• Title/Summary/Keyword: mullite ceramics

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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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Reinforcement of Porous Mullite Ceramics Using Ultra Fine Mullite Precursor Powders

  • Cho, Yong-Ick;Hisao Suzuki;Hidehiro Kamiya
    • The Korean Journal of Ceramics
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    • v.5 no.2
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    • pp.137-141
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    • 1999
  • To increase the strength of high-purity porous mullite ceramics, ultra fine mullite precursor powders of about 10nm in diameter were deposited at point of contact between primary coarse mullite particles of about 60$\mu\textrm{m}$. The deposited and hetero coagulated structures of ultra fine mullite precursor powders were controlled by pH. The optimum pH condition to form a uniform deposition of mullite powders between coarse mullite particles was in the range from 7 to 8. Deposition of the ultra fine powders did not form at pH < 7 and pH > 10 irregular deposition was observed from pH 8 to 9.

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Synthesis of Mullite Whisker from Fly Ash (플라이 애쉬로부터 뮬라이트 휘스커의 합성)

  • Kim, Sung-Hwan;Bang, Hee-Gon;Park, Sang-Yeup
    • Journal of the Korean Ceramic Society
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    • v.42 no.11 s.282
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    • pp.753-757
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    • 2005
  • In this study, we attempted to recycle the fly ash as a mullite whisker with addition of $Al_{2}O_{3}$ to obtain the high yield of mullite whisker. During the reaction process, mullite whisker was formed with the reaction of amorphous $\alpha$-Cristobalite and Anorthite above $1350^{\circ}C$. With increasing the heat treatment temperature and time, the mean length and aspect ratio of mullite whiskers was gradually increased.

Development of heat resistant body using Sanchung Kaolin and Jangsu gobdol sludge (산청고령토와 장수곱돌 슬러지를 사용한 내열소지 개발)

  • Kim, Sanggon
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.30 no.1
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    • pp.27-32
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    • 2020
  • The main cystal phases of traditional ceramics made of clay, quartz, and feldspar are mullite and cristobalite. Although mullite can provide strength to the ceramic body, it cannot be used for the heat resistant ceramics because the thermal expansion coefficient of it is relatively high as 5.3 × 10-6/℃. In this study, development of lightweight heat resistant ceramics was tried by producing cordierite phase, of which the thermal expansion coefficient is 2.6 × 10-6/℃, instead of forming mullite phase in the ceramic body by using Sanchung Kaolin and Jangsu gobdol sludge. It was concluded that ceramics having good heat resistant, bending strength, and refractoriness under load could be fabricated when 80 wt% of Sanchung Kaolin and 20 wt% of Jangsu gobdol sludge were used as raw materials. Also, the bulk specific gravity is 1.78, which is lighter than the existing Buncheong ware.

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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Fabrication and Machinability of Mullite-ZrO2-Al2TiO5 Ceramics

  • Shin, Young Been;Lee, Won Jae;Kim, Il Soo
    • Journal of the Korean Ceramic Society
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    • v.52 no.6
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    • pp.423-428
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    • 2015
  • The machinability of materials is an important factor in engineering applications. Many ceramic components that have complex shapes require machining, typically using diamond tools, which leads to high production cost. Machinable ceramics containing h-BN have recently been developed, but these materials are very expensive because of high cost of raw materials and machining. Therefore the development of low-cost machinable ceramics is desirable. In this study, mullite-$ZrO_2$ ceramics were prepared additions of $Al_2TiO_5$. $ZrSiO_4$, $Al_2O_3$, and $Al_2TiO_5$ powders mixed at various molar ratios with sintering at 1400, 1500, and $1600^{\circ}C$ for 1 hr. Phase formation and microstructure of the sintered ceramics were observed by XRD and SEM, respectively. The machinability of each specimen was tested using the micro-hole machining method. The machinability results show that the ceramics sintered at temperatures over $1500^{\circ}C$ can be used as good low-cost machinable mullite-$ZrO_2-Al_2TiO_5$ ceramics.

Effect of Template Content on Microstructure and Flexural Strength of Porous Mullite-Bonded Silicon Carbide Ceramics (기공형성제 함량이 다공질 Mullite-Bonded SiC 세라믹스의 미세구조와 강도에 미치는 영향)

  • Choi, Young-Hoon;Kim, Young-Wook;Woo, Sang-Kuk;Han, In-Sub
    • Journal of the Korean Ceramic Society
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    • v.47 no.6
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    • pp.509-514
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    • 2010
  • Porous mullite-bonded SiC (MBSC) ceramics were fabricated at temperatures ranging from 1400 to $1500^{\circ}C$ for 2 h using silicon carbide (SiC), alumina ($Al_2O_3$), strontium oxide (SrO), and poly (methyl methacrylate-coethylene glycol dimethacrylate) (PMMA) microbeads. The effect of template content on porosity, pore morphology, and flexural strength were investigated. The porosity increased with increasing the template content at the same sintering temperature. The flexural strength showed maximum after sintering at $1450^{\circ}C$/2 h for all specimens due to small pores and dense strut. By controlling the template content and sintering temperature, it was possible to produce porous MBSC ceramics with porosities ranging from 30% to 54%. A maximum flexural strength of ~51MPa was obtained at 30% porosity when no template were used and specimens sintered at $1450^{\circ}C$/2 h.

The Fabrication and Characteristics of Porous Ceramics by Pressureless Powder Packing Forming Method ; II, Mullite & Cordierite (무가압분말 충전성형법에 의한 다공성 세라믹스의 제조 및 특성 : II. 뮬라이트 & 코디어라이트)

  • 박정현;황명익;김동희;최환욱;김용남
    • Journal of the Korean Ceramic Society
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    • v.36 no.6
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    • pp.671-678
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    • 1999
  • Porous ceramics were fabricated from pressureless powder packing forming method using mullite and cordierite powders granulate by spray drying. The bending strength and shrinkage of porous ceramics were increased and their porosity were decreased with increasing temperature. It showed homogeneous distribution of 2$\mu\textrm{m}$ intergranular pores of mullite at 1400$^{\circ}C$, 2.5$\mu\textrm{m}$ intergranular pores of cordierite at 1300$^{\circ}C$ respedtively. Above that temperature intragranular particles were sintered and sintering by intergranular necking was extremely proceeded. In the test of thermal shock resistance sudden decrease of bending strength to $\Delta$T was not shown because intergranular large pore prevented sudden crack propagation.

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High Temperature and Fatigue Strength of crack-healed Mullite/Silicon Carbide Ceramics (균열 치유된 Mullite/SiC 세라믹스의 고온강도와 피로강도)

  • Ando, K.;Chu, M.C.;Tsuji, K.;Sato, S.
    • Journal of Power System Engineering
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    • v.6 no.1
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    • pp.88-95
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    • 2002
  • 본 연구에서는 균열 치유 거동을 가지는 소결된 Mullite/SiC의 모재, 열처리재, 균열재, 치유 균열재의 기계적 특성이 논의되었다. 반타원형 균열의 치수는 $100{\mu}m$$200{\mu}m$이다. 얻어진 결과는 다음과 같다. (a) Mullite/SiC 복합 세라믹스는 균열 치유 능력이 있었다. (b) 최적의 균열 치유 열처리 조건은 $1300^{\circ}C$, 1시간이었다. (c) 치유 가능한 최대 균열 길이는 직경 $100{\mu}m$의 반타원 균열이다. (d) 균열 치유부는 $1200^{\circ}C$이상에서 충분한 강도를 가졌고, 대부분의 시험편은 균열 치유부 이외의 영역에서 파단 하였다. (e) 공기중에서 예열처리는 본 재료의 피로강도 향상에 유용하였다.

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Freeze Cast Porous Mullite Ceramics and Recycling of Coal Fly Ash (동결주조 다공질 뮬라이트 세라믹스의 제조와 석탄회의 재활용)

  • Kim, Kyu Heon;Yoon, Seog Young;Park, Hong Chae
    • Korean Journal of Materials Research
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    • v.26 no.2
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    • pp.61-66
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    • 2016
  • In order to fabricate porous mullite ceramics with controlled pore structure and improved mechanical strength, a freeze casting route has been processed using camphene mixed with tertiary-butyl alcohol (TBA) and coal fly ash/alumina as the solvent and the ceramic material, respectively. After sintering, the solidification characteristics of camphene and TBA solvent were evident in the pore morphology, i.e., dendritic and straight pore channels formed along the solidification directions of camphene and TBA ice, respectively, after sublimation. Also, the presence of microcracks was observed in the bodies sintered at $1500^{\circ}C$, mainly due to the difference in solidification volume change between camphene and TBA. The compressive strength of the sintered bodies was found generally to be dependent, in an inverse manner, on the porosity, which was mainly determined by the processing conditions. After sintering at $1300{\sim}1500^{\circ}C$ with 30~50 wt% solid loading, the resulting mullite ceramics showed porosity and compressive strength values in ranges of 83.8~43.1% and 3.7~206.8 MPa, respectively.