• 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.

• Journal of Powder Materials
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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$_2$.

• 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.

• Journal of the Korean Ceramic Society
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• v.38 no.2
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• pp.238-238
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• 2001

15% Syn M, sintered mullite(SM) and fused mullite(FM) was added to produce high alumina refractory materials. Mullite content of SM, FM and Syn M was 93.17%, 86.79%, 97.57% repectively. Mechanical properties of specimens (added 15wt% mullite) ware investigated to be flexural strength 338.60MPa, compressive stcngth 9,427kgf/㎠. But the specimen which imported mullite was added showed 5~10%l lower stregth than syn M added.

• 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.

• 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.

• 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.

• 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.

• 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.

• Journal of the Korean Ceramic Society
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• v.38 no.2
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• pp.128-136
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• 2001

본 연구에서는 kaolin을 이용하여 반기상법, gel coating법, seed 첨가법으로 mullite를 합성하였으며 mullite 15 wt%를 고 알루미나질 내화물 원료에 첨가하여 내화물 시편을 제조하였다. 제조된 시편의 물성을 분석한 결과 seed 첨가법으로 제조된 mullite를 첨가한 시편의 물성이 338.60 MPa의 꺾임강도와 9,427 kgf/$\textrm{cm}^2$의 압축강도값을 나타내었다. 제조된 시편의 내화도 및 잔존선팽창수축률을 측정한 결과 나머지 두가지 방법으로 합성한 mullite나 일반적인 고 알루미나질 내화물에 비하여 좋은 특성을 나타내었다.