• 한국세라믹학회지
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• 제29권10호
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• pp.827-835
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• 1992

The effects of CeO2 on the properties of cordierite-based glass-ceramics and its applicability to low firing temperature substrate were examined. Glass-ceramics were prepared by sintering the glass powder compacts at 900~100$0^{\circ}C$ for 3 h. Density, bending strength, dielectric constant and thermal expansion coefficient of the glass-ceramics were measured as functions of CeO2 contents and sintering temperatures. By adding CeO2, dense glass-ceramics were obtained below 100$0^{\circ}C$. dielectric constant and bending strength were more dependent on the porosity of glass-ceramics containing 5 wt% CeO2, sintered at 100$0^{\circ}C$ for 3 h, were as follows; relative density is 95.3%, bending strength is 178$\pm$11 MPa, dielectric constant is 4.98$\pm$0.20 (at 1 MHz) and thermal expansion coefficient is 33.7$\times$10-7/$^{\circ}C$. Therefore, the glass-ceramics containing 5 wt% CeO2 appeared to be suitable for low firing temperature substrate of electronic devices.

• The Korean Journal of Ceramics
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• 제5권1호
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• pp.78-81
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• 1999

Aluminium titanate is highly anisotropic in thermal expansion. As a result, thermal stresses build up in the material and intergranular cracks can develop. Both the outstanding thermal shock resistance and the low mechanical strength of aluminium titanate ceramics are a result of intergranular microcracking. The authors have previously identified a possibility of remarkably increasing fracture toughness of aluminium titanate without excessive penalty on strength. The paper shows that sintered density and porosity measurements can be used for optimizing the sintering and microstructure of aluminium titanate for an ideal balance between toughness and strength and, hence, the best thermal shock resistance.

• 한국세라믹학회지
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• 제52권5호
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• pp.338-343
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• 2015

To prevent an interfacial reaction between the anode and the electrolyte layer during the conventional high-temperature co-firing process, an anode-supported type cell with a thin-film electrolyte was fabricated by low-temperature ceramic thick film coating process. Ni-GDC cermet composite was used as the anode material and YSZ was used as the electrolyte material. Open circuit voltage and maximum power density were found to strongly depend on the surface uniformity of the anode functional layer. By optimizing the microstructure of the anode functional layer, the open circuit voltage and maximum powder density of the cell increased to 1.11 V and $1.35W/cm^2$, respectively, at $750^{\circ}C$. When a GDC barrier layer was applied between the YSZ electrolyte and the LSCF cathode, the cell showed good stability, with almost no degradation up to 100 h. Anode-supported type SOFCs with high performance and good stability were fabricated using a coating process.

• 한국세라믹학회지
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• 제29권6호
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• pp.419-430
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• 1992

Fabrication possibility of low-shrinkage alumina without oxidation and wetting agent was presented on the basis of observation about oxidation behavior, microstructure and physical characteristics of such reaction agents free Al2O3-Al system. The composition less than Al 10w/o where Al can act as a sintering agent for Al2O3 was excluded. Under the condition of present experiments oxidation of Al2O3-Al system was dependent not on holding time but mainly on oxidation temperature. In thes case of Al powder not comminuted effectively during powder mixing of Al2O3-Al, columnar structure which would act as a hindrance to the densification during sintering developed more during oxidation with higher Al contents, and which made the fabrication of low-shrinkage Al2O3 ceramics impossible. If Al powder was comminuted effectively due to co-mixed Al2O3 characteristics, densification was improved because of no columnar structure and made the fabrication of sintered body with -2.7% dimensional change and 81% relative density possible. As a result, it is possible to fabricate dense low-shrinkage Al2O3 ceramics without oxidation and wetting agent under conditions such as smaller particle size of Al, Al contents below 50v/o, higher green density of Al2O3-Al compact and the use of Al2O3 powder used for high-density ceramics.

• 한국세라믹학회지
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• 제43권9호
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• pp.552-557
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• 2006

A low temperature processing route for fabricating porous SiC ceramics by carbothermal reduction has been demonstrated. Effects of expandable microsphere content, sintering temperature, filler content, and carbon source on microstructure, porosity, compressive strength, cell size, and cell density were investigated in the processing of porous silicon carbide ceramics using expandable microspheres as a pore former. A higher microsphere content led to a higher porosity and a higher cell density. A higher sintering temperature resulted in a decreased porosity because of an enhanced densification. The addition of inert filler increased the porosity, but decreased the cell density. The compressive strength of the porous ceramics decreased with increasing the porosity. Typical compressive strength of porous SiC ceramics with ${\sim}70%$ porosity was ${\sim}13 MPa$.

• 열처리공학회지
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• 제37권1호
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• pp.1-8
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• 2024

Phase stability of tetragonal crystals in yttria-stabilized zirconia ceramics is dependent on the content of yttria and the heat-treatment condition, related with mechanical properties. In this study, we fabricated the 1.5 mol% yttria-stabilized zirconia (1.5Y-YSZ) ceramics by cold isostatic pressing (CIP) and post-sintering at temperature range of 1200 to 1350℃ for 2 hours and investigated the sintered properties and microstructural evolution. Sintered and microstructural parameters, i.e, apparent density, grain size and phase composition of 1.5Y-YSZ ceramics were mainly dependent on the sintering temperature. Maximum sintered density of 99.4 % and average grain size of 200-300 nm could be obtained from the heat-treatment condition above sintering temperature at 1300℃ for 2 hours, possessing the superior mechanical hardness with 1200 Hv. However, phase stability of tetragonal grains in 1.5 YSZ ceramics is very low, inducing the phase transformation to monoclinic crystals on specimen surface during cooling after heat-treatment.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1250-1251
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• 2008

In this study, the dielectric ceramics with low loss were investigated for high frequency application. All sample of the $Ba_5M_4O_{15}$ (M=Ta, Nb) ceramics were prepared by the conventional mixed oxide method and sintered at $1325{\sim}1575^{\circ}C$. The bulk density and dielectric constant of the $Ba_5Ta_4O_{15}$ ceramics were increased continuously with increasing of sintering temperature. The quality factor was increased in the sintering temperature of $1375{\sim}1475^{\circ}C$ but decreased at the temperature above 1475$^{\circ}C$. In the case of $Ba_5Nb_4O_{15}$ ceramics, the bulk density, dielectric constant and quality factor were increased with sintering temperature but decreased above temperature of 1400$^{\circ}C$. The dielectric constant, quality factor and temperature coefficient of the resonant frequency (TCRF) of the $Ba_5Ta_4O_{15}$ and $Ba_5Nb_4O_{15}$ ceramics, sintered at 1475$^{\circ}C$ and 1400$^{\circ}C$, were 25.15, 53105 GHz, -3.06 ppm/$^{\circ}C$ and 39.55, 28052 GHz, 5.7 ppm/$^{\circ}C$, respectively.

• 한국세라믹학회지
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• 제56권1호
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• pp.84-90
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• 2019

The varistor properties and stability against dc-accelerated stress of $V_2O_5-Mn_3O_4-Co_3O_4-Dy_2O_3-Nb_2O_5-Bi_2O_3$ (VMCDNB)-doped zinc oxide ceramics sintered at $850-925^{\circ}C$ were investigated. Increasing the sintering temperature increased the average grain size from 4.6 to 8.7 mm and decreased the density of the sintered pellet density from 5.54 to $5.42g/cm^3$. The breakdown field decreased from 5919 to 1465 V/cm because of the increase in the average grain size. Zinc oxide ceramics sintered at $875^{\circ}C$ showed the highest nonlinear coefficient (43.6) and the highest potential barrier height (0.96 eV). Zinc oxide ceramics sintered at $850^{\circ}C$ showed the highest stability: the variation rate of the breakdown field was -2.0% and the variation rate of the nonlinear coefficient was -23.3%, after application of the specified stress (applied voltage/temperature/time).

• 한국세라믹학회지
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• 제25권1호
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• pp.54-58
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• 1988

In order to depress PbO vaporization during calcination and improve sinterability in low temperature, a method for preparing homogeous Lead-Zirconate-Titanate (PZT) powder from aqueous salt solution by precipitation is described. In this method, single phae PZT fine powders are formed at above 500$^{\circ}C$. PZT-ceramics using these powders have high sinterability, and good sintering characteristics relatively low temp. (-high apparent density, low porosity, low water adsorption etc.)

• 한국재료학회지
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• 제25권1호
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• pp.37-42
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• 2015

The effect of sintering temperature on the microstructure, electrical and dielectric properties of (V, Mn, Co, Dy, Bi)-codoped zinc oxide ceramics was investigated in this study. An increase in the sintering temperature increased the average grain size from 4.7 to $10.4{\mu}m$ and decreased the sintered density from 5.47 to $5.37g/cm^3$. As the sintering temperature increased, the breakdown field decreased greatly from 6027 to 1659 V/cm. The ceramics sintered at $900^{\circ}C$ were characterized by the highest nonlinear coefficient (36.2) and the lowest low leakage current density ($36.4{\mu}A/cm^2$). When the sintering temperature increased, the donor concentration of the semiconducting grain increased from $2.49{\times}10^{17}$ to $6.16{\times}10^{17}/cm^3$, and the density of interface state increased from $1.34{\times}10^{12}$ to $1.99{\times}10^{12}/cm^2$. The dielectric constant increased greatly from 412.3 to 1234.8 with increasing sintering temperature.