• Korean Journal of Materials Research
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• v.18 no.8
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• pp.422-426
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• 2008

The effects of an addition of $ZrO_2$ on the microstructure and electrical properties of MgO films as a protective layer for AC plasma display panels were investigated. MgO + a 200 ppm $ZrO_2$ protective layer prepared by e-beam evaporation exhibited a secondary electron emission coefficient ($\gamma$) that was improved by 21% compared to that of a pure MgO protective layer. The relative density and Vickers hardness increased with a further addition of $ZrO_2$. These results suggest that the discharge properties and optical properties of MgO protective layers are closely related to the relative density and Vickers hardness. The good optical and electrical properties of $\gamma$, at 0.080, a grain size of $19\;{\mu}m$ and an optical transmittance of 91.93 % were obtained for the MgO + 200 ppm $ZrO_2$ protective layer sintered at $1700^{\circ}C$ for 5 hrs.

• Nuclear Engineering and Technology
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• v.33 no.4
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• pp.386-396
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• 2001

Mixtures Of AUC-UO$_2$and Gd$_2$O$_3$ Powders doped With Cr$_2$O$_3$ or Cr$_2$O$_3$-SiO$_2$ were Pressed and sintered at 1730 t in hydrogen gas witk various water-vapor contents. The density of UO$_2$- 6wt% Gd$_2$O$_3$ pellets can be increased from 91% TD to 94.5% TD in 1 vol% $H_2O$-H$_2$ gases by the addition of 0.02wt% Cr$_2$O$_3$-(0.01~0.04) wt% SiO$_2$. The magnitude of density increase is much larger in (1~3 vol%) $H_2O$-H$_2$ gases than in 0.05 vol% $H_2O$-H$_2$ gas. The densification of U0$_2$- Gd$_2$O$_3$ compact is significantly delayed in the temperature range between 1300 and 1500 t , but that of compacts with Cr$_2$O$_3$-SiO$_2$ is not. The role of Cr$_2$O$_3$ and SiO$_2$ in densification is discussed.

• Transactions of Materials Processing
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• v.27 no.1
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• pp.48-53
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• 2018

Aluminum nitride (AlN) is used by the semiconductor industry that has requirements for high thermal conductivity. The theoretical thermal conductivity of single crystal AlN is 320W/mK. Whereas, the values measured for polycrystalline AlN ceramics range from 20 W/mK to 280 W/mK. The variability is strongly dependent upon the purity of the starting materials and non-uniform dispersibility of the sintering additive. The conventional AlN sintering additive used yttria ($Y_2O_3$), but the dispersibility of the powder in the mixing process was important. In this study, we investigated the mechanical and thermal conductivity of yttrium nitrate ($Y(NO_3)_3{\cdot}6H_2O$), as a sintering additive in order to improve the dispersibility of $Y_2O_3$. The sintering additives content was in the range of 2 to 4.5wt.%. The density of AlN gradually increased with increasing contents of sintering additive and the flexural strength gradually increased as well. The flexural strength of the sintered body containing 4 wt% of $Y_2O_3$ and $Y(NO_3)_3{\cdot}6H_2O$ was 334.1 MPa and 378.2 MPa, respectively. The thermal conductivities were 189.7W/mK and 209.4W/mK, respectively. In the case of hardness, there was only a slight difference and the average value was about 10 GPa. Therefore, densification, density and strength values were found to be proportional to its content. It was confirmed that AlN using $Y(NO_3)_3{\cdot}6H_2O$ displayed relatively higher thermal conductivity and mechanical properties than the $Y_2O_3$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.2
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• pp.90-94
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• 2016

In this work, [$Pb(Mg_{1/2}W_{1/2})_{0.03}(Ni_{1/3}Nb_{2/3})_x(Zr_{0.5}Ti_{0.5})_{0.97-x}O_3-BiFeO_3$] (x=0.02 to 0.12) composition ceramics were fabricated by the conventional soild state reaction method and their microstructure and piezoelectric properties were investigated according to PNN substitution. The addition of small amount of $BiFeO_3$, $Li_2CO_3$, and $CaCO_3$ were used in order to decrease the sintering temperature of the ceramics. The XRD (x-ray diffraction patterns) of all ceramics exhibited a perovskite structure. The sinterability of PMW-PNN-PZT-BF ceramics was remarkably improved using liquid phase sintering of $CaCO_3$, $Li_2CO_3$. However, it was identified from of the X-ray diffraction patterns that the secondary phase formed in grain boundaries decreased the piezoelectric properties. According to the substitution of PNN, the crystal structure of ceramics is transformed gradually from a tetragonal to rhombohedral phase. The x=0.10 mol PNN-substituted PMW-PNN-PZT-BF ceramics sintered at $920^{\circ}C$ showed the optimum values of piezoelectric constant($d_{33}$), piezoelectric figure of merit($d_{33{\cdot}}g_{33}$), planar piezoelectric coupling coefficient($k_p$) and density : $d_{33}=566$ [pC/N], $g_{33}=29.28[10^{-3}mV/N]$, $d_{33{\cdot}}g_{33}=16.57[pm^2/N]$, $k_p=0.61$, density=7.82 [$g/cm^3$], suitable for duplex ultrasonic sensor application.

• Journal of the Korean Ceramic Society
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• v.33 no.9
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• pp.1057-1063
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• 1996

Y2O3-CeO2-ZrO2 powders were prepared from water-soluble salts using a coprecipitation method. The forming process of oxide and the characteristics of the calcined powders treated in different drying conditions were investigated. The oxidation was occurred at the temperature of around 40$0^{\circ}C$ and the main crystallization of ZrO2 around $600^{\circ}C$. On calcination at $600^{\circ}C$ heating lamp-dried powders consisted of agglomerates of globular morphology with average agglomerate size of 2.27${\mu}{\textrm}{m}$ and specific surface area of 68.3m2/g and spray dried powders contained dense spheric particles with average agglomerate size of 1.35${\mu}{\textrm}{m}$ and specific surface area of 11.0m2/g which exhibited low agglomeration tendency. Removal of the water by a freeze-drying technique produced calcined powders containing flake-like secondary particle structures with wide agglomerate size distri-bution of 0.1-60${\mu}{\textrm}{m}$ and specific surface area of 24.5${\mu}{\textrm}{m}$. The 20 MPa-pressed density (36.8-41.4% T,D) of calcined powders did not nealy depend on drying methods whilst compaction ratio of calcined powders derived from freeze-drying was the highest ( 6.24) among three drying methods. On continuous heating up to 150$0^{\circ}C$ the sinterability of calcined powders derived from heating lamp-drying was superior to those derived from spray-and freeze-drying. The final sintered density of calcined powders was the highest (96% T,D at 150$0^{\circ}C$) in case of heating lamp-drying.

• Journal of the Korean Ceramic Society
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• v.43 no.8 s.291
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• pp.504-508
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• 2006

Functionally gradient porous $Al_2O_3-(t-ZrO_2)/HAp$ composites consist of 3 layers were fabricated using the multi-pass extrusion process at the various temperatures. The continuous pores were homogeneously formed in the $2^{nd}$ passed samples and their size was about $180{\mu}m$ in diameter. In the porous composites sintered at $1200-1400^{\circ}C$, the relative density and bending strength increased with the sintering temperature. The maximum values of relative density and bending strength in the $2^{nd}$ passed $Al_2O_3-(t-ZrO_2)/HAp$ composites were 62.2% and 107.8 MPa, respectively. In order to investigate the growth behavior of osteogenic cells on the functionally gradient porous $Al_2O_3-(t-ZrO_2)/HAp$ composites, an in vitro test was performed, using human osteoblast-like MG-63 cells. The cells were well attached and grown on the rough surface of the inside of the functionally gradient porous body.

• Journal of the Korean Ceramic Society
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• v.44 no.6 s.301
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• pp.291-296
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• 2007

Porous $Al_2O_3-(m-ZrO_2)$ composites were fabricated by pressureless sintering, using different volume percentages (40% - 60%) of poly methyl methacrylate (PMMA) powders as a pore-forming agent. The pore-forming agent was successfully removed, and the pore size and shape were well-controlled during the burn-out and sintering processes. The average pore size in the porous $Al_2O_3-(m-ZrO_2)$ bodies was about $200\;{\mu}m$ in diameter. The values of relative density, bending strength, hardness, and elastic modulus decreased as the PMMA content increased; i.e., in the porous body (sintered at $1500^{\circ}C$) using 55 vol % PMMA, their values were about 50.8%, 29.8 MPa, 266.4 Hv, and 6.4 GPa, respectively. To make the $Al_2O_3-(m-ZrO_2)$/polymer hybrid composites, a bioactive polymer, such as PMMA, was infiltrated into the porous $Al_2O_3-(m-ZrO_2)$ composites. After infiltration, most of the pores in the porous $Al_2O_3-(m-ZrO_2)$ composites, which were made using 60 vol % PMMA additions, were infiltrated with PMMA, and their values of relative density, bending strength, hardness, and elastic modulus remarkably increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.291-294
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• 1999

The effect of AI$_2$O$_3$+Y$_2$O$_3$additives on fracture toughness of $\beta$-SiC-ZrB$_2$composites by hot-pressed sintering were Investigated. The $\beta$-SiC-ZrB$_2$ ceramic composites were hot-presse sintered and annealed by adding 1, 2, 3wt% AI$_2$O$_3$+Y$_2$O$_3$(6:4wt%) powder as a liquid forming additives at 195$0^{\circ}C$ for 4h. In this microstructures, no reactions were observed between $\beta$-SiC and ZrB$_2$, and the relative density Is over 90.79% of the theoretical density and the porosity decreased with increasing AI$_2$O$_3$+Y$_2$O$_3$ contents. Owing to crack deflection and crack bridging of fracture toughness mechanism, the fracture toughness showed the highest of 5.5328MPa . m$^{1}$2/ for composites added with 2wt% AI$_2$O$_3$+Y$_2$O$_3$ additives at room temperature. But the standard deviation of fracture toughness of specimens decreased with increasing AI$_2$O$_3$+Y$_2$O$_3$ contents and showed the highest of 0.8624 for composite tilth 1wt%, AI$_2$O$_3$+Y$_2$O$_3$additives.

• Journal of the Korean Ceramic Society
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• v.48 no.5
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• pp.384-389
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• 2011

Gas pressure sintering (GPS) of reaction bonded silicon nitride (RBSN) was performed using $Lu_2O_3-SiO_2$ additive and the properties were compared with those of specimens prepared using high purity $Si_3N_4$ powder. The relative density of RBSN and compacted $Si_3N_4$ powder were 68.9 and 47.1%, and total linear shrinkage after sintering at $1900^{\circ}C$ were 14.8 and 42.9%, respectively. High nitrogen partial pressure (5MPa) was required during sintering at $1900^{\circ}C$ in order to prevent the decomposition of the nitride and to promote the formation of SiC. The relative density and 4-point bending strength of RBSN and $Si_3N_4$ powder compact were 97.7%, 954MPa and 98.2%, 792MPa, respectively, after sintering at $1900^{\circ}C$. The sintered RBSN also showed high fracture toughness of 9.2MPam$^{1/2}$.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.5
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• pp.221-225
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• 2001

The effect of $Al_2O_3+Y_2O_3$ additives on fracture toughness of ${\beta}-SiC-TiB_2$ composites by hot-pressed sintering was investigated. The ${\beta}-SiC-TiB_2$ ceramic composites were hot-press sintered and pressureless-annealed by adding 16, 20, 24 wt% ${\beta}-SiC-TiB_2$(6:4 wt%) powder as a liquid forming additives at low temperature(1800 $^{\circ}C$) for 4 h. Phase analysis of composites by XRD revealed mostly of ${\alpha}$-SiC(6H), $TiB_2$, and YAG($Al_5Y_3O_{12}$). The relative density was over 95-88 % of the theoretical density, and the porosity increased with increasing $Al_2O_3+Y_2O_3$ contents because of the increasing tendency of pore formation. The fracture toughness showed the highest value of 5.88 MPa${\cdot}m^{1/2}$ for composites added with 20 wt% $Al_2O_3+Y_2O_3$ additives at room temperature. The electrical resistivity showed the lowest value of $5.22{\times}10^{-4}\;{\Omega}\;{\cdot}\;cm$ for composite added with 20 wt% $Al_2O_3+Y_2O_3$ additives at room temperature, and was all positive temperature coefficeint resistance(PTCR) against temperature up to 900 $^{\circ}C$.