• Journal of Korea Foundry Society
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• v.10 no.5
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• pp.435-443
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• 1990

By using the centrifugal atomization, which is one of the rapid solidification processes, Al-5,10wt%Pb alloys which are monotectic alloys were melted at 150K over two liquid phase line in the phase diagram. The melted alloy was poured on the rotating disk, being made into atomized powders, and then the solidified microstructure and morphology of the powder were investigated. This study converted the produced powders into strips by strained powder rolling. According to sintering temperature, the microstructure and hardness were investigated. The solidified structure of the powders were almost cellular dendritic structure. Pb particles ($2.0-3.0{\mu}m$) were fairl distributed in the Al matrix. Powder shapes were irregular. Rolling property and the compacting was good, respectively, because of increasing mechanical interlocking and surface area in the small size powders. With increasing temperature, the boundarys of powders were in porous form due to the diffusion. Pb particles which were surrounding the pores were inverse-segregated at the surface of the powders. With increasing of sintering temperature, the hardness of the powders and the strips decreased. In particular rolling-strip, the hardness abruptly decreased due to the release of work-hardening.

• Journal of Powder Materials
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• v.14 no.2 s.61
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• pp.145-149
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• 2007

Nanocrystalline transient aluminas (${\gamma}$-alumina) were coated on core particles (${\gamma}$-alumina) by a carbonate precipitation and thermal-assisted combustion, which is environmentally friend. The ammonium aluminum carbonate hydroxide (AACH) as a precursor for coating of transient aluminas was produced from precipitation reaction of ammonium aluminum sulfate and ammonium hydrogen carbonate. The crystalline size and morphology of the synthetic, AACH, were greatly dependent on pH and temperature. AACH with a size of 5 nm was coated on the core alumina particle at pH 9. whereas rod shape and large agglomerates were coated at pH 8 and 11, respectively. The AACH was tightly bonded coated on the core particle due to formation of surface complexes by the adsorption of carbonates, hydroxyl and ammonia groups on the surface of the core alumina powder. The synthetic precursor successfully converted to amorphous- and ${\gamma}$-alumina phase at low temperature through decomposition of surface complexes and thermal-assisted phase transformation.

• Applied Chemistry for Engineering
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• v.18 no.6
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• pp.650-653
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• 2007

$SnO_2$-doped $TiO_2$ powder was obtained from tin (IV) bis(acetylacetonate) dichloride and titanium diisopropoxide bis(acetylacetonate) with quinacridone as the dye sensitizer molecule. The structural changes of the reaction mixture were monitored by fourier transform infrared (FT-IR) spectroscopy. The morphology and microstructure of gel powder were studied by field-emission scanning electron microscopy (FE-SEM) and X-ray diffractometry (XRD). The photocatalytic activity of these powders with the anatase structure was investigated by using indigo carmine solution as a test dye

• Applied Chemistry for Engineering
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• v.17 no.5
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• pp.561-564
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• 2006

$SnO_{2}$-doped anatase type $TiO_{2}$ powder was prepared by the polymerization complex route from tin(IV) bis (acetylacetonate) dichloride, titanium diisopropoxide bis (acetylacetonate) and polyethylene glycol (PEG) as a complexing agent. The structural changes of reaction mixture were monitored by fourier transform infarared (FT-IR) spectroscopy. The microstructure and morphology of gel powder were studied by field-emission scanning electron microscopy (FE-SEM) and X-ray diffractometry (XRD). The photocatalytic activity of these powders with the anatase structure was investigated by using indigo carmine solution.

• Journal of the Korean Ceramic Society
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• v.26 no.6
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• pp.737-746
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• 1989

After Ba-ferrite powders synthesized hydrothermally and its heated powders were dissolved partially with HCl treatment time, the BaO/Fe2O3 mole ratio of dissolved solutions and powders were measured by AAS, also, lattice constants, particle morphology and magnetic properties in HCl treated, heated and no-heated Ba-ferrite powders were abtained by means of XRD, SEM and VSM, respectively. From above analysis results, the effect of Ba/Fe mole ration in suspension(as starting material) on the BaO/Fe2O3 composition and particle characteristics of products were investigated, and the effect of heat treatment on magnetic properties of products examined. The composition, lattice constant and crystal phase of products depend on the Ba/Fe mole ratio in suspension. Ba content in surface or outer part of Ba-ferrite powder is higher than inner and heterogeneous, and the excess Ba ions in the inner part of particle move into the outer by heating, so that the mole ratio of BaO/Fe2O3 in the more jinner approaches more to the stoichiometric composition 1 : 6. The crystallinity, coercivity and saturation magnetization of products are increased by heat treatment, and the heat-treated samples synthesized hydrothermally in lower temperature are appreciated to have better powder characteristics.

• Journal of Powder Materials
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• v.11 no.2
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• pp.124-129
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• 2004

Nanosized WC and WC-Co powders were synthesised by chemical vapor condensation(CVC) process using the pyrolysis of tungsten hexacarbonyl(W(CO)$_6$) and cobalt octacarbonyl(Co$_2$(CO)$_8$). The microstructural changes and phase evolution of the CVC powders during post heat-treatment were studied using the XRD, FE-SEM, TEM, and ICP-MS. CVC powders were consisted of the loosely agglomerated sub-stoichimetric WC$_{1-x}$ and the long-chain Co nanopowders. The sub-stochiometric CVC WC and WC-Co powders were carburized using the mixture gas of CH$_4$-H$_2$ in the temperature range of 730-85$0^{\circ}C$. Carbon content of CVC powder controlled by the gas phase carburization at 85$0^{\circ}C$ was well matched with the theoretical carbon sioichiometry of WC, 6.13 wt％. During the gas phase carburization, the particle size of WC increased from 20 nm to 40 nm and the long chain structure of Co powders disappeared.

• Journal of Powder Materials
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• v.17 no.1
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• pp.7-12
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• 2010

In this work, effect of various process-control agents (PCAs) on the mechanical alloying of amorphous alloy of $Al_{85}Y_8Ni_5Co_2$ has been investigated. The dependence of the particle shape, size and crystallization behavior of the amorphous alloy powders on the type of PCAs and their concentrations was investigated by using X-ray diffraction, field-emission scanning electron microscopy and differential scanning calorimetry. It was found that the additive of toluene could affect positively the amorphization and thermally induced crystallization processes, as well as the size refinement, morphology and particle-size distribution of as-milled powders in comparison with alloy obtained without PCA.

• Journal of Powder Materials
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• v.15 no.2
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• pp.136-141
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• 2008

The mechanochemical process were employed to prepare the red phosphors (Y,Gd)$BO_3:Eu^{3+}$. The main factors affecting particle size, particle distribution, and luminescent properties of the product were investigated in details. Particles sized around 200-600 nm are formed after intensive milling. The phosphors were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectrum. Results revealed that phosphors with different morphology, small particle size and high luminescence intensity could be obtained by mechanochemical process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.515-515
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• 2007

$LiCoO_2$ powder was synthesized by Sol-Gel method using inorganic materials. The starting materials, $CH_3COOLi^*2H_2O\;and\;Co(CH_3COO)_2{^*}4H_2O$, were mixed in the atomic ratio Li/Co of 1 and dissolved in i-propanol with acetic acid. The solution was dried for gelation, and finally obtained the pre-powder. The pre-powder were studied by thermal analysis. Based on the TGA result, heat treatment was performed at various temperature(500 to $800^{\circ}C$) for 2h in air atmosphere. The crystal structure, morphology, electrochemical property were carried out using XRD, SEM, cyclic voltammetry(CV).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.339-339
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• 2007

Metal coating on ceramic powder has long been attracting interest for various applications such as superconductor where the brittle nature of high temperature ceramic superconductor was complemented by silver coating and metalloceramics where mechanical property improvement was achieved via electroless plating. More recently it has become of great interest in embedded passive device applications since metal coating on ceramic particles may result in the enhancement of the dielectric properties of ceramic-polymer composite capacitors. In our study, nickel ion-containing solution was used for coating commercial capacitor-grade $BaTiO_3$ powder. After filtering process, the powder was dried and heat-treated in 5% forming gas at $900^{\circ}C$. XRD and TEM were utilized for the observation of crystallization behavior and morphology of the particles. It was found that the nickel coating characteristics were strongly dependent on the several parameters and processing variables, such as starting $BaTiO_3$ particle size, nickel source, solution chemistry, coating temperature and time. In this paper, the effects of these variables on the coating characteristics will be presented in some detail.