• Journal of the Korean Ceramic Society
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• v.38 no.2
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• pp.199-206
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• 2001

납석-뮬라이트의 상변이 과정을 주로 에너지여과 투과전자현미경을 이용하여 연구하였다. 납석은 (OH)를 읽고 pyrophyllite dehydroxylate로 된 후 뮬라이트와 크리스토발라이트로 상변이한다. Pyrophyllite dehydroxylate의 장주기 질서는 105$0^{\circ}C$에서도 유지된다. 생성 초기단계에서 뮬라이트는 pyrophyllite dehydroxylate에 대해 topotaxy를 보이며, elongation direction이 c*인 침상 결정으로 자라기 때문에 textured ED pattern을 나타낸다. Pyrophyllite dehydroxylate는 120$0^{\circ}C$에서 완전히 분해되어 뮬라이트의 결정 성장과 비정질 실리카로부터 크리스토발라이트의 생성이 이루어진다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.210-210
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• 2003

휘스커상의 뮬라이트의 생성온도와 속도는 출발물질로 사용되는 알루미나와 실리카의 화학적 순도, 입자크기 그리고 결정형태에 의존하며, 알루미나와 실리카의 조성비에 따라 생성되는 뮬라이트의 형태가 변한다. 각 원료에 대한 반응성을 관찰하기 위하여 출발원료인 Al(OH)$_3$, 비정질 SiO$_2$, AlF$_3$를 혼합 각각 단일조성과 2상 및 3상의 원료를 혼합 분쇄하여 분무건조한 조립분말을 5$0^{\circ}C$ 구간으로 나누어 상온에서 130$0^{\circ}C$까지 튜브 로에서 열처리하였다. Al(OH)$_3$와 AlF$_3$를 단독으로 열처리하였을 경우에는 안정한 상태로 열처리가 진행되었으나, 혼합하였을 경우에는 40$0^{\circ}C$ 이상의 온도에서 서서히 반응하였다. 각 온도구간에서 열처리한 시편은 미세구조 관찰과 상분석을 통하여 플루오르 토파즈와 휘스커상의 뮬라이트의 생성을 관찰하였으며, 생성된 휘스커 뮬라이트는 조립의 형상을 원형대로 보존하였으며, 조립의 강도를 측정하기 위하여, 초음파 분산기와, 초음파 Homgeniger를 이용하여 처리한 결과 대부분 원래의 형상을 유지하였다.

• Korean Journal of Materials Research
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• v.9 no.6
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• pp.630-634
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• 1999

Porous mullites were fabricated using $Al(OH)_3$ and amorphous $SiO_2$ as starting materials by reaction sintering method. The molar ratios of alumina and silica varied from stoichiometric mullite composition to silica-rich and alumina-rich compositions. $AlF_3$ of 0, 1, 5, 10 wt% wad added to each composition, and the effects of composition and the additive for the formation of mullite were examined. The temperature of mullite formation decreased as the amount of $AlF_3$ increased, and themullite phase was formed in the stoichiometric composition in addition of 5 wt% $AlF_3$ at $1250^{\circ}C$ and porous whiskered mullite were synthesized in the sample sintered at $1300^{\circ}C$ and higher temperature. The effect of temperature on the mullite formation was not observed for the sample with 5 wt% or higher content of $AlF_3$, and the body showed little contraction after sintering.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.197-197
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• 2003

• Journal of the Korean Ceramic Society
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• v.41 no.1
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• pp.51-56
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• 2004

Mullite whiskers were synthesized using $Al(OH)_3$, amorphous $SiO_2$ and $AIF_3$ as starting materials by a vapor-solid reaction at relatively low temperature of $1100^{\circ}C$. Leaflet Fluorotopaz was observed for the specimen heat-treated at $800^{\circ}C$. Fluorotopaz was decomposed at $1000^{\circ}C$ and only mullite phase was observed for the specimen sintered at $1100^{\circ}C$ and above. It was found that the synthesized mullite at $1200^{\circ}C$ had grown to [001] direction and side planes were the {110}. The distance of (110} plane was $5.34^{\AA}C$. The amounts of $Al_2O_3$ in mullite was 73.56(1.39)wt%.

• Journal of the Korean Ceramic Society
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• v.38 no.6
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• pp.537-544
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• 2001

뮬라이트, 지르코니아, 뮬라이트/지르코니아 비수성 현탁액의 분산 및 레올로지에 미치는 공정보조제의 영향이 침전밀도, 점도, 입자크기를 측정함으로써 검토되었다. 현탁액의 분산안정성 (높은 침전밀도와 낮은 점도로 특징 된)은 분산제+가소제+결합제를 함유하는 경우에 비하여 분산제 또는 분산제+가소제를 함유하는 경우가 우수하였다. Ball mulling 후의 입자크기분포는 공정보조제의 종류에 거의 영향을 받지 않았다. 결합제를 부가적으로 함유하는 현탁액은 상대적으로 강한 shear thinning 거동을 나타내었다.

• Composites Research
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• v.13 no.5
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• pp.31-36
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• 2000

The effect of several important processing variables was investigated on formation of porous mullite with acicular microstructure. Experimental results demonstrated that microstructure and porosity of porous mullite are depending on concentration of $AlF_3$, holding time at $900^{\circ}C$ and starting material. Acicular mullite was developed by increasing amount of $AlF_3$ and holding time at $900^{\circ}C$. Mullite began to be formed at $1200^{\circ}C$ and the resultant microstructure sintered at this temperature is similar to those at higher temperatures. Porosity increases with increase in amounts of $AlF_3$ and holding time at $900^{\circ}C$ . Therefore, it is found that microstructure of reaction-sintered porous mullite can be controlled by governing the amount of $AlF_3$ and holding time at $900^{\circ}C$.

• Resources Recycling
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• v.10 no.6
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• pp.29-34
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• 2001

Fly ash powders were refined and separated into fine and coarse size by multi-air classification, and each particle was used for synthesizing mullite and zeolite. Mullite was prepared by sintering the mixture of fine fly ash with mean size of 6.5 $\mu$m and $A1_2$$O_3$powder at above $1450^{\circ}C$. Zeolite was synthesized through hydrothermal reaction with coarse fly ash mean size of $56.3\mu$m in 3.5 M NaOH solution at $120^{\circ}C$. The whole range of particle size can be recycled through size classification into fine and coarse fractions, which are used for syntheses of inorganic materials.

• Korean Journal of Materials Research
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• v.9 no.12
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• pp.1188-1195
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• 1999

The effect of aluminosilicate sol on the formation of mullite layer in zircon shell mold was investigated. Aluminosilicate sol was prepared by mixing of colloidal silica(NALCO(R) 1130) and an aqueous solution of aluminium nitrate at room temperature. The sol gelled at 50$^{\circ}C$ for 48 hrs. It was identified that the gel consists of aluminosilicate complexes and gibbsite. The coordination number of all aluminium ion bonded with silicon ion was four. Mullite phase formed by sintering above 1300$^{\circ}C$. XRD peak of mullite sharpened with increasing sintering temperature and the content of aluminium nitrate. Mullite phase displayed whisker-like 0.5~5${\mu}m $ particles. Separation between 1st and 3rd layers during sintering and the difference in thermal expansion coefficient between residual silica and mullite.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.6
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• pp.239-245
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• 2001

$Al/Al_2O_3$composites were prepared from the reaction of mullite preforms and amorphous silica in aluminum melt at $1100^{\circ}C$ for 5 hrs. The chemical reaction between mullite preform and aluminum melt has formed the interconnected microstructure. The metal content of $Al/Al_2O_3$composite was controlled with the variable of the apparent porosity according to the sintering temperature of mullite preforms; $1600^{\circ}C$,$ 1625^{\circ}C$, $1650^{\circ}C$ and $1700^{\circ}C$, the mechanical properties of $Al/Al_2O_3$composite were investigated upon the content of Al. The mullite preform sintered above $1600^{\circ}C$ showed the chemical reaction with the penetrated Al melt, but the mullite sintered at $1600^{\circ}C$ didnt react with aluminum melt owing to the non-wetting of Al melt/mullite preform. The influences of penetration direction on the mechanical properties of composites were considered with the two different models of the perpendicular pattern and the parallel pattern to the direction of Al melt penetration. With the increase of Al metal penetration content, the fracture strength of $Al/Al_2O_3$composite decreased and the fracture toughness of composite increased. The microstructure of $Al/Al_2O_3$composite was determined by the direction of metal penetration, but the fracture strength and fracture toughness of composite didnt show the dependence on metal penetration direction.