• Journal of the Korean Ceramic Society
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• v.46 no.1
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• pp.35-40
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• 2009

Using zirconia and poly (methyl methacrylate-coethylene glycol dimethacrylate) (PMMA) microbeads, macroporous zirconia ceramics were fabricated by a simple pressing method. Effects of template size and content on microstructure, porosity, and flexural and compressive strengths were investigated in the processing of the macroporous zirconia ceramics. Three different sizes of microbeads (8, 20, and $50{\mu}m$) were used as a template for fabricating the macroporous ceramics. The porosity increased with increasing the template size at the same template content. The flexural and compressive strengths were primarily influenced by the porosity rather than the template size. However, the strengths increased with decreasing the template size at the same porosity. By controlling the template size and content, it was possible to produce macroporous zirconia ceramics with porosities ranging from 58% to 75%. Typical flexural and compressive strength values at 60% porosity were ${\sim}30\;MPa$ and ${\sim}75\;MPa$, respectively.

• Journal of the Korean Ceramic Society
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• v.48 no.5
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• pp.360-367
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• 2011

Macroporous silicon carbide (SiC) ceramics were fabricated by powder processing and polymer processing using carbon-filled polysiloxane as a precursor. The effects of the starting SiC polytype, template type, and template content on porosity and flexural strength of macroporous SiC ceramics were investigated. The ${\beta}$-SiC powder as a starting material or a filler led to higher porosity than ${\alpha}$-SiC powder, owing to the impingement of growing ${\alpha}$-SiC grains, which were transformed from ${\beta}$-SiC during sintering. Typical flexural strength of powder-processed macroporous SiC ceramics fabricated from ${\alpha}$-SiC starting powder and polymer microbeads was 127 MPa at 29% porosity. In contrast, that of polymer-processed macroporous SiC ceramics fabricated from carbon-filled polysiloxane, ${\beta}$-SiC fillers, and hollow microspheres was 116MPa at 29% porosity. The combination of ${\alpha}$-SiC starting powder and a fairly large amount (10 wt%) of $Al_2O_3-Y_2O_3$ additives led to macroporous SiC ceramics with excellent flexural strength.

• Journal of the Korean Vacuum Society
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• v.6 no.S1
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• pp.66-69
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• 1997

Porosity is one important characteristic feature and structural index of sprayed coatings. A method of measurement of porosity, EPMA-EDS image processing is developed in the paper. The characteristics of pores can be determined by processing of the image obtained from an electron microscope via VISTA, Not only the porosity can be presented but also the statistical result of pore size distribution. Finally it can be drawn from this paper that EPMA-EDS is a quite effective method to completely characterize the pores in plasma sprayed coatings.

• Journal of the Korean Ceramic Society
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• v.43 no.9 s.292
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• pp.552-557
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• 2006

A low temperature processing route for fabricating porous SiC ceramics by carbothermal reduction has been demonstrated. Effects of expandable microsphere content, sintering temperature, filler content, and carbon source on microstructure, porosity, compressive strength, cell size, and cell density were investigated in the processing of porous silicon carbide ceramics using expandable microspheres as a pore former. A higher microsphere content led to a higher porosity and a higher cell density. A higher sintering temperature resulted in a decreased porosity because of an enhanced densification. The addition of inert filler increased the porosity, but decreased the cell density. The compressive strength of the porous ceramics decreased with increasing the porosity. Typical compressive strength of porous SiC ceramics with ${\sim}70%$ porosity was ${\sim}13 MPa$.

• 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.

• Electrical & Electronic Materials
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• v.10 no.3
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• pp.255-261
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• 1997

In this study, pore-containing barium titanate ceramics were prepared with different porosities and pore sizes, in order to better understand how porosity and pore size affect electrical breakdown of barium titanate ceramics. A granulated barium titanate powder was mixed with three grades of commercial polymer microspheres up to 11wt%. The electrical breakdown test was performed at two different temperatures of 30.deg. C(below Tc) and 150.deg. C(above Tc) for samples immersed in a silicon oil bath using a 60kV de power supply. Electrical breakdown strength of pore containing barium titanate ceramics with porosity lower than 10% decreased as pore size and porosity increased. However, above the 10% porosity region, electrical breakdown strength decreased as the pore connectivity increased. From the experimental results, an optimum electrical breakdown model is proposed in an attempt to explain the effect of pores.

• Journal of the Korean Ceramic Society
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• v.46 no.5
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• pp.488-492
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• 2009

Porous frit-bonded SiC ceramics were successfully prepared at a temperature as low as $800^{\circ}C$ from SiC, frit, and microbeads (glass or polymer). The effects of SiC starting particle size and microbead addition on microstructure, porosity, and flexural strength were investigated. The addition of hollow glass microbead improved the strength of frit-bonded SiC ceramics without the loss of porosity by acting additional binder phase between SiC grains. The 65 ${\mu}m$-sized SiC resulted in lower porosity and higher strength than 50 ${\mu}m$-sized SiC because of higher packing density. Typical flexural strengths of frit-bonded SiC were 23 MPa at 46% porosity and 19 MPa at 49% porosity.

• Journal of the Korean Ceramic Society
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• v.45 no.1
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• pp.65-68
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• 2008

A simple pressing process using zirconia and microbead for fabricating porous zirconia ceramics is demonstrated. Effects of microbead content and sintering temperature on microstructure, porosity, compressive and flexural strengths were investigated in the processing of porous zirconia ceramics using microbead as a pore former. By controlling the microbead content and the sintering temperature, it was possible to produce porous zirconia ceramics with porosities ranging from 43% to 70%. Typical compressive and flexural strength values at ${\sim}50%$ porosity were ${\sim}150\;MPa$ and ${\sim}35\;MPa$, respectively.

• Journal of the Korean Ceramic Society
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• v.45 no.7
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• pp.430-437
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• 2008

Porous self-bonded silicon carbide (SBSC) ceramics were fabricated at temperatures ranging from 1700 to $1850^{\circ}C$ using SiC, silicon (Si), and three different carbon (C) sources, including carbon black, phenol resin, and xylene. The effects of the Si:C ratio and carbon source on porosity and strength were investigated as a function of sintering temperature. Porous SBSC ceramics fabricated from phenol resin showed higher porosity than the others. In contrast, porous SBSC ceramics fabricated from carbon black showed better strength than the others. Regardless of the carbon source, the porosity increased with decreasing the Si:C ratio whereas the strength increased with increasing the Si:C ratio.

• 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.