• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.6
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• pp.258-263
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• 2008

The fine aggregates of below 2 mm size was fabricated using by the vertical furnace in which the aggregates could be sintered at floating state and its physical properties were analyzed. The liquid formed at the surface of specimens sintered at $1200{\sim}l300^{\circ}C$ induced a gas in core to expand so the denser shell and porous core could be produced. The C series specimen fabricated by crushing an extruded body had an irregular shape and sharp edges but those became spheroidized by bloating due to gas expansion inside. The fine aggregates fabricated in this study was as light as floating in the water and had an apparent density of $0.68{\sim}1.08$. The absorption rate was proportioned to a porosity showing that the pores in core was not closed completely. The properties of fine aggregates fabricated in vertical furnace were similar with those of in an electric muffle furnace but the sticking-together phenomenon by surface fusion was not occurred in the vertical furnace. The aggregates fabricated in this study had a little lower impact resistance than that of natural aggregate but satisfied the unit volume weight standard specified in KS.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.2
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• pp.71-75
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• 2006

The aggregates made of clay, carbon and $Fe_2O_3$ were prepared to investigate the mechanism of black core formation and the property differences at various sintering atmospheres. The aggregates were sintered at oxidized, neutralized and reduced atmospheres. The specific gravity, absorption rate, percent of black core area were measured at various compositions and sintering atmospheres. The aggregates sintered at oxidized atmosphere showed clear border between shell and black core area. Hence, the aggregates sintered at reduced and neutralized atmospheres showed only black core area in the cross-section of the aggregates. The specific gravity of the aggregates sintered at reduced atmosphere increased with increasing carbon contents and that was the lowest of all aggregates sintered at various atmospheres. Adsorption rate increased with increasing carbon contents at all atmospheres.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.619-625
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• 1998

The effect of softening point and glass amount of glass frit on the sintering behavior of low temperature cofirable glass/ceramic composites was studied and according to these results, glass/ceramic composites with high sintered density was fabricated. The density of composites was increased as the glass amount was increased. In case of using the glass with low softening point, the deformation of specimen was occurred though the ratio of the glass amount in the specimen was low. But, in case of using the glass with high softening point, the sintered density of composites was increased in accordance with glass amount. With the specimen of high softening point, the deformation was not happened. Therefore, it was found that the densification was progressed continuously in high glass amount. From the study on the effect of softening point of glass on sintering behavior, the suitable softening point and glass amount for fabrication of glass/ceramic composites can be anticipated. When glass frit with softening point of $790^{\circ}C$ was chosen according to this result, low temperature cofirable glass/ceramic composites with high density (97%) at $900^{\circ}C$ was fabricated.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.317-328
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• 2019

In this work, we investigated clay and raw materials from China (black clay, red clay, white clay) and Korea (Cheonan clay, Obu clay) used for the manufacture of porcelain products. According to chemical analysis results, feldspar components containing CaO, K₂O, Na₂O and quartz are found in clay materials besides primary clay such as kaollinte, for the clay materials from Korea, which is found more in clay materials from Korea than from China. For the Fe₂O₃ content, governing whiteness of porcelain products, more iron oxide (> 5 %) is found in Korean clays (Cheonan clay, obu clay, red clay) compared to those form China (black, white clay). Through X-ray diffraction analysis, kaolinite and Halloysite are found to be main phases for all the raw materials and second phases such as quartz and pyrophyllite are found. Using these clay materials, raw materials for porcelain products were produced, and the physicochemical properties were investigated for sintered samples. Absorption rate is in order of Baekja-A < Baekja-B < Yeonbuncheong < Jinbuncheong < Cheongja, and the sample, sintered at 1250℃ in reductive atmosphere, exhibits the lowest absorption rate. Comparing the color of the sintered samples, the samples sintered in oxidative atmosphere (L^* value: 86~95 %) show higher whiteness value than those sintered in reductive atmosphere (L^* value: 81~93 %). For the Cheongja and Buncheong, the samples sintered in reductive atmosphre shows higher whiteness, L^* values, and low a^*/b^* value, which is due to reduction of iron oxide (Fe₂O₃).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.626-633
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• 1998

For the fabrication of low temperature cofirable glass/ceramic with high dielectric constant, crystallizing glass [$SiO_2-TiO_2-RO (RO:BaO, CaO:SrO)$] was formed. The glass/ceramic composites were made by mixing this glass and alumina ceramic as filler, and its characteristics was investigated. With this glass compositon, it was possible to fabricate the glass which could be crystallized under $900^{\circ}C$. And it was found that the crystallizing temperature was changed in accordance with the composition of RO in glass. By adding $Bi_2O_3$ as flux, using $Al_2O_3$ as filler and sintering at $860^{\circ}C$, low temperature cofirable glass/ceramic with high dielectric constant was fabricated. The density of that composites was 3.96 g/$\textrm{cm}^3$, dielectric constant was 17 and Q. f was 600.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.2
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• pp.324-333
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• 1997

Porous alumina specimens with 80~92% relative densities were prepared from ultrasonic spray pyrolyzed alumina Powders by sintering at $1600^{\circ}$~ $1700^{\circ}C$. The exaggerated grain growth appeared to high sintering temperature and long soaking time. The microstructural development during sintering was investigated using image analysis. In the study of grain growth kinetics for sintering for spray prolyzed alumina powder, the activation energy for normal grain growth was 386.77 kJ/mol.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.209-212
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• 2001

It is known that the mim forming processes show somewhat different phenomena compared with the conventional metal forming processes, namely, the size effect, enhanced friction effect and etc. Such typical phenomena, however, are not predicted by the conventional finite element analysis, which has been an efficient numerical tool to predict the metal forming processes. It is due to the fact that the constitutive relations used does not describe the microstructural characteristics of the materials. In the present investigation, the finite element formulation using the rate-dependent rigid plastic crystal plasticity model of the face-centered cubic materials is conducted to predict the micro mechanical behaviors during the mim forming processes. The finite element analysis, however, provides mesh-dependent solutions for the intragranular deformations. Therefore, the couple stress energy is additionally introduced into the variational principle and formulated within the framework of the rigid plastic finite element method to obtain mesh-independent solutions. Micro deformations of single crystal and bicrystal with various orientations are calculated to show the potential of the developed formulation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.287-290
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• 2005

The shearing and punching processes are analyzed with the finite element method using an isotropic material model. The experimental result in the punching process shows that final radiuses of sheet metal according to the rolling direction and transverse direction are different because of the material anisotropy. The material anisotropy is induced by complicated large deformation in the polycrystalline aggregate. The contact region between the punch and sheet metal experiences severe deformation such as shear, compression and tension in the punching process. In this paper, the analysis of punching process for Al 1100 is performed with the ABAQUS Standard. The analysis of texture development and evolution is carried out based on the deformation history in the punching process. The deformation histories are extracted by UMAT in the ABAQUS Standard. The torture development is investigated with the pole figure and yield surface during the punching process.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.4
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• pp.199-204
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• 2003

Microstructure and chemical analysis of sintered bricks containing recycled wastes were investigated by SEM and EDS. The recycled wastes for which substitute ceramic raw materials were EAF (electric arc furnace) dust, fly ash and stone ash. Yellowish and brownish regions on the surface and brownish and blackish regions in the inside of bricks were observed. Main component of yellowish region on the surface turned out to be Zn. No chemical difference between the black-core region and brownish matrix. Mullite crystallites of 1 fm size were distributed in the inside of bricks and enclosed by glass phases. It seems that alumine-silicate mixtures of kaolin and fly ash were transformed to mullite crystallites during the sintering. Relatively large pores ot several ten fm size were observed in the black-core region in the inside of bricks. The main components of the inside of brick were Al and Si. The minor components were C, Na, Mg, K, Ca, and Fe. Particularly, the precipitates of Fe-rich crystallites were observed in the amorphous matrix. These precipitates were formed due to the local reduction atmosphere in the inside of bricks. Zn-rich covers were found on the surface of bricks because Zn diffused from the inside of bricks to the surface under the reduction atmosphere.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.6
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• pp.277-282
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• 2007

The artificial lightweight aggregate (ALA) was manufactured using coal bottom ashes produced from a thermoelectric power plant with clay and, the sintering temperature and batch composition dependence upon physical properties of ALA were studied. The bottom ash (BA) had 13wt% coarse particle (>4.75mm) and showed very irregular shape so should be crushed to fine particles to be formed with clay by extrusion process. Also the bottom ash contained a many unburned carbon which generates the gas by oxidation and lighten a aggregate during a sintering process. Plastic index of green bodies decreased with increasing bottom ash content but the extrusion forming process was possible for the green body containing BA up to 40wt% whose plastic index and plastic limit were around 10 and 22 respectively. The ALA containing $30{\sim}40wt%$ BA sintered at $1100{\sim}1200^{\circ}C$ showed a volume specific density of $1.3{\sim}1.5$ and water absorption of $13{\sim}15%$ and could be appled for high-rise building and super-long bridge.