• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.151-156
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• 2010

Porous mullite/alumina composites have been fabricated by a freeze casting technique using TBA-based coal fly ash/alumina slurry. After sintering, unidirectional macropore channels aligned regularly along the TBA ice growth direction were developed; simultaneously, small sized micropores fromed in the outer walls of the pore channels. The physical and mechanical properties (e.g. porosity and compressive strength) of the sintered porous composites were roughly dependant of processing conditions, due to the complexity of the factors affecting them. However, with increasing solid loading and sintering temperature, the compressive strength generally increased and the porosity decreased. After sintering $1500^{\circ}C$ for 2 h, the porous specimen (porosity: 52.1%) showed a maximum compressive strength of 70.0 MPa.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.2
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• pp.175-180
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• 1995

In order to clarify the part of thermal properties of coal fly ash, the change of mineral compositions of the heated coal fly ash was investigated by XRD, TG - DTA and SEM. It was found that the mineral composition of coal fly ash was quartz, mullite and glassy phase ( a b. 20 ~ 25 wt % ), and had no difference in the range of 105 to $1000^{\circ}C $. Only in the case of Ansan coal fly ash, calcite was detected besides the crystalline of quartz and mullite. And anorthite was produced by the reaction between thermal- decomposed calcite, quartz and $Al_2O_3$component in the glassy phase at $1200^{\circ}C $.

• Journal of the Korean Ceramic Society
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• v.48 no.6
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• pp.604-609
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• 2011

Additives for low temperature sintering of mullite ceramics were investigated for matching Mo-Cu conducting paste with that ceramics at 1,400$^{\circ}C$. $SiO_2$, MgO and $Y_2O_3$ were chosen as the additives for low temperature sintering, and the amounts of those additives were varied with sintering temperature of 1,400$^{\circ}C$ to 1,500$^{\circ}C$. With additives of 1.0 wt% of $SiO_2$, 1.0 wt% of MgO, and 1.5 wt% of $Y_2O_3$, the densest sintered body of 3.12 g/$cm^3$ was obtained at 1,400$^{\circ}C$ in reducing atmosphere. The flexural strength of that was 325 MPa and the CTE (Coefficient of thermal expansion) was 4.33 ppm/$^{\circ}C$.

• 보존과학연구
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• s.24
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• pp.99-130
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• 2003

This research carried out composition analysis the subject of potteries from kiln site at Gangwon-do, Chungcheong Nam∙Buk-do and the followings are the results. Firstly, XRD analysis results showed that soft potteries were consisted of $\alpha$-quartz, feldspar and soil minerals while hard potteries were consisted of high temperature crystals like mullite, tridymite and cristobalite. Secondly, the firing temperatures of the soft potteries were determined using XRD analysis. It ranged from $550^{\circ}C$ to $870^{\circ}C$.While the firing temperatures of the hard potteries were divided into 3 groups; Group Ⅰ: Potteries with Mullite and Feldspar - ranged from $1000^{\circ}C$ to$1200^{\circ}C$. Group II : Potteries with Mullite and Tridymite - ranged from $875^{\circ}C$ to $1200^{\circ}C$. Group III : Potteries with Cristobalite - ranged above $1200^{\circ}C$.Thirdly, the result of correlation analysis using trace element such asSc, Rb of the potteries form Gangwon do and Chungcheong Nam.Bukdokilns allowed us to divide the area with their own characteristics into 4-groups. Using the same result, kilns sited at Chungcheong Nam.Buk-do were classified into 3-groups.

• Journal of the Korean Ceramic Society
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• v.37 no.7
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• pp.693-699
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• 2000

Casting behavior of Zr(Y,Ce)O2 TZP/Mullite suspension during pressure filtration was investigated to prepare multi-layered Functionally Gradient Materials(FGM). The dispersion stabilities of each layer suspension were investigated by examination of zeta potential and viscosity. The each suspensions with 20 vol.% solid loading and 100 첸 of viscosity was prepared after fix of the dispersing agent (Sodium hexa-meta phosphate) and the binder (Hydroxyethyl cellulose), and then the cakes were formed at the 2.5 MPa~10.0MPa pressure range. The cake thickness of all suspensions was increased with the square root of time at the constant pressure, and the relations between filtration pressure(P)a nd dehydration rate (Q=dh/dt) showed that the flows of filtrates in the consolidated layers were laminar. The permeabilities were nearly constant during filtration, and kozeny constants(Kc) of the suspensions were 4.8~6.7. These valumes were seen as close to 5, which might be homogeneous particle packing during filtration. On the basis of those data, the multi layered compaction with 9 mm thickness and 52.5% green density was prepared by continuous pressure filtration.

• Journal of the Korean Ceramic Society
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• v.26 no.3
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• pp.347-360
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• 1989

Spinel, mullite, forsterite and cordierite composition powders were synthesized from Mg(NO3)2.6H2O, Al(NO3)3.9H2O and SiCl4-ethanol solution by spray pyrolysis method and the sinterability of these powders were investigated. The bulk density of spinel and mullite specimens sintered at 1,$700^{\circ}C$ for 1hr was 3.56g/㎤(99.5% relative density) and 3.16g/㎤(99.7% relative density), respectively. (Green compacts were made from powders prepared at 1,00$0^{\circ}C$). The bulk density of forsterite and cordierite specimens sintered at 1,480 and 1,40$0^{\circ}C$ for 2hrs were 3.217 and 2.155g/㎤, respectively. (Green compacts were made from powders prepared at 1,00$0^{\circ}C$). The constituent compositions of spinel and mullite specimens sintered at 1,$700^{\circ}C$ for 1hr were 27.5wt% MgO and 70.5wt% Al2O3, respectively. Vickers microhardness and fracture toughness of spinel sintered at the above condition were 13.7GPa and 2.6MN.m3/2, respectively, and room temperature bending strength, 425MPa, was nearly maintained even at the elevated temperature. In the case ofmullite specimens, those values were 13.5GPa, 2.2MN/m3/2 and 430MPa, respectively.

• Journal of the Korean Ceramic Society
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• v.32 no.5
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• pp.626-634
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• 1995

The SiC-porcelain powder mixtures containing 51.9wt% SiC are produced as by-products from the surface abrasion process of porcelain cores. This raw powders were used as starting materials for the synthesis of SiC containing ceramics. The specimen, which was fired at 135$0^{\circ}C$ from raw powders, had SiC, $Al_{2}O_{3}$, , cristobalite, mullite as crystalline phases, and the fractured microstructure showed dispersed SiC crystalline particles almost wetted with glassy matrix and spherical pores. Although the oxidation of SiC containing powder compacts wetted with glassy matrix and spherical pores. Although the oxidation of SiC containing powder compacts started at the range of 600~80$0^{\circ}C$ form the analysis of weight gain, the presence of $SiO_{2}$ crystallien phase and cristobalite was confirmed at 100$0^{\circ}C$ by XRD analysis. Mullitization of specimens was accelerated by preheating before the final firing. The specimen sintered at 135$0^{\circ}C$ after 100$0^{\circ}C$ preheating consisted of SiC, cristobalite, mullite as crystalline phases, and revealed 2.24g/$cm^{3}$ bulk density, 11.73% water adsorption, porous microstructure with small amount of glassy phase. SiC contents of specimens, which was 51.9 wt% in the raw powders, reduced to 37~22 wt% after firing at 135$0^{\circ}C$ depending on the preheating condition.

• Proceedings of the Materials Research Society of Korea Conference
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• 1999.11a
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• pp.114-114
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• 1999

• Proceedings of the Materials Research Society of Korea Conference
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• 2001.05a
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• pp.20-20
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• 2001

• 한국전자현미경학회:학술대회논문집
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• 2004.11a
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• pp.86-88
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• 2004