• Korean Journal of Materials Research
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• v.23 no.4
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• pp.246-249
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• 2013

Nano-sized ${\beta}$-SiC nanoparticles were synthesized combined with a sol-gel process and a carbothermal process. TEOS and carbon black were used as starting materials for the silicon source and carbon source, respectively. $SiO_2$ nanoparticles were synthesized using a sol-gel technique (Stober process) combined with hydrolysis and condensation. The size of the particles could be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) within the micro-emulsion. The average particle size and morphology of synthesized silicon dioxide was about 100nm and spherical, respectively. The average particles size and morphology of the used carbon black powders was about 20nm and spherical, respectively. The molar ratio of silicon dioxide and carbon black was fixed to 1:3 in the preparation of each combination. $SiO_2$ and carbon black powders were mixed in ethanol and ball-milled for 12 h. After mixing, the slurries were dried at $80^{\circ}C$ in an oven. The dried powder mixtures were placed in alumina crucibles and synthesized in a tube furnace at $1400{\sim}1500^{\circ}C$ for 4 h with a heating rate of $10^{\circ}C$/min under flowing Ar gas (160 cc/min) and furnace cooling down to room temperature. SiC nanoparticles were characterized by XRD, TEM, and SAED. The XRD results showed that high purity beta silicon carbide with excellent crystallinity was synthesized. TEM revealed that the powders are spherical shape nanoparticles with diameters ranging from 15 to 30 nm with a narrow distribution.

• Journal of the Korean Ceramic Society
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• v.54 no.3
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• pp.211-216
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• 2017

ZnO nanopowder was synthesized using a relatively facile and convenient glycol process. ZnO nanopowder was successfully synthesized at temperatures as low as $125^{\circ}C$ using zinc acetate as the Zn source and 1,4-butanediol as the solvent. Then, the effects of water content on the growth process and morphological evolution of ZnO powders were investigated using 1,4-butanediol and water as binary solvent mixtures. Using pure 1,4-butanediol at a temperature above $125^{\circ}C$, the prepared hexagonal ZnO nanopowder exhibited a quasi-spherical shape with average crystalline size of approximately 30 - 50 nm. It is also demonstrated that the morphology of ZnO powders can be controlled by the addition of various water content in 1,4-butanediol. With increasing water content, the morphologies of the ZnO powders changed sequentially from quasi-spherical to hexagonal plate and pyramid, and finally to hexagonal prismatic with a pyramidal tip. A sharp peak centered at 384 nm in the UV region and a weak broad peak in the visible region between 450 and 700 nm were shown in the room temperature PL spectra of the ZnO synthesized using the glycol process, regardless of the addition of water, suggesting that ZnO nanopowders with the best crystallinity were obtained under these conditions.

• Korean Journal of Materials Research
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• v.24 no.7
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• pp.351-356
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• 2014

A spherical $Sr_4Al_{14}O_{25}:Eu^{2+}$ phosphor for use in white-light-emitting diodes was synthesized using a liquid-state reaction with two precipitation stages. For the formation of phosphor from a precursor, the calcination temperature was $1,100^{\circ}C$. The particle morphology of the phosphor was changed by controlling the processing conditions. The synthesized phosphor particles were spherical with a narrow size-distribution and had mono-dispersity. Upon excitation at 395 nm, the phosphor exhibited an emission band centered at 497 nm, corresponding to the $4f^65d{\rightarrow}4f^7$ electronic transitions of $Eu^{2+}$. The critical quenching-concentration of $Eu^{2+}$ in the synthesized $Sr_4Al_{14}O_{25}:Eu^{2+}$ phosphor was 5 mol%. A phosphor-converted LED was fabricated by the combination of the optimized spherical phosphor and a near-UV 390 nm LED chip. When this pc-LED was operated under various forward-bias currents at room temperature, the pc-LED exhibited a bright blue-green emission band, and high color-stability against changes in input power. Accordingly, the prepared spherical phosphor appears to be an excellent candidate for white LED applications.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.4
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• pp.501-508
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• 1996

Strontium barium niobate powders were prepared by NaCl-KCl molten salt, and reaction process and morphology change of strontium barium niobate were investigated as a function of reaction temperature, time, and amount of molten salt. With increasing the reaction temperature and time, the reacted fraction was increased and the morphology of powder was changed from lumpy shape into meedle-like shape. With increasing the amount of molten salt, reacted fraction was increased rapidly, but the morphology of powder was changed from needle-like shape into spherical shape. Strontium barium niobate powder, over 90 % in fraction reacted, was obtained from the reaction conditions at $1000^{\circ}C$ for small flux ratio (=1) and at $650^{\circ}C$ for large flux ratio (=4).

• Advances in nano research
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• v.4 no.4
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• pp.295-307
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• 2016

The present research work reports a low temperature ($40^{\circ}C$) chemical precipitation technique for synthesizing hydroxyapatite (HAp) nanoparticles of spherical morphology through a simple reaction of calcium nitrate tetrahydrate and di-ammonium hydrogen phosphate at pH 11. The crystallinity of the single-phase nanoparticles could be improved by calcinating at $600^{\circ}C$ in air. Thermogravimetric and differential thermal analysis (TG-DTA) revealed the synthesized HAp is stable up to $1200^{\circ}C$. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies confirmed the formation of spherical nanoparticles with average size of $23.15{\pm}2.56nm$ and Ca/P ratio of 1.70. Brunauer-Emmett-Teller (BET) isotherm of the nanoparticles revealed their porous structure with average pore size of about 24.47 nm and average surface area of $78.4m2g^{-1}$. Fourier transform infrared spectroscopy (FTIR) was used to confirm the formation of P-O, OH, C-O chemical bonds. Cytotoxicity and MTT assay on MG63 osteogenic cell lines revealed nontoxic bioactive nature of the synthesized HAp nanoparticles.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2133-2139
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• 2012

A new system using $TiO_2$ (nano-sized, band-gap 3.14 eV)-impregnated spherical ZnS (micro-sized, band-gap 2.73 eV) nano/micro-composites (Ti 0.001, 0.005, 0.01, and 0.05 mol %/ZnS) was developed to enhance the production of hydrogen from methanol/water splitting. The ZnS particles in a spherical morphology with a diameter of about 2-4 mm which can absorb around 455 nm were prepared by hydrothermal method. This material was used as a photocatalyst with loading by nano-sized $TiO_2$ (20-30 nm) for hydrogen production. The evolution of $H_2$ from methanol/water (1:1) photo splitting over the $TiO_2$/ZnS composite in the liquid system was enhanced, compared with that over pure $TiO_2$ and ZnS. In particular, 1.2 mmol of $H_2$ gas was produced after 12 h when 0.005 mol % $TiO_2$/ZnS nano/micro-composite was used. On the basis of cyclic voltammeter (CV) and UV-visible spectrums results, the high photoactivity was attributed to the larger band gap and the lower LUMO in the $TiO_2$/ZnS composite, due to the decreased recombination between the excited electrons and holes.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.16-17
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• 2006

In order to obtain spherical fine powder, we have developed a new method of high-pressure water atomization system using swirl water jet with the swirl angle $(\omega)$. The effect of nozzle apex angle $(\theta)$ upon the morphology of atomized powders was investigated. Molten copper was atomized by this method, with $\omega=0.2$ rad (swirl water jet) and $\omega=0$ rad (conical water jet). It was found that the median diameter $(D_{50})$ of atomized powders decreased with decreasing $(\theta)$ down to 0.35 rad in each $\omega$, but under ${\theta}<\;0.35$ rad, $D_{50}$ increased abruptly with decreasing $\theta$ for $\omega=0$ rad, while it was still decreased with decreasing $(\theta)$ for $\omega=0.2$ rad.

• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.191-195
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• 2016

Among the lithium metal oxides for hybrid-capacity, $Li_4Ti_5O_{12}(LTO)$ is an emerging electrode material as zero-stain material in volume change during the with the charging and discharging processes. However, LTO has a limitation of low ionic and electronic conductivity. To enhance the ionic and electronic properties of $Li_4Ti_5O_{12}(LTO)$, we synthesized the spherical LTO/CNT composite by sol-gel process for hybrid capacitors. CNT interconnection networks between CNT-LTO particles enhanced electronic conductivity and electrochemical charging/discharging properties. All of the LTO samples was observed to show the spinel structure and spherical morphology with the diameter of $5{\sim}10{\mu}m$. Especially, spherical LTO/CNT composite of the CNT-3 wt% showed the enhanced capacity from 110 mAh/g to 140 mAh/g at 10 C.

• Macromolecular Research
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• v.16 no.6
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• pp.539-543
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• 2008

Many natural proteins self-assemble in complex ways, either to fulfill their biological function or introduce particular properties, such as high strength and toughness. We report the morphological transition in water from a spherical to rod-like shape of Bombyx mori silk fibroin by reducing the pH. Transmission electron microscopy, scanning electron microscopy, and dynamic light scattering were used to characterize the dilute solutions of silk fibroin in an aqueous environment, and provide direct visualization of the transformation of spherical micelles at pH 6.8 to nanofibrils at pH 4.8. This change in morphology occurred as a result of the stretching entropy due to the formation of $\beta$-sheets, which was analyzed using circular dichroism spectroscopy. This study demonstrates the self-assembly of silk fibroin as a function of pH.

• Current Research on Agriculture and Life Sciences
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• v.32 no.3
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• pp.125-130
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• 2014

This study used transmission electron microscopy (TEM) to investigate the micro-morphological features of two formaldehyde to urea (F/U) mole ratio liquid urea-formaldehyde (UF) resins with three hardener levels as a function of the curing time. The micro-morphological features of the liquid UF resins were characterized after different curing times. As a result, the TEM examination revealed the presence of globular/nodular structures in both liquid UF resins, while spherical particles were only visible in the low F/U mole ratio resins. The high F/U mole ratio liquid UF resins also showed extensive particle coalescence after adding the hardener, along with the appearance of complex filamentous networks. When the resins were cured with a higher amount of hardener and longer curing time, the spherical particles disappeared. For the low mole UF resins, the particles tended to coalesce with a higher amount of hardener and longer curing time, although discrete spherical particles were still observed in some regions. This is the first report on the distinct features of the crystal structures in low F/U mole ratio UF resins cured with 5% hardener and after 0.5 h of curing time. In conclusion, the present results indicate that the crystal structures of low F/U mole ratio UF resins are formed during the curing process.