• Journal of the Korean Ceramic Society
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• v.46 no.2
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• pp.189-199
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• 2009

The Powder characteristics and sintering behavior of $SiO_2$ coated $BaTiO_3$ were studied. $BaTiO_3$ powders were synthesized by the liquid mix method developed by Pechini, and silica coating was prepared by alkoxide hydrolysis method with TEOS and ethanol. The particle size of the $BaTiO_3$ powders was 35 nm and the thickness of the $SiO_2$ coating layer was 5 nm. As the $SiO_2$ content increased, the $SiO_2$ layers improved the powder dispersion by increasing electrostatic repulsion between the $BaTiO_3$ particles. Effects of MgO coating on microstructure and dielectric properties of $BaTiO_3$ have been studied compared with mechanically MgO mixed $BaTiO_3$. MgO coated $BaTiO_3$ particles were prepared by a homogeneous precipitation method using $MgCl_2\cdot 6H_2O$ and urea. MgO coated $BaTiO_3$ exhibited homogeneous microstructure compared with mixed samples. XRD analysis revealed that Mg substitution for the Ti site in the MgO mixed sample was much greater than in the coated one. Electrical properties of MgO mixed and coated $BaTiO_3$ were affected by the diffusion behavior of Mg in $BaTiO_3$ lattice.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2305-2308
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• 2012

Perovskite structured barium titanate particles ($BaTiO_3$) platelets were synthesized by molten salt synthesis and topochemical microcrystal conversion. As the precursors of $BaTiO_3$, plate-like $BaBi_4Ti_4O_{15}$ particles were first synthesized by the reaction of $Bi_4Ti_3O_{12}$, $BaCO_3$, and $TiO_2$ at $1080^{\circ}C$ for 3 h in $BaCl_2$-KCl molten salt. After the topochemical reactions, layer-structured $BaBi_4Ti_4O_{15}$ particles transformed to the perovskite $BaTiO_3$ platelets. $BaTiO_3$ particles with thickness of approximately $0.5{\mu}m$ and a length of $10-15{\mu}m$ retained the morphology feature of the $BaBi_4Ti_4O_{15}$ precursor. For <001> $Pb(Mg_{1/3}Nb_{2/3})O_3-32.5PbTiO_3$ (PMNT)-5 wt % PbO piezoelectric ceramics textured with 5 vol % of $BaTiO_3$ templates, the Lotgering factor reached 0.82, and $d_{33}$ was 870 pC/N.

• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.182-185
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• 2012

N-doped $TiO_2$nanotubes have been newly prepared by two stage sol-gel and strong-alkali hydrothermal process using $TiCl_4$ and hydrazine/ammonia aqueous solution as raw materials. These nanotubes revealed a well developed anatase crystalline phase and perfect nanotube morphology with the diameter around 10nm and the wall thickness below 3 nm. Also, they showed a superior visible light activity and yellowish color due to the light absorption redshifted by ~35 nm and ~25 nm compared to undoped $TiO_2$ nanotubes and anatase nanoparticles, respectively.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.82-88
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• 1999

In this study, the formation of mullite phase with mineralizer have been investiagated Hadong Kaolin and boehmite were used as starting materials and also of TiCl4 and MnCl4 aquous solution were used as a mineralizer. In the addition of 3.5% MnO as a mineralizer, mullite single phase could be obtained at 125$0^{\circ}C$ without any other second phases. However in the addition of TiO2 as a mineralizer, mullite single phase is obtained at above 135$0^{\circ}C$. Therefore the formation of mullite is lowered in the case of MnO as a mineralizer than of TiO2. Because it is easy to obtain mullite single phase in the case of MnO addition, all the characteristics improved. The values of bulk density, water absorption and bending strength at room temperature were 2.72g/㎤, 0.27% and 180 MPa, respectively.

• Journal of Powder Materials
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• v.16 no.2
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• pp.98-103
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• 2009

The ultrafine titanium carbonitride particles ($TiC_{0.7}N_{0.3}$) below 100nm in mean size were successfully synthesized by Mg-thermal reduction process. The nanostructured sub-stoichiometric titanium carbide ($TiC_{0.7}$) particles were produced by the magnesium reduction at 1123K of gaseous $TiC_{l4}+xC_2Cl_4$ and the heat treatments in vacuum were performed for five hours to remove residual magnesium and magnesium chloride mixed with $TiC_{0.7}$. And final $TiC_{0.7}N_{0.3}$ phase was obtained by nitrification under normal $N_2$ gas at 1373K for 2 hrs. The purity of produced $TiC_{0.7}N_{0.3}$ particles was above 99.3% and the oxygen contents below 0.2 wt%. We investigated in particular the effects of the temperatures in vacuum treatment on the particle refinement of final product.

• Bulletin of the Korean Chemical Society
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• v.30 no.3
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• pp.667-670
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• 2009

The understanding of behaviors of hydroperoxyl/superoxide anion radicals (${H_2O_2}^./{O_2}^{-.}$) generated from a photoirradiated $TiO_2$ surface is essential to improve the efficiency of $TiO_2$ photocatalytic reactions by decreasing the recombination of photoinduced electron-hole ($e^--h^+$) pairs. In contrast with previous studies, we found that ${H_2O_2}^./{O_2}^{-.}$ generated on the surface of illuminated $TiO_2$ particles are mobile. ${H_2O_2}^./{O_2}^{-.}$ formed by the photocatalysis of $TiO_2$ particles immobilized onto the inner surface of a coil-quartz tube were forced under a continuous flow through a knotted tubing reactor (KTR) and into the aqueous phase completely separated from the $TiO_2$ particles, and were measured by a chemiluminescence (CL) technique using 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[ 1,2-a]pyrazin-3-one (MCLA) as the reagent. The initial concentration of the ${H_2O_2}^./{O_2}^{-.}$ stream entering the KTR was determined by its half-life (98 s) at pH 5.8. We suggests that the efficiency of $TiO_2$ photocatalytic reactions may be further improved by utilizing the mobility of ${H_2O_2}^./{O_2}^{-.}$.

• Journal of Dental Rehabilitation and Applied Science
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• v.28 no.4
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• pp.339-347
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• 2012

In previous studies, methods for enhancing cellular response on the Hydroxyapatite coated implant surface were described. In this study, the changes of surface characteristics such as surface roughness, contact angle, surface energy and surface morphology were observed when Hydroxyapatite coated Ti discs were immersed in NaCl solution for various time. Hydroxyapatite coated Ti discs were immersed in 0.9% NaCl solution for 7, 14 and 21 days at $37^{\circ}C$. The control group comprises dry identical discs not immersed in a solution. (n=3) All discs were dried in air completely and the surface roughness was measured using confocal laser scanning microscopy(CLSM). Static contact angle was recorded by video contact angle analyzer after dropping distilled water on the surface. The surface energy was calculated from contact angles of the three liquids. Surface was observed using a field emission-scanning electron microscope(FE-SEM). As a result, the surface roughness of immersed Hydroxyapatite coated Ti discs increased significantly and the contact angle decreased comparing with control group discs. The surface energy of immersed discs increased except for discs immersed for 14 days.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.3
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• pp.14-19
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• 2010

Partial anodic oxidation of Ti-mesh with a wire diameter of ~200[${\mu}m$] produces self-aligned $TiO_2$ nanotube arrays (~50[${\mu}m$] in length) on Ti-mesh substrate. The electrolyte used for anodic oxidation was an ethylene glycol solution with an addition of 1.5 vol. % $H_2O$ and 0.2 wt. % $NH_4F$. A dye-sensitized solar cell utilizing the photoanode structure of $TiO_2$-nanotube/Ti-mesh was fabricated without a transparent conducting oxide (TCO) layer, in which Ti-mesh replaced the role of TCO. The 1.93[%] photoconversion efficiency was low, which can be attributed to both insufficient dye molecules attachment and limited electrolyte flow to dye molecules. The optimized nanotube diameter and length as well as the $TiCl_4$ treatment can improve cell performance.

• Korean Journal of Materials Research
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• v.11 no.8
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• pp.690-696
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• 2001

$TiO_2$ coated coal fly ash has been prepared in order to develop the low price $TiO_2$ photocatalyst and spread out its utilizing field. $TiO_2$ particles is coated on the surface of coal fly ash by precipitation method. In this method, $TiCl_4$ aqueous solution was used as a titanium stock solution and $NH_4HCO_3$ was used as a precipitant. The titanium hydroxide precipitated on the surface of coal fly ash in these neutralizing reaction process was oxidized by heat treatment in temperature ranges of $300~700^{\circ}C$. The crystal structure of the generated titanium dioxide showed anatase type. The crystal size of titanium dioxide increased with raising the temperature of heat treatment, but the removal ability of NO gas decreased. When the titanium dioxide was heated at temperature ranges of $300~ 400^{\circ}C$ for 2 hours, the crystal size of titanium dioxide appeared about 9nm, and the removal rate of NO gas showed 85~ 92%. The whiteness of $TiO_2$ coated coal fly ash increased with raising the coating rate of titanium dioxide and the temperature of heat treatment.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.68-68
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• 2010

Electroluminescence (EL) characteristics of green-emission ZnS:Cu,Cl-based ac-type inorganic powder electroluminescent structures were examined by inserting carbon nanotubes (CNTs) into or next to the dielectric layer. For the top-emission type EL structure, where the luminescent light was emitted from the top of the structure, was fabricated by assembling in order, a top electrode, an emitting layer, a dielectric layer, and a bottom electrode from the top. $BaTiO_3$ powder mixed with CNTs was used as a dielectric layer or CNTs were deposited between the bottom electrode and $BaTiO_3$ dielectric layer in order to improve the role of the dielectric layer in the structure. Luminance of an EL structure with CNTs inclusion was greatly enhanced possibly due to the high dielectric constant in the dielectric layer of $BaTiO_3$/CNTs, which is one of hot research topics utilizing nano-objects for intensifying dielectric constant and reducing dielectric loss at the same time. A variation on the CNTs themselves and their inclusion methods in the dielectric layer has been exhorted, and the underlying mechanism for the role of CNTs in the EL structure will be explained in the poster. In order to extend the flexibility of EL devices, EL devices were fabricated on the paper substrate and their performance was compared other EL devices on the plastic-based substrate.