrosion cracking (SCC) of steam generator (SG) tubes in nuclear power plants. The polarization curves showed that the electrochemical properties on the surface of Alloy 600 MA changed with the addition of inhibitors. The SCC tests were conducted by using a m-RUB specimen in a 10% NaOH solution at a temperature of 315°C. The effects on the SCC of the compounds, TiO2, TyzorLA and CeB6, were tested for several types of SG tubing materials. The test with the addition of TiO2 (P25) and CeB6 showed an effect in decreasing the SCC for the SG tubing material. However, CeB6 caused some more SCC for Alloy 800. The penetration property into a crevice of the inhibitors was investigated by using Alloy 600 specimens with different gap sizes and an AES analysis was performed on the oxide layer of the specimen.
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Authors: Eun Hee Lee, Kyung Mo Kim, Uh Chul Kim
Abstract: The stress corrosion cracking (SCC) susceptibility of Alloy 600 MA has been studied in deaerated 0.01 M sodium sulfate (Na2SO4) and sodium thiosulfate (Na2S2O3) solutions at 340°C. Pre-strained reverse U-bend (RUB) specimens are tested using a static-autoclave system. The specimens show an intergranular SCC and a higher resistance to SCC in a Na2S2O3 solution than in a Na2SO4 solution. The results of the deposits and surface analyses by using XRD and SEM/EDS confirm the existence of the sulfides. The SCC of Alloy 600 MA is associated with the reduced sulfur species and protective oxide film properties formed on the alloy surface in the Na2SO4 and Na2S2O3 solutions.
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Authors: Eun Hee Lee, Kyung Mo Kim
Abstract: The stress corrosion cracking (SCC) susceptibility of Alloy 600 MA, Alloy 600 TT, Alloy 800, and Alloy 690 TT were investigated in a deaerated 0.01 M solution of sodium tetrathionate using reverse u-bend test samples at 340 °C. The results showed that SCC occurred in all alloys, excluding Alloy 690 TT. The SCC susceptibility of the alloys increased in the following order: Alloy 690 TT, Alloy 800, Alloy 600 TT, and Alloy 600 MA. The SCC susceptibility decreased with an increase in the chromium content of the alloys. The results of the deposits and spectra taken from an energy dispersive X-ray system confirmed the existence of a reduced sulfur causing SCC.
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