• Ceramist
• /
• v.1 no.2
• /
• pp.55-62
• /
• 1998

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1998.04a
• /
• pp.139-145
• /
• 1998

This paper addresses the R-curve properties, wear resistance, and erosion resistance of the two silicon carbide ceramics with different microstructures, i.e. , fine grained SiC and in situ-toughened SiC(IST SIC). Fine grained SiC exhibits a relatively flat R-curve behavior whereas the IST SiC exhibits a increasing R-curve behavior. The increasing R-curve behavior in IST SiC is attributed to relatively weak grain boundaries. The rate of material removal during wear tests and erosion tests was higher for IST SiC than that for fine grained SiC. This is attributed to the weaker grain boundaries in IST SiC than that in fine grained SiC. It is implied that fracture toughness in short crack regime should be taken into consideration in the interpretation of the microscopical material removal process. We show that the higher the strength of grain boundaries is, the higher wear and erosion resistances are.

• Korean Journal of Metals and Materials
• /
• v.50 no.11
• /
• pp.839-845
• /
• 2012

The effect of an AlN additive on the thermoelectric properties of SiC ceramics was studied. Porous SiC ceramics with 48-54% relative density were fabricated by sintering the pressed ${\alpha}-SiC$ powder compacts with AlN at $2100-2200^{\circ}C$ for 3 h in an Ar atmosphere. In the undoped specimens, the Seebeck coefficients were positive (p-type semiconducting) possibly due to a dominant effect of the acceptor impurities (Al, Fe) contained in the starting powder. With AlN addition, the reverse phase transformation of 6H-SiC to 4H-SiC was observed during the sintering process. The electrical conductivity of the AlN doped specimen was larger than that of the undoped specimen under the same conditions, which might be due to a reverse phase trans-formation. The Seebeck coefficient of the AlN doped specimen was also larger than that of the undoped specimen. The density of specimen and the amount of addition had significant effects on the thermoelectric properties.

• Journal of the Korean Ceramic Society
• /
• v.30 no.11
• /
• pp.941-948
• /
• 1993

The powder mixture of Si3N4-AlN-Y2O3, Si3N4-AlN-CeO2 and Si3N4-AlN-Y2O3-CeO2 system was hot-pressed at 175$0^{\circ}C$ for 2h in N2 to prepare $\alpha$-Sialon ceramics. The mechanical property and oxidation behaviour of the prepared $\alpha$-Sialon ceramics were investigated. At 120$0^{\circ}C$, oxidation resistance was best for the Y2O3 added $\alpha$-Sialon ceramics and oxidation rate increased when the amount of CeO2 increased. But when the mixture of Y2O3 and CeO2 added $\alpha$-Sialon ceramics showed a good oxidation resistance. Fracture toughness of (Y2O3＋CeO2) added $\alpha$-Sialon ceramics was higher than Y2O3 added $\alpha$-Sialon ceramics.

• Journal of the Korean Ceramic Society
• /
• v.56 no.2
• /
• pp.205-210
• /
• 2019

Bioactive glass (BG) finds limited use as a bone replacement material owing to its low mechanical properties. In order to solve this problem, the micro-sized 13-93 BG was prepared as a fabric composite with SiC microfibers, and its mechanical properties and biocompatibility were investigated in this study. The tensile strengths of BG-SiC fiber-bundle composites increased in proportion to the number of SiC fibers. In particular, even when only one SiC fiber was substituted, the tensile strength increased by 81% to 1428 MPa. In the early stage of the in-vitro test, a silica-rich layer was formed on the surface of the 13-93 BG fibers. With time, calcium phosphate grew on the silica-rich layer and the BG fibers were delaminated. On the other hand, no products were observed on the SiC fibers for 7 days, therefore, SiC fibers are expected to maintain their strength even after transplantation in the body.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.13 no.12
• /
• pp.1017-1024
• /
• 2000

Effect of the microwave dielectric properties and the microstructure on a mole fraction(x=0.1~0.9) of (1-x)Mg$_2$SiO$_4$-xZnAl$_2$O$_4$ ceramics was investigated. When (1-x)Mg$_2$SiO$_4$-xZnAl$_2$O$_4$(x=0.1~0.9) ceramics were sintered at 130$0^{\circ}C$, 135$0^{\circ}C$ and 140$0^{\circ}C$ for 2hr, the microwave dielectric properties were obtained $\varepsilon$r=6.8~8.3, Q.f$_{0}$=36000~77600. On the other hand, the temperature coefficients of resonant frequency($\tau$$_{f}$) were obtained in the properties of -62ppm/$^{\circ}C$ to -49ppm/$^{\circ}C$. In order to adjust the temperature coefficient of resonant frequency($\tau$$_{f}$), CaTiO$_3$was added in (1-x)Mg$_2$SiO$_4$-xZnAl$_2$O$_4$ceramics. 0.7Mg$_2$SiO$_4$-0.2ZnAl$_2$O$_4$-0.1CaTiO$_3$ceramics sintered at 135$0^{\circ}C$ for 2hr showed the excellent microwave dielectric properties of $\varepsilon$r=7.7, Q.f$_{0}$=32000, and $\tau$$_{f}$=-7.9 ppm/$^{\circ}C$.EX>.>.EX>.

• The Korean Journal of Ceramics
• /
• v.5 no.4
• /
• pp.317-323
• /
• 1999

Si3N4-TiC composites have been known as electrically conductive ceramics. $Si_3N_4-TiC$ composites with 2 wt% $Al_2O_3$ and 4 wt% $Y_2O_3$ were hot pressed in $N_2$ environment. The mechanical properties including hardness, fracture toughness, and flexural strength and tribological properties were investigated as a function of TiC content. $Si_3N_4-40$ vol% TiC composite was hot pressed at $1,750^{\circ}C$, $1,800^{\circ}C$, and $1,850^{\circ}C$ for 1, 3 and 5 hours in $N_2$ gas. Mechanical and tribolgical properties depended on microstructures, which were controlled by hte TiC content, hot press temperature, and hot press holding time. However, mechanical properties and tribological behaviors were degraded by the chemical reaction between TiC and N. The chemically reacted products such as TiCN, SiC, and $SiO_2$ were detered by the X-ray diffraction analysis.

• Journal of Powder Materials
• /
• v.25 no.2
• /
• pp.144-150
• /
• 2018

$Al_2O_3-SiC$ ceramic composites are produced using pressureless sintering, and their plasma resistance, electrical resistance, and mechanical properties are evaluated to confirm their applicability as electrostatic-discharge-safe components for semiconductor devices. Through the addition of Mg and Y nitrate sintering aids, it is confirmed that even if SiC content exceeded 10%, complete densification is possible by pressureless sintering. By the uniform distribution of SiC, the total grain growth is suppressed to about $1{\mu}m$; thus an $Al_2O_3-SiC$ sintered body with a high strength over 600 MPa is obtained. The optimum amount of SiC to satisfy all the desired properties of electrostatic-discharge-safe ceramic components is obtained by finding the correlation between the plasma resistance and the electrical resistivity as a function of SiC amount.

• Journal of Powder Materials
• /
• v.1 no.1
• /
• pp.15-20
• /
• 1994

The effect of SiC addition on sintering behaviors and microstructures of TiB2 ceramics were studied. The sintering of TiB2 was limited due to the surface diffusion and rapid grain growth at high temperature. However the addition of SiC to TiB2 ceramics improved the densification to above 99% of the theoretical density. The sintering of TiB2-SiC composite starts at 120$0^{\circ}C$ with the melting of the oxides in particle surface as impurities. After the reduction of the oxide by additional cabon at above 140$0^{\circ}C$, the grain boundary diffusion through the interface of TiB2-SiC play an important role. TEM observation showed neither chemical reactions nor other phases formed at the TiB2-SiC interfaces but the microcracks were observed due to the mismatch of thermal expansion between TiB2-SiC.

• Journal of the Korean Ceramic Society
• /
• v.33 no.12
• /
• pp.1301-1310
• /
• 1996

Generally it requires high sintering temperatures more than 135$0^{\circ}C$ to make semiconductive BaTiO3 ceramics. Also it is very difficult to achieve a homogeneous mixing in solid-state reaction method. Therefore the liquid phase distributed to non-uniform dilute the characteristics of PTCR. In order to improve the uniformity this study is used the sol-gel coating method. Using this method we studied the new manufacturing process that had a high reproducibility and mass production capability. Tetraethyl orthosilicate (TEOS) was used as a source of Si. The semiconductive BaTiO3 ceramics which was produced by sol-gel method for the SiO2 addition and sintered between 124$0^{\circ}C$ and 130$0^{\circ}C$ showed almost same resistivity at room temperature among 125$0^{\circ}C$ and 130$0^{\circ}C$. As the results We could be sintered the semiconducting BaTiO3 ceramics at lower temperature even at 125$0^{\circ}C$ maintaining the same specific resistivity ratio ($\rho$max/$\rho$min) at 130$0^{\circ}C$. The specific resistivity both below and above the Curie temperature were increased by slow cooling and the steepness of the plots in the reasion of transition from low to high resistance increased as the cooling rate decreased.