• Journal of Magnetics
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• v.15 no.3
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• pp.112-115
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• 2010

We have investigated a surfactant-assisted sonochemical approach to produce monodisperse $Fe_3O_4$ nanoparticles (NPs). The non-ionic surfactant Igepal CO-520 (Poly(oxyethylene)(5) nonylphenyl ether) has been used for the preparation of NPs and the effects on the NP size, size distribution, and magnetic properties have been studied. The $Fe_3O_4$ NPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The results reveal that the NPs prepared by a Igepal CO-520-assisted sonochemical method exhibit a narrow range of size distributions and a high monodispersity compared to the NPs from the conventional sonochemical method. The analysis of NPs prepared in the presence of the surfactant suggested that it could be used not only as a protector to prevent the oxidation of Fe (II), but also as a controller to vary the size of the NPs.

• KSBB Journal
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• v.19 no.3
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• pp.178-186
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• 2004

The aim of this study was to investigate the skin-whitening effect of okyong-san and to develop new drug delivery carrier The extracts of okyong-san were found to have the whitening effect and Eudragit$\^$ⓡ/ L 100-55 (EUD) coated solid lipid nanoparticle (E-SLN) was prepared by solvent evaporation method and melt dispersion technique. As a result, E-SLN have a 144-170 nm of particle size, spherical shape, and 33-41% encapsulation efficiency, After release test in vitro, release profile of E-SLN depended on pH and temperature. Lastly, closed patch test and skin-whitening test was peformed clinically. In conclusion, test sample had non-stimulation and high % whiteness. The results suggest that okyong-san and E-SLN is useful as cosmeceuticals for whitening cosmetics.

• Korean Journal of Materials Research
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• v.17 no.8
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• pp.437-441
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• 2007

Preparation and morphology control of $TiO_2$ nano powders for gas sensor applications are investigated. $TiO_2$ nanopowders with rutile and anatase structures were prepared by controlling the pH value of a precursor solution without any heat treatment. The mean particle size of $TiO_2$ powders were below 10nm. The prepared $TiO_2$ nano powders were hydrothermal treated by NaOH solution. The sample was washed in HCl solution. As a result and $TiO_2$ nanotubes were formed. The lengths of $TiO_2$ nanotube were $1{\mu}m$ and the diameters were 10nm. Crystal structure and microstructure of $TiO_2$ nanotube were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). As-prepared $TiO_2$ nanotube powders have several advantages of nano particle size and high surface area and could be a prominent candidate for nano-sensors. The sensitivity of $TiO_2$ nanotube sensor was measured for toluene and NO in this study.

• Journal of the Korean Electrochemical Society
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• v.18 no.2
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• pp.68-74
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• 2015

To compare the microstructure and electrochemical properties between two binary alloys (Cr-Si, Ni-Si), two composition of binary alloys with the same capacity were selected using phase-diagram and prepared by matrix-stabilization method to suppress the volume expansion of Si by inactive-matrix. Master alloys were made by Arc-melting followed by fine structured ribbon sample preparation by Rapid Solidification Process (RSP, Melt-spinning method) under the same conditions. Also powder samples were produced by wet grinding for X-Ray Diffraction (XRD) and electrochemical measurements. As predicted from the phase diagram, only active-Si and inactive-matrix ($CrSi_2$, $NiSi_2$) were detected. The results of Scanning Electron Microscope (SEM) and Transmission Electron Microscopy - Energy Dispersive X-ray Spectroscopy (TEM-EDS) show that Cr-Si alloy has finer microstructure than Ni-Si alloy, which was also predictable through phase diagram. The electrochemical properties related to microstructure were evaluated by coin type full- and half-cells. Separately, self-designed test-cells were used to measure the volume expansion of Si during reaction. Volume expansion of Cr-Si alloy electrode with finer microstructure was suppressed significantly and improved in cycle capability, in comparison Ni-Si alloy with coarse microstructure. From these, we could infer the correlation of microstructure, volume expansion and electrochemical degradation and these properties might be predicted by phase diagram.

• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.901-908
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• 2018

Graphite is used as a sample anode active material. However, since the maximum theoretical capacity is limited to $372mA\;h\;g^{-1}$, a new anode active material is required for the development of a high capacity lithium ion battery. The maximum theoretical capacity of Si is $4200mA\;h\;g^{-1}$, which is higher than that of graphite. However, it is not suitable for direct application to the anode active material because it has a volume expansion of 400%. In order to minimize the decrease of the discharge capacity due to the volume expansion, the Si was pulverized by the dry method to reduce the mechanical stress and the volume change of the reaction phase, and the change of the volume was suppressed by coating the carbon layers to the particle size controlled Si particles. And carbon fiber is grown like a thread on the particle surface to control secondary volume expansion and improve electrical conductivity. The physical and chemical properties of the materials were measured by XRD, SEM and TEM, and their electrochemical properties were evaluated. In this study, we have investigated the synthesis method that can be used as anode active material by improving cycle characteristics of Si.