• Title/Summary/Keyword: Alumina Ceramics

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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.

Synthesis of Microcellular Cordierite Ceramics Derived from a Preceramic Polymer (Preceramic Polymer를 이용한 마이크로셀룰라 코디어라이트 세라믹스의 합성)

  • Song, In-Hyuck;Kim, Young-Mi;Kim, Hai-Doo;Kim, Young-Wook
    • Journal of the Korean Ceramic Society
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    • v.44 no.5 s.300
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    • pp.184-189
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    • 2007
  • In this study, a novel-processing route for producing microcellular cordierite ceramics has been developed. The proposed strategy for making the microcellular cordierite ceramics involves three steps: (i) fabricating ceramic-filled preceramic foams by heating a mixture of polysiloxane, expandable microspheres, talc, and alumina in a mold, (ii) cross-linking the foamed body, and (iii) transforming the body into microcellular cordierite ceramics by sintering. Cu jig was used for near net shaping in the foaming step. The experimental variables such as the shape of foaming jig and the content of expendable microsphere were investigated. By controlling the content of expendable microsphere, it was possible to make the porous cordierite ceramics with cell density of ${\sim}1.0{\times}10^9\;cells/cm^3$.

Surface Strengthening of 3Y-TZP Ceramics by Boehmite Sol Infiltration (Boehmite Sol 함침에 의한 3Y-TZP 소결체의 표면 강화)

  • Choi, Ki-Sik;Kim, Young-Jung;Kim, Hwan
    • Journal of the Korean Ceramic Society
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    • v.31 no.6
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    • pp.671-677
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    • 1994
  • To improve the low resistance of ceramics to tensile stress, many techniques, for introducing and retaining surface compressive stress have been suggested. In present work, in order to introduce the compressive stress on the surface of TZP ceramics TZP-Al2O3 composites were made with infiltration technique. Highly porous 3Y-TZP pre-sintered specimens were submerged in AlOOH(boehmite) sol and the sol penetrated into them through open pore channels with moderate depth after that specimens were sintered. It was known that controlling the number of infiltration time can vary the amount of Al2O3 phase and the fraction of alumina at surface reached up to 18%. The depth of composite surface layer were 100~200 ${\mu}{\textrm}{m}$, and these were acceptable in surface strengthening which were proved by Vickers hardness indentation method.

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Effects of Intermediate Layer in DLC Thin Film on Al2O3 for Improvement of High Temperature Strength

  • Ok, Chul-Ho
    • Transactions on Electrical and Electronic Materials
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    • v.8 no.3
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    • pp.125-130
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    • 2007
  • DLC coating on ceramics is very useful for manufacturing the materials with hardness and low friction. Adhesion of DLC thin film on ceramics, on the other hand, is usually very weak. Adhesion of DLC film depends on many parameters such as contamination and chemical bonding between thin film and substrate. In this study, adhesion of DLC film on ceramics was improved by the intermediate layer when the plasma immersion ion deposition (PIID) technique was applied. It is found that the chemical composition and the thickness of intermediate layer have significantly an effect on the adhesion of DLC thin film on $Al_2O_3$.

A Study on the Crystallization of Glass-Ceramics for Dental Crown (인공치관용(人工齒冠用) Glass-Ceramics의 결정화(結晶化)에 관(關)한 연구(硏究))

  • Chung, In-Sung
    • Journal of Technologic Dentistry
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    • v.14 no.1
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    • pp.95-118
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    • 1992
  • Glass ceramics for crown were prepared by adding 3$\sim$11 wt% TiO2 to the weight percent composition of 34.7 CaO, 27.8 SiO2, 18.3P2O5, 12.6MgO and 6.6 TiO2. The starting glasses were prepared by melting the powdered batch in alumina crucible at 1350$\sim$1400 for 1 hr and then quenching into a distilled water. The nucleation and crystallization of the crystalline glass ceramics for crown were studied by DTA, SME and X-ray diffraction analysis. Frit containing 9.11 wt% TiO2 had crystallization temperature of 850$\sim$1075 and major crystalline phase was identified by X-ray diffraction as diopside(CaO-MgO-2SiO2). Activation energies for the crystallization processes were obtained from DTA by varing rates for the fits, and were calculated from modified Ozawa and Kissinger equations. Activation energy for the crystallization processes of the S-4 frit was 489.6 KJ/mol.

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Shrinkage Free Sintering of Low Temperature Cofired Ceramics by Glass Infilteration

  • Yeo, Dong-Hun;You, Jung-Hun;Shin, Hyo-Soon;Kim, Jong-Hee
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09b
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    • pp.1218-1219
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    • 2006
  • The shrinkage variation of Low Temperature Cofired Ceramics(LTCC) limits the size of the substrates that impose limitations on embedded passive components. This paper focuses on the method of minimizing or controlling planar shrinkage and reducing distortion during firing. The laminated sheets of alumina and glass were sintered at varying temperature, and depending on the amount of the glass ceramics. When the sintered of multi-layer structure with $Al_2O_3/Glass/Al_2O_3$, the glass infiltrated entirely into $Al_2O_3$ layer at the temperature of about $950^{\circ}C$ or higher.

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Turning the Machining Characteristics of Feed-through Ceramics (피드스루용 세라믹의 선삭 가공 특성에 관한 연구)

  • Park, Se-Jin;Ha, Jun-Tae;Yang, Dong-Ho;Lee, Jong-Chan
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.19 no.10
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    • pp.81-86
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    • 2020
  • A ceramic vacuum chamber feedthrough ceramic insulator is made of Al2O3; the manufacturing process involves filling alumina powder into a urethane mold and pressing it with a rubber press to produce a molded body. Thereafter, manufacturing is completed through primary shape processing, sintering, and secondary shape processing in the green body, which is a pressurized molding body, This work is intended to prevent defects in the first shape processing by improving the ceramic insulator in the green body, and to improve the productivity of the ceramic insulator by determining the optimal processing conditions.

Green and Hard Machining Characteristics of Zirconia-alumina Composites for Dental Implant (치과 임플란트용 지르코니아-알루미나 복합체의 생 가공 및 경 가공 특성)

  • Lim, Hyung-Bong;Tang, Dongxu;Lee, Ki-Ju;Cho, Won-Seung
    • Journal of the Korean Ceramic Society
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    • v.48 no.2
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    • pp.152-159
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    • 2011
  • The green and hard machining characteristics of dental ceramics are of great interest to dental industry. The green bodies of TZP/$Al_2O_3$ composites were prepared by the cold isostatic pressing, and machined on the CNC lathe using PCD (polycrystalline diamond) insert under various machining conditions. With increasing nose radius of PCD insert, surface roughness initially increased due to increased cutting resistance, but decreased by the onset of sliding fracture. The lowest surface roughness was obtained at spindle speed of 1,300 rpm and lowest feed rate. Hard bodies were prepared by pressureless sintering the machined green bodies at several temperatures. The grinding test for sintered hard body was conducted using electroplated diamond bur with different grit sizes. During grinding, grain pull out in the composite was occurred due to thermal expansion mismatch between the alumina and zirconia. The strength of the composite decreased with alumina contents, due to increased surface roughness and high monoclinic phase transformed during grinding process. The final polished samples represented high strength by the elimination of a phase transformation layer.

Change of Phase Transformation and Microstructure of Alumina Membrane: I. Effect by Porosity of Support (알루미나 여과막의 상전이와 미세구조 변화: I. 지지체의 기공율에 의한 영향)

  • Cheong, Hun;Hwang, Kwang-Taek;Choi, Duck-Kyun;Cheong, Deock-Soo
    • Korean Journal of Materials Research
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    • v.12 no.3
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    • pp.205-210
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    • 2002
  • The HPS(High Porosity Support, 39.3%) and the LPS( Low Porosity Support, 18.7%) were fabricated to investigate the phase transformation and the chance of microstructure with porosity of alumina support. Alumina sol was made using aluminum tri-sec $butoxide(ATSB,\; Al(O-Bu)_3)$, the membrane on porous support with different porosity and the membrane without support were fabricated. The $\theta$-to ${\alpha}-A1_2O_3$ phase transformation in the membranes was investigated using thin film X-ray diffraction (XRD), and the change of microstructure was observed using scanning electron microscopy(SEM). XRD patterns showed that the membrane on LPS and HPS had 10$0^{\circ}C$, 5$0^{\circ}C$ higher $\theta$-to ${\alpha}-A1_2O_3$ transformation temperature compared to the unsupported membrane. A similar effect was also observed in microstructure of the membranes, theoritical temperature difference were 97$^{\circ}C$ and 44$^{\circ}C$ by Crapeyron equation.