• 한국세라믹학회지
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• 제29권10호
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• pp.757-764
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• 1992

The platelet reinforced mullite-zirconia composites were prepared by pressurelss sintering with addition of Al2O3 or SiC platelets. The sintered density of 10 vol% Al2O3 platelet reinforced mullite-zirconia composite was 98.3% at 1700$^{\circ}C$. The fracture strength (290 MPa) and fracture toughness (4.9 MPa$.${{{{ SQRT { m} }}) in the Al2O3 platelet reinforced mullite-zirconia composite were enhanced compared with those of mullite-zirconia due to the crack deflection and load transfer effect of platelets. Whereas, the SiC platelet reinforced mullite-zirconia composite sintered at 1650$^{\circ}C$ showed relatively lower density (95.7%), fracture strength (170 MPa), and fracture toughness (3.9 MPa$.${{{{ SQRT { m} }} than the Al2O3 platelet reinforced mullite-zirconia composite.

• 한국세라믹학회지
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• 제37권5호
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• pp.497-504
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• 2000

In this study, mullite-zirconia comosite was fabricated by adding ZrOCl2.8H2O using of boehmite gel coating to Hadong kaolin (pink A grade) in order to enhance strength of the mullite specimens. The influence of ZrOCl2.8H2O content and fireing temperature on the crystall phase, microstructure, bulk density, strength of the specimens was investigated. Mullite-zirconia composite was produced in the process of coating zirconia to mullite powder synthesized thereafter and mixing simultaneously of starting materials with boehmite-zirconia gel. Maximum strength with in this study was 251 sintered at 1$600^{\circ}C$ for 2h. Bulk density and strength of the composite with zirconia coated mullite was higher than simultaneous on mixture of starting materials.

• 한국세라믹학회지
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• 제36권10호
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• pp.1080-1086
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• 1999

Mullite/zirconia composite was synthesized by adding zirconia and Zircon to mixture of Hapcheon kaolin(grade pink A) and aluminium nitrate salt in order to enhance strength of the mullite specimens. Kaolin and aluminium nitrate salt was mixed milled and calcined at 100$0^{\circ}C$ and then 5wt% mullite seed was added to increase mullite content. The influence of the additives(ZrO2 and ZrSiO4) and sintering temperature on the strength of the sintered specimens was investigated. The flexural strength of the specimens containing 10wt% zirconia was enhanced from 150MPa without the additive up to 300MPa after heat treatment at 156$0^{\circ}C$ In the case of addition of 15wt% zircon the strength of the specimens systhesized at 1$600^{\circ}C$ was 225 MPa.

• 한국분말재료학회지
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• 제4권1호
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• pp.9-17
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• 1997

The mullite-zirconia composites were prepared by the pressureless sintering with addition of 10~20 vol% ZrO$_2$(TZ3Y) in the fused mullite and sol-gel mullite matrix. The densification rate of sol-gel mullite was higher than that of fused mullite, and the addition of ZrO$_2$(TZ3Y) was effective on the densification of fused mullite. The enhancement of densification and anisotropic growth of mullite in ZrO$_2$added specimen can be explained by the solid solution effect of $Zr^{+4}$ ion in mullite. Both mechanical strength and fracture toughness of mullite-zirconia composite were enhanced compared to those of mullite. The enhancement of mechanical properties is attributed to the hinderance of grain growth and the combined toughening effects of tetra-mono phase transformation and crack deflection due to the residual stress between mullite/ZrO$_2$.

• 한국세라믹학회지
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• 제31권12호
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• pp.1475-1482
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• 1994

Compositionally triphasic boehmite-silica-zirconia composite gels were prepared by a multiphasic sol-gel route. Phase-formation characteristics and densification behavior of the gel compacts were examined with and without $\alpha$-Al2O3 seeding. In the unseeded triphasic gels, both $\alpha$-Al2O3 and mullite crystallize simultaneously at 130$0^{\circ}C$. On the other hand, the $\alpha$-Al2O3 seeding selectively induces the formation of corundum phase ($\alpha$-Al2O3) at a significantly lower temperature (~110$0^{\circ}C$) and facilitates an epitaxial growth of $\alpha$-Al2O3 between 1100~130$0^{\circ}C$. The densification of alumina-mullite-zirconia composite (derived from the triphasic gels) was also enhanced by the $\alpha$-Al2O3 seeding, and this was attributed to the delayed crystallization of mullite in the $\alpha$-Al2O3 seeded gel.

• Structural Engineering and Mechanics
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• 제70권2호
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• pp.233-243
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• 2019

This paper depicts the development and characterizations of laminated composites made with cellulosic giant cane (Arundinaria gigantea) fiber mats and epoxy resin. Zirconia-toughened mullite (ZTM) is used as a filler material in the laminated composite which was prepared from sillimanite through plasma processing technique. The mechanical characterizations of this composite have been carried out as per ASTM standards to evaluate its usability as a structural material. The effects of varying weight percentages of the filler and two different fiber orientations namely, angle-ply [$+45^{\circ}/-45^{\circ}/+45^{\circ}$] and balanced cross-ply [$0^{\circ}/90^{\circ}/0^{\circ}$] on the physical and mechanical properties such as density, microhardness, impact strength, tensile strength and interlaminar shear strength of the layered composite specimens have been investigated. The study indicates that the inclusion of zirconia-toughened mullite in the composite laminate as filler improves its mechanical properties. Moreover, the use of giant cane fiber mat in the laminate is more eco-friendly than the synthetic fibers. This research also helps in generating additional data to enrich the repository of natural fiber reinforced laminated composites.

• 한국세라믹학회지
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• 제28권7호
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• pp.549-555
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• 1991

Mullite-zirconia (0∼4 mol% yttria) composites were obtained by In-situ sintering of zircon and alumina mixture, and their mechanical properties were studied in conjuction with microstructure observation. Martensitic transformation temperature (Ms) of zirconia dispersed in the mullite matrix decreased with Y2O3 contents and was about 600$^{\circ}C$ for ZrO2 containing 4 mol% Y2O3. On cooling of this composites, tetragonal to monoclinic phase transformation induced microcracks at the grain boundary of mullite matrix. The microcracks seemed to absorb the fracture energy in stress field during mechanical tests. Therefore, toughening mechanisms of this composite were considered to nucleation and extension of microcrack, and crack deflection mechanism due to the difference of thermal expansion coefficient between matrix and dispersed phase.

• 한국세라믹학회지
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• 제37권2호
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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.

• 한국세라믹학회지
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• 제29권9호
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• pp.719-728
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• 1992

ZrO2/Al2O3-Mullite composites were prepared by infiltration of the silica sol to the porous ZrO2/Al2O3 bodies. The porous ZrO2/Al2O3 bodies for infiltration were fabricated using ZrO2 (20wt%)/Al2O3 composite powders synthesized by the emulsion-hot kerosene drying method. The preparation of silica sols was conducted by the hydrolysis-peptization of an alcoholic TEOS solution. When ZrO2/Al2O3-Mullite and ZrO2/Al2O3 composites were sintered at 1$650^{\circ}C$ for 4 hrs, both of them showed an excellent sinterability. As the amount of mullite added in the composites increased, the ratio of the tetragonal phase of zirconia to the monoclinic phase at the room temperature became higher. It was known that values of the fracture toughness of the ZrO2/Al2O3-Mullite composites were about 5.48 MPa.m1/2 much larger than that of the ZrO2/Al2O3 system.

• 한국재료학회지
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• 제17권1호
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• pp.18-24
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• 2007

Mullite-PSZ composite was prepared by sol-gel method using $Al(sec-OC_4H_9)_3,\;Si(OC_2H_5)_4,\;ZrOCl_2\;8H_2O\;and\;Y_2O_3$. The sinterability ana mechanical properties of powder compacts sintered at $1,650^{\circ}C$ for 4 hrs were investigated for various PSZ contents. In result Al-Si spinel formed at $980^{\circ}C$ from amorphous dried gel, and zirconia as well as mullite crystal formed above $1,200^{\circ}C$. The sintered body was densified to $97{\sim}98%$ except the specimen containing 25vol% PSZ which showed the relative density of about 95% obtained by sintering at $1,650^{\circ}C$ for 4 h. The flexural strength of the sintered body was a maximum value of 290 MPa in 20 vol% PSZ, which was also considerably larger than the value of 200 MPa without PSZ. The value of the fracture toughness increased linearly with increase of PSZ content and showed a maximum value of $4.3MPam^{1/2}$ in 25 vol% PSZ, Namely this value was remarkably larger than the $value(2.6MPam^{1/2})$ of pure mullite without PSZ.