• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.5
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• pp.397-403
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• 2003

Microwave dielectric properties of (1-x)ZnW $O_4$-xTi $O_2$ ceramic systems were investigated with calcination temperatures and Ti $O_2$ contents. The ZnW $O_4$ ceramic could be suitably sintered at 1075$^{\circ}C$ and showed the dielectric constant of 13.6, quality factor(Q$\times$ $f_{O}$value) of 22,000 and temperature coefficient of resonant frequency($\tau$$_{f}$) of -65$\pm$2ppm/$^{\circ}C$. Increasing the amount of Ti $O_2$ in the range of 0.25 to 0.45 mol, the dielectric constant and $\tau$$_{f}$ increased due to the role of Ti $O_2$ but the quality factor decreased due to the increase of phase boundaries. The 0.7ZnW $O_4$-0.3Ti $O_2$ ceramic showed the dielectric constant of 19.8, qualify factor(Q$\times$ $f_{0}$) of 20,000 and $\tau$$_{f}$ of -3$\pm$1ppm/$^{\circ}C$.>.EX>.>.>.

• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.163-168
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• 2010

Effects of compositions on the microwave dielectric properties of the MgO-$TiO_2$ system were investigated as a function of the molar ratio of MgO to $TiO_2$ ($0.9{\leq}MgO/TiO_2\;(x){\leq}1.2$). With the compositional changes, secondary phases of $MgTi_2O_5$ and $Mg_2TiO_4$ were also detected along with $MgTiO_3$. Microwave dielectric properties of the specimens were dependent on the types of phases developed in the sintered specimens. A single phase of $MgTiO_3$ showed a dielectric constant (K) of 18.2, a quality factor (Qf) of 198,000 GHz, and a temperature coefficient of resonant frequency (TCF) of $-51\;ppm/^{\circ}C$. However, the dielectric properties of the specimens with a secondary phase of $MgTi_2O_5$ (K=19.9, Qf=48,000 GHz) and/or $Mg_2TiO_4$ (K=15.6, Qf=56,000 GHz) were worsened. Dependence of the microwave dielectric properties on the secondary phase of the MgO-$TiO_2$ system was also discussed in terms of dielectric mixing rules.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1488-1490
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• 2002

The (Bi,Ba,Sr)$TiO_3$[BBST] thin films were fabricated on Pt/Ti/$SiO_2$/Si substrate by RF sputtering method. We investigated the effects of Ar/$O_2$ rates on the structural properties of BBST thin films. Decreasing the $O_2$ rates, the intensity of $BaBi_4Ti_4O_{15}$ and $Bi_4Ti_3O_{12}$ peaks were increased but the $(Ba_{0.5}Sr_{0.5})TiO_3$ peak was decreased. In the case of BBST thin films deposited with condition of 90/10 (Ar/$O_2$) ratio, the composition of Ba/Sr/Bi was 0.35/0.4/0.25. Also, in the BBST thin films deposited with condition of 80/20(Ar/$O_2$) ratio, the composition of Br,Sr and Ti were relatively uniform. But the component of Bi and Ti were diffused into the Pt layers.

• Journal of the Korean Ceramic Society
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• v.23 no.4
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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.

• Journal of Environmental Science International
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• v.16 no.12
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• pp.1431-1437
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• 2007

Cobalt titanates($CoTiO_x$), such as $CoTiO_3$ and $Co_2TiO_4$, have been synthesized via a solid-state reaction and characterized using X-ray diffraction(XRD) and X-ray photoelectron spectroscopic(XPS) measurement techniques, prior to being used for continuous wet trichloroethylene(TCE) oxidation at $36^{\circ}C$, to support our earlier chemical structure model for Co species in 5 wt% $CoO_x/TiO_2$(fresh) and(spent) catalysts. Each XRD pattern for the synthesized $CoTiO_3$ and $Co_2TiO_4$ was very close to those obtained from the respective standard XRD data files. The two $CoTiO_x$ samples gave Co 2p XPS spectra consisting of very strong main peaks for Co $2p_{3/2}$ and $2p_{1/2}$ with corresponding satellite structures at higher binding energies. The Co $2p_{3/2}$ main structure appeared at 781.3 eV for the $CoTiO_3$, and it was indicated at 781.1 eV with the $Co_2TiO_4$. Not only could these binding energy values be very similar to that exhibited for the 5 wt% $CoO_x/TiO_2$(fresh), but the spin-orbit splitting(${\Delta}E$) had also no noticeable difference between the cobalt titanates and a sample of the fresh catalyst. Neither of all the $CoTiO_x$ samples were active for the wet TCE oxidation, as expected, but a sample of pure $Co_3O_4$ had a good activity for this reaction. The earlier proposed model for the surface $CoO_x$ species existing with the fresh and spent catalysts is very consistent with the XPS characterization and activity measurements for the cobalt titanates.

• Journal of Industrial Technology
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• v.17
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• pp.241-247
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• 1997

A numerical model has been proposed for a diffusion flame reactor to manufacture ultrafine $TiO_2$ powders. The model equations such as mass balance equation, the 0th, 1st, and 2nd moment equations of aerosols were considered. The phenomena such as $TiCl_4$ reaction rate, $TiO_2$ nucleation rate and the coagulation of $TiO_2$ powders were included in the aerosol dynamic equation. It is found that the $TiO_2$ particle concentration becomes higher, as the inlet $TiCl_4$ concentration and the total gas flow rate increase, and also as the flame temperature decreases. The $TiO_2$ particle size increases, as the flame temperature and the inlet $TiCl_4$ concentration increase and the total gas flow rate decreases.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.6
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• pp.538-542
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• 2005

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 miked oxide method and the sintering temperature was $1425\~1500^{\circ}C$. The hexagonal phase of $Mg_4Ta_2O_9$ and the cubic phase of $SrTiO_3$ 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, 82,596 GHz and $-3.14\;ppm/^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
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• v.38 no.3
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• pp.225-230
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• 2001

저전압용 형광체로 주목받고 있는 SrTiO$_3$:Pr,Al 형광체를 고상반응법으로 제조하였다. 부활성체 Al이 23 mol% 첨가되었을 때 SrTiO$_3$:Pr 형광체는 최대 발광 강도를 보여주었다. 최대 발광 강도를 보인 형광체에 대해 제한시야회절상과 투과전자현미경을 이용하여 SrTiO$_3$:Pr,Al 적색 형광체내 2차상 형성에 대한 연구를 행하였고 또한 에너지 분산 분광 분석을 행하여 SrTiO$_3$:Pr,Al 형광체내 주입된 부활성제 Al의 함량을 결정하였다. 제한시야회절상의 결과에 의하면 SrTiO$_3$:Pr,Al 적색 형광체내에 단사정 SrAl$_2$O$_4$, 삼사정 Ti$_4$O$_{7}$, 육방정 SrAl$_{12}$O$_{19}$가 2차상으로 존재함을 보여 주었다. 에너지 분산 분광 분석 결과 부활성제 Al의 함량 중 일부는 SrTiO$_3$:Pr,Al 적색 형광체 격자에 고용되고 일부 Al은 SrAl$_{12}$O$_{19}$와 SrAl$_2$O$_4$의 2차상을 형성하는데 소모됨을 보여주었다.주었다.

• Journal of the Korean Ceramic Society
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• v.31 no.6
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• pp.651-659
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• 1994

BaTiO3 ceramics were sintered on Al2O3, MgAl2O4, MgO and Mg-, Ca-, Y-stabilized zirconia setters. Then the influence of setters on the microstructure of BaTiO3 ceramics and the stability of setters were investigated by SEM, EDAX and XRD analyses. The microstructure of BaTiO3 ceramics sintered on Al2O3, MgAl2O4, MgO and Mg-PSZ showed large grain growth, but little grain growth on Ce-TZP(Tetragonal Zirconia Policrystal). Mg-PSZ(Partially Stabilized Zirconia), Ca-PSZ, Ce-TZP setters showed extensive phase transformation. Y-TZP and fused Y-SZ (Stabilized Zirconia) setters were stable. The liquid sintering aids of BaTiO3 ceramics accelerate mass transport. The reaction of SrTiO3 in BaTiO3 with ZrO2 resulted in the formation of SrZrO3.

• Bulletin of the Korean Chemical Society
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• v.25 no.5
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• pp.657-664
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• 2004

Titanium sulfate supported on $TiO_2$was prepared by impregnation of powdered $TiO_2$with an aqueous solution of titanium sulfate followed by calcining in air at high temperature. For Ti$(SO_4)_2/TiO_2$ samples calcined at 300 $^{\circ}C$, no diffraction lines of titanium sulfate are observed at $Ti(SO_4)_2$loading up to 30 wt%, indicating good dispersion of $Ti(SO_4)_2$ on the surface of $TiO_2$. The acidity of the catalysts increased in proportion to the titanium sulfate content up to 20 wt% of $Ti(SO_4)_2$. 20 wt% $Ti(SO_4)_2/TiO_2$ calcined at 300 $^{\circ}C$ exhibited maximum catalytic activities for 2-propanol dehydration and cumene dealkylation. The catalytic activities for these reactions, were correlated with the acidity of catalysts measured by ammonia chemisorption method.