• Journal of the Korean Ceramic Society
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• v.46 no.2
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• pp.189-199
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• 2009

The Powder characteristics and sintering behavior of $SiO_2$ coated $BaTiO_3$ were studied. $BaTiO_3$ powders were synthesized by the liquid mix method developed by Pechini, and silica coating was prepared by alkoxide hydrolysis method with TEOS and ethanol. The particle size of the $BaTiO_3$ powders was 35 nm and the thickness of the $SiO_2$ coating layer was 5 nm. As the $SiO_2$ content increased, the $SiO_2$ layers improved the powder dispersion by increasing electrostatic repulsion between the $BaTiO_3$ particles. Effects of MgO coating on microstructure and dielectric properties of $BaTiO_3$ have been studied compared with mechanically MgO mixed $BaTiO_3$. MgO coated $BaTiO_3$ particles were prepared by a homogeneous precipitation method using $MgCl_2\cdot 6H_2O$ and urea. MgO coated $BaTiO_3$ exhibited homogeneous microstructure compared with mixed samples. XRD analysis revealed that Mg substitution for the Ti site in the MgO mixed sample was much greater than in the coated one. Electrical properties of MgO mixed and coated $BaTiO_3$ were affected by the diffusion behavior of Mg in $BaTiO_3$ lattice.

• Proceedings of the Materials Research Society of Korea Conference
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• 2002.05a
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• pp.147-147
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• 2002

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2004.04a
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• pp.51-52
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• 2004

• Proceedings of the Korean Ceranic Society Conference
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• 2004.04b
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• pp.37.2-37.2
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• 2004

• Journal of Environmental Health Sciences
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• v.18 no.1
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• pp.1-5
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• 1992

A study was performed to measure the heavy metal concentrations of suspended particles in iron castings during February, 1990. The heavy metal concentrations were analyzed using patricles atomic absorption spectrophotometer. The results were as fellows 1. The concentrations of suspended paticles by casting process were at furnace 4.19mg/m$^{3}$ at pouring 2.93mg/m$^{3}$ at nonferrous furnace 3.90mg/m$^{3}$, at molding 1.17mg/m$^{3}$, jung ja 2.23mg/m$^{3}$, desanding 5.42mg/m$^{3}$, sand treatment 4.82mg/m$^{3}$, finishing 1,20mg/m$^{3}$. 2. Among the total of 8 iron casting workplaces, the concentrations Fe of furnace was 0.36mg/m$^{3}$, Cu of nonferrous furnace 0.02mg/m$^{3}$, Pb of pouring 0.02mg/m$^{3}$, Cr of desanding 0.01mg/m$^{3}$ and Mn of furnace 0.03mg/m$^{3}$.

• Journal of Environmental Health Sciences
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• v.32 no.6
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• pp.543-555
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• 2006

During a twenty-day period in 2005, a nine-stage Andersen cascade impactor was used to determine the seasonal size distribution of atmospheric particles and its inorganic ion species sampled for 24hr in Iksan city, located southwest of the Korean peninsula. Samples were analyzed for major water-soluble ion species using Dionex-100 ion chromatograph. Average fine and coarse mass concentrations of atmospheric particles were, respectively, 31.4 and $82.6{\mu}g\;m^{-3}$ in spring and 35.8 and $73.4{\mu}g\;m^{-3}$ in fall-winter during the sampling period of 2005, while measurements of 69.8 and 9.9 were obtained in the sampling period of summer, The size distribution of particulate mass concentration during the non-Asian dust period was generally bimodal, whereas the size distribution of particulate mass concentration during the Asian dust period was unimodal due to the significant increase of coarse particles, which originated from long-range transport of soil dust particles from loess regions of the Asian continent. Among ionic species, $SO{_4}^{2-},\;NH{_4}^+,\;K^+$ were mainly distributed in fine particles due to their characteristics of emission sources and gas-to-particle conversion, while $Na^+,\;Mg^{2+}\;and\;Ca^{2+}$ were dominantly in coarse particles. However, $NO_3{^-}\;and\;Cl^-$ were distributed in both coarse particles and fine particles. Although $SO{_4}^{2-}$ was mainly distributed in fine particles, the size distributions of $SO{_4}^{2-}$ in coarse mode were significantly increased during the Asian dust events compared to those during the non-Asian dust period. $Ca^{2+}$ showed the most abundant species in the atmospheric particles during the Asian dust period. $NH{_4}^+$ was found to mainly exist as $(NH_4)_2SO_4$ in fine particles.

• Korean Journal of Materials Research
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• v.15 no.8
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• pp.496-502
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• 2005

Green-light emitting $BaMgAl_{10}O_{19}:Mn^{2+}$ (BAM:Mn) phosphor particles were prepared by spray Pyrolysis. The effect of reactor temperature and flow rate of carrier gas in the spray Pyrolysis on the morphology, crystallinity and photoluminescence characteristics under vacuum ultraviolet were investigated. The morphology of the as-Prepared Particles obtained by spray Pyrolysis had spherical shape and non-aggregation characteristics regardless of the reactor temperature. The spherical shape of the as-prepared Particles obtained by spray pyrolysis at low temperature disappeared after Post-treatment. On the other hand the as-Prepared Particles obtained by spray Pyrolysis at $1600^{\circ}C$ maintained spherical shape and non-aggregation characteristics after post-treatment at $1400^{\circ}C$ for 3 h under reducing atmosphere. The BAM:Mn Phosphor Particles Prepared by spray Pyrolysis at different reactor temperatures had pure crystal structure and high photoluminescence intensities under vacuum ultraviolet after post-treatment. BAM:Mn phosphor particles prepared by spray Pyrolysis at low How rate of carrier gas had complete spherical shape and filed morphology and high photoluminescence intensity after post-treatment under reducing atmosphere.

• Korean Journal of Materials Research
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• v.22 no.3
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• pp.136-139
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• 2012

Magnetic nanoparticles for ferromagnetic fluids and magnetorheological fluids were prepared by chemical coprecipitation and mechanical milling, respectively. The surface-treated particles were dispersed at various weight ratios into a medium of polyethylene glycol. In order to evaluate the elastic modulus of the fluids, ultrasonic pulse velocities were measured with an ultrasonic test using transducers of 5MHz and 2.25MHz. The ultrasonic signals were only available with a transducer of 2.25 MHz at fluid concentrations of 5 mg/ml and lower. In the case of applying transducers over 2.25 MHz and concentrations over 5 mg/ml to the fluids, it was impossible to observe effective ultrasonic signals due to an excessive scattering of the pulses by the dispersed particles. Elastic moduli of the magnetorheological fluids were 5.44 GPa and 6.13 GPa with concentrations of 25 mg/ml and 50 mg/ml, respectively; these values were higher by 40% than the values of 4.04 GPa and 4.28 GPa of ferromagnetic fluids at the same concentrations. As for the effect of an external magnetic field on these dilute fluids, the ultrasonic signals were positioned in a very similar way, which was probably due to insufficient arrangement of the particles even though the reflection energy of the ultrasonic waves apparently increased.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.132-139
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• 1995

Tnermomechanical treatment consisting of homogenizing, hot and warm rolling were introduced to Al-MgCu-Mn alloys for obtaining superplasticity. The factors affecting the superplasticity of the alloys were investigated by optical and transmission electron microscopy. Large particles which had not been decomposed during homogenizing treatments remained stable in the hot and warm rolling processes. These particles were a source of cavitation and poor elongation in superplastic deformation. On the other hand, fine precipitates were produced during thermomechanical processing, and resulted in improvement of superplasticity by stabilizing microstructure. Two-step homogenizing and air cooling process was more effective than onestep homogenizing and furance cooling process in removing microsegregations and producing fine particles.

• Journal of Powder Materials
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• v.16 no.1
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• pp.63-67
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• 2009

In order to investigate the effect of rapid solidification on the microstructure and the mechanical properties of Al-Zn-Mg system alloys, water atomization was carried out, since the water atomization beared the highest solidification rate among the atomization processes. The as atomized alloy powders consisted of fine grains less than 4 ${\mu}m$ in diameter, and the second particles were not detected on XRD. The microstructure as solidified was maintained even after the spark plasma sintering at the heating rate of 50 K/min. On the other hand, lower rate of 20 K/min induced a formation of $MgZn_2$ particles, resulting in strengthening of the matrix. The density was almost constant at the temperature above 698K. The sintering temperature above 698K had no effect on the strength of the sintered materials.