• 한국세라믹학회지
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• 제48권5호
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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.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 추계학술대회 논문집
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• pp.110-114
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• 2012

We studied on the nondestructive evaluation of the elastic wave signal of SiC ceramics and SiC/SiC composite ceramics under monotonic tensile loading. The elastic wave signal of cross and unidirectional SiC/SiC composite ceramics were obtained by pencil lead method and bending test. It was applied for the time-frequency method which used by the discrete wavelet analysis algorithm. The time-frequency analysis provides time variation of each frequency component involved in a waveform, which makes it possible to evaluate the contribution of SiC fiber frequency. The results were compared with the characteristic of frequency group from SiC slurry and fiber. Based on the results, if it is possible to shift up and design as a higher frequency group, we will can make the superior material better than those of exiting SiC/SiC composites.

• 한국세라믹학회지
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• 제37권2호
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• pp.158-163
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• 2000

Six different SiC ceramics with SiO2-Re2O3 (Re=Yb, Er, Y, Dy, Gd, Sm) as sintering additives have been fabricated by hot-pressing the SiC-Re2Si2O7 compositions at 1850$^{\circ}C$ for 2 hr under a pressure of 25 MPa. The room temperature strneth and the fracture toughness of the hot-pressed ceramics were characterized and compared with those of the ceramics sintered with YAG (Y3Al5O12). Five SiC ceramics (Re=Yb, Er, Y, Dy, Gd) investigated herein showed sintered densities higher than 94% of theoretical. Tthe SiC-Re2Si2O7 compositions showed lower strength and comparable toughness to those from SiC-YAG composition, owing to the chemical reaction between SiO2 and SiC during sintering. SiC ceramics fabricated from a SiC-Y2Si2O7 composition showed the best mechanical properties of 490 MPa and 4.8 MPa$.$m1/2 among the compositions investigated herein.

• 한국세라믹학회지
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• 제50권6호
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• pp.410-415
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• 2013

$ZrB_2$-SiC ceramics are fabricated via hot pressing with different ratios of submicron or nano-sized SiC in a $ZrB_2$-20 vol%SiC system, in order to examine the effect of the SiC size ratio on the microstructures and physical properties, such as thermal conductivity, hardness, and flexural strength, of $ZrB_2$-SiC ceramics. Five different $ZrB_2$-SiC ceramics ($ZrB_2$-20 vol%[(1-x)SiC + xnanoSiC] where x = 0.0, 0.2, 0.5, 0.8, 1.0) are prepared in this study. The mean SiC particle sizes in the sintered bodies are highly dependent on the ratio of nano-sized SiC. The thermal conductivities of the $ZrB_2$-SiC ceramics increase with the ratio of nano-sized SiC, which is consistent with the percolation behavior. In addition, the $ZrB_2$-SiC ceramics with smaller mean SiC particle sizes exhibit enhanced mechanical properties, such as hardness and flexural strength, which can be explained using the Hall-Petch relation.

• 한국세라믹학회지
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• 제46권5호
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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.

• 한국세라믹학회지
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• 제47권6호
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• pp.546-552
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• 2010

The achievement of high gas permeability is a key factor in the development of porous SiC ceramics for applications of hot gas filter, vacuum chuck, and air spindle. However, few reports on the gas permeability of porous SiC ceramics can be found in the literature. In this paper, porous SiC ceramics were fabricated at temperatures ranging from $1600^{\circ}C$ to $1800^{\circ}C$ using the mixing powders of SiC, silicon, carbon and boron as starting materials. In some samples, expanded hollow microspheres as a pore former were used to make a cellular pore structure. It was possible to produce Si bonded SiC ceramics with porosities ranging from 42% to 55%. The maximum bending strength was 58MPa for the carbon content of 0.2 wt% and sintering temperature of $1700^{\circ}C$. The increase of air permeability was accelerated by addition of hollow microsphere as a pore former.

• 한국세라믹학회지
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• 제27권3호
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• pp.412-422
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• 1990

Porous SiC ceramics were proposed to be promising materials for high-temperature thermoelectric energy conversion. Throughthe thermoelectric property measurements and microstructure observations on the porous alpha SiC and the mixture of $\alpha$-and $\beta$-SiC, it was experimentally clarified that elimination of stacking faults and twin boundaries by grain growth is effective to increase the seebeck coefficient and increasing content of $\alpha$-SiC gives rise to lower electrical conductivity. Furthermore, the effects of additives on the thermoelectric properties of 6H-SiC ceramics were also studied. The electrical conductivity and the seebeck coefficient were measured at 35$0^{\circ}C$ to 105$0^{\circ}C$ in argon atmospehre. The thermoelectric conversion efficiency of $\alpha$-SiC ceramics was lower than that of $\beta$-SiC ceramics. The phase homogeneity would be needed to improve the seebeck coefficient and electrical conductivity decreased with increasing the content of $\alpha$-phase. In the case of B addition, XRD analysis showed that the phase transformation did not occur during sintering. On the other hand, AlN addiiton enhanced the reverse phase transformation from 6H-SiC to 4H-SiC, and this phenomenon had a great effect upon the electrical conductivity.

• 한국세라믹학회지
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• 제49권5호
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• pp.412-416
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• 2012

Porous SiC ceramics were prepared by using recycled SiC sludge, which is an industrial waste generated from solar cell industry. Polycarbosilane derivatives, such as polycarbosilane (PCS), polyphenylcarbosilane (PPCS) and hydridopolycarbosilane (HPCS) were used as binding agents for the fabrication of porous SiC ceramics at $1800^{\circ}C$ under Ar atmosphere. The effects of the various binding agents having different C/Si ratios were discussed on the sintering and porosity of the SiC ceramics. The prepared porous SiC ceramics were characterized by X-ray Diffraction (XRD) and Field-Emission Scanning Electron Microscope (FE-SEM). Thermal conductivity and porosity of SiC ceramics were measured at room temperature, and they were 56.7W/mK and 29.8%, respectively.

• 한국세라믹학회지
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• 제38권4호
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• pp.314-318
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• 2001

SiC-TiC composites have been fabricated by using a mechanochemical processing of a mixture of Si, Ti, and C at room temperature and subsequent hot pressing. TiC powders have been obtained by the mechanochemical processing of a mixture of Ti and C whereas SiC powders has not been obtained from a mixture of Si and C. By using the exothermic reaction between Ti and C, SiC-TiC powder could be obtained from the mixture of Si, Ti, and C using the mechanochemical processing for more than 12h. The X-ray diffraction analysis has shown that the powder subjected to the mechanochemical processing consisted of the particles having crystallite size below 10nm. Fully densified SiC-TiC composites have been obtained by hot-pressing of the powder at 1850$\^{C}$ for 3h and it has shown comparable mechanical properties to those of the SiC-TiC composites prepared from the commercially available SiC and TiC powders. Flexural strength of 560 MPa and fracture toughness of 4.8 MP$.$am$\_$1/2/ have been shown for the SiC-TiC composites with composition corresponding to 0.75:0.25:1 mole ratio of Si:Ti:C.

• 한국세라믹학회지
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• 제49권6호
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• pp.625-630
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• 2012

Highly porous silicon carbide (SiC) ceramics were fabricated from polysiloxane, SiC and carbon black fillers, AlN-$Y_2O_3$ additives, and poly (ether-co-octene) (PEOc) and expandable microsphere templates. Powder mixtures with a fixed PEOc content (30 wt%) and varying SiC filler contents from 0-21 wt% were compression-molded. During the pyrolysis process, the polysiloxane was converted to SiOC, the PEOc generated a considerable degree of interconnected porosity, and the expandable microspheres generated fine cells. The polysiloxane-derived SiOC and carbon black reacted and synthesized nano-sized SiC with a carbothermal reduction during a heat-treatment. Subsequent sintering of the compacts in a nitrogen atmosphere produced highly porous SiC ceramics with porosities ranging from 78 % to 82 % and a flexura lstrength of up to ~7 MPa.