• 반도체디스플레이기술학회지
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• 제21권2호
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• pp.1-6
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• 2022

This computational investigation of micro-sized particle dispersion concerns the fume particle contamination over target surface in high-precision laser line machining process of semiconductor and display device materials. Employing the random sampling based on probabilistic fume particle generation distributions, the effects of sphericity for nonspherical fume particles are analyzed for the fume particle dispersion and contamination near the laser machining line. The drag coefficient correlation for nonspherical particles in a low Reynolds number regime is selected and utilized for particle trajectory simulations after drag model validation. When compared to the corresponding results by the assumption of spherical fume particles, the sphericity of nonspherical fume particles show much less dispersion and contamination characteristics and it also significantly affects the particle removal rate in a suction air flow patterns.

• 한국응용과학기술학회지
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• 제31권4호
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• pp.679-687
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• 2014

본 연구에서는 캐비테이션에 의한 부식에 강한 도료를 개발하기 위하여 고탄성의 우레탄 수지에 내마모 성능을 향상시키기 위한 첨가제로서 Multi wall과 Single wall type의 Carbon nano tube(CNT)와 Spherical과 Fiber type의 Graphite 나노 입자를 첨가하여 물성과 캐비테이션에 대한 저항성, 작업성 등을 비교 평가하였다. 나노 입자로서 Graphite에서는 캐비테이션 저항성($t_{50}$)이 Spherical type($t_{50}$ 182min)보다는 Fiber type($t_{50}$ 292min)이 높은 캐비테이션 저항성을 갖는 것으로 관찰되었다. 또한 CNT에서는 Single wall type의 캐비테이션 저항성($t_{50}$ 286min)이 Multi wall보다는 더 높은 것으로 관찰되었다. 나노 입자중에서 가격 및 캐비테이션 저항성을 감안하면 가장 최적의 나노 입자는 Fiber type의 Graphite로 관찰되었다. 도료의 작업성 평가에서 수동 작업에 의해 제작된 표면은 매끈한 표면을 가지고 있으나 Spray 작업에 의해 제작된 표면은 표면이 균일하지 않으며 Spray시 발생된 Dust가 표면에 고착된 형태로 관찰되었다.

• 한국재료학회지
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• 제25권11호
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• pp.602-606
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• 2015

Porous W with spherical and directionally aligned pores was fabricated by the combination of sacrificial fugitives and a freeze-drying process. Camphene slurries with powder mixtures of $WO_3$ and spherical PMMA of 20 vol% were frozen at $-25^{\circ}C$ and dried for the sublimation of the camphene. The green bodies were heat-treated at $400^{\circ}C$ for 2 h to decompose the PMMA; then, sintering was carried out at $1200^{\circ}C$ in a hydrogen atmosphere for 2 h. TGA and XRD analysis showed that the PMMA decomposed at about $400^{\circ}C$, and $WO_3$ was reduced to metallic W at $800^{\circ}C$ without any reaction phases. The sintered bodies with $WO_3$-PMMA contents of 15 and 20 vol% showed large pores with aligned direction and small pores in the internal walls of the large pores. The pore formation was discussed in terms of the solidication behavior of liquid camphene with solid particles. Spherical pores, formed by decomposition of PMMA, were observed in the sintered specimens. Also, microstructural observation revealed that struts between the small pores consisted of very fine particles with size of about 300 nm.

• 대기
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• 제22권2호
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• pp.175-186
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• 2012

In this study, we investigate the effects of elliptical shape of Asian dust particles on the estimation of aerosol optical depth by implementing T-matrix method into WRF/Chem Dust Model. The phase function calculated by assuming elliptical particle shape near $110{\sim}160^{\circ}$ of scattering angle showed about 20 times larger than that calculated by assuming spherical particle shape. Significant difference of extinction efficiency was found with an increase of size parameter and aspect ratio. From the simulations of two Asian dust events occurred on 1 April 2007 and 16 March 2010, we found that the difference of extinction efficiency between elliptical and spherical particle shape was about 5~8%. The aerosol optical depth calculated by assuming elliptical particle shape with 1.6, 1.4 and 1.2 of aspect ratio was about $4.0{\pm}0.5%$, $2.0{\pm}0.2%$, and $1.0{\pm}0.1%$ larger than those estimated by assuming spherical particle shape.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 하계학술대회 논문집
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• pp.217-220
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• 1991

Ni-Zn ferrite powders in the few hundred angstrum size range and up have been synthesized by a wet direct method. The coprecipitate were prepared by adding alkaline solution into the constituent metal ions solution. and subsequent calcined at various temperature. At 95, the particles were ultrafine spherical shaped particles of about 500(A) in diameter.

• 한국대기환경학회:학술대회논문집
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• 한국대기환경학회 2001년도 추계학술대회 논문집
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• pp.101-102
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• 2001

Monodisperse aerosols containing spherical particles of known size, shape and density are the most widely used to calibrate particle-size measuring instruments and to determine the effects of particle size on the sampling device. However, these tests are time-consuming because monodisperse aerosols with different particle sizes are generated and tested in a series of experiments. Polydisperse aerosols may be used to determine the calibration or to simulate equipment under controlled laboratory condition. (omitted)

• 한국재료학회지
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• 제17권3호
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• pp.167-172
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• 2007

The separation of the small colloidal particles from the mixture of two different sized particles using AC dielectrophoresis phenomenon was studied. The spherical mono-dispersed polystyrene particles dispersed in pure water were put into a perfusion chamber on a substrate, and AC electric fold was applied to the glass substrate with Au electrodes in 4 mm distance. The AC frequency was fixed at 1 kHz and the intensity of the field was varied from 25 V/cm to 160 V/cm. After applying the AC field, the degree of the chain formation that resulted from the particle movements by dielectrophoresis was observed by optical microscope. The mixture of the $1\;{\mu}m\;and\;5\;{\mu}m$ sized polystyrene particles at 0.5 vol% concentrations for each size was set in the dielectrophoresis conditions of 1 kHz and 100 V/cm. At this condition large $5\;{\mu}m$ sized polystyrene particles formed chains, on the contrary the $1\;{\mu}m$ sized polystyrene particles formed no chains. After water flowing for 20 min, it was found that small particles that were floating in the chamber had been removed by the water flowing.

• Journal of the Korean Physical Society
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• 제73권9호
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• pp.1334-1339
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• 2018

Spherical nickel ferrite nanoparticles were synthesized using the thermal decomposition method and coated with cetyl trimethyl ammonium bromide (CTAB) after the synthesis. Transmission electron microscopy images showed that the average diameter of the particles was 9.40 nm. The status of the CTAB-coating on the surface of the particles was checked using Fourier-transform infrared spectroscopy. Their hysteresis curve showed that the particles exhibited a superparamagnetic behavior. The $T_1$ and the $T_2$ relaxations of the nuclear spins were observed in aqueous solutions of the particles with different particles concentrations by using a magnetic resonance imaging (MRI) scanner, which showed that the $T_1$ and the $T_2$ relaxivities of the particles in water were $0.57mM^{-1}{\cdot}s^{-1}$ and $10.42mM^{-1}{\cdot}s^{-1}$, respectively. In addition, using an induction heating system, we evaluated their potentials for magnetic hyperthermia applications. The aqueous solution of the particles with a moderate concentration (smaller than 6.5 mg/mL) showed a saturation temperature larger than the hyperthermia target temperature of $42^{\circ}C$. These findings show that the CTAB-coated nickel ferrite particles are suitable for applications as $T_2$ contrast agents in MRI and heat generators in magnetic hyperthermia.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2002년도 International Meeting on Information Display
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• pp.788-791
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• 2002

The phosphors of high luminous efficiency for PDP application must have high purity, single phase, and dense surface. In this work, the polymeric reaction was applied to preparation of spherical phosphor by aerosol pyrolysis in order to enhance mechanical and optical characteristics. The red phosphor of (Y,Gd)$BO_3$:Eu was prepared from polymeric precursor, in which citric acid and ethylene glycol were used as ion carriers, i.e monomers. For enhancing the luminescence intensity and mechanical characteristics. optimum synthesizing condition were investigated through concentration of monomers, synthetic temperature. doped activator concentrations, and annealing process. The phosphors synthesized with monomers showed quite different morphology from those without monomers. It was observed that polymeric precursor made an effect on particle formation mechanism and status of particles surface. The resultant spherical phosphors show the comparable luminescent properties to the commercial product (product by Nichia co.). Also, they were observed to have the rigid surface.

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.229-235
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• 2000

The spherical silica powder was synthesized by varying the kinds of solvent and mixing energy in emulsion method. The stirring speed varied from 500 to 1000 r.p.m. at 5$0^{\circ}C$ for 2h. Toluene in benzyl groups and a series of alkanes were used as dispersant. The average size of spherical silica particles decreased with increasing the stirring speed and the chain length o solvents used in this work. The average size was controlled in the range of 134~28$\mu\textrm{m}$ by selecting a proper solvent and stirring speed. The optimum processing parameters were described in details.