• Journal of the Korean Ceramic Society
• /
• v.25 no.5
• /
• pp.473-478
• /
• 1988

In order to obtain the high purity $\beta$-SiC powder that possesses the excellent sinterability and is close to the spherical shape, the carbon black was mixed into the composition of Si(OC2H5)4-H2O-NH3-C2H5OH which the monodispersed spherical fine particles is formed the hydrolysis of Ethylsilicate and the mixture was carbonized under an argon atmosphere. Particle shpae, size and the yield of $\beta$-SiC powder were investigated according to the molar ratio of carbon/alkoxide and variations of reaction temperature and reaction time. The results of this study are as follow ; 1) The yield of $\beta$-SiC gained from the reaction for one hour at 150$0^{\circ}C$ almost got near 100% and the particle size of $\beta$-SiC from the reaction for 15 hrs at 150$0^{\circ}C$ was 0.2${\mu}{\textrm}{m}$ on the average and close to the spherical shape agglomerate state. 2) When the molar ratio carbon/alkoxide is over 3.1 and the reaction occurs at 145$0^{\circ}C$ for 5hrs, the carbon content has not an effect on the kind of crystal of product.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.12 no.2
• /
• pp.80-86
• /
• 2002

$Al_{2}O_{3}/SiC$ nanocomposites were made by infiltrating partially sintered alumina bodies with polycarbosilane (PCS) solutions, which is a SiC polymer precursor, with pressureless sintering. The SiC content, densification, phases, strength, and microstructure were investigated with the processing parameters such as PCS solution concentration and heat treatment condition for PCS pyrolysis and sintering. The results were compared with those for pure alumina and nanocomposite samples made by the existing polymer precursor route (i.e. the PCS addition process). The SiC contents of up to 1.5 vol% were obtained by the PCS infiltration. PCS pyrolysis, followed by air heat treatment, was needed before sintering to avoid a cracking problem and to attain a densification as high as 98 % of theoretical. The nanocomposites exhibited significantly higher strength than pure alumina and those prepared by the PCS addition process despite larger grain size. Besides $\alpha-Al_{2}O_{3}/SiC$ and $\beta-SiC$ phases, mullite was present a little in the nanocomposites, which resulted from the reaction of $SiO_{2}$ in the pyrolysis product of PCS with the $Al_{2}O_{3}$ matrix during sintering. The nanocomposites had intagranular particles believed to be SiC, which is a typical feature of $Al_{2}O_{3}/SiC$ nanocomposites.

• Journal of the Korean Ceramic Society
• /
• v.26 no.3
• /
• pp.416-422
• /
• 1989

The particle size of synthesized SiC powders was decreased with increasing carbon content when the mixture of carbon and silica was carbonized at 1, 45$0^{\circ}C$ after hydrolysis of the mixture with the ranges of 3.1 to 3.5 in the mole ratio of Carbon/Alkoxide. The reacted fraction of $\beta$-SiC nearly had nothing to do with the mole ratio of Carbon/Alkoxide. When the reaction was made by adding 0.5wt% additives in the composition of 3.1 in the mole ratio of carbon/alkoxide, the additives decreased the yield of $\beta$-SiC and its sequence was Ba2O3>B>Fe>Al>Al2O3>Si. The effect of additives promoted the transformation of $\beta$-SiC to $\alpha$-SiC form and shwoed the increasing tendency of lattice constant. The two colors of $\beta$-SiC powder came out : one was the black grey with addition of Al, Al2O3 and B the other the light grey with addition of Fe, B2O3 and Si.

• Korean Journal of Materials Research
• /
• v.12 no.11
• /
• pp.889-893
• /
• 2002

The reactions of $Cu/Ti/SiO_2$ structures at temperatures ranging from 200 to $700^{\circ}C$ have been studied for various Ti thicknesses. The reaction products initially formed, at around $300^{\circ}C$, were a series of Cu-Ti intermetallics ($Cu_3$Ti/CuTi) with the oxygen dissolved in the Ti moving from the compounds into the remaining unreacted Ti. At $500^{\circ}C$, the $Cu_3$Ti was converted into Cu-rich intermetallics, $Cu_4$Ti, which grew at the expense of the CuTi due to the increased oxygen content in the Ti. In addition, the outdiffusion of Ti, to the Cu surface, and the $Ti-SiO_2$ reactions, caused an abrupt increase in the oxygen content in the Ti layer, which placed thermodynamic restraints on further Ti reactions. Furthermore, thinner Ti layers showed a higher increasing rate of oxygen accumulation for the same consumption of Ti, which led to significantly reduced Ti consumption. The $SiO_2$ film under the Ti diffusion barrier was more easily destroyed with increasing Ti thickness.

• Resources Recycling
• /
• v.23 no.2
• /
• pp.46-52
• /
• 2014

This study was conducted to observe the removal efficiency of oil-contaminated soil by various tests using microwaves and high-temperature heating elements. The water content was measured with the treatment amount, which was lowered to 300g in a relatively short amount of time. The treatment rate of TPH(Total Petroleum Hydrocarbons) showed the highest value with 70.1% when the SiC-activated carbon heating element was at 4 kW/kg, compared to the SiC heating element used alone. In particular, the higher electric power became, the higher treatment rate became, except at 3 kW. In the case of the heating element made by the fusion of SiC and activated carbon, the internal temperature exceeded $300^{\circ}C$ and again fell when it was treated at 4 kW for about 2 minutes. Then, after about 8 minutes, it rose again. On the basis of such results, the energy content necessary for the sample was calculated according to the electric power of microwaves, and tthe constant of TPH treatment was measured by tests on the treatment characteristics of oil-contaminated soil.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1091-1092
• /
• 2006

Silicon nitride - silicon carbide composite was developed by using an abrasive SiC powders as a raw material. The composites were prepared by mixing abrasive SiC powder with silicon, pressing and sintering at $1400^{\circ}C$ under nitrogen atmosphere in atmosphere controlled vacuum furnace. The proportion of silicon in the initial mixtures varied from 20 to 50 wt%. After sintering, crystalline phases and microstructure were characterized. All composites consisted of ${\alpha}-Si_3N_4$ and ${\beta}-Si_3N_4$ as the bonding phases in SiC matrix. Their physical and mechanical properties were also determined. It was found that the density of the obtained composites increased with an increase in the $Si_3N_4$ content formed in the reaction.

• Korean Journal of Materials Research
• /
• v.29 no.1
• /
• pp.7-10
• /
• 2019

Cr-Al alloys are attracting attention as oxidation resistant coating materials for high temperature metallic materials due to their excellent high temperature stability. However, the mechanical properties and oxidation resistance of Cr-Al alloys can be further enhanced, and such attempts are made in this study. To improve the properties of Cr-Al alloys, Si is added up to 5 wt%. Casting specimens with different amounts of Si content are prepared by a vacuum arc remelting method and isothermally heated under steam conditions at $1,100^{\circ}C$ for 1 hour. The as-cast microstructure of low Si alloys is mainly composed of only a Cr phase, while $Al_8Cr_5$ and $Cr_3Si$ phases are also observed in the 5 % Si alloy. In the high Si alloy, only Cr and $Cr_3Si$ phases remain after the isothermal heating at $1,100^{\circ}C$. It is found that Si additions slightly decrease the oxidation resistance of the Cr-Al alloy. However, the microhardness of the Cr-Al alloy is observed to increase with an increasing Si content.

• Journal of the Korean Ceramic Society
• /
• v.42 no.8 s.279
• /
• pp.542-547
• /
• 2005

Keys to the attainment of tailored properties in SiC ceramics are microstructure control and judicious selection of the sintering additives. In this study, three different strategies for controlling microstructure of liquid-phase-sintered SiC ceramics (LPS-SiC) have been suggested: control of the initial $\alpha-SiC$ content in the starting powder, a seeding technique, and a post-sintering heat treatment. The strategies suggested offer substantial flexibility for producing toughened SiC ceramics whereby grain size, grain size distribution, and aspect ratio can be effectively controlled. The present results suggest that the proposed strategies are suitable for the manufacture of toughened SiC ceramics with improved toughness.

• The Korean Journal of Ceramics
• /
• v.1 no.3
• /
• pp.125-130
• /
• 1995

Electrical discharge machinable $SiC-TiB_2$ composites were fabricated by hot-pressing. Their mechanical and electrical properties were determined as a function of $TiB_2$ content. The addition of $TiB_2$ to SiC matrix increased the strength and toughness and decreased electrical resistivity. The flexural strength and fracture toughness of SiC-40 vol% $TiB_2$ composited were approximately 50% higher than those of monolithic SiC ceramics. Microstructural analysis showed that the toughening was mainly due to the crack deflection, with some possible contribution from crack branching or microcracking.

• Journal of the Korean Ceramic Society
• /
• v.35 no.12
• /
• pp.1249-1256
• /
• 1998

${\beta}$-Silicon carbide(${\beta}$-SiC) whiskers could be synthesized by the carbothermal reduction of kaolin at tem-peratures between 1400 and 1500$^{\circ}C$. The whiskers were grown up to about 1150 of aspect ratio by VS mechanism (showing tapering tips) and to about 45 of that by VLS mechanism (showing round droplet tips) respectively. Hydrocarbon like methane in the reaction atmosphere promoted the formation of gaseous il-icon monoxide(SiO) from silicon dioxide(SiO2) and subsequently reacted with it to form whiskers. The for-mation of ${\beta}$-SiC whiskers increased with increasing carbon content(to 30 wt%) and reaction temperatures. The max. yield of ${\beta}$-SiC whiskers was 15% at 1500$^{\circ}C$ under 20%CH4/80%H2.