• Macromolecular Research
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• v.16 no.5
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• pp.399-403
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• 2008

Monodisperse, micron-sized, hybrid particles having a core-shell structure were prepared by coating the surface of poly(methyl methacrylate)(PMMA) microspheres with silica and by copolymerizing acrylamide (AAm) to supply the hydrogen bonding effect by means of the amide groups. Tetraethoxysilane (TEOS) was then slowly dropped onto the medium under certain conditions. Because of the hydrogen bonding between the amide of the PMMA particles and the hydroxyl group of the hydrolyzed silanol, a silica shell was generated on the PMMA core particles. The morphology of the hybrid particles was investigated with transmission (TEM) and scanning (SEM) electron microscopy as a function of the medium conditions and the amount of TEOS. Improved thermal properties were observed by TGA analysis.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.570-573
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• 1999

High brightness (Y$_{x}$/Gd$_{1-x}$ )$_2$O$_3$:Eu Phosphor Particles were directly Prepared in the spray Pyrolysis by adding flux materials such as LiCl and HBO$_3$. The (Y$_{x}$/Gd$_{1-x}$ )$_2$O$_3$:Eu particles prepared from solution with flux material had higher PL (photoluminescence) intensities than those prepared from solution without flux. In the spray pyrolysis, the flux acts as promoter of the growth of crystallite and activation of doping material as in the solid state reaction method. Additionally, the flux improved PL intensity of (Y$_{x}$/Gd$_{1-x}$ )$_2$O$_3$:Eu phosphor particles by densifying the internal structure and eliminating the defect existing inside and surface of (Y$_{x}$/Gd$_{1-x}$ )$_2$O$_3$:Eu phosphor particles.r particles.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1172-1177
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• 2004

The evolution of incipient soot particles has been examined by high resolution electron microscopy (HRTEM) and elemental analyzer in ethylene-air inverse diffusion flames. Laser Induced Incandescence(LII) and laser scattering methods were introduced for examining the change of soot volume fraction and morphological properties in combustion generated soot qualitatively. Soot particles, collected by thermophoretic sampling were analyzed by using HRTEM to examine the nano structure of precursor particles. HRTEM micrographs apparently reveal a transformation of condensed phase of semitransparent tar-like material into precursor particles with relatively distinct boundary and crystalline which looks like regular layer structures. During this evolution histories C/H analysis was also performed to estimate the chemical evolution of precursor particles. The changes of C/H ratio of soot particles with respect to residence time can be divided into two parts: one is a very slowly increasing regime where tar-like materials are transformed into precursor particles (inception process) the other is an increasing region with constant rate where surface growth affects the increase of C/H ratio dominantly (surface growth region). These results provide a clear picture of a transition to mature soot from precursor materials.

• Journal of the Korean Society of Combustion
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• v.9 no.2
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• pp.38-44
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• 2004

The evolution of incipient soot particles has been examined by high resolution electron microscopy (HRTEM) and elemental analyzer in ethylene-air inverse diffusion flames. Laser Induced Incandescence(LII) and laser scattering methods were introduced for examining the soot volume fraction and morphological properties in combustion generated soot qualitatively. Soot particles, collected by thermophoretic sampling, were analyzed by using HRTEM to examine the nano structure of precursor particles. HRTEM micrographs apparently reveal a transformation of condensed phase of semitransparent tar-like material into precursor particles with relatively distinct boundary and crystalline which looks like regular layer structures. During this evolution histories, C/H analysis was also performed to estimate the chemical evolution of precursor particles. The changes of C/H ratio of soot particles with respect to residence time can be divided into two parts: one is a very slowly increasing regime where tar-like materials are transformed into precursor particles (inception process) the other is an increasing region with constant rate where surface growth affects the increase of C/H ratio dominantly (surface growth process). These results provide a clear picture of a transition to mature soot from precursor materials.

• Journal of Powder Materials
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• v.24 no.5
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• pp.384-388
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• 2017

The effect of the mixing method on the characteristics of hybrid-structure W powder with nano and micro sizes is investigated. Fine $WO_3$ powders with sizes of ${\sim}0.6{\mu}m$, prepared by ball milling for 10 h, are mixed with pure W powder with sizes of $12{\mu}m$ by various mixing process. In the case of simple mixing with ball-milled $WO_3$ and micro sized W powders, $WO_3$ particles are locally present in the form of agglomerates in the surface of large W powders, but in the case of ball milling, a relatively uniform distribution of $WO_3$ particles is exhibited. The microstructural observation reveals that the ball milled $WO_3$ powder, heat-treated at $750^{\circ}C$ for 1 h in a hydrogen atmosphere, is fine W particles of ~200 nm or less. The powder mixture prepared by simple mixing and hydrogen reduction exhibits the formation of coarse W particles with agglomeration of the micro sized W powder on the surface. Conversely, in the powder mixture fabricated by ball milling and hydrogen reduction, a uniform distribution of fine W particles forming nano-micro sized hybrid structure is observed.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.1
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• pp.55-59
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• 2022

In this paper, we compared the electric field and absorptance of nano particles in nanostructures by amplifying the electric field around the nanoparticles through plasmon resonance and comparing the structure that can increase the absorptance with the nanostructure by using the Finite Different Time Domain (FDTD) simulation. In addition, the width of the nanostructure was adjusted to 240 nm ~ 300 nm, and the light absorptance rate was higher as the gap between the particles was short. In addition, a study was conducted on the formation of nanoparticles and nanostructures on the surface through UV imprint. In order to form particles in the structure, the nano particles were first arranged in the mold used for the fabrication of the structure using spray coating, and then fabricated through UV imprinting. The nanostructure and particles were formed together by scanning electron microscopy.

• Journal of Korea Foundry Society
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• v.13 no.4
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• pp.369-381
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• 1993

Aluminum alloy(AC8A) matrix composites reinforced with SiC particles(10% in vol.) were fabricated by Centrifugal Spray Deposition(CSD) process. The microstructures were investigated in order to evaluate both the mixing mode between aluminum matrix and SiC particles, and the effect of SiC particles on the cooling behaviours of droplets during flight and preforms deposited. A non-continuum mathematical calculation was performed to explain and to quantify the evolution of microstructures in the droplets and preforms deposited. Conclusions obtained are as follows; 1. The powders produced by CSD process showed, in general, ligament type, and more than 60% of the powders produced were about 300 to 850 um in size. 2. AC8A droplets solidified during flight showed fine dendritic structure, but AC8A droplets mixed with SiC particles showed fine equiaxed grain structure, and eutectic silicon were formed to crystallize granularly between fine aluminum grains. 3. SiC particles seem to act as a nucleation sites for pro-eutectic silicon during solidification of AC8A alloy. 4. The microstructure of composite powders formed by CSD process showed particle embedded type, and resulted in dispersed type microstructure in preforms deposited. 5. The pro-eutectic silicon crystallized granularly between fine aluminum grains seem to prohibit grains from growth during spray deposition process. 6. The interfacial reactions between aluminum matrix and SiC particles were not observed from the deposit performs and the solidified droplets. 7. The continuum model seem to be useful in connecting the processing parameters with the resultant microstructures. From these results, it was concluded that the fabrication of aluminum matrix composites reinforced homogeneously with SiC particles was possible.

• Current Optics and Photonics
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• v.5 no.4
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• pp.450-457
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• 2021

Upconversion (UC) properties of Y₂O₃:Ho³⁺/Yb³⁺ spherical particles synthesized by spray pyrolysis were investigated by changing the dopant concentration and calcination temperature. Citric acid (CA), ethylene glycol (EG) and N, N-dimethylformamide (DMF) were used to control the microstructure of Y₂O₃:Ho³⁺/Yb³⁺ particles. In terms of achieving the highest UC green emission intensity, the optimal concentrations of Ho³⁺ and Yb³⁺ were found to be 0.3% and 3.0%, respectively. In addition, the UC intensity of Y₂O₃:Ho³⁺/Yb³⁺ showed a linear relationship with the crystallite size. The use of organic additives allows Y₂O₃:Ho³⁺/Yb³⁺ particles to have a spherical and dense structure, resulting in significantly reducing the surface area while maintaining high crystallinity. As a result, the UC emission intensity of Y₂O₃:Ho³⁺/Yb³⁺ particles having a dense structure showed the UC emission intensity about 3.8 times higher than that of hollow particles prepared without organic additives. From those results, when Y₂O₃:Ho³⁺/Yb³⁺ particles are prepared by the spray pyrolysis process, the use of the CA/EG/DMF mixtures as organic additives has been suggested as an effective way to substantially increase the UC emission intensity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.867-876
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• 2003

The Lagrangian dispersion of fluid particles in inhomogeneous turbulence is investigated by a direct numerical simulation of turbulent channel flow. Four points Hermite interpolation in the homogeneous direction and Chebyshev polynomials in the inhomogeneous direction is adopted to simulate the fluid particle dispersion. An inhomogeneity of Lagrangian statistics in turbulent boundary layer is investigated by releasing many particles at several different wall-normal locations and tracking those particles. The fluid particle dispersions and Lagrangian structure functions of velocity are scaled by the Kolmogorov similarity. The auto-correlations of velocity and acceleration are shown at the different releasing locations. Effect of initial particle location on the dispersion is analyzed by the probability density function at the several downstreams and time instants.

• Journal of the Korean Applied Science and Technology
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• v.20 no.1
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• pp.27-32
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• 2003

The core-shell latex particles were prepared by sequential emulsion polymerization of alkyl methacrylate and styrene(ST) by using an water-soluble initiator(APS) after preparing monomer pre-emulsion in the presence of an anionic surfactant(SDBS). In organic/organic core-shell polymerization, the pre-emulsion method, which minimized required quantity of sulfactant, has been used to increase the conversion rate and the stability of core-shell latex particles as well as to reduce the formation of secondary particle that cause problems of soap-free emulsion during shell polymerization. We used several methods to observe the core-shell structure. The core-shell structure was studied by measuring pH change during hydrolysis by NaOH, glass transition temperature($T_g$) by differential scanning calorimeter(DSC), morphology of latex by transmission electron microscope(TEM) and change of particle size and distribution by a particle analyzer.