• 한국세라믹학회지
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• 제35권8호
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• pp.775-782
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• 1998

This experiment is third study concerning BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} (Ln=Sm, Nd, Pr, La..) system which is known to show a high dielectric constant and Q value in microwave dielectric materials. The process of cry-stallization and the microwave dielectric properties of the specimens sintered at 1220-140$0^{\circ}C$ for 2 hr was investigated in the BaO-(Na,{{{{ { { Pr})_{2 }O }_{3 } }}-{{{{ { TiO}_{2 } }} as well as BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} system. The single phase BaPr2Ti5O14 and Ba(Nd,{{{{ { { Pr})_{2 }O }_{3 } }}Ti5O14 was finally formed from the Pr2Ti2O7 (Nd, Pr)2Ti2O7 as a secondary phase in the BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} and BaO-(Nd, {{{{ { { Pr})_{2 }O }_{3 } }}-{{{{ { TiO}_{2 } }} system respectively The dielectric constant of the specimens sint-ered at 1280~131$0^{\circ}C$ showed the maximum value as 105(BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} system) and 88 (BaO-(Nd,{{{{ { { Pr})_{2 }O }_{3 } }}-{{{{ { TiO}_{2 } }} system) and the Q values of them showed higher value than 1800 which are due to the maximum den-sity. However the dielectric properties of the specimens sintered at higher temperature than 131$0^{\circ}C$ were reduced due to the increases of pore which were resulted from the sudden grain growth.

• E2M - 전기 전자와 첨단 소재
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• 제10권8호
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• pp.819-829
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• 1997

The microwave dielectric materials of the BaO-Nd$_2$O$_3$-TiO$_2$and BaO-(Sm, Nd)$_2$O$_3$-TiO$_2$system were synthesized by conventional ceramic processing and sintered 1220 to 140$0^{\circ}C$ for 2 hours respectively. Their crystallization and dielectric properties were examined. In the BaO-Nd$_2$O$_3$-TiO$_2$ and BaO-(Sm, Nd)$_2$O$_3$-TiO$_2$system. Nd$_2$Ti$_2$O$_{7}$ and (Sm, Nd)$_2$Ti$_2$O$_{7}$ were observed as a second phase respectively. The maximum relative dielectric constant were 79,99 for the BaO-Nd$_2$O$_3$-TiO$_2$system and 105.07 for the BaO-(Sm,Nd)$_2$O$_3$-TiO$_2$system and their Q-value were over 2000 at 3GHz.GHz.

• 한국세라믹학회지
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• 제31권2호
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• pp.213-219
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• 1994

The formations of spinel and colors of ZnO-Fe2O3-TiO2-SnO2 system have been researched on the basis of ZnO-Fe2O3 system. Specimens were prepared by substituting Fe3+, with Ti4+ or Sn4+ when mole ratios between Fe3+ and Ti4+ or between Fe3+ and Sn4+ were 0.2 mole. The reflectance measurement and X-ray diffraction analysis of the formation of spinel and the colors of there specimens were carried out. ZnO-Fe2O3 system in which Fe2O3 was substituted with SnO2 and TiO2 was formed the spinel structure of 2ZnO.TiO2, 2ZnO.SnO2, ZnO.Fe2O3. The stable stains which were colored with yellow and brown could be manufactured.

• 한국대기환경학회지
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• 제24권1호
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• pp.91-99
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• 2008

A multilayer tower-type photoreactor, in which $TiO_2$-coated glass-tubes were installed, was used to measure the vapor-phase BTEX removal efficiencies by ozone oxidation ($O_3$/UV), photocatalytic oxidation ($TiO_2$/UV) and the combination of ozone and photocatalytic oxidation ($O_3/TiO_2$/UV) process, respectively. The experiments were conducted under various relative humidities, temperatures, ozone concentrations, gas flow rates and BTEX concentrations. As a result, the BTEX removal efficiency and the oxidation rate by $O_3/TiO_2$/UV system were highest, compared to $O_3$/UV and $TiO_2$/UV system. The $O_3/TiO_2$/UV system accelerated the low oxidation rate of low-concentration organic compounds and removed organic compounds to a large extent in a fixed volume of reactor in a short time. Therefore, $O_3/TiO_2$/UV system as a superimposed oxidation technology was developed to efficiently and economically treat refractory VOCs. Also, this study demonstrated feasibility of a technology to scale up a photoreactor from lab-scale to pilot-scale, which uses (i) a separated light-source chamber and a light distribution system, (ii) catalyst fixing to glass-tube media, and (iii) unit connection in series and/or parallel. The experimental results from $O_3/TiO_2$/UV system showed that (i) the highest BTEX removal efficiencies were obtained under relative humidity ranging from 50 to 55% and temperature ranging from 40 to $50^{\circ}C$, and (ii) the removal efficiencies linearly increased with ozone dosage and decreased with gas flow rate. When applying Langmuir-Hinshelwood model to $TiO_2$/UV and $O_3/TiO_2$/UV system, reaction rate constant for $O_3/TiO_2$/UV system was larger than that for $TiO_2$/UV system, however, it was found that adsorption constant for $O_3/TiO_2$/UV system was smaller than that for $TiO_2$/UV system due to competitive adsorption between organics and ozone.

• 한국세라믹학회지
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• 제24권5호
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• pp.484-490
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• 1987

Diffusion coupling experiment was done to study expansion of body and soild reaction in BaCO3-TiO2 system. Specimen of BaCO3 and TiO2 was formed with Pt-mark's method. Each specimen was fired at interval of 25℃ from 900℃ to 1000℃ for 2hrs. After that, specimen was fixed with resin and polished. Product layers of specimen were observed with SEM and EDS. The result were following; 1. Diffusion component is Ba2+, which diffuse toward TiO2. 2. Large crack between layer of BaCO3 and Ba2TiO4 was generated because of difference of thermal expansion coefficient. 3. Ba2TiO4 is formed to TiO2 body by the reaction of BaTiO3 and BaO and its structure is very porous. 4. BaTiO3 changes immediately to Ba2TiO4 by the reaction of BaO. But BaTiO3 which formed by the reaction of TiO2 and Ba2TiO4 exsists as layer because the diffusion distance of Ba2+ is far.

• 한국세라믹학회지
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• 제28권4호
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• pp.305-314
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• 1991

This study was conducted to research the formation and the color development of NiO-ZnO-Fe2O3-TiO2-SnO2 system for the purpose of synthesizing the spinel pigments which are stable at high temperature. After preparing ZnO-Fe2O3 as a basic composition, {{{{ chi }}NiO.(l-{{{{ chi }})ZnO.Fe2O3 system, {{{{ chi }}NiO.(l-{{{{ chi }})ZnO.TiO2 system, and {{{{ chi }}NiO.(l-{{{{ chi }})ZnO.SnO2 system were prepared with {{{{ chi }}=0, 0.2, 0.5, 0.7, 1 mole ratio respectively. The manufacturing was carried out at 128$0^{\circ}C$ for 30 minutes. The reflectance measurement and the X-ray analysis of these specimens were carried out and the results were summarized as follows. 1. In the specimens which included NiO, it was difficult for the spinel structure to be formed. 2. As increasing the contents of NiO and Fe2O3, all the groups which were yellow or green colored changed to brown. 3. NiO-ZnO-Fe2O3 system and NiO-ZnO-TiO2 system formed the spinel structure and the illmenite structure appeared in NiO-TiO2 system.

• 한국안전학회지
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• 제20권4호
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• pp.29-33
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• 2005

In this paper, reflectance and the dielectric characteristics for $P_2O_5-ZnO-BaO$ system and $SiO_2-ZnO-B_2O_3$ system have been investigated as a function of contents of $TiO_2$. The reflectance was decreased with increasing the contents of $TiO_2$ and the reflectance of $P_2O_5-ZnO-BaO$ system was lowered than that of $SiO_2-ZnO-B_2O_3$ system. The dielectric constant of $P_2O_5-ZnO-BaO$ system was higher than $SiO_2-ZnO-B_2O_3$ system, and the dielectric constant in the both system was increased with increasing of $TiO_2$ contents. This can be explained as the space charge effects. These results are could be applied to the under plate dielectrics of PDP required high reflective ratio and breakdown strength.

• 한국세라믹학회지
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• 제21권4호
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• pp.341-348
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• 1984

$BaTiO_3$ and $SrTiO_3$ were mixed with the mole ratio of 35:65， 50:50 and 65:35 and heated at 1100~120$0^{\circ}C$ for 1~64 hours. The dielectrics of $BaTiO_3$-$SrTiO_3$ system were investigated as a function of amount of solid solution formed. The dielectric constant was increased and Curie temperature was shifted to higher temperature with increasing of heating of soaking time for the same composition and heating temperature. This can be explained by the homogeneous distribution of $Ba^{2+}$ and $Sr^{2+}$ ion in the $BaTiO_3$ system. The Curie temperature was shifted to lower temperature with increasing $SrTiO_3$ in the $BaTiO_3$-$SrTiO_3$system because of decreasing the lattice constant.

• 한국세라믹학회지
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• 제31권9호
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• pp.995-1004
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• 1994

Phase relation and microwave dielectric properties of the system BaO.(Nd1-xSmx)2O3.TiO2 (n=4, 5) were studied. With n=5 (1 : 1 : 5), Ba2Ti9O20 and TiO2 formed in case of X$\leq$0.7, and Ba2Ti9O20 and Sm2Ti2O7 formed at X=1.0 as the second phases dispersed in fine-grained orthorhombic matrix phase. With n=4 (1 : 1 : 4). on the contrary, only fine grains of an ortho-rhombic phase were observed irrespective of Nd/Sm ratio. The compositions of these two stable orthorombic phases having distinct lattic constants even with the same Nd/Sm ratio were estimated as 4BaO.5(Nd1-xSmx)2O3.18TiO2 and BaO.(Nd1-xSmx)2O3.4TiO2 with n=5 and n=4 in the system BaO.(Nd1-xSmx)2O3.TiO2, respectively. Consequently the composition BaO.(Nd1-xSmx)2O3.5TiO2 lies in the compatible triangle of 4BaO.5(Nd1-xSmx)2O3.18TiO2 and the second phases mentioned above. The microwave dielectric properties (~4 GHz) of BaO.(Nd1-xSmx)2O3.5TiO2 can be controlled effectively by adjusting Sm content : with increasing X from 0 to 0.7, both dielectric constant and the temperature coefficient of resonant frequency decreased monotonically from 82 to 65 and from 91 (ppm/$^{\circ}C$) to -19(ppm/$^{\circ}C$), respectively, while unloaded Q(Qo) remained constant at about 2,600.

• 한국세라믹학회지
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• 제32권8호
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• pp.915-921
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• 1995

The morphotropic phase boundary and phase transitions of the solid solutiion system, (1-x)(Na1/2Bi1/2)TiO3-PbTiO3＋xPbTiO3 were studied by investigating changes in crystal structure, variations in permittivity with temperature, and calorimetric behavior. It was observed that the morphotropic phase boundary (MPB) of this solid solutiion system was at near 14 mol% of PbTiO3. Compositions containing less than 10mol% PbTiO3 (x<0.1) exhibited a phase transition, i.e. ferroelectric rhombohedrallongrightarrowparaelectric paraelectric cubic, with increasing temperature. Composition containing more than 14 mol% PbTiO3 (x 0.14) showed a phase transition from ferroelectric tetragonal to paraelectric cubic. In the composition range of 0.1$\varepsilon$ (T) curve, which coincided with a phase transition from ferroelectric rhombohedral to an intermediate phase, was also found.