• Title, Summary, Keyword: Ceramics

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Research Progress in SiC-Based Ceramic Matrix Composites

  • Dong, Shaoming;Wang, Zhen;Zhou, Haijun;Kan, Yan-Mei;Zhang, Xiangyu;Ding, Yusheng;Gao, Le;Wu, Bin;Hu, Jianbao
    • Journal of the Korean Ceramic Society
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    • v.49 no.4
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    • pp.295-300
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    • 2012
  • SiC-based ceramic matrix composites show many advantages over their monolithic ceramic counterparts, which makes them potential candidates for applications in various fields. Depending strongly on the chemical composition and microstructure of the fiber reinforcement, matrix as well as the fiber/matrix interphase in the material, the properties of ceramic matrix composites(CMCs) are highly tailorable. In this paper, the latest progresses in the interphase design, matrix modification and fiber reinforcement decoration of CMCs are reviewed, their effects on the properties of the CMCs are introduced.

Comparison between the Electrical Properties of Bismuth Layer-Structured and Intergrowth Bismuth Layer-Structured Ferroelectric Ceramics

  • Cho, Sam Yeon;Choi, Gi Ppeum;Bu, Sang Don
    • Journal of the Korean Physical Society
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    • v.70 no.10
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    • pp.934-938
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    • 2017
  • Bismuth layer-structured ferroelectric (BLSF)-type $Bi_4Ti_3O_{12}$ (BiT), $Bi_{3.25}La_{0.75}Ti_3O_{12}$ (BLaT), and $Bi_{3.1}Nd_{0.9}Ti_3O_{12}$ (BNdT) ceramics and intergrowth BLSF-type $BiT-CaBi_4Ti_4O_{15}$ (CBTO), BLaT-CBTO, and BNdT-CBTO ceramics were prepared using the solid-state reaction method. The electrical and the high-temperature properties of the intergrowth BLSF ceramics were compared with those of BLSF ceramics to investigate the possibility of using the former for high-temperature applications. The X-ray diffraction (XRD) analysis revealed well-formed stable structures in all BLSF and intergrowth BLSF ceramics without any second-phase formation. When their electrical properties were examined, the intergrowth BLSF ceramics BiT-CBTO, BLaT-CBTO, and BNdT-CBTO were found to outperform the BLSF ceramics BiT, BLaT, and BNdT, respectively, in terms of the remanent polarization and piezoelectric coefficient values. Among the intergrowth BLSF ceramics, those doped with rare-earth ions La and Nd, i.e., BLaT-CBTO and BNdT-CBTO ceramics, were found to have improved electrical properties compared to the BiT-CBTO ceramics. In particular, the dielectric constants and the piezoelectric coefficients of the BNdT-CBTO ceramics were observed to be as high as 146 and 15.4 pC/N, respectively, which were 28% and 10% higher than those of BNdT ceramics. In the thermal depoling behavior measured to examine high-temperature stability, the intergrowth BLSF ceramics, compared to the BLSF ceramics, demonstrated improvements in the thermal depoling temperature ranging from 100 to $300^{\circ}C$.

Investigation on the Pore Properties of the Microcellular ZrO2 Ceramics Using Hollow Microsphere (중공형 미세구를 이용한 마이크로셀룰라 지르코니아의 가공 특성 고찰)

  • Lee, Eun-Jung;Song, In-Hyuek;Kim, Hai-Doo;Kim, Young-Wook;Bae, Ji-Soo
    • Journal of the Korean Ceramic Society
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    • v.46 no.1
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    • pp.108-115
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    • 2009
  • In this study, a novel-processing route for producing microcellular zirconia ceramics has been developed. The proposed strategy for making the microcellular zirconia ceramics involves hollow microsphere as a pore former which has extremely low density of $0.025\;g/cm^3$. Effects of hollow microsphere content and sintering temperature on microstructure, porosity, pore distribution, and compressive strength were investigated in the processing of microcellular zirconia ceramics. By controlling the content of hollow microsphere, it was possible to make the porous zirconia ceramics with porosities ranging from 45% to 75%. Typical compressive strength value of microcellular zirconia ceramics with ${\sim}65%$ porosity was over 50 MPa. By adjusting the mixing ratio of large and small zirconia powders, it was possible to control the pore structure from close to open pores.

Characteristics of Large Green and Sintered Alumina Ceramics by Filter Pressing (필터 프레싱으로 제조한 대형 알루미나 세라믹스 성형체 및 소결체의 특성)

  • Lee, Hyun-Kwuon;Cho, Kyeong-Sik;Jang, Min-Hyeok;Jang, Chul-Woo;Kim, Sang-Mo;Kim, Mi-Young
    • Journal of the Korean Ceramic Society
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    • v.46 no.3
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    • pp.306-312
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    • 2009
  • The size of various alumina ceramics used in semiconductor and display industry is also required to increase with increase in wafer and panel size. In this research, large alumina ceramics was fabricated by filter pressing of alumina slurry using commercial powder and thereafter sintering at $1600^{\circ}C$ in gas furnace. The characteristics of large alumina ceramics thereby were compared to those of small alumina ceramics prepared by pressure forming such as uniaxial pressing and CIP. Careful control of properties of alumina slurry and filter pressing made the fabrication of large alumina ceramics possible, and its characteristics were equivalent to those of small alumina ceramics. The large alumina ceramics, prepared by sintering the green body of 63% relative density at $1600^{\circ}C$, exhibited both dense microstructure corresponding to 98.5% of relative density and 99.8% of high purity as in starting powder.

Microstructural Characterization of $CaTiO_3-NdAlO_3$-Based Ceramics

  • Suvorov, Danilo;Drazic, Goran;Valant, Matjaz;Jancar, Bostjan
    • Korean Journal of Crystallography
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    • v.11 no.4
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    • pp.195-199
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    • 2000
  • Ceramics based on CaTiO₃-NdAlO₃ solid solutions were synthesized in order to study their dielectric microwave properties. Microstructural analysis was performed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) using different analytical methods such as energy-dispersive X-ray spectroscopy (EDXS). It was observed that the heating conditions during sintering and cooling strongly affect the microstructural development of CaTiO₃-NdAlO₃-based ceramics. Various types and concentrations of structural defects were identified, for example, dislocations, twins and/or antiphase boundaries. all such defects resulted in a degradation of the dielectric microwave properties, in particular the quality factor Q. Dielectric properties of CaTiO₃-NdAlO₃-based ceramics can be improved by an appropriate thermal treatment of ceramics which results in a decrease in the concentrations of the identified microstructural defects.

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Optimization for Permeability and Electrical Resistance of Porous Alumina-Based Ceramics

  • Kim, Jae;Ha, Jang-Hoon;Lee, Jongman;Song, In-Hyuck
    • Journal of the Korean Ceramic Society
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    • v.53 no.5
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    • pp.548-556
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    • 2016
  • Recently, porous alumina-based ceramics have been extensively applied in the semi-conductor and display industries, because of their high mechanical strength, high chemical resistance, and high thermal resistance. However, the high electrical resistance of alumina-based ceramics has a negative effect in many applications due to the generation of static electricity. The low electrical resistance and high air permeability are key aspects in using porous alumina-based ceramics as vacuum chucks in the semi-conductor industry. In this study, we tailored the pore structure of porous alumina-based ceramics by adjusting the mixing ratio of the starting alumina, which has different particle sizes. And the electrical resistance was controlled by using chemical additives. The characteristics of the specimens were studied using scanning electron microscopy, mercury porosimetry, capillary flow porosimetry, a universal testing machine, X-ray diffraction, and a high-resistance meter.