• Title/Summary/Keyword: Mullite decomposition

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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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Synthesis and Characterization of Submicrometer Monodispersed Ceramic Powders of Aluminium Titanate-Mullite Composite by Sol-Gel Process

  • Kim, Ik-Jin;Kim, Do-Kyung;Lee, Hyung-Bock;Ko, Young-Shin
    • 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.

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Preparations of Nano-scale Mullite Powder from Solution Combustion Synthesis (용액연소합성에 의한 나노크기 물라이트 분말의 제조)

  • Lee, Sang-Jin;Yun, Jon-Do;Gwon, Hyeok-Bo;Jeon, Byeong-Se
    • Korean Journal of Materials Research
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    • v.11 no.9
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    • pp.797-801
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    • 2001
  • In this study, the solution combustion method was employed to synthesize stoichiometric mullite, and hence the attrition process was employed to prepare ultrafine mullite particles with nano size. The thermal decomposition behavior and partial pressure of equilibrium species of both oxidizer and fuel were considered during solution combustion process. The synthesized product was mullite phase with 40 nm crystalline size, and the alumina contents of the product by TEM/EDS quantity analysis was 3.12$\pm$04 mole. The result showed that the synthesized mullite was almost close to the it's stoichiometric composition. For attrition process, the dispersion behavior of the mullite suspension was controlled and was comminuted with the condition of 800 rpm for 4 hours using 0.3 mm zirconia ball media. As a result of comminution, the mean particle size was 80 nm.

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Synthesis of $\beta$-SiC Whiskers by Decomposition-Carbonization of Mullite (물라이트의 환원분해 및 탄화법에 의한 $\beta$-SiC 휘스커의 합성)

  • 김종엽;남원식;최상욱
    • Journal of the Korean Ceramic Society
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    • v.32 no.10
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    • pp.1139-1146
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    • 1995
  • $\beta$-SiC whiskers could be formed from a system of mullite-carbon-hydrogen by VLS mechanism at elevated temperatures. It was considered that methane gases were generated from the reaction of hydrogen gases with carbon black, and were reacted with mullite to produce two kinds of gases; silicon suboxide (SiO) and carbon monoxide (CO) of precursors of SiC. With increasing the synthesizing temperature up to 146$0^{\circ}C$, the formation of $\beta$-SiC whisker increased from 0.58 mg/$\textrm{cm}^2$ to 3.98 mg/$\textrm{cm}^2$ on the basis of unit area of carbon block, and the diameters of whiskers had their uniformity due to the reduction in stacking faults.

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Fabrication of Porous Mullite Ceramics and Its Properties (다공성 Mullite 세라믹스 제조 및 그 특성)

  • 김병훈;나용한
    • 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.

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Mixed Grinding Effect on Kaolinite-Aluminum Trihydroxide Mixture and Its Influence on Mullite Formation (Kaolinite-Aluminum Trihydroxide의 혼합물의 혼합분쇄효과 및 Mullite의 생성에 미치는 영향)

  • 류호진
    • 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.

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Fabrication of Mullite-Bonded Porous SiC Using Ti3AlC2 MAX Phase

  • Septiadi, Arifin;Yoon, Dang-Hyok
    • Journal of the Korean Ceramic Society
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    • v.56 no.2
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    • pp.191-196
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    • 2019
  • This study assessed the feasibility of a Ti3AlC2 MAX phase as an Al-source for the formation of a mullite bond in the fabrication of porous SiC tubes with high strength. The as-received Ti3AlC2 was partially oxidized at 1200℃ for 30 min before using to minimize the abrupt volume expansion caused by oxidation during sintering. Thermal treatment at 1100-1400℃ for 3 h in air led to the formation of Al2O3 by the decomposition of Ti3AlC2, which reacted further with oxidation-derived SiO2 on the SiC surface to form a mullite phase. The fabricated porous SiC tubes with a relative density of 48 - 62 % exhibited mechanical strengths of 80 - 200 MPa, which were much higher than those with the Al2O3 filler material. The high mechanical strength of the Ti3AlC2-added porous SiC was explained by the rigid mullite neck formation along with the retained Ti3AlC2 with good mechanical properties.

Thermal Behavior of Dickite (딕카이트의 열적 특성 연구)

  • 조현구
    • Journal of the Mineralogical Society of Korea
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    • v.12 no.1
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    • pp.11-22
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    • 1999
  • Thermal behavior of dickite was studied by thermal analysis, X-ray diffraction analysis, electron microprobe analysis, and scanning electron microscopy, Dickite has an endothermic peak at about$ 650^{\circ}C$ and an exothermic one at $960^{\circ}C$ in the differential thermal analysis. The endothermic reaction is assigned to the decomposition of dickite to meta-dickite. Hydroxyl radicals are removed from dickite structure by the reaction, resulting in the weight loss about 10.5~14.5% and appearance of a 14$\AA$ phase different from other kaolin minerals. The reaction slowly proceed in the range of $200^{\circ}C$. As the completion of decomposition, aciclular mullite forms at the expense of meta-dickite plates with random crystallographic relationship. Mullites have diverse silica versus alumina ratio. The exothermic reaction without weight loss seems to be due to the formation of spinel and amorphous silica. The spinel phase shows cryptocrystalline globular morphology accompanying a little amount of silica. From spinel phase shows cryptocrystalling globular morphology accompanying a little amount of silica. From this work, it is suggested that mullite is formed from meta-dickite much lower temperature than the reported one in the previous works.

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Alumimium Titanate-Mullite Composites : Part1,Thermal Durability (Alumimium Titanate-Mullite 복합체: Part1, 열적 내구성)

  • Kim, Ik-Jin;Gang, Won-Ho;Go, Yeong-Sin
    • Korean Journal of Materials Research
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    • v.3 no.6
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    • pp.624-631
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    • 1993
  • The composites in the system aluminium titanate-mullite were synthesized by stepwise alkoxide hydrolysis of tetraethylorthosilicate, Si(OCLH5), and titaniumtetraethoxide, $Ti(OC_{2}H_{5})_4$ in $Al_{2}O_{3}$ ethanolic colloidal solution. All particles produced by sol-gel-process were amorphous, monodispesed and had a narrow particle size distribution. Sintered bodies at $1600 ^{\circ}C$ for 2h were subjected to prolonged durability tests-on the one hand annealing at the critical decomposition temperature of $1100 ^{\circ}C$ for lOOh and on the other cyclic thermal shock between 750 and $1400 ^{\circ}C$ for 100h. The best thermal durability was achieved by a composition containing 70 and 80 vol% aluminium titanate, which showed little change in microstructure and thermal expansion cycles during the tests. The microstructural degradation of samples studied using scanning electron microscopy, X-ray diffraction, and dilatometry, was presented here. The study was conducted in order to predict the service life of aluminium titanate-mullite ceramics formed by this processing route.

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