• Journal of the Korean Applied Science and Technology
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• v.35 no.4
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• pp.1057-1072
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• 2018

In this study, micro-sized $CeO_2$ particles were synthesized by spray pyrolysis, and EG(ethylene glycol) and CA(citric acid) as organic additives were added to obtain hollow and porous particle during spray pyrolysis, and characteristics of obtained ceria were investigated according to the amount of added organic additives. Spray pyrolysis, postheat and ball-milling were combined to give 6 paths. $CeO_2$ nano-sized particle was obtained by the path which has sequence of Spray Pyrolysis with 0.5 M of EG and CA${\rightarrow}$Post-heat${\rightarrow}$Ball-milling${\rightarrow}$Post-heat among 6 paths. The average particle size(24 nm with standard deviation of 3.8 nm) of $CeO_2$ nano-sized particle by TEM analysis is close to the primary particle size(20 nm) which was calculated by Debye-Scherrer equation. To investigate the morphological characteristics and structure of the synthesized nanoparticle powders, SEM(Scanning Electron Microscopy), XRD(X-Ray Diffractometer) and TEM(Transmission Electron Microscopy) were used.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.30 no.2
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• pp.181-187
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• 2004

Preparations of mesoporous materials using various templates and their applicability have been intensively investigated for many years. We studied on synthesizing mesoporous Ti02 with pores in which sensitive compounds having weak physico-chemical properties such as thermal or UV irradiation and low solubility in solvent are trapped. Prior to trapping OMC in the pores of mesoporous titania, OMC was nano-emulsified in O/W system using Lecithin. Thereafter the OMC was trapped in the pores of mesoporous titania using sol-gel method. Main focus of this work is to prepare OMC-trapped mesoporous titania and to trace the stability and solubility of nano-emulsified OMC in the pores of mesoporous titania, and compared with that of mesoporous silica. OMC-trapped mesoporous Inorganic-Organic hybrid titania showed higher factors in sun protecting and a skin penetration phenomenon was reduced.

• Journal of Powder Materials
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• v.12 no.4 s.51
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• pp.273-278
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• 2005

Nanostructured TiN/$TiB_2$/$TiSi_2$ and TiN/$TiB_2$/$Ti_5Si_2$ composite powders have been prepared by mechanochemical reaction from mixtures of Ti, BN, and $Si_3N_4$ powders. The raw materials have reacted to form a uniform mixture of TiN, $TiB_2$ and $TiSi_2$ or $Ti_5Si_3$ depending on the amount of $Si_3N_4$ used in the starting mixtures, and the reaction proceeded through so-called mechanically activated self-sustaining reaction (MSR). Fine TiN and $TiB_2$ crystallites less than a few tens of nanometer were homogeneously dispersed in the amorphous $TiSi_2$ or $Ti_5Si_3$ matrix after milling for 12 hours. These amorphous matrices became crystalline phases after annealing at high temperatures as expected, but the original microstructure did not change significantly.

• Journal of Powder Materials
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• v.26 no.3
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• pp.237-242
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• 2019

In this study, ultrasonic spray pyrolysis combined with salt-assisted decomposition, a process that adds sodium nitrate ($NaNO_3$) into a titanium precursor solution, is used to synthesize nanosized titanium dioxide ($TiO_2$) particles. The added $NaNO_3$ prevents the agglomeration of the primary nanoparticles in the pyrolysis process. The nanoparticles are obtained after a washing process, removing $NaNO_3$ and NaF from the secondary particles, which consist of the salts and $TiO_2$ nanoparticles. The effects of pyrolysis temperature on the size, crystallographic characteristics, and bandgap energy of the synthesized nanoparticles are systematically investigated. The synthesized $TiO_2$ nanoparticles have a size of approximately 2-10 nm a bandgap energy of 3.1-3.25 eV, depending on the synthetic temperature. These differences in properties affect the photocatalytic activities of the synthesized $TiO_2$ nanoparticles.

• Journal of Powder Materials
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• v.26 no.1
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• pp.34-39
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• 2019

Current synthesis processes for titanium dioxide ($TiO_2$) nanoparticles require expensive precursors or templates as well as complex steps and long reaction times. In addition, these processes produce highly agglomerated nanoparticles. In this study, we demonstrate a simple and continuous approach to synthesize $TiO_2$ nanoparticles by a salt-assisted ultrasonic spray pyrolysis method. We also investigate the effect of salt content in a precursor solution on the morphology and size of synthesized products. The synthesized $TiO_2$ nanoparticles are systematically characterized by X-ray diffraction, transmission electron micrograph, and UV-Vis spectroscopy. These nanoparticles appear to have a single anatase phase and a uniform particle-size distribution with an average particle size of approximately 10 nm. By extrapolating the plots of the transformed Kubelka-Munk function versus the absorbed light energy, we determine that the energy band gap of the synthesized $TiO_2$ nanoparticles is 3.25 eV.

• Journal of Powder Materials
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• v.28 no.2
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• pp.127-133
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• 2021

One-dimensional (1D) piezoelectric nanostructures are attractive candidates for energy generation because of their excellent piezoelectric properties attributed to their high aspect ratios and large surface areas. Vertically grown BaTiO₃ nanotube (NT) arrays on conducting substrates are intensively studied because they can be easily synthesized with excellent uniformity and anisotropic orientation. In this study, we demonstrate the synthesis of 1D BaTiO₃ NT arrays on a conductive Ti substrate by electrochemical anodization and sequential hydrothermal reactions. Subsequently, we explore the effect of hydrothermal reaction conditions on the piezoelectric energy conversion efficiency of the BaTiO₃ NT arrays. Vertically aligned TiO₂ NT arrays, which act as the initial template, are converted into BaTiO₃ NT arrays using hydrothermal reaction with various concentrations of the Ba source and reaction times. To validate the electrical output performance of the BaTiO₃ NT arrays, we measure the electricity generated from each NT array packaged with a conductive metal foil and epoxy under mechanical pushings. The generated output voltage signals from the BaTiO₃ NT arrays increase with increasing concentration of the Ba source and reaction time. These results provide a new strategy for fabricating advanced 1D piezoelectric nanostructures by demonstrating the correlation between hydrothermal reaction conditions and piezoelectric output performance.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.7
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• pp.455-461
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• 2018

Boron nitride (BN) nanofibers were fabricated using BN nanoparticles (70 nm) by electrospinning. Morphologies such as the diameter and density of the BN nanofibers are strongly influenced by the viscosity and dispersion state of the precursor solution. In this study, the precursor solution was prepared by ball milling BN nanoparticles and polyvinylpyrrolidone (PVP, Mw~1,300,000) in ethanol, which was electrospun and then calcined to produce BN fibers. High-quality BN nanofibers were well fabricated at a BN concentration of 15 wt% with their diameters in the range of 500 nm to 800 nm; the viscosity of the precursor solution was $400mPa{\cdot}S$. The calcination of the as-electrospun BN fibers seemed to be completed by holding them at $350^{\circ}C$ for 2 h considering the TGA data. The morphologies and phases of the BN fibers were investigated by scanning electron microscopy (SEM) and X-ray diffractometry (XRD), respectively; Fourier transform infrared (FT-IR) was also used for structure analysis.

• Journal of the Korean Magnetics Society
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• v.21 no.5
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• pp.157-162
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• 2011

The effect of ferrous/ferric molar ratio and precipitants on the formation of nano size magnetite particle was investigated by coprecipitation method. Ferrous sulfate and ferric sulfate were used as iron sources and sodium hydroxide and ammonium hydroxide was used as a precipitant. Single phase magnetite was synthesized with all of experiment conditions (ferrous/ferric molar ratios and precipitants). Particle size was smaller, and particle size distribution was narrower when NaOH was used than $NH_4OH$ was used. The crystallinity and particle size was increased and narrower particle size distribution with increasing molar ratio ferrous/ferric sulfate with the same precipitant. Super paramagnetism could be obtained at all of experiment conditions. The highest saturation magnetization (72 emu/g) was obtained when the ferrous/ferric molar ratio was 2.5 and precipitant was used $NH_4OH$.

• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.789-794
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• 2002

In this study, nano-sized Si-C-N precursor powders were synthesized by Chemical Vapor Condensation Method(CVC) using TMS(Tetramethylsilane: $Si(CH_3)_4$), $NH_3$ and $H_2$ gases under the various reaction conditions of the reaction temperature, TMS/$NH_3$ ratio and TMS/$H_2$ ratio. XRD and FESEM were used to analysis the crystalline phase and the average particle size of the synthesized powders. It was found that the obtained powders under the considering conditions were all spherical amorphous powder with the particle size of 87∼130 nm. The particle size was decreased as the reaction temperature increased and TMS/$NH_3$ and TMS/$H_2$ ratio decreased. As the results of EA analysis, it was found that the synthesized powders had been formed the powders composed of Si, N, C and H. Through FT-IR results, it was found that the synthesized powders were Si-C-N precursor powders with Si-C, Si-N and C-N bonds.

• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.25-29
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• 2012

$TiO_2$ nanotubes are prepared from rutile prticles via an alkaline hydrothermal synthesis and the consequent heat treatment at $300{\sim}500^{\circ}C$. The physical and electrochemical properties of the $TiO_2$ nanotubes are characterized for use as a anode material of rechargeable lithium battery. In particular, the microscale dusts as an impurity component occurred in the purification step after the hydrothermal reaction are completely removed to yield $TiO_2$ nanotube with a higher specific surface area and more obvious crystalline phases. As the annealing temperature increases, the specific surface area is slightly decreased due to some aggregation between the isotropically dispersed nanotubes. Highest initial discharge capacity of 250 mAh $g^{-1}$ is achieved for the $TiO_2$ nanotube annealed at $300^{\circ}C$, whereas the $400^{\circ}C$ $TiO_2$ nanotube shows the superior cycle performance and high-rate capability.