• Journal of the Korean Ceramic Society
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• v.53 no.1
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• pp.99-104
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• 2016

High purity Si-C (99.999%) powder prepared by mechanical alloying was added to a commercial SiC powder as a sintering additive. Reaction bonded silicon carbide balls and jars with high purity (99.98%) were used for the mechanical alloying. As a result, the purity of the sintered Si-C was higher than 99.99%. When sintered at $2200^{\circ}C$ under 50 MPa pressure for 1 h, SiC containing 10 wt% of high purity Si-C showed a relative density of 95.3%, similar to the relative density of commercial SiC (95%). However, the relative density of SiC decreased to 90.6% without the additive when the applied pressure decreased to 40 MPa. In contrast, the relative density was nearly unaffected by the decrease of the pressure when using the Si-C additive. Therefore, the addition of Si-C powder promoted the densification of SiC above $2000^{\circ}C$ under 40 MPa pressure.

• Journal of the Korean Ceramic Society
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• v.45 no.9
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• pp.531-536
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• 2008

Reaction bonded silicon carbide (RBSC) composite for heat-exchanger was fabricated by molten Si infiltration method. For enforcing fracture toughness to reaction bonded silicon carbide composite, the surface of carbon fiber has coating layer by SiC or pyro-carbon. For SiC layer coating, CVD method was used. And for carbon layer coating, the phenol resin was used. In the case of carbon layer coating, fracture toughness and fracture strength were enhancing to 4.4 $MPa{\cdot}m^{1/2}$ and 279 MPa.

• Journal of the Korean Ceramic Society
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• v.45 no.8
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• pp.486-492
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• 2008

Reaction bonded silicon carbide(RBSC) composite for heat-exchanger was fabricated by molten Si infiltration method. The raw materials with variable particle sizes were used in this experience. The finer the particle size in sintered silicon carbide was the more increasing 3-point bending strength and fracture toughness. As the adaptable particle sizes had been occupied interstice arising from packing sample, the mechanical properties were increased. In the PCS1-1 sample, the 3-point bending strength and fracture toughness were 323MPa and $4.9\;MPa{\cdot}m^{1/2}$, respectively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1869-1876
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• 1992

The effect of particle property on FOD(foreign object damage) and strength degradation in structural ceramics especially, silicon carbide was investigated by accelerating a spherical particle having different material and different size. The damage induced showed significant differences in their patterns with increase of impact velocity. Also percussion cone was formed at the back part of specimen when particle size became large and its impact velocity exceeded a critical value. The extent of ring cracks was linearly related to particle size, however the impact of steel particle produced larger ring cracks than that of SiC particle. Increasing impact velocity the residual strength showed different degradation behaviors according to particle and its size. In the region the impact site represents nearly elastic deformation behavior, the residual strength was dependent upon the depth of cone crack regardless of particle size. However in elastic- plastic deformation region, the radial cracks led to rapid drop in residual strength.

• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.2
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• pp.75-83
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• 2017

In this paper, we investigate the capacity of the lock-in infrared thermography technique for the evaluation of non-uniform top layers of a silicon carbide coating with a nickel based superalloy sample. The method utilized a multilayer heat transfer model to analyze the surface temperature response. The modelling of the sample was done in ANSYS. The sample consists of three layers, namely, the metal substrate, bond coat and top coat. A sinusoidal heating at different excitation frequencies was imposed upon the top layer of the sample according to the experimental procedures. The thermal response of the excited surface was recorded, and the phase angle image was computed by Fourier transform using the image processing software, MATLAB and Thermofit Pro. The correlation between the coating thickness and phase angle was established for each excitation frequency. The most appropriate excitation frequency was found to be 0.05 Hz. The method demonstrated potential in the evaluation of coating thickness and it was successfully applied to measure the non-uniform top layers ranging from 0.05 mm to 1 mm with an accuracy of 0.000002 mm to 0.045 mm.

• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.747-750
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• 2007

The thermal conductivities of nano-sized fumed silica-based insulation media were investigated by varying a mean particle size of the silicon carbide opacifiers and ceramic fiber content. Opacifying effect of ceramic fiber and silicon carbide powders was discussed in terms of their content and the mean particle size of them. As the fiber contents increased from 10 wt% to 30 wt% in a material, its thermal conductivity at temperatures of about $620^{\circ}C$ decreased from 0.171 $Wm^{-1}K^{-1}$ to 0.121 $Wm^{-1}K^{-1}$. Meanwhile, the thermal conductivity at temperatures of about $625^{\circ}C$ decreased from 0.128 $Wm^{-1}K^{-1}$ to 0.092 $Wm^{-l}K^{-1}$ as the mean SiC particle size decreased from $31{\mu}m$ to $10{\mu}m$.

• Carbon letters
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• v.15 no.3
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• pp.180-186
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• 2014

This study highlights a novel method and mechanism for the rapid and effective milling of carbon fibers (CFs) in silicon carbide (SiC) powder, and also the dispersion of CFs in SiC powder. The composite powders were prepared by chopping and exfoliation of CFs, and ball milling of CFs and SiC powder in isopropyl alcohol. A wide range of CFs loading, from 10 to 50 vol%, was studied. The milling of CFs and SiC powder was checked by measuring the average particle size of the composite powders. The dispersivity of CFs in SiC powder was checked through scanning electron microscope. The results show that the usage of exfoliated CF tows resulted in a rapid and effective milling of CFs and SiC powder. The results further show an excellent dispersion of CFs in SiC powder for all CFs loading without any dispersing agent.

• Korean Journal of Materials Research
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• v.23 no.12
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• pp.702-707
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• 2013

High-quality ${\beta}$-silicon carbide (SiC) coatings are expected to prevent the oxidation degradation of carbon fibers in carbon fiber/silicon carbide (C/SiC) composites at high temperature. Uniform and dense ${\beta}$-SiC coatings were deposited on carbon fibers by low-pressure chemical vapor deposition (LP-CVD) using silane ($SiH_4$) and acetylene ($C_2H_2$) as source gases which were carried by hydrogen gas. SiC coating layers with nanometer scale microstructures were obtained by optimization of the processing parameters considering deposition mechanisms. The thickness and morphology of ${\beta}$-SiC coatings can be controlled by adjustment of the amount of source gas flow, the mean velocity of the gas flow, and deposition time. XRD and FE-SEM analyses showed that dense and crack-free ${\beta}$-SiC coating layers are crystallized in ${\beta}$-SiC structure with a thickness of around 2 micrometers depending on the processing parameters. The fine and dense microstructures with micrometer level thickness of the SiC coating layers are anticipated to effectively protect carbon fibers against the oxidation at high-temperatures.

• Journal of Powder Materials
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• v.25 no.5
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• pp.402-407
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• 2018

Molybdenum silicide has gained interest for high temperature structural applications. However, poor fracture toughness at room temperatures and low creep resistance at elevated temperatures have hindered its practical applications. This study uses a novel powder metallurgical approach applied to uniformly mixed molybdenum silicide-based composites with silicon carbide. The degree of powder mixing with different ball milling time is also demonstrated by Voronoi diagrams. Core-shell composite powder with Mo nanoparticles as the shell and ${\beta}-SiC$ as the core is prepared via chemical vapor transport. Using this prepared core-shell composite powder, the molybdenum silicide-based composites with uniformly dispersed ${\beta}-SiC$ are fabricated using pressureless sintering. The relative density of the specimens sintered at $1500^{\circ}C$ for 10 h is 97.1%, which is similar to pressure sintering owing to improved sinterability using Mo nanoparticles.

• 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 ${\sim}13 MPa$.