• Title, Summary, Keyword: mullite

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Influence of mullite-seed on the mullite synthesis from various compositions (Mullite 합성에 있어서 조성에 따른 Mullite-seed 첨가효과)

  • 김인섭;강상원;박주석;이명웅;이병하;이경희
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.10 no.1
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    • pp.48-54
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    • 2000
  • Influence of seed addition on the mullite synthesis was investigated from mixture powders of kaolin and aluminium trihydroxide which contain various $Al_2O_3$/SiO_2$ ratio (silica rich, stoichiometric, alumina rich). The flexural strength increases with the increase of the mullite-seed content in case of silica rich and stoichiometric mullite, but flexural strength decreases with the increase of the mullite-seed content in case of alumina rich mullite. Microstructural investigation revealed that aspect ratio of mullite grains increased with higher alumina content, along with lower sintered density. Mullite contents of specimens are increased with seed content regardless of $Al_2O_3$/SiO_2$ ratio of the mixture composition.

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Sintering Behavior and Mechanical Properties of Mullite-Zirconia Composites (Mullite-Zirconia 복합체의 소결거동 및 기계적 성질)

  • 박상엽
    • Journal of Korean Powder Metallurgy Institute
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    • v.4 no.1
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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$_2$.

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Synthesis of Mullite from Kaolin by Seed Addition Method (Kaolin으로부터 Seed 첨가법에 의한 Mullite 합성)

  • 김인섭;박주석;이명웅;이병하;소유영
    • Journal of the Korean Ceramic Society
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    • v.35 no.8
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    • pp.878-884
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    • 1998
  • Synthesis of high purity mullite from korean resourceful kaolin and water-soluble aluminium salts was in-vestigated by addition of mullite seed. Single phase of mullite was formed at 1350$^{\circ}C$ however its mullite con-tent was 31-33% Maximum content of mullite synthesized from kaoin aluminium nitrate and 8wt% mul-lite seed was 98% at 1600$^{\circ}C$ for 4 hours.

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Effect of Mullite on High Alumina Refractory (II) (고 알루미나질 내화물에 미치는 Mullite의 영향(II))

  • 김세훈;김인섭;박주석;강지연;이경희;이병하
    • Journal of the Korean Ceramic Society
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    • v.38 no.3
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    • pp.238-244
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    • 2001
  • 본 연구에서는 Seed 첨가법에 의하여 제조된 mullite(Syn M)와 외국산 mullite 2종류(sintered mullite : SM, fused mullite : FM)를 고알루미나질 내화물 원료에 적용하여 내화물 시편을 제조하였으며 mullite에 따른 결정상, 미세구조, 부피비중, 강도를 조사하였다. SM, FM, Syn M의 mullite 함유량은 93.17%, 86.79%, 97.57%이었으며 mullite를 15 wt% 첨가하여 제조한 시편의 물성을 조사한 결과 Syn M을 함유한 시편이 꺾임강도 338.60 MPa, 압축강도 9,427kgf/$\textrm{cm}^2$을 나타내었다. 외국산 mullite를 첨가한 시편의 강도는 Syn M을 첨가한 것보다 약 5~10% 정도 낮은 강도를 보였다.

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Synthesis of Mullite Powder from Alkoxides and the Properties of the Mullite-Zircocnia Composites (알콕사이드로부터 Mullite 분말의 합성 및 Mullite-Zirconia 복합체의 특성)

  • 함종근;이홍림
    • Journal of the Korean Ceramic Society
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    • v.27 no.2
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    • pp.201-210
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    • 1990
  • The mullite-15v/o ZrO2 composites were prepared by dispersing ZrO2-3m/o Y2O3 powders into the mullite matrix in order to improve the mechanical properties of the mullite. The densification and retention of t-ZrO2 in the matrix of synthetic mullite were also investigated. From IR spectroscopic analysis, the obtained amorphous SiO2-Al2O3 powder was observed to have Si-O-Al chemical bond in its structure which might result in the homogeneous mullite composition. The lattice parameter of the mullite powder calcined above 130$0^{\circ}C$ (a0=7.5468$\AA$) is nearly close to the value of stoichiometric mullite (71.8wt% Al2O3, a0=7.5456$\AA$). The sintering behavior, microstructure, flexural strength and fracture toughness of the mullite and mullite-15v/o ZrO2 composites have been studied. The mullite-15v/o ZrO2(+3m/o Y2O3) ceramics with relative densities of 96% were obtained when sintered at 1$600^{\circ}C$. The flexural strength and fractrue toughness of the composites sintered at 1$600^{\circ}C$(calcination temperature of mullite powders ; 125$0^{\circ}C$) had maximum values of 307MPa and 2.50MPa.m1/2, respectively. The fracture toughness improvement in the mullite-ZrO2 cmoposite is assumed to be resulted from the combined effect of the stress-induced phase transformation of tetragonal ZrO2 and the crack deflection due to microcracking by the monoclinic ZrO2 formation.

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Sintering Phenomena and Thermodynamic Analysis in the SiC Whisker-Reinforced Mullite Matrix Ceramic Composites During RF Plasma Sintering

  • Park, Youngsoo;:Michael J. MeNallan
    • The Korean Journal of Ceramics
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    • v.2 no.4
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    • pp.231-237
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    • 1996
  • Mullite ceramics can be sintered by rf plasma sintering to densities as high as 97% compared to the theoretical density of the mullite, while SiC whisker-reinforced mullite matrix ceramic composites were not sintered by plasma sintering. Decomposition of mullite occurs in a superficial regins at the outside surface of the specimen by volatilization of SiO at elevated temperature by plasma. SiC whiskers were destroyed, and the matrix was converted to alumina from SiC-whisker reinforced mullite matrix ceramic composites during the plasma sintering. Accelerated volatilization from the SiC whisker in the mullite prevents sintering. The volatile species are mainly SiC and CO gas species. The effects of plasma on mullite and SiC-whisker reinforced mullite matrix composites are interpreted by thermodynamic simulation of the volatile species in the plasma environment. The thermodynamic results show that the decomposition will not occur during hot pressing.

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A Synthesis of Mullite-Cordierite Composite Powders by Solution-Polymerization Route Based on Polyvinyl Alcohol (PVA를 이용한 Solution-Polymerization 합성법에 의한 Mullite-Cordierite 복합분말의 합성)

  • Lee, Yong-Seok;Lee, Byung-Ha
    • Journal of the Korean Ceramic Society
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    • v.41 no.9
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    • pp.663-669
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    • 2004
  • Mullite and cordierite, which were stable oxides having excellent thermal and chemical characteristics, were widely used as an engineering and electronic materials. However, thermal shock resistance of the mullite was detriorated, and strength of the cordierite was also reduced at high temperatures. The mullite-cordierite composite powders were synthesized for solving these problems in this study. The mullite-cordierite composite powders were manufactured by the solution-polymerization method using mixtures of fused silica, aluminium nitrate, magnesium nitrate, and PVA. Crystallinity, phase formation, density, and surface area of the synthesis powders were characteristics. Fine mullite-cordlerite composite powders were successfully synthesized at 1300$^{\circ}C$ and their surface areas were about 20㎡/g after planetary milling for 1h. With increasing the milling time, surface area increased to 23 ㎡/g for 4h ana 24㎡/g for 8h.

The Synthesis of Mullite by GAS - SOLID Reaction (반 기상법에 의한 Mullite의 합성)

  • 이경희;이병하;강현주;조재우
    • Journal of the Korean Ceramic Society
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    • v.38 no.1
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    • pp.9-14
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    • 2001
  • 본 연구는 우리나라 하동지방에서 다량으로 산출되는 저급 Kaoline을 활용하여 Mullite를 합성하는데 목적이 있다. 저질 Kolin을 AlF$_3$와 충분히 혼합한 후 130$0^{\circ}C$에서 반응시키면 거의 순간적으로 Mullite의 합성이 가능하였으며 이때에 얻어진 Mullite는 X-ray 회절결과 순수한 Mullite 단일상으로 나타났으며 소결체의 특성에 보면 1$600^{\circ}C$ 3시간 소결 후 비중은 2.8g/$m^2$이며 굽힘강도는 170 MPa을 나타내었다.

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Microstructure and Mechanical Properties of Infiltrated Zirconia-Mullite Composite (침투된 지르코니아-뮬라이트 복합체의 미세구조 및 기계적 성질)

  • 손영권;이윤복;김영우;오기동;박홍채
    • 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.

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Reinforcement of Porous Mullite Ceramics Using Ultra Fine Mullite Precursor Powders

  • Cho, Yong-Ick;Hisao Suzuki;Hidehiro Kamiya
    • The Korean Journal of Ceramics
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    • v.5 no.2
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    • pp.137-141
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    • 1999
  • To increase the strength of high-purity porous mullite ceramics, ultra fine mullite precursor powders of about 10nm in diameter were deposited at point of contact between primary coarse mullite particles of about 60$\mu\textrm{m}$. The deposited and hetero coagulated structures of ultra fine mullite precursor powders were controlled by pH. The optimum pH condition to form a uniform deposition of mullite powders between coarse mullite particles was in the range from 7 to 8. Deposition of the ultra fine powders did not form at pH < 7 and pH > 10 irregular deposition was observed from pH 8 to 9.

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