• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.337-341
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• 2012

Mechanochemical processing (MCP) involves several high-energy collisions of powder particles with the milling media and results in the increased reactivity/sinterability of powder. The present paper shows results of mechanochemical processing (MCP) of silicon nitride powder mixture with the relevant sintering additives. The effects of MCP were studied by structural changes of powder particles themselves as well as by the resulting sintering/densification ability. It has been found that MCP significantly enhances reactivity and sinterability of the resultant material: silicon nitride ceramics could be pressureless sintered at $1500^{\circ}C$. Nevertheless, a degree of a silicon nitride crystal lattice and powder particle destruction (amorphization) as detected by XRD studies, is limited by the specific threshold. If that value is crossed then particle's surface damage effects are prevailing thus severe evaporation overdominates mass transport at elevated temperature. It is discussed that the cross-solid interaction between particles of various chemical composition, triggered by many different factors during mechanochemical processing, including a short-range diffusion in silicon nitride particles after collisions with other types of particles plays more important role in enhanced reactivity of tested compositions than amorphization of the crystal lattice itself. Controlled deagglomeration of $Si_3N_4$ particles during the course of high-energy milling was also considered.

• Bulletin of the Korean Chemical Society
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• v.29 no.10
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• pp.1965-1968
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• 2008

The effects of carbon-coated silicon/graphite (Si/Gr.) composite anode on the electrochemical properties were investigated. The nanosized silicon particle shows a good cycling performance with a reasonable value of the first reversible capacity as compared with microsized silicon particle. The carbon-coated silicon/graphite composite powders have been prepared by pyrolysis method under argon/10 wt% propylene gas flow at $700{^{\circ}C}$ for 7 h. Transmission electron microscopy (TEM) analysis indicates that the carbon layer thickness of 5 nm was coated uniformly onto the surface silicon powder. It is confirmed that the insertion of lithium ions change the crystalline silicon phase into the amorphous phase by X-ray diffraction (XRD) analysis. The carbon-coated composite silicon/graphite anode shows excellent cycling performance with a reversible value of 700 mAh/g. The superior electrochemical characteristics are attributed to the enhanced electronic conductivity and low volume change of silicon powder during cycling by carbon coating.

• Clean Technology
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• v.19 no.1
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• pp.44-50
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• 2013

Tin-based materials for lithium ion battery have been proposed as new anode candidates owing to their higher specific capacity and relatively high lithium insertion potential. Tin-based materials have been extensively studied as possible replacements for carbon anodes in lithium ion batteries. However, the large volume expansion results in severe particle cracking with loss of electrical contact, giving irreversible capacity losses which prevent the widespread use of tin-based materials in lithium batteries. So remaining studies of tin-based materials are alleviating volume expansion and improving cycle performance. In this work, $SnO_2-SiO_2$ composites were manufactured with sol-gel method to overcome their volume expansion. Carbon was coated with 10 vol% propylene gas. The characteristics of active material and the effect of heat treatment were investigated with TG/DTA, XRD, SEM and FT-IR. Electrochemical characteristics of these composites were measured with CR2032 type coin cells. Carbon coated $SnO_2-SiO_2$at $300^{\circ}C$ heat treatment showed the best electrochemical performance.

• Journal of the Korean Ceramic Society
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• v.42 no.5 s.276
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• pp.333-337
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• 2005

In order to improve the performance of green emitting phosphors for plasma display panel, the $Zn_2SiO_4:Mn,Al$ phosphors were synthesized using sol-gel technique and studied using SEM and VUV photoluminescence spectrometer. pH values of the starting solutions (pH = 0.5$\~$2.34) were controled by HCl as the catalysis of hydrolysis and wet gels were dried at $80^{\circ}C$ and $120^{\circ}C$, respectively. We investigated the effects of pH and drying temperatures during sol-gel processes. The results indicated that the phosphor prepared at pH = 1 showed the maximum emission intensity in both drying conditions and the effect of pH of the starting solution on morphology were increased with particle size as HCl and phosphor dried at high temperature showed more spherical and smaller particles than at low.

• Journal of the Korean Ceramic Society
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• v.42 no.2 s.273
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• pp.127-131
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• 2005

We examined the effect of low temperature heat-treatment on the optical properties of the photonic crystals self-assembled using a monodispersed spherical $SiO_2$ nanoparticle. When the heat treatment temperature increased, the reflectance peak, which is induced by the photonic band gap, moved to a shorter wavelength direction, and the peak intensity of Fabry-Perot fringes also increased. The highest reflectance peak intensity was obtained in the sample heat-treated at $250\~300^{\circ}C$. The heat-treatment reduced the average particle size and the quantity of defects, and increased the packing density of the photonic crystal.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.428-433
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• 2000

The consolidation behavior of multicomponent particles prepared by the flame hydrolysis deposition process is examined to identify the effects of Si substrate temperature. To fabricate multi-component particles, a vapor-phase ternary mixture of $SiCl_4(100 cc/min),\;BCl_3(30cc/min)\;and\;POCl_3,(5cc/min)$ was fed into a coflow diffusion oxy-hydrogen flame burner. The doped silica soot bodies were deposited on silicon substrates under various deposition conditions. The surface temperature of the substrate was measured by an infrared thermometer. Changes in the chemical states of the doped silica soot bodies were examined by FT-IR(Fourier-transformed infrared spectroscopy). The deposited particles on the substrate were heated at $1300^{\circ}C$ for 3h in a furnace at a heating rate of 10K/min. Si-O-B bending peak has been found when surface temperature exceeds $720^{\circ}C$. Correspondingly, the case with substrate temperatures above loot produced good consolidation result.

• Transactions on Electrical and Electronic Materials
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• v.4 no.2
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• pp.20-23
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• 2003

Piezoelectric powder with the composition of PbTiO$_3$-PbZrO$_3$-Pb(Mn$\_$1/3/Nb$\_$2/3/)O$_3$ and small particle size of 0.3 $\mu\textrm{m}$ was investigated for low-temperature firing of PZT thick films. PbTiO$_3$-PbZrO$_3$-Pb(Mn$\_$1/3/Nb$\_$2/3)O$_3$ ceramics showed dense microstructure and superior piezoelectric properties, electromechanical coupling factor (k$\_$p/) of 0.501 and piezoelectric constant (d$\_$33/) of 224. The PZT paste was made of the powder and organic vehicles, and screen-printed on Pt(450nm)/YSZ(110nm)/SiO$_2$(300nm)/Si substrates and fired at 800∼900$^{\circ}C$. Any interface reaction between the PZT thick film and the bottom electrode was not observed in the PZT thick films. The PZT thick film fired at 800$^{\circ}C$ showed moderate electrical properties, the remanent polarization(p$\_$r/) of 16.0 ${\mu}$C/$\textrm{cm}^2$, the coercive field(E$\_$c/) of 36.7 ㎸/cm, and dielectric constant ($\varepsilon$$\_$r/) of 531. Low-temperature sinterable piezoelectric composition and high activity of fine particles reduced the sintering temperature of the thick film. This PZT thick film could be utilized for piezoelectric microactuators or microsensors that require Si micromachining technology.

• Journal of the Korean Magnetics Society
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• v.18 no.1
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• pp.43-47
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• 2008

[ $ZnO-Bi_2O_3-Al_2O_3-B_2O_3-SiO_2$ ] nano-glass has been prepared by sol-gel method. The mean particle size was 60.3 nm with narrow size distribution. The nano-galss has been used as a sintering aid for the densification of the NiZnCu ferrites. The ferrite was sintered with nano-glass sintering aids at $840{\sim}900^{\circ}C$, 2 h and the initial permeability, quality factor, density, and saturation magnetization were also measured. The initial permeability of 0.5 wt% nano-glass added toroidal sample for NiZnCu ferrites sintered at $900^{\circ}C$ was 193.3 at 1 MHz. The initial permeability and saturation magnetization were increased with increasing annealing temperature. As a result, $ZnO-Bi_2O_3-Al_2O_3-B_2O_3-SiO_2$ nano-glass systems were found to be useful as sintering aids for multilayer chip inductors.

• Journal of the Korea Safety Management & Science
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• v.9 no.6
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• pp.197-204
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• 2007

Ceramic pigments were developed by using 4 kinds of Brass scraps. Each Brass scraps were mixed with same weight-ratio of Husk ash, and fine-ground by Rotate ring mill(RRG-120, Armstech industrial. co. Ltd, Korea) after firing at $900^{\circ}C$, $1000^{\circ}C$ and $1100^{\circ}C$. As a result, analysis of particle size of synthetic pigments by particle size analyser, they are $3{\mu}m$ as average. The resulting pigments were characterized by using XRD, FT-IR, SEM Structure of the crystals are Zn2SiO4,, and ZnO, Cu2O, CuO, and cristobalite are existed and particles' shape are plate or needle. As a result of analysis of chemical composition by XRF, synthetic pigments have high SiO2 and CuO content and have SnO2, ZnO and NiO, too. 1wt%, 3wt% and 5wt% pigments were added in each lime glaze, lime-barium glaze and lime-magnesia glaze, and fired at oxidation and reducing atmosphere to figure hue in glazes out. As a result of analysis of color, chroma and brightness by UV, colors of glazes fired at oxidation atmosphere turned into green from sky blue, and colors of glazes fired at reducing atmosphere turned into pink and red.

• Journal of the Korean Ceramic Society
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• v.42 no.10 s.281
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• pp.672-677
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• 2005

In this study we prepared the Sr-ferrite powders and magnet by a molten salt method using the (NaCl+KCl) salt mixture. Starting materials of $Fe_{2}$$O_{3}$ and Sr$Co_{3}$ were mixed as the molar ratio of 5.70:1, and 0.08 mol$ \% $ $Al_{2}$$O_{3}$, 0.10 mo1$ \% $ Si$O_{2}$ and 0.12 mo1$ \% $ CaO were added as additives. Sr-ferrite powders synthesized at the reaction temperatures of 800$\∼$1200$ ^{\circ}C $ showed the typical M-type hexagonal ferrite phase, and hexagonal plate-like morphology with uniform distribution of 1$\∼$3 $\mu$m particle size. The bulk density of the sintered Sr-ferrite magnet prepared with powders by the molten salt method showed the maximum density of 4.82 g/$cm^{3}$ at the sintering temperature of 1200$^{\circ}C $. The maxima of remanent flux density (Br, 45 emu/g) and coercive force (iHc, 3.75 kOe) occurred at the sintering temperatures of 1150$ ^{\circ}C$ and 1200$^{\circ}C $.