• Journal of the Korean Ceramic Society
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• v.29 no.10
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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.

• Journal of the Korean Ceramic Society
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• v.33 no.8
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• pp.915-920
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• 1996

Fine mullite precursor was prepared by colloidal sol-gel processes. Aluminum isopropoxide $[Al(i-OC_3H_7)_3]$ as a starting material of $Al_2O_3$ and silicic acid extracted by THF from sodium silicate as a starting material of $SiO_2$ were used. Sodium silicate was first acidified by dilute sulfuric acid to form silicic acid. ; followed by extraction using THF, Mullite precursor was synthesized by sol-gel processes from aluminum isopropoxide and sillicic acid considering the degree of extraction of Si and the removal efficiency of Na. The impurity content of silicic acid extracted by THF was below 0.04% Synthetic mullite precursor consisted of $3Al_2O_3{\cdot}2SiO_2$ and showd spherical particles of $0.05{\mu}m$ diameter and below 0.462% of impurites. The mullite precursor was characterized by EDS, XRD, TG/DSC SEM, FT-IR spectroscopy ICP and TEM.

• Journal of the Korean Ceramic Society
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• v.34 no.2
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• pp.195-201
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• 1997

The present paper describes the effect of dry mixed grinding on kaolinite-aluminum trihydroxide mixture with a planetary ball mill before sintering and its influence on mullite formation during sintering. The size reduction of the mixture is market in the early stage of grinding and the obtained fine particles agglomerate subsequently with an increase of grinding time. The crystal structure of the mixture is collapsed easily into an amorphous one by planetary ball milling, of which amount increases with an increase of grinding time. Only mullite phase except for anatase as an inherent impurity in kaolinite appeared in the sintered body of the mixtures with mixed grinding as relatively lower temperature 1523K, while corundum, cristobalite, and Al-Si spinel phases, besides mullite were formed in the sintered body of the mixture without mixed grinding. Therefore, the mixed grinding treatment is very effective to improve the homogeneous mixing and disp-ersion of the mixture of raw materials on a micro scale and to decrease the thermal decomposition tem-perature by crystal structure change of them so as to obatin direct preparation of mullite with high purity at relatively low temperature.

• Journal of the Korean Ceramic Society
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• v.28 no.7
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• pp.503-508
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• 1991

High pure and fine mullite powders were synthesized from Al-secbutoxide[Al(OC4H9)3] and TEOS[Si(OC2H5)4] (SiO2/Al2O3=2/3 mole). Sol-Gel process by partial hydrolysis technique, as it were, first, TEOS was partially hydrolysized and then mixed with Al-secbutoxide for complete hydrolysis was used. The mullite precursor was synthesized within 30 hrs, which was reduced about a half of synthetic time in comparison with the other's study. Al-Si spinel was formed at 980℃ and mullite crystal was formed at 1200℃. Mullite powders synthesized in this study was spherical type like those of the other studies and particle sizes were very fine. Also mullite powders calcined at 1,600℃ had a stoichiometric composition (3Al2O3·2SiO2) and lattice constants were coincided with known theoretical values.

• Journal of the Mineralogical Society of Korea
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• v.11 no.1
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• pp.32-44
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• 1998

The transformation sequence of kaolinite to mullite is examined with new electron diffraction data obtained mainly by an energy filtering transmission electron microscope. Kaolinite is transformed finally into mullite and cristobalite through several steps of continuous reactions by heating, which result in metakaolinite, microcrystalline spinel-type phase and amorphous silica. Metakaolinite maintains a short-range order in its structure ven at $920^{\circ}C$. Spinel phase results from a topotactictransformation of metakaolinite apart from the breakdown of metakaolinite structure. the first strong exothermic peak on DTA curve is mainly due to the extraction of amorphous silica from metakaolinite and the gradual nucleation of mullite. Metakaolinite decomposes around$ 940^{\circ}C$ to mullite that doesn't show a clear crystallographic relationship to the parent metakaolinite structure. However, spinel phase produced previously is maintained. The initially formed spinel and mullite phases are suggested to be Al-rich, but progressively gain Si in their structures at higher temperatures. Spinel phase decomposes completely through a second weak exothermic reaction promoting the growth of mullite, and crystallization of amorphous silica to cristobalite.

• Journal of the Korean Ceramic Society
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• v.28 no.2
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• pp.153-159
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• 1991

Polymeric alumina sol and polymeric silica sol were synthesized from aluminum sec-butoxide and tetraethyl orthosilicate, respectively as starting materials. A clear mullite sol was obtained by mixing these sols. When the mullite sol had a proper viscosity which was dependent on drying time, the fibers were fabricated by spinning. The optimum viscosity for fabrication of mullite fibers was 103-104 cps, and the fibers with various sizeswere made using the sols. The mullite was a major phase of the calcined fibers and the diameters of the fibers were about 50$\mu\textrm{m}$.

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.611-619
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• 1997

Optimal Mullite sol was synthesized by sol-gel process using Aluminium sec-butoxide(ASB), Tetraethoxysilane(TEOS) and then, Mullite films were dip-coated with various holding time in sol bath and heat-treated at 130$0^{\circ}C$ above for crystallization. The thickness of coated film increased linearly with holding time in sol bath and average pore size was controllable within 20~30$\AA$.

• Korean Journal of Materials Research
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• v.16 no.12
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• pp.719-724
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• 2006

Ultrafine mullite powder was prepared from aluminium-secbutoxide and tetraethyl orthosilicate(TEOS) in the molar $Al_2O_3/SiO_2$=3/2. Sol-gel method by partial hydrolysis technique, as it were, first, TEOS was partially hydrolysized and then mixed with Al-secbutoxide for complete hydrolysis was used. X-ray diffraction, infrared spectroscopy and transmission electron microscopy, etc. confirmed that the mullite powder prepared by this method is in the stoichiometric $Al_2O_3/SiO_2$ ratio. Al-Si spinel was formed at $980^{\circ}C$ and ultrafine mullite powder with about 20 nm particle size was obtained above $1,200^{\circ}C$. Also mullite powders calcined at $1,600^{\circ}C$ had a stoichiometric composition, $3Al_2O_3{\cdot}2SiO_2$ and the lattice constants of the mullite powders calcined above $1,200^{\circ}C$ were almost coincided with theoretical values.

• Journal of the Korean Ceramic Society
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• v.31 no.3
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• pp.275-281
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• 1994

Mullite ceramics have recently been utilized as ceramic gas filters for high-temperature treatment of solid wastes due to their low thermal expansion coefficient and high refractoriness under load. In this experiment, mechanical, thermal and microstructural properties of porous mullite ceramics, which were used as carriers and high-temperature gas filters in food industry, were investigated as a function of starting raw materials. Porous mullite ceramics showed different microstructures depending on their starting materials. The specimen M2 had excellent resistance to thermal spalling and high mechanical strength. The average pore size varied from 0.3 ${\mu}{\textrm}{m}$ to 16.6 ${\mu}{\textrm}{m}$, and porous mullite ceramics fabricated by thermal decomposition of Al(OH)3 had very large pores and broad distribution of pore size.

• The Korean Journal of Ceramics
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• v.1 no.1
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• pp.1-6
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• 1995

Submicrometer, monosized ceramic powder of $Al_2TiO_5$$Al_2O_3$ ethanolic solutions. All particles produced by sol-gel-process were amprphous, monodispersed and with a narrow particle-size distribution. Compacts fired above $1300^{\circ}C$ formed aluminium titanate. Mullite formed first at $1480^{\circ}C$. After decomposition test at $1100^{\circ}C$, and cyclic thermal decomposition test at 750-1400-$750^{\circ}C$ for 100hrs., aluminium titanate was well stablized by composition with mullite.