• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.949-956
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• 1994

In order to investigate the relationship between pore size distribution and freezing-thawing resistance of mortars, polymer-cement mortars were prepared by using styrene-butadiene rubber latex, ethylene-vinyl acetate emulsion and polyacrylic ester emulsion with various polymer-cement ratios at constant flow. From the results of the test, polymer-cement mortars had a good pore size distribution for freezing-thawing resistance compared with unmodified mortars because of having a small pore volume in the pore radius range of 103~104 $\AA$ affecting on the frost damage. And the freezing-thawing resistance of polymer-cement mortars was improved with increasing polymer-cement ratio.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.6
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• pp.509-516
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• 2008

Multi-layer circuit card for semiconductor inspection was fabricated by LTCC technology. After a proper impedance design without electrical interference, ceramic tapes with the composition of $CaO-Al_2O_3-SiO_2-B_2O_3$ glass and $Al_2O_3$ were prepared. The electrode with silver paste printed on the tape. Printed ceramic sheets were then laminated and sintered. Densities and dielectric properties were measured. The microstructure, fracture surface of the region of via and matching state of substrate-electrode were observed. The durability of plated outside electrode were examined by hardness and scratch test.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.131-136
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• 1998

The creep behavior and failure mechanism of the 30 vol% hot-pressed $SiC_t/Si_3N_4$ ceramic composite was experimentally investigated at $1200^{\circ}C$ and at various stress levels in air. The creep threshold stress for zero creep rate after 100 hr was found to be approximately 60 MPa. The stress exponent was estimated to be n~1, which suggests that fiber-reinforcement reduced the stress sensitivity of the HPSN matrix with the stress exponent of 2. The tertiary stage leading to creep rupture was found at 250 MPa but was very short. The microstructure of the crept specimen showed random fiber fracture and no matrix cracking. Interfacial debonding was absent.

• Journal of Powder Materials
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• v.6 no.4
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• pp.320-324
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• 1999

The formation, microstructure and properties of novel ceramic composite materials manufactured by active-filler-controlled polymer pyrolysis were investigated. In the presence of active filler particles such as transition metals, bulk components of various geometry could be fabricated from siliconorganic polymer. Molybdenum- and tungsten-filled polymer suspensions were prepared and their conversion to ceramic composites by annealing in $CH_4$ atmosphere were studied. Dimensional change. porosity and phase distribution (filler network) were analyzed and correlated to the resulting hardness values. Molybdenum and tungsten as active filler were carburized completely to $Mo_2C$, $W_2C$ and WC in $CH_4$ atmosphere. Consequently, microcrystalline composites with the filler reaction products embedded in a silicon oxycarbide glass matrix were formed. Hardness was increased with increasing carburization and reached 8.6-9.5 GPa in the specimen pyrolyzed in $CH_4$ atmosphere.

• Journal of Powder Materials
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• v.20 no.5
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• pp.345-349
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• 2013

Carbon nanotube-dispersed bismuth telluride matrix (CNT/$Bi_2Te_3$) nanopowders were synthesized by chemical routes followed by a ball-milling process. The microstructures of the synthesized CNT/$Bi_2Te_3$ nanopowders showed the characteristic microstructure of CNTs dispersed among disc-shaped $Bi_2Te_3$ nanopowders with as an average size of 500 nm in-plane and a few tens of nm in thickness. The prepared nanopowders were sintered into composites with a homogeneous dispersion of CNTs in a $Bi_2Te_3$ matrix. The dimensionless figure-of-merit of the composite showed an enhanced value compared to that of pure $Bi_2Te_3$ at the room temperature due to the reduced thermal conductivity and increased electrical conductivity with the addition of CNTs.

• Journal of the Korean Ceramic Society
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• v.29 no.6
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• pp.441-450
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• 1992

The microstructur and LPG sensing properties of maghemite (${\gamma}-Fe_2O_3$) ceramics have been studied. The acicular and fine spherical shaped iron oxide particles were sintered at below $900^{\circ}C$. The maghemite ceramics were prepared by reduction-oxidation of sintered iron oxide. With the microstructure of acicular and/or fine grains, the maghemite ceramics have good LPG sensing properties. Increased sintering temperature deteriorates the LPG sensitivity of maghemite ceramics due to the grain growth. The maghemite ceramics prepared from the mixed iron oxide, of a large amount of acicular particles and a small amount of spherical ones, have a lower LPG sensitivity than that of the acicular iron oxide ceramics. But, they seem to be of higher mechanical strength. The optimum working temperature for LPG sensing of the maghemite ceramics was found to be $300~350^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.29 no.9
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• pp.750-756
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• 1992

Reaction bonded si-SiC composites were prepared by silicon infiltration technique at temperature of 1$600^{\circ}C$ for 30 minutes in vaccum atmosphere. The microstructure and mechanical properties of Si-SiC composites were investigated and characterized. UF-15 and SE-10 as SiC powders, phenolic resin and carbon black as carbon source, and metallic silicon powder as molten Si source were used as starting materials. New SiC crystallines nucleatd and grown by reaction of Si and C were detected by TEM and SEM-EDS. The bonding between new and original SiC was found to be strong. But the wetting of SiC by unreacted metallic Si and the rapid grain growth of new SiC decreased density and fracture toughness. Fracture toughness and modulus of rupture of Si-SiC composite were about 3.2 MPa.m1/2 and 480 MPa, respectively.

• Journal of the Korean Ceramic Society
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• v.29 no.1
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• pp.1-8
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• 1992

The effect of CaO impurity on the microstructural evolution during the sintering of ultrapure alumina(>99.999%) was studied under "clean" firing conditions. The sinterability of undoped alumina was low, but its microstructure was maintained uniform. In the case of CaO-doped alumina, the distribution of grain size and that of grain boundary dihedral angle became wider, and facetted pores observed frequently. When MgO was doped in addition to CaO, the sinterability increased drastically and the uniform microstructural characteristics resumed. This study suggests that the effect of CaO is to induce inhomogeneous microstructures presumably by anisotropic segregation to grain boundaries and pore surfaces, and that MgO suppresses the anisotropic segregation of Ca.

• Journal of the Korean Ceramic Society
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• v.29 no.1
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• pp.9-14
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• 1992

Some of non-isothermal analysis methods are applied to CaO-MgO-Al2O3-SiO2 glass system to find the kinetics parameters of crystallisation, activation energy, Avrami component and frequency factor. The results using the non-isothermal analysis were compared to that of microstructure experiment. Analysis of the result has enabled to some methods to be to recommend as being the most appropriate equation to use in a glass system. It was shown that in the thermal analysis using the non-isothermal method of Kissinger, Augis-Bennett, Bansal, and Marotta, the calculation of activation energy is not much different, while Avrami component and frequency factor are different from applied each methods.

• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1169-1175
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• 1994

Five Al2O3/SiC/metal composites with four different particle sizes of green SiC abrasive grains are grown by the directed oxidation of an commercially available Al-alloy. Oxidation was conducted in air at 100$0^{\circ}C$, 96 hours long. Slip casted SiC-fillers were placed on the alloy or SiC powder deposited up to the required layer thickness. Their microstructures are described and measurements of density, elastic constants, frexural strength, fracture toughness and work of fracture are reported. The results are compared with those of commercial dense sintered Al2O3. The properties of produced materials have a strong relationship to not only the properties of Al2O3, SiC, Al and Si but also to the phase share and phase distribution. The composite materials are dense (0.5% porosity), tough (KIC = 3.4~6.4 MPa{{{{ SQRT { m} }}), strong ({{{{ sigma }}B = 170~345 MPa) and reasonably shrinkage free producible. The reinforcements is attained mainly through the plastic deformation of ductile metal phase.