• 한국세라믹학회지
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• 제49권1호
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• pp.118-123
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• 2012

GDC20($Ce_{0.8}Gd_{0.2}O_{1.9}$) powder was synthesized from Ce and Gd nitrate solutions using ammonium carbonate($(NH_4)_2CO_3$) as a precipitant. Attrition-milling of the powder, which had been calcined at $700^{\circ}C$ for 4 h, decreased an average particle size of 2.2 ${\mu}m$ to 0.5 ${\mu}m$. The milled powder consisted of nano-sized spherical primary particles. Due to the excellent sinterability of the powder, sintering of the powder compacts for 4 h showed relative densities of 80% at 1000 $^{\circ}C$ and 96.5% at $1200^{\circ}C$, respectively. Densification was found to almost complete at $1300^{\circ}C$, resulting in a dense and homogeneous microstructure with a relative density of 99.5%. The grains of ~0.2 ${\mu}m$ in size at $1200^{\circ}C$ grew to ~1 ${\mu}m$ in size at $1300^{\circ}C$ as a result of a rapid grain growth.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1309-1310
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• 2006

High-purity and super-hard nano-polycrystalline diamond has been successfully synthesized by direct conversion from high-purity graphite under static pressures above 15 GPa and temperatures above $2300^{\circ}C$. This paper describes research findings on the formation mechanism of nano-structure and on the contributing factor leading to high hardness.

• 한국분말재료학회지
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• 제23권5호
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• pp.353-357
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• 2016

In this study, $TiO_2$ powders are synthesized from ammonium hexafluoride titanate (AHFT, $(NH_4)_2TiF_6$) as a precursor by heat treatment. First, we evaluate the physical properties of AHFT using X-ray diffraction (XRD), particle size analysis (PSA), thermogravimetric analysis (TGA), and field-emission scanning electron microscopy (FE-SEM). Then, to prepare the $TiO_2$ powders, is heat-treated at $300-1300^{\circ}C$ for 1 h. The ratio of anatase to rutile phase in $TiO_2$ is estimated by XRD. The anatase phase forms at $500^{\circ}C$ and phase transformation to the rutile phase occurs at $1200^{\circ}C$. Increase in the particle size is observed upon increasing the reaction temperature, and the phase ratio of the rutile phase is determined from a comparison with the calculated XRD data. Thus, we show that anatase and rutile $TiO_2$ powders could be synthesized using AHFT as a raw material, and the obtained data are utilized for developing a new process for producing high-quality $TiO_2$ powder.

• 한국세라믹학회지
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• 제42권12호
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• pp.808-815
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• 2005

[ $Bi_xCe_{l-x}O_{2-x/2}$ ](BD C : Bismuth Doped Ceria) powders with x = 0.1, 0.2, and 0.3 were synthesized using the Glycine Nitrate Process (GNP). They were then calcined at $500^{\circ}C$ for 2 hand sintered in a pellet or rod form at 900, 1000 or $1100^{\circ}C$ for 4 h for characterization as the alternative electrolyte material for intermediate temperature solid oxide fuel cells. The BDC powder consisted of a single phase of $CeO_2-Bi_2O_3$ solid solution in the as-synthesized state as well as in the as-calcined state with a mean powder size of 4.5nm in the former state and 6.5 - 10.1nm in the latter. On the contrary, the second phase of $\alpha-Bi_2O_3$ was observed to have been formed in the sinter with its amount increasing roughly with increasing temperature or $Bi_2O_3$ content. The BOC powder was superior in sinterability to other alternative electrolyte materials such as GDC, ScSZ, and LSGM with the minimum sintering temperature for a relative density of $95\%$ or larger as low as $1100^{\circ}C$. The ionic conductivity of BOC increased with $Bi_2O_3$ content and the maximum value of 0.119 S/cm was obtained at $800^{\circ}C$ for $Bi_{0.3}Ce_{0.7}O_{1.85}$.

• 한국분말재료학회지
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• 제27권1호
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• pp.14-24
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• 2020

In this work, the electrical explosion of wire in liquid and subsequent spark plasma sintering (SPS) was introduced for the fabrication of Ni-graphite nanocomposites. The fabricated composite exhibited good enhancements in mechanical properties, such as yield strength and hardness, but reduced the ductility in comparison with that of nickel. The as-synthesized Ni-graphite (5 vol.% graphite) nanocomposite exhibited a compressive yield strength of 275 MPa (about 1.6 times of SPS-processed monolithic nickel ~170 MPa) and elongation to failure ~22%. The hardness of Ni-graphite composite had a value of 135.46 HV, which is about 1.3 times higher than that of pure SPS-processed Ni (105.675 HV). In terms of processing, this work demonstrated that this processing route is a novel, simple, and low-cost method for the synthesis of nickel-graphite composites.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2005년도 International Meeting on Information Displayvol.II
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• pp.836-837
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• 2005

In order to enhance discharge efficiency of Plasma Display Panel (PDP), we used an electride as electron emission layer for PDP during PDP discharge process. As the electride used in this study, $12CaO7Al_2O_3$, has low work function, it is expected to yield high electron emission during glow discharge process. $12CaO7Al_2O_3$ powder was synthesized from $CaCO_3$ and $Al(OH)_3$ powder and Ca treated for realization of electride characteristics. The $12CaO7Al_2O_3$ powder was coated on the surface of dielectric layer of PDP and discharge characteristics of electride material were evaluated.

• 한국분말재료학회지
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• 제24권5호
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• pp.351-356
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• 2017

Tin dioxide nanoparticles are prepared using a newly developed synthesis method of plasma-assisted electrolysis. A high voltage is applied to the tin metal plate to apply a high pressure and temperature to the synthesized oxide layer on the metal surface, producing nanoparticles in a low concentration of sulfuric acid. The particle size, morphology, and size distribution is controlled by the concentration of electrolytes and frequency of the power supply. The as-prepared powder of tin dioxide nanoparticles is used to fabricate a gas sensor to investigate the potential application. The particle-based gas sensor exhibits a short response and recovery time. There is sensitivity to the reduction gas for the gas flowing at rates of 50, 250, and 500 ppm of $H_2S$ gas.

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.229-235
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• 2000

The spherical silica powder was synthesized by varying the kinds of solvent and mixing energy in emulsion method. The stirring speed varied from 500 to 1000 r.p.m. at 5$0^{\circ}C$ for 2h. Toluene in benzyl groups and a series of alkanes were used as dispersant. The average size of spherical silica particles decreased with increasing the stirring speed and the chain length o solvents used in this work. The average size was controlled in the range of 134~28$\mu\textrm{m}$ by selecting a proper solvent and stirring speed. The optimum processing parameters were described in details.

• 한국분말재료학회지
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• 제18권1호
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• pp.73-77
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• 2011

$Y(OH)_3$ nanowires were synthesized by a hydrothermal reaction of metallic Y with aqueous solution of LiOH. The morphology and the size of the nanowires changed with varying the volume of the LiOH solution inside the autoclave. $Y(OH)_3$ nanowires transformed to $Y_2O_3$ by a subsequent heat-treatment without morphological change. By a proper control of hydrothermal reaction parameter and heat-treatment, the yield of pure $Y_2O_3$ nanowires up to 97% was attained.

• 한국분말재료학회지
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• 제27권2호
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• pp.154-163
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• 2020

Fluorescent nanoparticles are characterized by their unique properties such as luminescence, optical transparency, and sensitivity to various chemical environments. For example, semiconductor nanocrystals (quantum dots), which are nanophosphors doped with transition metal or rare earth ions, can be classified as fluorescent nanoparticles. Tuning their optical and physico-chemical properties can be carried out by considering and taking advantage of nanoscale effects. For instance, quantum confinement causes a much higher fluorescence with nanoparticles than with their bulk counterparts. Recently, various types of fluorescent nanoparticles have been synthesized to extend their applications to other fields. In this study, State-of-the-art fluorescent nanoparticles are reviewed with emphasis on their analytical and anti-counterfeiting applications and synthesis processes. Moreover, the fundamental principles behind the exceptional properties of fluorescent nanoparticles are discussed.