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

• The Korean Journal of Ceramics
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• v.3 no.1
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• pp.47-51
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• 1997

The dense sintered bodies of Si/SiC composite with various Si contents could be fabricated by changing the green density in the forming process. The Si/SiC/graphite composites with various graphite contents could be also fabricated by changing a graphite content in the starting composition. Their mechanical and tribological properties were characterized and wear mechanism was also studided. The hardness and strength of the Si/SiC and the Si/SiC/graphite were decreased with increasing the contents of free Si and graphite, respectively. However, the friction coefficient and specific wear rate had no specific relations to their hardness and strength. Adhesion of free Si was a main factor to determine a wear resistance of the Si/SiC composite. In the case of the Si/SiC/graphite, solid lubricationl and liquid reservoir of the graphite particles played the main role of the reduction of the friction force. In the torque test to estimate the possibility of practical of practical applications, the value of torque between the Al2O3 disk and Si/SiC/graphite disk was 1/6 lower compared with two $Al_2O_3$ disks on the basis of 100,000 cycles.

• The Korean Journal of Ceramics
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• v.2 no.4
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• pp.226-230
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• 1996

A small amount of fine particle graphite was added to $\alpha$-SiC and $\beta$-SiC having certain particle distributions, and they were mixed clay and frit. After forming, they were sintered at 140$0^{\circ}C$ for 3 hours. Tribological properties of sintered $\alpha$-SiC-$\beta$-SiC-graphite-clay (frit) system showed that kinetic friction coefficient was 0.108, specific wear rate was 1.3${\times}10^-8\;mm^2$.$kgf^1$, and torque was 0.01kgf.cm at the wrench torque of 100 kgf.cm.

• Journal of the Korean Ceramic Society
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• v.50 no.1
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• pp.31-36
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• 2013

${\beta}$-SiC powders were synthesized by a carbothermal reduction process using $SiO_2$-C precursors fabricated by a sol-gel process using phenol resin and TEOS as starting materials for carbon and Si sources, respectively. The C/Si molar ratio was selected as an important parameter for synthesizing SiC powders using a sol-gel process, and the effects of the C/Si molar ratio (1.4-3.0) on the particle size, particle size distribution, and yield of the synthesized ${\beta}$-SiC powders were investigated. It was found that (1) the particle size of the synthesized ${\beta}$-SiC powders decreased with an increase in the C/Si molar ratio in the $SiO_2$-C hybrid precursors, (2) the particle size distribution widened with an increase in the C/Si molar ratio, and (3) the yield of the ${\beta}$-SiC powder production increased with an increase in the C/Si molar ratio.

• Journal of the Korean Ceramic Society
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• v.29 no.3
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• pp.223-231
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• 1992

CaO and ZnO were added to Al2O3-SiO2 binary system respectively as flux, then ZrO2 and TiO2 were applied as nucleating agent to these CaO-Al2O3-SiO2 and ZnO-Al2O3-SiO2 ternary system glass. The transparency could not be kept in CaO-Al2O3-SiO2 system glass, whereas the transparent glass-ceramics were prepared in ZnO-Al2O3-SiO2 system glass containing ZrO2 as the nucleating agent. At this time the optimum heating temperatures for the nucleation and the crystal growth were 78$0^{\circ}C$ and 97$0^{\circ}C$. The sizes of the precipitated crystals in the transparent glass-ceramics were below 0.1 ${\mu}{\textrm}{m}$, and their light transmissibilities were more than 80%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.113-114
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• 2009

Silicon carbide is one of the most attractive and promising wide band-gap semiconductor material with excellent physical properties and huge potential for electronic applications. Up to now, the most successful method for growth of large SiC crystals with high quality is the physical vapor transport (PVT) method [1, 2]. Since further reduction of defect densities in larger crystal are needed for the true implementation of SiC devices, many researchers are focusing to improve the quality of SiC single crystal through the process modifications for SiC bulk growth or new material implementations [3, 4]. It is well known that for getting high quality SiC crystal, source materials with high purity must be used in PVT method. Among various source materials in PVT method, a SiC powder is considered to take an important role because it would influence on crystal quality of SiC crystal as well as optimum temperature of single crystal growth, the growth rate and doping characteristics. In reality, the effect of powder on SiC crystal could definitely exhibit the complicated correlation. Therefore, the present research was focused to investigate the quality difference of SiC crystal grown by conventional PVT method with using various SiC powders. As shown in Fig. 1, we used three SiC powders with different particles size. The 6H-SiC crystals were grown by conventional PVT process and the SiC seeds and the high purity SiC source materials are placed on opposite side in a sealed graphite crucible which is surrounded by graphite insulation[5, 6]. The bulk SiC crystal was grown at $2300^{\circ}C$ of the growth temperature and 50mbar of an argon pressure. The axial thermal gradient across the SiC crystal during the growth is estimated in the range of $15\sim20^{\circ}C/cm$. The chemical etch in molten KOH maintained at $450^{\circ}C$ for 10 min was used for defect observation with a polarizing microscope in Nomarski mode. Electrical properties of bulk SiC materials were measured by Hall effect using van der Pauw geometry and a UV/VIS spectrophotometer. Fig. 2 shows optical photographs of SiC crystal ingot grown by PVT method and Table 1 shows electrical properties of SiC crystals. The electrical properties as well as crystal quality of SiC crystals were systematically investigated.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.6
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• pp.271-276
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• 2020

In this study, an amorphous SiC block was manufactured using polycarbosilane (PCS), an organosilicon polymer. The dense SiC blocks were easily fabricated in various shapes via pyrolysis at 1100℃, 1200℃, 1300℃, 1400℃ after manufacturing a PCS molded body using cured PCS powder. Physical and chemical properties were analyzed using a thermogravimetric analyzer (TGA), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and universal testing machine (UTM). The prepared SiC block was decomposed into SiO and CO gas as the temperature increased, and β-SiC crystal grains were grown in an amorphous structure. In addition, the density and flexural strength were the highest at 1.9038 g/㎤ and 6.189 MPa of SiC prepared at 1100℃. The manufactured amorphous silicon carbide block is expected to be applicable to other fields, such as the previously reported microwave assisted heating element.

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.462-466
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• 2015

This paper reports the microstructure of hot-pressed $ZrB_2$-SiC ceramics with added $B_4C$ as characterized by transmission electron microscopy. $ZrB_2$ has a melting point of $3245^{\circ}C$, a relatively low density of $6.1g/cm^3$, and specific mechanical properties at an elevated temperature, making it a candidate for application to environments with ultra-high temperatures which exceed $2000^{\circ}C$. Due to the non-sinterability of $ZrB_2$-based ceramics, research on sintering aids such as $B_4C$ or $MoSi_2$ has become prominent recently. From TEM investigations, an amorphous layer with contaminant oxide is observed in the vicinity of $B_4C$ grains remaining in hot-pressed $ZrB_2$-SiC ceramics with $B_4C$ as an additive. The effect of a $B_4C$ addition on the microstructure of this system is also discussed.

• Journal of the Korean Ceramic Society
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• v.29 no.11
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• pp.877-887
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• 1992

Tetragonal zirconia powder with 3 mol% Y2O3 mas mixed with up to 30 vol% of ${\beta}$-SiC powders, and the mixtures were hot-pressed at 1500$^{\circ}C$ for 60 min under a pressure of 30 MPa in Ar atmosphere. Flexural strength and fracture toughness were measured at room-and high-temperature (1000$^{\circ}C$). Evolution of microstructure was also conducted to investigate the effects of SiC addition on the properties of 3Y-TZP ceramics. Average grain size of the composites was about 0.5 $\mu\textrm{m}$, and decreased with SiC addition. Both room- and high-temperature mechanical properties of the composites were improved with SiC content. Particularly, high-temperature strength and fracture toughness of 3Y-TZP/30v/o SiC composite were twice as high as those of 3Y-TZP. The hardness of the composites also increased with SiC content and reached maximum value at 3Y-TZP/30v/o SiC composite.

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