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  • Author: J.-M. Koo x
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J.-K. Kim, H.M. Shim, M.-J. Park and K.-K. Koo

Abstract

Although phosphinic acid (H3PO2) has a powerful reduction potential, the reduction of silver ions by phosphinic acid salt has not yet been reported. In this work, colloidal silver has successfully synthesized by reducing silver ions in ethanol with phosphinic acid as a reducing agent. The effects of [AgNO3]/[H3PO2] ratios and reaction temperature were considered. Spherical silver nanoparticles with cubic structure were successfully prepared and their diameters were measured to be 8.5±0.9 nm − 11.3±0.2 nm. Half-life analysis showed that the reduction of silver ions proceeded with the reaction order of 1.30 on concentration of phosphinic acid and activation energy of 120.7 kJ/mol.

Open access

E.-B. Kim, J.-M. Koo and S.-J. Hong

Abstract

In this study, p-type Bi0.5Sb1.5Te3 based nanocomposites with addition of different weight percentages of Ga2O3 nanoparticles are fabricated by mechanical milling and spark plasma sintering. The fracture surfaces of all Bi0.5Sb1.5Te3 nanocomposites exhibited similar grain distribution on the entire fracture surface. The Vickers hardness is improved for the Bi0.5Sb1.5Te3 nanocomposites with 6 wt% added Ga2O3 due to exhibiting fine microstructure, and dispersion strengthening mechanism. The Seebeck coefficient of Bi0.5Sb1.5Te3 nanocomposites are significantly improved owing to the decrease in carrier concentration. The electrical conductivity is decreased rapidly upon the addition of Ga2O3 nanoparticle due to increasing carrier scattering at newly formed interfaces. The peak power factor of 3.24 W/mK2 is achieved for the base Bi0.5Sb1.5Te3 sintered bulk. The Bi0.5Sb1.5Te3 nanocomposites show low power factor than base sample due to low electrical conductivity.

Open access

H.-S. Kim, B. Madavali, T.-J. Eom, C.-M. Kim, J.-M. Koo, T.-H. Lee and S.-J. Hong

Abstract

In this research, effect of the various mechanical milling process on morphology and microstructural changes of nano and micron Al-powders was studied. The milling of Al-powders was performed by both high energy and low energy ball milling process. The influence of milling (pulverizing) energy on the structural changes of Al-powders was studied. Al-nanoparticles were agglomerated during the MA and its size was increased with increasing milling while micron Al-powder gets flattened shape during high energy ball milling due to severe plastic deformation. Meanwhile, structural evolution during high energy ball milling of the nano powder occurred faster than that of the micron powder. A slight shift in the position of X-ray diffraction peaks was observed in nano Al-powders but it was un-altered in macro Al-powders. The variation in lattice parameters was observed only for nano Al powders during the high energy ball milling due to lattice distortion.

Open access

J.Y. Han, O.E. Femi, F. Kilicaslan, C.U. Jeong, C.H. Baeg, S.J. Hong and J.M. Koo

Abstract

In this study, the mechanical properties of Al-Si alloys was improved by selecting higher Si content and avoiding distortion in Al-Si matrix by adding an extrusion process such that the fabrication processes casting and extrusion were in sequence. Cast billets were extruded at ratios 4:1 and 10:1 to obtained two extruded bars with different processing parameters. The as-extruded samples were characterized and investigated for microstructure and mechanical properties. Optical Microscope was used to examined phase morphologies and microstructures of the extruded Al-Si bars. Mechanical properties were conducted on each sample to study the effectiveness of the additional extrusion process in high Si content Al-Si alloys. The result shows that by increasing the extrusion ratio, the size of the primary Si particle reduces leading to a higher density, better tensile and yield strength compared to the cast billet.

Open access

A. Nam, S.M. Kim, J.W. Jeong, K.H. Song, T.S. Koo and K.W. Seo

Abstract

This study compared the pharmacokinetics of Prednisolone (PDS) in small- and large breed dogs with a dosing format based on body surface area (BSA) or body weight (BW). The maximum concentration and area under the curve in large-breed dogs orally administered 2 mg/kg PDS were significantly greater than those in small-breed dogs given 2 mg/kg and in large-breed dogs given 40 mg/m2. The higher blood concentrations that result from BW-based dosing of oral PDS in large-breed dogs can be more than required for effect. Meanwhile, BSA dosing at 40 mg/m may be suboptimal. These findings confirm important differences between standard PDS dosing schemes in dogs while highlighting the need to further optimize PDS dosing in large-breed dogs.