• Korean Journal of Materials Research
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• v.12 no.1
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• pp.58-67
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• 2002

In this study copper chloride(CuCl$_2$) solution was used as raw material to produce the fine copper oxide powder which has less than 1 $\mu\textrm{m}$ average particle size and has uniform particle size distribution by spray pyrolysis process. In the present study, the effects of reaction temperature, the injection speed of solution and air, the nozzle tip size and the concentration of raw material solution on the properties of produced powder were studied. The structure of the powder became much more compact with increasing the reaction temperature regardless of copper concentration of the raw material solution. The particle size of the powder increased accordingly with increasing the reaction temperature in case of 30 g/$\ell$ copper concentration of the solution. The particle size of the powder increased accordingly, and the surface structure of the powder became more porous with increasing the copper concentration of the raw material solution. When copper concentration in raw material solution was more than 100 g/$\ell$, all produced powder was CuCl regardless of reaction temperatures. When copper concentration in solution was below 30 g/$\ell$ and reaction temperature was higher than 90$0^{\circ}C$, CuO was the main phase. The surface of the powder tended to become porous with increasing the injection speed of solution. Particle size was increased and the surface of the powder showed severely disrupted state with increasing the nozzle tip size. The particle size was decreased and the particle size distribution was more uniform with increasing the air pressure through the nozzle.

• Applied Chemistry for Engineering
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• v.22 no.6
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• pp.703-710
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• 2011

As the spacer in the membrane module provide the channel space to flow the feed solution smoothly and induce the flow turbulence, it could help to reduce both the concentration polarization and to take the long-term operation of membrane modules with high permeate flux by mixing the accumulated contaminants on the membrane surface into the bulk solution. In this study, the concentration distribution in membrane module with respect to the spacers which have the cross-sectional shapes of circle, cross, diamond and hexagon, the angles of spacer configuration, solute rejection and permeate flux were interpreted and optimized numerically using the "COMSOL Multiphysics" software. The concentration on the membrane surface was kept the lowest level for the cross-shape among the above four types of spacers. Also the 30 degree spacer configuration was showed as the most efficient case. The concentrations on the membrane surface at the module outlet for without spacer and the cross shape with the 30 degree spacer configuration were 2.09 and 1.29 times higher than those at inlet, respectively. The reduction effect of concentration polarization increased rapidly as the permeate flux increased.

• Korean Chemical Engineering Research
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• v.56 no.5
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• pp.679-686
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• 2018

Reverse osmosis (RO) concentration of sodium chloride, sodium acetate, and sodium citrate solutions has been performed by polyamide RO membrane. Concentration polarization phenomena was also studied by changing pressure, solute kinds, and initial solution concentration. Pressure effect on permeation flux was that the increase of flux was accompanied by the increase of pressure. Flux increase was observed by the decrease of initial solution concentration. Surface concentration on the RO membrane increases and so flux declines due to the concentration polarization. In the later phase of concentration, concentration polarization effect was decreased by the back diffusion of solute from the polariztion layer. In case of sodium citrate, its large ion size and charge density resulted in the discrepancy between theory and experimental data of concentration polarization. It may be due to electric repulsion on the membrane surface.

• Journal of The Korean Astronomical Society
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• v.13 no.1
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• pp.27-33
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• 1980

Surface density distributions for globular clusters were obtained from photoelectric surface photometry (using centered aperture photometry). These surface brightness profiles were then compared with the theoretical surface density distribution of King's model. From the comparison of the theoretical and observed surface density distributions, we determine he structural parameters of the clusters (the core radius $r_c$, the tidal cut off $r_t$, and the concentration factor C).

• Journal of the Korean Society for Heat Treatment
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• v.24 no.6
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• pp.318-326
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• 2011

This study has been performed to investigate the effect of Al addition on High Temperature Gas Nitriding (HTGN) in 13%Cr-0.16%C stainless steel with different Al contents of 0.54%, 1.76% and 2.36%, respectively. HTGN treatment was carried out at $1100^{\circ}C$ for 1 hr, 5 hrs and 10 hrs. Nitrogen-permeated surface layers showed round type carbides of $Cr_{23}C_6$ and needle type nitrides of AlN in the matrix of martensite, representing 600~700 Hv. And the thickness of the surface layer increased with increasing Al content and HTGN treatment time. The inner region that was not permeated nitrogen showed chromium carbides in the mixed phase of martensite and ferrite for the 0.53% Al alloyed steel, however chromium carbides in the matrix of ferrite single phase were shown for the steels with the addition of 1.76%Al and 2.36%Al, representing the hardness of ~200 Hv. During nitrogen permeation from surface to the interior, substitutional elements of Cr, Al and Si moved toward the surface and interstitial element of carbon also moved from interior to the surface. This movement of alloying elements leads high concentration of these elements at the outmost surface, subsequently the lowest peak of substitutional elements were shown in the vicinity of near surface. After showing the lowest peak, the high concentration region of Al and C were formed due to the continuous movement of Al toward the surface. The long discontinuous precipitates of $Cr_{23}C_6$ and AlN were formed along the outmost surface owing to the high concentration of these alloying elements.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2002.05a
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• pp.13-13
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• 2002

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.10a
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• pp.16-17
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• 1999

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.10a
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• pp.18-18
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• 1999

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.05a
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• pp.142-143
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• 1999

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2000.11a
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• pp.33-34
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• 2000