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Na S.-M.,YJC Co. | Lee S.-J.,Mokpo National University
Journal of the Korean Ceramic Society | Year: 2013

Porcelain with high thermal shock resistance was successfully fabricated by a lithium solution infiltration method with a lithium hydroxide solution. Lithium hydroxide solutions having various lithium concentrations were infiltrated into pre-sintered porcelain bodies. The porcelain sample infiltrated by the 9 wt% lithium solution and heat treated at 1250 °C for 1 h showed a low thermal expansion coefficient of 1.0 × 10-6/°C with excellent thermal shock resistance. The highly thermally resistant porcelain had a welldeveloped β-spodumene phase with the general phases observed in porcelain. Furthermore, the porcelain showed a denser structure of 2.41 g/cm3 sintering density and excellent whiteness in comparison with commercial thermally resistible porcelains. The lithium hydroxide in the samples readily reacted with moisture, and liquid phase reactants were formed during the fabrication process. In the case of an excess amount of lithium in the sample body, the lithium reactants were forced to the surface and re-crystallized at the surface, leaving large pores beneath the surface. These phenomena resulted in an irregular structure in the surface area and led to cracking in samples subjected to a thermal shock test.

This invention relates to a fireproof container with improved circulation of heat and safer use. According to an embodiment of this invention, a fireproof container, to be loaded in an industrial furnace to perform a thermal treatment of a powder or a target, includes a prominent member formed on the outer walls thereof Also, according to another embodiment of this invention, a fireproof container for use in thermal treatments has a hexahedral shape with a space having a predetermined volume in which a powder or a target to be thermally treated is placed, and includes a protrusion block having a predetermined shape formed on at least one of the external front surface, rear surface, left side surface, and right side surface of the fireproof container.

Na S.-M.,YJC Co. | Go S.-I.,YJC Co. | Lee S.-J.,Mokpo National University
Journal of the Korean Ceramic Society | Year: 2011

Aluminum nitride (AlN) has excellent thermal conductivity, whereas it has some disadvantage such as low sinterability. In this study, the effects of sintering additive content and sintering condition on thermal conductivity of pressureless sintered AlN ceramics were examined on the variables of 1∼3 wt% sintering additive (Y2O3) content at 1900 °C in N2 atmosphere with holding time of 2∼10 h. All AlN specimens showed higher thermal conductivity as the Y2O3 content and holding time increase. The formation of secondary phases (yttrium aluminates) by reaction of Y2O3 and Al2O3 from AlN surface promoted the thermal conductivity of AlN specimens, because the secondary phases could reduce the oxygen contents in AlN lattice. Also, thermal conductivity was increased by long sintering time because of the uniform distribution and the elimination of the secondary phases at the grain boundary by the evaporation effect during long holding time. A carbothermal reduction reaction was also affected on the thermal conductivity. The thermal conductivity of AlN specimens sintered at 1900 °C for 10 h showed 130∼200W/mK according to the content of sintering additive.

Lim K.Y.,University of Seoul | Kim Y.-W.,University of Seoul | Song I.-H.,Korea Institute of Materials Science | Bae J.-S.,YJC Co.
Journal of the Korean Ceramic Society | Year: 2011

Macroporous silicon carbide (SiC) ceramics were fabricated by powder processing and polymer processing using carbon-filled polysiloxane as a precursor. The effects of the starting SiC polytype, template type, and template content on porosity and flexural strength of macroporous SiC ceramics were investigated. The β-SiC powder as a starting material or a filler led to higher porosity than aα-SiC powder, owing to the impingement of growing aα-SiC grains, which were transformed from β-SiC during sintering. Typical flexural strength of powder-processed macroporous SiC ceramics fabricated from aα-SiC starting powder and polymer microbeads was 127 MPa at 29% porosity. In contrast, that of polymer-processed macroporous SiC ceramics fabricated from carbon-filled polysiloxane, β-SiC fillers, and hollow microspheres was 116MPa at 29% porosity. The combination of aα-SiC starting powder and a fairly large amount (10 wt%) of Al2O 3-Y2O3 additives led to macroporous SiC ceramics with excellent flexural strength.

Kim S.-I.,YJC Co. | Go S.-I.,YJC Co. | Lee S.-R.,Mokpo National University | Lee S.-J.,Mokpo National University
Journal of Ceramic Processing Research | Year: 2013

The effects of debinding condition on the thermal conductivity of AlN pressureless sintered at 1850°C for 5 h in a N2 atmosphere were investigated. Spray dried AlN powder compacts incorporating 3 ~ 5 wt% Y2O3 sintering additive and 0.5 wt% PVB binder were calcined in air or a N2 atmosphere for binder burn-out. The debinding condition affected the second phase, the second phase distribution, and the thermal conductivity of the sintered AlN samples. All sintered AlN samples were densified to higher than 98% theoretical density. The sample debinded in a N2 atmosphere showed higher thermal conductivity (170W/mk) than that of the sample debinded in an air atmosphere (< 140 W/mk). In the sample debinded in the air atmosphere, a YAG phase, Y3Al5O12, was observed as the secondary, intergranular phase showing a wide distribution. On the other hand, when the debinding process was conducted in a N2 atmosphere, Y4Al2O9, YAlO3 and Y2O3 phases were observed at the triple point, and the sample color was different at the sample surface and interior due to the residual carbon. In this study, a commercial, spray dried AlN powder was also sintered and examined to confirm the obtained results.

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