• Journal of the Korean Ceramic Society
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• v.37 no.2
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• pp.174-180
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• 2000

Y-TZP/mullite composites were prepared by the infiltration of Y-TZP precursor into partially reaction-sintered mullite. The addition of Y-TZP(~7.2 wt%) increased the bend strength(207 MPa), fracture toughness(4.6MPa.m1/2) and Vickers microhardness(853kg/$\textrm{mm}^2$) of the uninfiltrated mullite sintered at 162$0^{\circ}C$ for 10h by more than 75, 70 and 105%, respectively. Residual alumina-rich glass was observed at a mullite/mullite junction, due to the mullitization reaction of silica melt with crystalline $\alpha$-Al2O3 during a final sintering. Although ZrO2 inclusions improved the final sintered density of mullite they did not effectively prevent its grain growth.

• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.101-109
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• 1996

The mechanical propertieso f sintered AlN with the addition of alumina were investigated The flexural strength of the AlN dispersed ALON specimens was higher than that of ALON and fracture toughness showed similar tendency. The high-temperature flexural strength of specimens which 50 and 64.3 mol% alumina was added to AlN was constant up to 100$0^{\circ}C$ with about 290 and 420 MPa respectively but abruptly decreased at 120$0^{\circ}C$ In the specimens which contained 5 and 30mol% alumina the flexural strength increased to about 14% at 100$0^{\circ}C$ and did not decrease at 120$0^{\circ}C$ compared to at room temperature.

• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.1053-1059
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• 1994

The influence of ZrO2 addition on microstructre and mechanical strength of magnesia ceramics were discussed. ZrO2 was existed as a cubic phase resulted from MgO solubility into ZrO2 on firing at temperature range from 130$0^{\circ}C$ to 1$600^{\circ}C$ for 2 h. The addition of ZrO2 markedly promoted the densification of MgO also above 150$0^{\circ}C$ and the sintered density at 1$600^{\circ}C$, 2 h reached to 95.2% of the theoretical. The solubility of MgO into c-ZrO2 was about 7.68 wt% and it was segregated at grain boundary on cooling to room temperature. ZrO2 existing as a second phase retarded the grain growth of MgO. The bending strength were increased to 240 MPa with the amount of ZrO2.

• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.1021-1029
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• 1994

SiC ultrafine particles of 1, 10, 20 and 30 vol% were dispersed in $\alpha$-Si3N4 matrix and hot-pressed under the condition of 30 MPa at 1800 and 190$0^{\circ}C$ respectively. Physical, mechanical properties and microstructures of sintered Si3N4-SiC nanocomposites were investigated. Flexural strength and density of Si3N4-10 vol% SiC nanocomposites hot-pressed at 190$0^{\circ}C$ represented the 1002 MPa and 97.9%T.D respectively, and it was confirmed as a remarkable improvement of 67% compared to Si3N4 monolith. Fracture toughness was shown as 7.2 MPa.m1/2 when the same composition was hot pressed at 180$0^{\circ}C$. This effect was supposed to be due to the improvement of microstructure by the adequate suppression of the excessive growth of Si3N4 grain with SiC nano-particles.

• Journal of the Korean Ceramic Society
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• v.36 no.12
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• pp.1390-1395
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• 1999

Zr(Y,Ce)O2 TZP ceramics were prepared by sintering compacts of 3 mol% Y2O3-TZP(3Y-TZP) powders with different amount of 12 mol% CeO2-TZP(12Ce-TZP) in air at 140$0^{\circ}C$ for 2 h. The phase changes microstructure and mechanical properties of Zr(Y. Ce)O2 TZP after hydrothermal aging(20$0^{\circ}C$ 5h) were investigated. Although an addition of 12Ce-TZP accelerated the grain growth of Zr(Y, Ce)O2 TZP it restrained the transformation of tetragonal to the monoclinic phase during aging. The degradation in mechanical properties of sintered bodies was governed by the formed monoclinic phase and chemical composition. Induced Vickers indentation crack was propagated intergranually. From SEM observation of the fracture surfaces the pull-out of individual grain was confirmed.

• Journal of the Korean Ceramic Society
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• v.32 no.11
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• pp.1255-1261
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• 1995

Mullite-spinel-zirconia composites were prepared by reaction sintering of calcined alumina and magnesia, and zircon powders. The influence of calcining temperature on densification processes and on mechaical properties of subsequently sintered compacts was investigated. The mullite was formed by the reaction of $\alpha$-Al2O3 and amorphous SiO2 at firing temperatures over 141$0^{\circ}C$. The mullitization proceeded more rapidly in the specimen calcined at 110$0^{\circ}C$ than at either 120$0^{\circ}C$ or 130$0^{\circ}C$. Microstructures before and after the mullitization (or mullite dissociation) showed different morphologies, and their effects on mechanical properties were significant. The flexural strength and fracture toughness of the specimen calcined at 130$0^{\circ}C$ and subsequently fired at 145$0^{\circ}C$ were 316 MPa and 4.2Mpa.m1/2, respectively.

• Journal of the Korean Ceramic Society
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• v.32 no.9
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• pp.1085-1091
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• 1995

Molybdenum disilicide (MoSi2) was synthesized from Mo, MoO3, Si and Al powders by self-propagating high temperature synthesis (SHS). The effect of processing parameters such as Mo/MoO3 molar ratio, Ar gas pressure in the reactor and pressing pressure of compacts in synthesis of MoSi2 were investigated. h-MoSi2 was transformed into t-MoSi2 with increasing the Mo/MoO3 mole ratio, and only t-MoSi2 phase was identified above 3.5 : 1 (molar ratio). The synthesized phases did not change with the variation of Ar gas pressure and pressing pressure of compacts. It was found that the combustion temperature was above 2,50$0^{\circ}C$. The products were separated into MoSi2 (s) and $\alpha$-Al2O3 by the difference of their specific grativities. Bending strength, hardness and density of sintered specimen exhibited 82 MPa, 5.368 GPa and 5.43 g/㎤, respectively.

• Journal of the Korean Ceramic Society
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• v.29 no.10
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• pp.791-796
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• 1992

SiC(p)-TiC(p) composites were prepared by gas pressure sintering technique. B4C powder and phenolic resin were added as sintering aids by 0.3 wt%-B and 3 wt%-C, TiC powder were dispersed in SiC by 0, 10, 20, 30 and 50 vol%. Flextural strength, fracture toughness and theoretical density of 70 vol% SiC-30 vol% TiC composite sintered at 220$0^{\circ}C$ by gas pressing were 540 MPa, 5.5 MPa.m1/2 and 98.8% respectively.

• Journal of the Korean Ceramic Society
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• v.30 no.12
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• pp.999-1006
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• 1993

Si3N4(p)-SiC(p) composites were prepared by gas pressure sintering at 190$0^{\circ}C$ for 1 hour. $\alpha$-SiC with average particle size of 0.48${\mu}{\textrm}{m}$ were dispersed from zero to 50vol% in $\alpha$-Si3N4 with average particle size of 0.5${\mu}{\textrm}{m}$. Y2O3-Al2O3 system was used as sintering aids. When 10vol% of SiC was added to Si3N4, optimum mechanical properties were observed; relative density of 98.8%, flextural strength of 930MPa, fracture toughness of 5.9MPa.m1/2 and hardness value of 1429kg/$\textrm{mm}^2$. Grain growth of $\beta$-Si3N4 was inhibited as the amount of added SiC was increased. SiC particles were found inside the $\beta$-Si3N4 intragrains in case of 10, 20 and 30vol%SiC added composites.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.179-186
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• 1989

The preparation of the fine BN powders by ammonia-nitridation of ammonia-decaborane derivate was attempted at temperature between 300 to 150$0^{\circ}C$. The formation mechanism of BN was examined and the resulant BN powder was characterized by means of IR, XRD, SEM and PSA method. In the nitridation below 80$0^{\circ}C$ bonding materials were identified with mainly BH and NH but above 80$0^{\circ}C$ with BN by IR spectra and X-ray patterns. Crystalite size, lattice constant and particle size distribution of hexagonal BN prepared at 1, 50$0^{\circ}C$ were La=470$\AA$, Lc=180$\AA$, a=2.5062$\pm$1$\AA$, c=6.8285$\pm$2$\AA$ and 2.0-5.4${\mu}{\textrm}{m}$, respectively.