• Title, Summary, Keyword: Porous ceramics

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Strength and Reliability of Porous Ceramics Measured by Sphere Indentation on Bilayer Structure

  • Ha, Jang-Hoon;Kim, Jong-Ho;Kim, Do-Kyung
    • Journal of the Korean Ceramic Society
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    • v.41 no.7
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    • pp.503-507
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    • 2004
  • The importance of porous ceramics has been increasingly recognized and adequate strength of porous ceramics is now required for structural applications. Porosities of porous ceramics act as flaws in inner volume and outer surface which result in severe strength degradation. The effect of pore structure, however, on strength and reliability of porous ceramics has not been clearly understood. We investigate the relationship between pore structure and mechanical properties using a sphere indentation on bilayer structure, porous ceramic top layer with soft polymer substrate. Porous alumina and silica were prepared to characterize the isolated pore structure and interconnected pore structure, respectively. The porous ceramic with 1mm thickness were bonded to soft polycarbonate substrate and then fracture strengths were estimated from critical loads for radial cracking of porous ceramics during sphere indentation from top surface. This simple and reproducible technique provides Weibull modulus of strength of porous ceramics with different pore structure. It shows that the porous ceramics with isolated pore structure have higher strength and higher Weibull modulus as well, than those with interconnected pore structure even with the same porosity.

A Study on the Porous Glass-Ceramics in the Phosphate System (인산염계 다공질 결정화 유리에 관한 연구)

  • 박용완;현부성;김태호
    • Journal of the Korean Ceramic Society
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    • v.32 no.7
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    • pp.858-864
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    • 1995
  • A porous glass-ceramics body was prepared in the phosphate system. The glass composition of 47.2CaO-22.2TiO2-30.6P2O5 (mol%) containing a few weight percent of ZrO2 was suitable for a mother glass of a porous glass-ceramics. The dense glass-ceramics body was made by a two-step heat treatment of the mother glass. The crystalline phases of the glass-ceramics were $\beta$-Ca3(PO4)2 and CaTi4(PO4)6. The $\beta$-Ca3(PO4)2 phase could be selectively leached out with HCl solution and thus a crystalline $\beta$-Ca3(PO4)2 skeleton was remained. The dimension and shape of the porous glass-ceramics were nearly the same as the those of the first formed glass. The specific surface area and average proe radius of the porous glass-ceramics were 19$m^2$/g and 22 nm, respectively.

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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.

Effects of Pre-sintered Granules on the Characteristics of Porous Zirconia (가소결된 그레뉼이 다공질 지르코니아 세라믹스의 특성에 미치는 영향)

  • Lee, Eun-Jung;Ha, Jang-Hoon;Kim, Yang-Do;Song, In-Hyuck
    • Journal of the Korean Ceramic Society
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    • v.49 no.6
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    • pp.566-574
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    • 2012
  • Porous zirconia ceramics are widely considered to be important due to their unique properties and potential applications. In this paper, we propose a novel approach to produce porous zirconia ceramics. The linear shrinkage of the prepared porous zirconia ceramics could be controlled to 4% by incorporating pre-sintered zirconia granules and hollow polymeric spheres. We also investigated the effect of pre-sintered zirconia granules on the microstructure and the properties, such as the porosity, pore distribution, and bending strength of the porous zirconia ceramics.

Piezoelectric properties of porous PZT ceramics for hydrophone Applications (수중청음기 응용을 위한 다공질 PZT 세라믹스의 압전특성)

  • 박정학;이수호;공사건;배진호
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.45 no.4
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    • pp.558-561
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    • 1996
  • PZT powders were prepared by the molten salt synthesis method. The porous PZT ceramics were made from a mixture of PZT and polyvinylalcohol(PVA) by BURPS(Burnout Plastic Sphere) technique. The porous PZT bodies were fabricated from the green compacts with various amounts of PVA spheres. The piezoelectric coefficient d$_{33}$ (334~350*10$^{-12}$ C/N)of porous PZT ceramics(364*10$^{-12}$ C/N). The figure of merit(d$_{h}$g$_{h}$) of porous PZT specimens evaluating the sensitivity for ultrasonic transducer applications was improved significantly(11~70times) in comparison with that of single phase PZT ceramics(100*10$^{-15}$ m$^{2}$/N). The thickness mode coupling factor k$_{t}$(0.5~0.6) of porous specimens was comparable with that of single phase PZT ceramics(k$_{t}$=0.7). The mechanical quality factor of porous PZT specimens was smaller than 10, and thus these porous PZT ceramics would be believed as a good candidate for broad band hydrophone applications. (author). 10 refs., 7 figs.igs.igs.

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Effect of Template Size Ratio on Porosity and Strength of Porous Zirconia Ceramics (기공형성제 크기 비(ratio)가 다공질 지르코니아 세라믹스의 기공율과 강도에 미치는 영향)

  • Chae, Su-Ho;Kim, Young-Wook;Song, In-Hyuek;Kim, Hai-Doo;Bae, Ji-Soo
    • Journal of the Korean Ceramic Society
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    • v.45 no.9
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    • pp.537-543
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    • 2008
  • Effect of template size ratio on porosity and mechanical properties of porous zirconia ceramics were investigated using two different size (${\sim}8{\mu}m$ and ${\sim}50{\mu}m$ in diameter) of polymethyl methacrylate-coethylene glycol dimethacrylate (PMMA) microbeads as sacrificial templates. Porosity of the porous zirconia ceramics increased with decreasing the template size ratio ($8{\mu}m: 50{\mu}m$) whereas the compressive and flexural strengths of the porous zirconia ceramics increased with increasing the template size ratio. By controlling the template size ratio, sintering temperature and sintering time, it was possible to produce porous zirconia ceramics with porosities ranging from 57% to 69%. Typical flexural and compressive strength values of porous zirconia ceramics with ${\sim}60%$ porosity were ${\sim}37\;MPa$ and ${\sim}85\;MPa$, respectively.

Microsotructure Designed Porous Apatite Ceramics Prepared by Hydrothermal Method

  • Ioku, Koji;Fukuhara, Michiko;Fujimori, Hirotaka;Goto, Seishi
    • The Korean Journal of Ceramics
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    • v.5 no.2
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    • pp.162-164
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    • 1999
  • Microsotructure designed porous ceramics of calcium hydroxyapatite $(Ca_{10}(PO_4)_6(OH)_2)$ were prepared by hydrothermal method. The particle size, shape, and the micro-pore size of the porous hydroxyapatite ceramics could becontrolled. The hydroxyapatite was non-stoichiometric apatite with calcium deficient compositions (Ca/P ratio < 1.67). The composition of non-stoichiometric hydroxyapatite ceramics could be controlled from 1.50 to 1.63 in Ca/P ratio. The hydroxyapatite ceramics preparedc at $105^{\circ}C$ under the saturated vapor pressure for 20h were composed of rod-shaped crystals with about 10$\mu\textrm{m}$ in length with the mean aspect ratio of 40. The porous ceramics of calcium deficient hydroxyapatite had about 45% porosity with the inter-connecting pore structure. Porous hydroxyapatite ceramics prepared hydrothermally had the compressive strength of about 10 to 30 MPa. In addition, porous ceramics of $\beta$-tricalcium phosphate ($\beta-Ca_3(PO_4)_2$) were prepared from the calcium deficient hydroxyapatite.

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Enhanced Production of Epothilone by Immobilized Sorangium cellulosum in Porous Ceramics

  • Gong, Guo-Li;Huang, Yu-Ying;Liu, Li-Li;Chen, Xue-Feng;Liu, Huan
    • Journal of Microbiology and Biotechnology
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    • v.25 no.10
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    • pp.1653-1659
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    • 2015
  • Epothilone, which is produced by the myxobacterium Sorangium cellulosum, contributes significant value in medicinal development. However, under submerged culture conditions, S. cellulosum will accumulate to form bacterial clumps, which hinder nutrient and metabolite transportation. Therefore, the production of epothilone by liquid fermentation is limited. In this study, diatomite-based porous ceramics were made from diatomite, paraffin, and poremaking agent (saw dust). Appropriate methods to modify the porous ceramics were also identified. After optimizing the preparation and modification conditions, we determined the optimal prescription to prepare high-performance porous ceramics. The structure of porous ceramics can provide a solid surface area where S. cellulosum can grow and metabolize to prevent the formation of bacterial clumps. S. cellulosum cells that do not form clumps will change their erratic metabolic behavior under submerged culture conditions. As a result, the unstable production of epothilone by this strain can be changed in the fermentation process, and the purpose of increasing epothilone production can be achieved. After 8 days of fermentation under optimized conditions, the epothilone yield reached 90.2 mg/l, which was increased four times compared with the fermentation without porous ceramics.

The Effect of MnO2 Content on the 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.54 no.4
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    • pp.331-339
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    • 2017
  • Porous alumina-based ceramics are of special interest due to their outstanding mechanical properties and their thermal and chemical stability. Nevertheless, the high electrical resistance of alumina-based ceramics, due to the generation of static electricity, leads to difficulty in applying a vacuum chuck in the semi-conductor process. Therefore, development of alumina-based ceramics for applications with vacuum chucks aims to have primary properties of low electrical resistance and high air permeability. In this study, we tailored the electrical resistance of porous alumina-based ceramics by adjusting the amount of $MnO_2$ (with $TiO_2$ fixed at an amount of 2 wt%) and by using coarse alumina powder for high air permeability. The characteristics of the specimens were studied using scanning electron microscopy, mercury porosimeter, capillary flow porosimetry, universal testing machine, X-ray diffraction and high-resistance meter.

Treatment Characteristics of Acid Mine Drainage by Porous Zeolite-Slag Ceramics Packed in a Column Reactor System (컬럼반응조 내 충진된 다공성 zeolite-slag 세라믹에 의한 산성광산배수의 처리특성)

  • Yim, Soo-Bin
    • Journal of Korean Society of Water Science and Technology
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    • v.26 no.5
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    • pp.39-54
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    • 2018
  • The objective of this research is to investigate the removal characteristics of heavy metals and sulfate ion from acid mine drainage (AMD) in a column reactor system by spherical-type porous zeolite-slag ceramics (ZS ceramics). The hydraulic retention time (HRT) condition of 24 hours in the column reactor system was found to more efficiently treat the AMD than that of 12 hours. The increment of mixing amount of converter slag in porous ZS ceramics from 1:1(Z:S) to 1:3(Z:S) was observed to enhance the removal efficiency of Cu, Cd, Mn, and Zn by 13.4%, 32.6%, 22.0%, and 48.2%, respectively. In addition, the 1:3(Z:S) porous ZS ceramics increased the alkali-supply capacity and average cycling period of back-washing relative to 1:1(Z:S) porous ZS ceramics. The average removal efficiencies of heavy metals and sulfate ion from AMD by the 1:3(Z:S) porous ZS ceramics in the column reactor under the HRT condition of 24 hours were Al 97.2%, As 98.3%, Cd 89.9%, Cu 95.5%, Fe 99.5%, Mn 76.0%, Pb 97.5%, Zn 73.2%, and $SO_4{^{2-}}$ 75.9% during 71 days of operation time. The experimental results exhibited that the porous ZS ceramics in the column reactor system could function as an efficient media for the long-term treatment of heavy metals and sulfate ion from AMD.