• Journal of the Korean Ceramic Society
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• v.24 no.4
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• pp.376-384
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• 1987

Kaolin was treated by HF and fired at high temperature in order to reduce silica and impurity minerals of kaolin, and eventually to increase the yield of mullite. The kaolin structure was destroyed by HF-treatment and transformed into mullite at lower temperature than those of non-treated kaolin. Not only the silica content of kaolin was reduced, but also the crystalline structure of it was destroyed by HF-treatment.

• Economic and Environmental Geology
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• v.32 no.4
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• pp.411-418
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• 1999

Mullitization of halloysite was examined with special attention to the influence of polytypism and impurities on the phase transformation. The phase transformation sequence in halloysite is identical with those in kaolinite and in dickite. Difference in the phase transformation above $1000^{\circ}C$ in kaolin minerals is attributed to the different crystal structures of metakaolins or the effect of impurities. Growth of mullite crytals in the discordered kaolinte including halloysite or illite occurs at about $100^{\circ}C$ lower temperature. Cristobalite is also hardly produced.

• Korean Journal of Materials Research
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• v.9 no.8
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• pp.843-848
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• 1999

The efect of A1 addition and sintering condition on mutization behavior between alumina and silica in alumina-based shell mold was investigated. A1 addition and high sintering temperature increased the degree of mullitization between alumina/silica but decreased the room temperature strentgh of the shell molds. It was identified that the sintered strength of the shell molds was in range of 2.0~2.6kg/$\textrm{mm}^2$. Al addition suppressed deflection of the shell molds at high temperature. Especially, no deflection was observed in the specimen which was sintered at $1000^{\circ}C$ for 1hr with 2.5wt% Al. The specimen sintered at $1500^{\circ}C$ for 4hrs with no Al addition also displayed no deflection.

• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.625-630
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• 1989

Aluminium silicate gels were prepared by gel-technique using Al(OH)3 and TEOS as starting materials. Aluminium silicate gel as formed mullite at 120$0^{\circ}C$. From this method, homogeneous mullite was formed available needle-like shaped and close compacted. As excess SiO2 mullite composition, the needle-like shaped crystal, size according to increased with SiO2, was increased from 3${\mu}{\textrm}{m}$ to 7${\mu}{\textrm}{m}$ but liquid phase did not affect the formation of needle-like shaped mullite. As excess Al2O3 mullite composition, the needle-shape mullite crystal could not be detected because Al2O3 acted as chunky behavior.

• Economic and Environmental Geology
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• v.32 no.4
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• pp.399-409
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• 1999

Mullitization of kaolinite and dickite was examined with special attention to the influence of polytypism and impurities on the phase transformation. The phase transformation sequence in dickite is identical with that in kaolinite except that cristobalite is crystallized at $50^{\circ}C$ higher temperature in dickite. Difference in phase transformation above $1000^{\circ}C$ in kaolin minerals is attributed to the different crystal structures of metadickite and metakaolinite on the effect of impurities. A part of quartz is transformaed into cristobalite. Spinel-type phase produced in disordered kaolins including illite occurs over a short range of temperatures. Primary mullite is transformed into orthorhombic mullite at higher temperature as well. These results sustain the idea that disintegration of methkaolin and the spinel-type phase supplies extra sillica and promotes the growth of mullite cristobalite.

• Journal of the Korean Ceramic Society
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• v.23 no.2
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• pp.7-12
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• 1986

As the other silicate minerals such as kaolinite and pyrophyllite kyanite ($Al_2O_3$.$SiO_2$) is transformed to mullite and free silica or glassy phase at high temperature. Therefore $Al_2O_3$ is commonly added to kyanite in order to increase the mullite-yield. In case of $Al_2O_3$-addition mullite-yield depends on the reactivity of added $Al_2O_3$ with free silica which occurs from transformation of kyanite or exists as accessory minerals. It is well known that addition of activated $Al_2O_3$Al powder is added to kyanite to utilize the aluminothermal reac-tion of Al powder in reaction of mullite-formation.

• 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.26 no.3
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• pp.361-370
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• 1989

Mullite powders were synthesized from the common solution of aluminum sulfate and sodium silicate solutions by the emulsion-hot kerosene technique. The reaction temperature and mechanism for mullitization and the characteristics of synthesized mullite powders were investigated. The effect of Na components introduced from sodium silicate solution on the physical property and microstructure of sintered mullite was also examined. It was proved that mullites were formed at 75$0^{\circ}C$ through the reaction mechanism of Na2O.2.2SiO2＋3.3Al2(SO4)3longrightarrow1.1(3Al2O3.2SiO2)＋Na2SO4＋8.9SO3. Synthetic mullite powders consisted of the compositiion of 3Al2O3.2SiO2 and showed highly agglomeration of hollow spherical particles of 1${\mu}{\textrm}{m}$ diameter. The density and fracture toughness of sintered mullites were somewhat reduced because of the effect of a very small amount of residual Na components.

• Journal of the Korean Ceramic Society
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• v.20 no.2
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• pp.123-128
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• 1983

This research is aimed to synthesize the mullite by adding Al powder of $Al_2O_3$ to kaolin. Specimens fired at 1400, 1450 and 150$0^{\circ}C$ were compared in their X-ray diffraction patterns quantitative analysis of mullite formed and fine microstructures with those containing reactive $Al_2O_3$ activated $Al_2O_3$ as alumina source The experiment of Al oxdiation was also performed by measuring the weight increase of specimens. Two different shapes of mullites acicular and chunky were observed by SEM and the yield of mullites were in-creased by the order of adding activated $Al_2O_3$ reactive $Al_2O_3$ and Al powder to kaolin.

• Journal of the Korean Ceramic Society
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• v.49 no.3
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• pp.216-220
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• 2012

Mullite formation in a porcelain body was promoted extensively by replacing kaolinite with pyrophyllite. Effects of mullite formation and vitrification by substitution of kaolinite with pyrophyllite on the mechanical and thermal properties were investigated. Addition of 45-55% pyrophyllite (pyrophyllite (45-55%)-feldspar (30%)-Gairome clay (20%)) could vitrify the sintered samples (water absorption : 0.05%, bulk density : 2.66g/cc) and improve the flexural strength (122MPa) when fired at $1280^{\circ}C$. Mullite formation was found to be decreased with increasing content of pyrophyllite. On the contrary, beyond 50% of pyrophyllite quartz and cristobalite phases was found to be increased. Thermal expansion coefficient of the samples decreased with increase of mullite phase. In triaxial system of pyrophyllite-feldspar-clay, the mullite formation of the samples with 50% pyrophyllite reaches about 78.7% and thermal expansion coefficient was found to be $5.4{\times}10^{-6}/K$.