• Advances in environmental research
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• v.4 no.2
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• pp.69-81
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• 2015

A new magnetite-silica core/shell nanocomposite ($Fe_3O4@nSiO_2@mSiO_2$) was synthesized and functionalized with trimethylchlorosilane (TMCS). The prepared nanocomposite was used for the removal of diesel oil from aqueous media. The characterization of magnetite-silica nanocomposite was studied by X-ray diffraction (XRD), Fourier transform infrared (FTIR), transmission electron microscopy (TEM), surface area measurement, and vibrating sample magnetization (VSM). Results have shown that the desired structure was obtained and surface modification was successfully carried out. FTIR analysis has confirmed the presence of TMCS on the surface of magnetite silica nanocomposites. The low- angle XRD pattern of nanocomposites indicated the mesoscopic structure of silica shell. Furthermore, TEM results have shown the core/shell structure with porous silica shell. Adsorption kinetic studies indicated that the nanocomposite was able to remove 80% of the oil contaminant during 2 h and fit well with the pseudo-second order model. Equilibrium studies at room temperature showed that the experimental data fitted well with Freundlich isotherm. The magnetic property of nanocomposite facilitated the separation of solid phase from aqueous solution.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.292-293
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• 2006

We have Investigated dielectric properties depending on bias voltage in organic lightemitting diodes using 8-hydroxyquinoline aluminum($Alq_3$) as an electron transport and emissive material. We analyzed the dielectric properties of organic light emitting diodes using impedance characteristics measurement by the auto-balancing bridge technique and equivalent cirrcuit of ITO/$Alq_3$/Al. Impedance characteristics was measured complex impedance Z and phase ${\theta}$ in the frequency range of 40 [Hz] to $10^8$ [Hz]. We obtained complex electrical conductivity, dielectric constant, and loss tangent ($tan{\delta}$) of the device at room temperature. From these analyses, we are able to interpret a conduction mechanism and dielectric properties contributed by an interfacial and orientational polarization.

• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1159-1168
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• 1994

We powders were synthesized from W powders in differnet particle sizes by Self-propagating High-temperature Synthesis process (SHS) using a chemical furnace. The effects of the mole ratio of chemical fuel content, pellet thickness and the mole ratio between carbon and tungsten (C/W Ratio) on synthesis were investigated with the tungsten powders have different particle size each other. Compositional and structural characterization of these powders was carried out by scanning electron microscope (SEM0 and x-ray diffractometer. Powder characterization was carried out by the measurement of particle size distribution with laser-particle size analyzer. The amounts of WC obtained by SHS process depend very much on the particle size of tungsten powder and heat contents given in a product, i.e. as the particle size of W powder is smaller, the amounts of WC produced increase. Also the more heat contents is given, the more amounts of WC increase. By optimizing the synthesis conditions, it is possible to fabricate WC powders which have little secondary phases (W2C, C).

• The Korean Journal of Ceramics
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• v.4 no.1
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• pp.15-19
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• 1998

Defects formation of Chemical Vapor Deposition (CVD) diamond on $^4He^{2+}$ irradiation and after remote hydrogen plasma treatment(RHPT) were investigated by cathodoluminescence(CL). As calculated in the TRIM simulation, the light elements of $^4He^{2-}$ can be penetrated into the diamond bulk structure at 3~4 $\mu\textrm{m}$ depth. The effects of the implantation region were observed when 5 keV~20 keV electron energy (insight 0.3~4.0$\mu\textrm{m}$) of CL measurement was irradiated to diamond at temperature 80 K. After the RHPT, rehybridization of irradiation damaged diamond was studied. The intensity of 5RL center(intrinsic defect of C) was diminished. The 2.16 eV center (N-V center) occurring usually by annealing could not be seen after RHPT. The diamond was rehybridized by hydrogen radicals without etching and thermal degradation by the RHPT.

• Journal of Electrochemical Science and Technology
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• v.5 no.2
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• pp.58-64
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• 2014

The surface of an ordered mesoporous silica (OMS) was functionalized using 1H,1H,2H,2H-perfluorooctyltrimethoxysilane at $20^{\circ}C$ and $60^{\circ}C$. It was shown that only elevated temperature allows lyophobic properties on the walls of OMS, eventually preventing pore flooding with nonaqueous electrolytes. The functionalized OMSs (OMS-F) were characterized with various techniques: wettability test, $N_2$ sorption measurement, high-resolution transmission electron microscopy (HR-TEM). Cathodes of $10mg/cm^2$ loading were prepared with a commercial Pt/C catalyst and polyvinylidene fluoride (PVDF, 2.5 wt.%) binder using a typical doctor blade method on a commercial gas diffusion layer (GDL) in the presence or in the absence of OMS-F additives. Subsequent discharge-charge curves were taken in a 1M LiTFSI-TEGDME electrolyte at 60oC in pure oxygen atmosphere. It was found that the discharge capacity was significantly affected by OMS-F: 5 wt.% of additive extended discharge capacity by a factor 1.5. On the other hand, a similar OMS material but synthesized at $20^{\circ}C$ did not show lyophobic properties and deteriorated cathode capacity.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.67.2-67.2
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• 2017

Korea Astronomy and Space Science Institute (KASI) plans to develop a coronagraph to measure the coronal electron density, temperature, and speed using four different filters around 400 nm, where strong Fraunhofer lines from the photosphere are scattered by coronal electrons. During the total solar eclipse occurring on August 21 across USA, KASI will organize an expedition team to demonstrate the coronagraph measurement scheme and the instrumental technology. The observation site is in Jackson Hole, Wyoming, USA. We plan to build two coronagraphs without occulter to improve signal to noise ratio. In addition, images of white light corona, wide field background, and all sky are planned to be taken with DSLR cameras. We will present the preliminary results of the expedition.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.2
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• pp.31-35
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• 2014

The thickness dependent electrical, structural, and optical properties of ZnO films grown by atomic layer deposition (ALD) at various growth temperatures were investigated. In order to deposit ZnO films, diethylzinc and deionized water were used as metal precursor and reactant, respectively. ALD process window was found at the growth temperature range from $150^{\circ}C$ to $250^{\circ}C$ with a growth rate of about $1.7{\AA}/cycle$. The electrical properties were studied by using van der Pauw method with Hall effect measurement. The structural and optical properties of ZnO films were analyzed by using X-ray diffraction, field emission scanning electron microscopy, and UV-visible spectrometry as a function of thickness values of ZnO films, which were selected by the lowest electrical resistivity. Finally, the figure of merit of ZnO films could be estimated as a function of the film thickness. As a result, this investigation of thickness dependent electrical, structural, and optical properties of ZnO films can provide proper information when applying to optoelectronic devices, such as organic light-emitting diodes and solar cells.

• Biomaterials and Biomechanics in Bioengineering
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• v.1 no.2
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• pp.63-71
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• 2014

This study aimed to develop a novel bioactive hybrid xerogel consisting of silk fibroin /$SiO_2-CaO-P_2O_5$ by sol-gel process at room temperature. Scanning electron microscopy (SEM), FT-IR Spectroscopy, pore measurement, mechanical property testing, in vitro bioactivity test and cytotoxicity assay were performed to characterize the xerogel for bone tissue engineering application. We have found that the xerogel possessed excellent pore structures and mechanical property. Once immersed in a simulated fluid (SBF), the xerogel exhibited profound bioactivity by inducing hydroxyapatite layers on its surfaces. The cell toxicity study also demonstrated that there was little toxic to MC3T3-E1 cells. These results indicate that silk fibroin /$SiO_2-CaO-P_2O_5$ hybrid xerogel potentially could be used as a bone tissue engineering material.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.12
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• pp.1691-1701
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• 1998

Fly ash produced in coal combustion is a fine-grained material consisting mostly of spherical, glassy, and porous particles. A study on the formation mechanism of the fly ash from coal particles in the pulverized coal power plant is investigated with a physical, morphological, and chemical characteristic analysis of fly ash collected from the Samchonpo power plant. This study may contribute to the data base of domestic fly ash, the improvement of combustion efficiency, fouling phenomena and ash collection in the electrostatic precipitator. The physical property of fly ash is determined using a particle counter for the measurement of ash size distribution. Morphological characteristic of fly ash is performed using a scanning electron micrograph. The chemical components of fly ash are determined using an inductively coupled plasma emission spectrometry(ICP). The distribution of fly ash size was bi-modal and ranged from 12 to $19{\mu}m$ in mass median diameter. Exposure conditions of flue gas temperature and duration within the combustion zone of the boiler played an important role on the morphological properties of the fly ash such as shape, particle size and chemical components. The evolution of ash formation during pulverized coal combustion has revealed three major mechanisms by large particle formation due to break-up process, gas to particle conversion and growth by coagulation and agglomeration.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.166-170
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• 2000

Nuclear fuel $UO_{2+x}$ power was produced from concentrated $UF_6$ by the DCP(Dry Conversion Process). The characterstics of $UO_{2+x}$ powder, prepared with respect to steam flowing conditions and temperature variations in a rotary kiln reactor, have been investigated with a uranium analyzer, water vapor measurement, and SEM. Fluorine content of the powder could be reduced to 8ppm. The moisture content was found to be optimized.