• Korean Journal of Materials Research
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• v.8 no.7
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• pp.601-606
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• 1998

The $SrTi0_3$:Al, Pr red phosphors were prepared by solid state reaction method. Phosphor preparation parameters such as sintering temperature and time were optimized for the photoluminescence(PU intensity and the cathodoluminescence(CL) intensity. Powder samples showed the characteristic X-ray diffraction patterns of the perovskite structure and the average particle size of 3~5/$\mu\textrm{m}$ for particle size distribution(PSD) analysis. Also, scanning electron microscopy for the powder samples showed that the particles are reasonably crystallized with spherical shape. Especially, higher low voltage CL properties of $SrTi0_3$:Al, Pr phosphors than commercial $Y_2O_3$:Eu phosphors are expected to be applied for a low voltage field emission display(FED).

• Elastomers and Composites
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• v.47 no.4
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• pp.318-328
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• 2012

In this study, the one-component curable polyurethane resin was manufactured using blocked isocyanate and hybrid technology. To prepare the one-component curable hybrid polyurethane, silica hybrids including hydroxyl group was synthesized, and the size, shape and distribution of hybrid particle in polyurethane resin were confirmed. Then the dissociation property, mechanical property and molding property of blocked isocyanate were investigated. The dissociation property of blocked isocyanate in one-component curable polyurethane became better as the heating temperature and treatment time increased. The synthesized silica hybrid had spherical appearance and size of 23~27 nm in diameter, and it was observed that the hybrid particles were homogeneously distributed in polyurethane structure. In the case of hybrid polyurethane, the mechanical property, anti-abrasion and thermal property were higher than those of general polyurethane, and it was observed that the mechanical property was maintained when the plasticizer was introduced.

• Applied Chemistry for Engineering
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• v.17 no.2
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• pp.132-137
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• 2006

Polyurethane acrylate hybrid emulsions were prepared by seeded polymerization techniques. In the synthesis, seeded polyurethane dispersion containing a carboxylic group was used to endow hydrophilicity to the hybrid emulsion and various acrylates such as methyl methacrylate (MMA), 2-hydroxy ethylmethacrylate (2-HEMA), n-butyl acrylate (n-BA) and acrylic acid (AAc) were used to endow hydrophobicity. The particle size and distribution of various emulsion particles such as polyurethane acrylate hybrid emulsion, polyurethane dispersion homopolymer, acrylate emulsion, and physical blending emulsion were measured by a particle size analyzer. The average particle size of hybrid emulsion was greater than physical blending emulsion. And tensile strength, 100% modulus, elongation, and swelling properties of the polyurethane acrylate hybrid emulsion were studied and compared with those of polyurethane homopolymer, acrylate emulsion, and physically blended compositor, respectively. To improve chemical and physical resistance, this paper review a melamine hardener and compares it for effects on the physical properties of cured coating.

• Journal of the Korean Magnetics Society
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• v.15 no.5
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• pp.282-286
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• 2005

Ni-Cu-Zn ferrites were prepared by the co-precipitation and ferrite microwave absorbers on low temperature sintering were investigated in this work. The properties of its microwave absorbing and physical were analyzed into variations of Ni addition, calcination temperature, sintering temperature. From the analysis of X-ray diffraction patterns, we can see that all the particles have only a single phase spinel structure. In addition, the powders particle size distribution obtained the nano size. By increasing the Ni additive, the permeability of the powders was decreased and the loss factor increased at sintering temperature $1100^{\circ}C$. Also, we considered that it can used high frequency rage. We found that the $(Ni_{0.7}Cu_{0.2}Zn_{0.1}O)_{1.02}(Fe_{2}O_3)_{0.98}$ appeared microwave absorbing properties better than other composition.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1947-1955
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• 2013

The purpose of this paper is to present an photoelasticity technique for measuring the displacement and stress distribution in particle assembly subjected to shallow foundation loading. Photoelastic measurement technique was employed to visualize the force transmission of a particle assembly. A model assembly bounded by a steel frame was built by stacking bi-dimensional circular particles made of polycarbonate elastomer. Each particle was coated by a thin photoelastic sheet so that the force transmission represented by bright light stripes can be visualized. In a contacted particle, both magnitude and orientation of principal stress difference can also be measured via the photoelasticity technique. The different distributions of the contact stresses at the initial loading and near the failure were quantitatively compared. The photoelastic patterns and displacement fields observed in the pre-failure state disappears immediately after the buckling of confined force chains.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.4
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• pp.169-173
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• 2008

$Eu^{3+}$ and $Bi^{3+}$ co-doped $YVO_4$ phosphors were produced by a microwave heating process. When the microwave heating method was synthesized,. the particle size was very small and the particles tended to agglomerate. However, as the heating time increased, the particle size increased and the agglomeration decreased. The emission spectrum exhibited a weak band for $^5D_0{\longrightarrow}^7F_1$ at 594.91 and 602.3 nm and strong sharp peaks at 616.7 and 620.0 nm due to the $^5D_0{\longrightarrow}^7F_2$ transition of $Eu^{3+}$. Microwave heating synthesis can provide a product without long time heating as well as good homogeneous distribution of activators.

• Atmosphere
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• v.15 no.3
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• pp.149-153
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• 2005

A balloon-borne Optical Particle Counter (hereafter "OPC Sonde"), which was developed by the atmospheric research group of Nagoya University, is used for getting the information of vertical profile of particle size and concentration in Anmyeon ($36^{\circ}32^{\prime}N$ $126^{\circ}19^{\prime}E$) on 18 March 2005. A range of five different particle sizes is shown in the vertical profile of aerosol number density estimated from the OPC Sonde. It was found that small size particles have vertically larger aerosol number density than relatively big ones. For all size ranges the vertical aerosol number density shows a decreased pattern as the altitude becomes higher. The aerosol number density of $0.3{\sim}0.5{\mu}m$, $0.5{\sim}0.8{\mu}m$, $0.8{\sim}1.2{\mu}m$ size ranges at the 10km height, which is the tropopause approximately, are $1,000,000ea/m^3$, $100,000ea/m^3$, $10,000ea/m^3$ respectively. The data of OPC Sonde are also compared with the data of PM10 $\beta$-ray) and Micro Pulse Lidar which are operating at Korea Global Atmosphere Watch Observatory in Anmyeon.

• Applied Chemistry for Engineering
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• v.25 no.6
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• pp.607-612
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• 2014

The physical properties of mercaptoundecanoic-acid layer formed on gold surfaces, which may affect the distribution of either gold particles adsorbed to the zirconium dioxide surface or vice versa, were investigated. To conduct this investigation, the surface forces were measured between the surfaces with respect to the salt concentration and pH value using atomic force microscope (AFM). The forces were quantitatively converted by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to the surface potential and charge density of surfaces. The converted-value dependence on the salt concentration and pH was described with the law of mass action, and the dependence was consistent with the theoretical prediction. It was found that the mercaptoundecanoic-acid layer had higher values for the surface charge densities and potentials than the $ZrO_2$ surfaces, which may be attributed to the ionized-functional-groups of the mercaptoundecanoic-acid layer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.4
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• pp.290-297
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• 2016

A two-phase Large Eddy Simulation(LES) has been conducted to investigate breakup and atomization of a liquid jet in a cross turbulent flow in a rectangular duct. Gas-droplet two-phase flow was solved by a coupled Eulerian-Lagrangian method which tracks every individual particles. Effects of liquid breakup models, sub-grid scale models, and a order of spatial discretization was investigated. The penetration depth in cross flow was comparable with experimental data by varying breakup model and LES scheme. SMD(Sauter Mean Diameter) distribution downstream of jet was analyzed.

• Journal of the Korean Ceramic Society
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• v.34 no.10
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• pp.1083-1091
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• 1997

As one of the chemical powder fabrication methods, the powder preparation method by using oxalate has the following advantages; (1) easy to control the chemical stoichiometry, (2) easy to fabricate homogeneous and fine particles, and (3) easy to be thermaly decomposed at low temperature. In the present study, the initial morphology and size distribution of the powder were controlled and the homogeniaty was improved. By carefully controlling the pH with NH4OH, the Bi(Pb)-Sr-Ca-Cu-O superconducting powders were prepared and investigated for their properties. The microstructures and the superconducting properties of the pelletized samples were investigated. Also, the microstructures and electrical properties of the samples prepared by tape casting method were investigated. The fabricated powders were spherical with less than 400 nm, but most of them were agglomerated to be 1~3 ${\mu}{\textrm}{m}$ in size. The critical temperature of the pelletized sample annealed at 84$0^{\circ}C$ for 72 hours in air was 110K. And the critical currents of annealed samples in air prepared by tape casting process for 24 hours and 72 hours were 0.6 A (Jc=600A/$\textrm{cm}^2$) and 1.9A (Jc=1, 900A/$\textrm{cm}^2$) respectively.