• 한국세라믹학회지
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• 제21권2호
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• pp.165-173
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• 1984

It is desirable to establish reliable synthetic methods for electro-ceramic materials. To synthesize $SrTiO_3$ in this study direct solid state reactions and wet chemical processes were used. Previous study of $SrTiO_3$ synthesis included oxalated-method($SrTiO(C_2O_4)_2$.$4H_2O$) co-precipitation$(SrCO_3+TiO(OH)_2)$ and direct solid state reaction$(SrCO_3+TiO(OH)_2)$ The methods in question lead to intermediate inclusion during the reactions and less controllable in particle sizes of $SrTiO_3$. To obtain highly pure $SrTiO_3$ so-called "direct wet process method" was added in this investigation. In the study the "direct wet process" was for the first time applied to synthesize chemically pure and fine particle $SrTiO_3$. $SrCl_2$ and $TiCl_4$<\ulcornerTEX> at KOH solution at room temperature to 10$0^{\circ}C$ precipitated $SrTiO_3$ The particle size increased as temperature increased.mperature increased.

• 대한화장품학회지
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• 제22권2호
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• pp.52-69
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• 1996

Nano-Sized TiO$_2$ particles with diameter between 2 and 5 nm are synthesized in Water/Triton X-100/n-Hexane microemulsion. Particles show the amorphous structure and partially hydroxide form. The optical absorbance of particles appears at 250nm and band edge at 340nm. Gold metal is deposited on the surface of TiO$_2$ particles by reduction reaction of Au(III) ion with sodium hypophosphite. The size of gold-deposited particles is 20nm, and the optical absorbance appears at 270nm and at 550nm. So particles show the red color. The dense precipitation is formed by aggregation in the TiO$_2$ nano-sized particles of about 5nm size. But the bulky precipitation is formed by agglomeration phenomena in the gold-deposited particles of 20nm size. And also gold-deposited particles is easily dispersed by being re-dispersed in PEG/Water solution. This study has compared those things measuring the SPF characteristics of the cosmetics made of the synthesized particles. If the particle size is controlled appropriately, then the SPF value will be higher, or more colorless cosmetics will be made.

• 한국세라믹학회지
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• 제23권4호
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• pp.11-16
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• 1986

$BaTiO_3$ ceramics powder was prepared by coprecipitation method either in oxalic acid solution or in potassium hydroxide solution. Thermal decomposition of coprecipitated $BaTiO(C_2O_4)_2$.$4H_2O$ powder in oxalic acid solution was investigated by means of Themogravimetry Differential Thermal Analysis and X-ray Diffraction Analysis. Low temperature decomposition of coprecipitated $BaTiO(C_2O_4)_2$.$4H_2O$ caused narrow particle size distribution whereas high temperature decomposition caused fairly wide particle size distribution by partial sintering. As the reaction time increased the average particle size of coprecipitated $BaTiO_3$ powder in KOH solution was increased. The most narrow paticle size distribution was obtained when the coprecipi-tates were ripened for 4hrs.

• 한국세라믹학회지
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• 제41권11호
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• pp.842-850
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• 2004

BaO$_2$-TiO$_2$-환원제-입자제어제계에서 자전연소합성법을 이용한 BaTiO$_3$ 분말의 제조에 대하여 고찰하였다. 환원제로서 C, Mg를 사용하였고, 입자제어제로서 NaCl을 사용하였다. 자전연소합성법을 이용한 BaTiO$_3$ 분말의 제조에 있어 최적의 반응계에서 환원제의 종류와 농도, 입자제어제, 반응량의 변화에 따른 생성물의 영향을 조사하였다. 최적의 반응계 및 조성은 Ae반응 분위기에서 BaO$_2$+TiO$_2$+0.1Mg+0.2C+0.75NaCl이었다. 희석제로서 첨가된 NaCl은 연소온도의 조절 뿐 아니라 반응생성물의 입도를 제어하는 효과를 나타냄을 알 수 있었다. 최적의 조건에서 제조된 순수 BaTiO$_3$ 분말의 입도는 약 0.5 $mu extrm{m}$ 이하였으며, 반응량을 증가시킬수록 균일한 반응성을 나타내었다 제조된 BaTiO$_3$ 분말의 유전특성을 측정하기 위하여 130$0^{\circ}C$, 2시간동안 대기중에서 소결실험을 행하였고 이때 상온에서의 유전상수는 약 2290이었고, 큐리점(129$^{\circ}C$)에서의 유전상수는 약 13800을 나타내었다.

• 한국세라믹학회지
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• 제37권10호
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• pp.944-948
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• 2000

TiCl$_4$, 물 및 propanol의 혼합용액으로부터 가수분해하여 미립의 TiO$_2$분말을 제조할 때 HPC 첨가와 HPC 존재하에서 TiCl$_4$mole 농도 및 유기용매 처리를 했을 때 입자크기, 응집성 및 형태 등을 관찰하였다. HPC는 TiO$_2$합성시 steric dispersant로 작용하여 응집을 적게 하는 경향을 나타내었고 HPC를 첨가한 상태에서 TiCl$_4$의 mole 농도 변화는 입자크기에 크게 영향을 주었는데 TiCl$_4$mole 농도가 증가함에 따라 입자크기는 증가하였다. 또한 유기용제 처리는 분산 효과가 있었다.

• 한국입자에어로졸학회지
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• 제9권2호
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• pp.51-57
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• 2013

A graphene(GR)-$TiO_2$ composite was synthesized from colloidal mixture of graphene oxide(GO) nanosheets and $TiO_2$ nanoparticles by an aerosol assisted self-assembly. The morphology, specific surface area and pore size of asprepared GR-$TiO_2$ composite were characterized by FE-SEM, BET, and BJH respectively. The shape of GR-$TiO_2$ composite was spherical. The average particle size was 0.5-1 ${\mu}m$ in diameter and the pore diameter ranged 20-50 nm. Photovoltaic characteristics of a mixture of the GR-$TiO_2$ and $TiO_2$ nanoparticles were measured by a solar simulator under simulated solar light. The highest photoelectric conversion efficiency of the mixture photoanode was 5.1%, which was higher than that of $TiO_2$ photoanode.

• 한국재료학회지
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• 제22권7호
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• pp.352-357
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• 2012

$SnO_2$-mixed and Sn-doped $TiO_2$ nanoparticles were synthesized via a hydrothermal process. $SnO_2$-mixed $TiO_2$ nanoparticles prepared in a neutral condition consisted of anatase $TiO_2$ nanoparticles(diamond shape, ~25 nm) and cassiterite $SnO_2$ nanoparticles(spherical shape, ~10 nm). On the other hand, Sn-doped $TiO_2$ nanoparticles obtained under a high acidic condition showed a crystalline phase corresponding to rutile $TiO_2$. As the Sn content increased, the particle shape changed from rod-like(d~40 nm, 1~200 nm) to spherical(18 nm) with a decrease in the particle size. The peak shift in the XRD results and a change of the c-axis lattice parameter with the Sn content demonstrate that the $TiO_2$ in the rutile phase was doped with Sn. The photocatalytic activity of the $SnO_2$-mixed $TiO_2$ nanoparticles dramatically increased and then decreased when the $SnO_2$ content exceeded 4%. The increased photocatalytic activity is mainly attributed to the improved charge separation of the $TiO_2$ nanoparticles with the $SnO_2$. In the case of Sn-doped $TiO_2$ nanoparticles, the photocatalytic activity increased slightly with the Sn content due most likely to the larger energy bandgap caused by Sn-doping and the decrease in the particle size. The $SnO_2$-mixed $TiO_2$ nanoparticles generally exhibited higher photocatalytic activity than the Sn-doped $TiO_2$ nanoparticles. This was caused by the phase difference of $TiO_2$.

• 한국입자에어로졸학회지
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• 제7권3호
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• pp.79-85
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• 2011

Porous $TiO_2-SiO_2$ particles were synthesized by co-assembly of nanoparticles of $TiO_2$ and $SiO_2$ in evaporating aerosol droplets. Poly styrene latex (PSL) particles were employed as a template of porous particles. Flowrate of dispersion gas, weight ratio of $TiO_2/SiO_2$ and $SiO_2$ concentration in the precursor, and PSL size were chosen as process variables. The morphology, crystal structure, chemical bonding, and pore size distribution were analyzed by FE-SEM, XRD, FT-IR, BET. The morphology of porous $TiO_2-SiO_2$ particles was spherical and the average particle size range were from 1 to $10{\mu}m$. The particles were composed of meso and macro pores. The average particle diameter and pore volume of the as prepared particles were dependant on process variables. It was found that UV-Vis absorption of the porous particles was comparable with pure $TiO_2$ nanoparticles even though $TiO_2/SiO_2$ ratio is low in the porous particles.

• 분석과학
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• 제30권4호
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• pp.159-166
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• 2017

Exposure to UV light, i.e., UV-A (320-400 nm) or UV-B (290-320 nm) radiation, can cause skin cancer. Titanium dioxide ($TiO_2$) effectively disperses UV light. Therefore, it is used as a physical UV filter in many UV light blockers. Usually, the $TiO_2$ content in commercialized UV blockers is 25 % at most. To block UV-B, a chemical UV blocker, octyl-methoxy cinnamate (OMC) is used. OMC is commonly used in combination with $TiO_2$. In this study, $TiO_2$ and OMC were mixed in different proportions to produce UV blockers with different compositions. Also the changes in the sun protection factor (SPF) based on the composition and $TiO_2$ particle sizes were investigated. In order to analyze the $TiO_2$ particle size, dynamic light scattering (DLS) and asymmetrical flow field-flow fractionation (AsFlFFF) were used. The results showed that the SPF was influenced by the proportion of $TiO_2$ and OMC, where the proportion of $TiO_2$ induced a more significant influence. In addition, changes in the $TiO_2$ particle size based on the proportion of OMC were observed.

• 한국재료학회지
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• 제29권5호
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• pp.282-287
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• 2019

The photovoltaic properties of $TiO_2$ used for the electron transport layer in perovskite solar cells(PSCs) are compared according to the particle size. The PSCs are fabricated and prepared by employing 20 nm and 30 nm $TiO_2$ as well as a 1:1 mixture of these particles. To analyze the microstructure and pores of each $TiO_2$ layer, a field emission scanning electron microscope and the Brunauer-Emmett-Teller(BET) method are used. The absorbance and photovoltaic characteristic of the PSC device are examined over time using ultraviolet-visible-near-infrared spectroscopy and a solar simulator. The microstructural analysis shows that the $TiO_2$ shape and layer thicknesses are all similar, and the BET analysis results demonstrate that the size of $TiO_2$ and in surface pore size is very small. The results of the photovoltaic characterization show that the mean absorbance is similar, in a range of about 400-800 nm. However, the device employing 30 nm $TiO_2$ demonstrates the highest energy conversion efficiency(ECE) of 15.07 %. Furthermore, it is determined that all the ECEs decrease over time for the devices employing the respective types of $TiO_2$. Such differences in ECE based on particle size are due to differences in fill factor, which changes because of changes in interfacial resistance during electron movement owing to differences in the $TiO_2$ particle size, which is explained by a one-dimensional model of the electron path through various $TiO_2$ particles.