• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.363-366
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• 2004

The structural and microwave dielectric properties of $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics with sintering temperature were investigated. All the sample of the $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics were prepared by conventional mixed oxide method and sintered at $1425^{\circ}C{\sim}1500^{\circ}C$. According to XRD Patterns, hexagonal $Mg_4Ta_2O_9$ phase and cubic $SrTiO_3$ Phase were coexisted. The porosity of $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics were reduced with increasing sintering temperature. In the case of $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics sintered at $1475^{\circ}C$, dielectric constant, quality factor and temperature coefficient of resonant frequency were 14.51, 82,596GHz and $-3.14ppm/^{\circ}C$, respectively.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.98-100
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• 2003

The microwave dielectric properties and microstructure of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics were investigated. All sample of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics were prepared by conventional mixed oxide method. The sintering temperature was $1375^{\circ}C{\sim}1450^{\circ}C$. The structural properties of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics were investigated by X-ray diffractormeter. According to the X-ray diffraction patterns of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics, the major phase of the hexagonal $Mg_4Ta_2O_9$ were presented. In the case of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics sintered at $1425^{\circ}C$, density, dielectric constant, quality factor were $5.799g/cm^2$, 23.26, 40,054 GHz, respectively.

• Journal of the Korean Ceramic Society
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• v.32 no.4
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• pp.507-515
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• 1995

The monolithic dry gels of the Li2O-Al2O3-TiO2-SiO2 system were prepared by the sol-gel technique using metal alkoxides as starting materials to obtain monolithic glass-ceramics at low temperature without melting. Activation energy for the crystal growth of the gel with 6.05% TiO2, nucleating ageng, for the preparation of Li2O-Al2O3-TiO2-SiO2 system glass-ceramic was 101.14kcal/mol. As a result of the analysis of DTA & XRD, it was confirmed that the crytallization of Li2O-Al2O3-TiO2-SiO2 system glass-ceramic was the most efficient when 6.05% TiO2, nucleating agent, was added. $\beta$-eucryptite solid solution crystals and $\beta$-spodumene solid solution crystals were detected in the sample heat treated above 85$0^{\circ}C$. The sintered gel heat treated at 85$0^{\circ}C$ had the specific surface area of 185$m^2$/g, the pore volume of 0.19cc/g and the average pore radius of 20.8$\AA$. This shows that the sintered gel is also comparatively porous material. In temperature range of 25~85$0^{\circ}C$ thermal expansion coefficient of the specimen which was crystallized for 10hrs at 85$0^{\circ}C$ was 6.7$\times$10-7/$^{\circ}C$, which indicated that the crystallized specimen was turned out to be the glass-ceramic with low thermal expansion.

• Journal of the Korean Chemical Society
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• v.44 no.1
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• pp.60-67
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• 2000

The wavelength of the surface plasmon absorption depends on the dielectric matrix. $TiO_2/SiO_2$ complex oxide films doped with Au nanoclusters were prepared by sol-gel spin-coating method using $Ti(OPr^i)_4$, $Si(OEt)_4$, and $HAuCl_4{\cdot}7H_2O$. The wavelength of the maximum absorption of Au nanoehrsters in the $TiO_2/SiO_2$ thin films was obtained with lineality from 540 nm to 615 nm depending on the molar ratio of $TiO_2$. The particle sizes and structures of these nanoclusters have been identified through a TEM and X-ray diffraction patterns. The dielectric constants of $TiO_2/SiO_2$ thin films were calculated from the experimental results.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.567-572
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• 1998

The crystalline structure of $LaTi_{0.8}V_{0.2}O_3$ solid solutions, prepared by arc-melting palletized mixtures of predried $La_2O_3,\;V_2O_3,\;TiO_2$, and Ti, was investigated by transmission electron microscopy and computer image simulation. Computer image simulations were performed by the multislice method for a wide range of sample thickness and defocusing value. The structure of $LaTi_{0.8}V_{0.2}O_3$ was determined as a $GdFeO_3$-type orthorhombic $(a\approx5.58{\AA},\;b\approx7.89{\AA},\;and\;c\approx5.58{\AA})$ with a space group $P_{nma-}$. No evidence of ordering of Ti and V atoms in $SaTi_{0.8}V_{0.2}O_3$ was found.

• The Journal of Natural Sciences
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• v.8 no.1
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• pp.61-69
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• 1995

It is hard to synthesize pure $BaTiO_3$ from $BaCO_3$ and $TiO_2$ in solid reaction for the activity of BaO and secondary phase. For this reason, the wet chemical techniques have been studied. Starting material which was used in these methods were expensive and the properties of powder which was synthesized in same defined. So, some process have been studying again to improve soild reaction method. This study which was one of those was to defin the forming mechanism of $Ba_2TiO_4$ and to control some condition of $Ba_2TiO_4$. The synthesis temperature of $BaTiO_3$ in solid reaction was near $1120^{\circ}C$. The quantity and forming temperature of $Ba_2TiO_4$ could be controlled by atmosphere heat treatment. $Ba_2TiO_4$ was related to expansion in Ba-rich region of $BaTiO_3$. $BaTiO_2O_5$ and $BaTiO_3O_7$ was reason to expand in Ti-rich region. The dielectrics of $CeAIO_3$ which was synthesized and sintered in reduction atmosphere and $BaTiO_3$ system were affected by $CeO_2$ which was formed for the decomposition of $CeAIO_3$ heat treatment in air.

• Korean Journal of Materials Research
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• v.11 no.1
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• pp.44-47
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• 2001

Effects of $Er_2O_3$ addition on the dielectric properties of non-reducible $BaTi_3$-based X7R dielectrics with Ni electrode have been studied in reducing atmosphere. X7R with moderate temperature-dependence was developed after addition of $Er_2O_3$ with $MnO_2-MgO$; room-temperature dielectric constant and dissipation factor were >2900 and < 1.0%, respectively. The addition of $Er_2O_3$ greater than 3.0 mol% improved the temperature dependence of dielectric properties, but a significant decrease of the dielectric constant at room-temperature was observed. The TCC curves rebated clockwise with increasing MnO$_2$ content at a given additive system, 1.5 mol% $Er_2O_3$ and 2.0 mol% MgO.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.04a
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• pp.147-148
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• 2007

In this study, the technology to grow oriented nanotube thin film from dip-coated $TiO_2$ using hydrothermal method has been successfully developed. The effects of preparation parameters, such as reaction temperature, duration and post treatment conditions on the film morphologies and the adherence to the substrate, have been examined. A general formation mechanism of oriented titanate nanotube thin film is proposed in terms of the detailed observation of the products via two dimensional surface FESEM studies and HRTEM images. The overall formation of $TiO_2-based$ nanotube thin film can be summarized with three successive steps: (1) $TiO_2$ dissolving and amorphous $Na_2TiO_3$ deposition process; (2) layered $Na_2Ti_3O_7$ formation via spontaneous crystallization and rapid growth process; (3) formation of nanotube thin film via $Na_2Ti_3O_7$ splitting and multilayer scrolling process of (100) planes around the c axis of $Na_2Ti_3O_7$.

• Korean Journal of Materials Research
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• v.14 no.6
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• pp.394-398
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• 2004

A Ti47Al1.7W-3.7Zr alloy was oxidized between $900^{\circ}C$ and $1050^{\circ}C$, and the oxide scales formed were studied. The oxide scales consisted primarily of an outer$TiO_2$ layer, an intermediate $Al_2$$O_3$-rich layer, and an inner mixed ($TiO _2$ + $Al_2$$O_3$) layer. Besides $TiO_2$ and $Al_2$$O_3$, oxidation led to the formation of some $Ti_2$AlN and TiN. Both W and Zr were preferentially segregated below the intermediate $Al_2$$O_3$-rich layer. Tungsten in the oxide scale was present as $WO_3$ and ${Ti}_{x}$$W_{1-x}$, whereas zirconium as monoclic-$ZrO_2$ and tetragonal-$ZrO_2$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.713-719
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• 2016

The NOx conversion properties of Mn-Cu-$TiO_2$ and $V_2O_5$/$TiO_2$ catalysts were studied for the selective catalytic reduction (SCR) of NOx with ammonia. The performance of the catalysts was investigated in terms of their $NOx$ conversion activity as a function of the reaction temperature and space velocity. The activity of the Mn-Cu-$TiO_2$ catalyst decreased with increasing reaction temperature and space velocity. However, the activity of the $V_2O_5$/$TiO_2$ catalyst increased with increasing reaction temperature. High activity of the Mn-Cu-$TiO_2$ catalyst was observed at temperatures below $200^{\circ}C$. H2-TPR and XPS analyses were conducted to explain these results. It was found that the activity of the Mn-Cu-$TiO_2$ catalyst was influenced by the thermal shock caused by the change of the initial reaction temperature, whereas the $V_2O_5$/$TiO_2$ catalyst was not affected by the initial reaction temperature. In the case of catalyst C, the $NO_x$ conversion efficiency decreased with increasing space velocity. The decrease in the $NO_x$ conversion efficiency with increasing space velocity was much less for catalyst D than for catalyst C.