• Journal of the Korean Society for Precision Engineering
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• v.22 no.1
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• pp.39-46
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• 2005

In this study, unsintered, presintered and full-sintered low purity alumina ceramics were machined with various tools to clarify the machinability and the optimum cutting conditions. The main conclusions obtained were as follows. (1) Machined with alloy steel tool, the machinability of the presintered ceramics becomes better with the decrease of presintering temperature, but that of unsintered ceramics(white body) was extremely poor. (2) In the case of carbide, K01, the tool life in machining the white body was the longest, and the machinability of presintered ceramics becomes poorer with the increase of the presintering temperature. (3) The K01 tools exhibit longer life than the P10 tools in machining both the white body and the ceramics presintered at $1450^\circC$ or higher temperatures, but the P10 tools shows longer tool life than the K10 tools in machining of the ceramics presintered at temperatures below $1450^\circC$.

• Journal of the Korean Ceramic Society
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• v.43 no.10 s.293
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• pp.626-634
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• 2006

Ceramics manufacturers in the nation produced more than 5000 tons of ceramics wastes a year increasing industrial waste quantity: However, almost no researches were made to reduce environmental pollution and to recycle waste ware. In this study, white ware scraps that were produced at Icheon, Gyeonggi-do were recycled to make use of them as raw materials of ceramics body and to develop new ceramics body that had economic advantages and good quality. The findings showed that the addition of waste ware had limit of 20 wt% considering molding. The addition of waste ware of 20 wt% to white ware lowered baking temperature of the white ware that was added by waste ware of 20 wt% by 30$^{\circ}C$ than existing white ware, and property values were good, for instance, porosity of 3% in average and water absorptivity of 2% in average, and the bending strength recorded more than 800 kgf/$cm^2$ to be high than that of existing white ware being sold in market. The waste ware could be used to produce new ware body and to recycle resources and to solve environmental problems caused by burial and to improve property of ceramics and to save transportation costs as well as baking costs.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.33-38
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• 1995

In this study, unsistered, pre-sintered and sintered low purity alumina ceramics were machined with various tools to clarify the machniability, the optimum tool materials and the optimum tool materials and the optimum cutting conditions. The maon conclusions obtained were as follows. (1) Machined withalloy steel tool, the machinabilty of te pre-sintered ceramics becomes better with the decrease of pre-sintering temperature, but that of unsintered ceramics(white body) was extremely poor. (2) In the case of carbide tool K01, the tool life in machining white body was the longest, and the machinabilty of pre-sintered ceramics becomes poorer with the increase of the pre-sintering temperature. (3) In the case of ceramic tool, the 10000-1100 .deg. C pre-sintered ceramics showed te best machinability within a certain cutting speed range. So far as dry machining, the above combination and conditions showed the highest productivity. (4) When the pre-sintered ceramics were wet machined withsintered diamond tool, the tool life becomes extremelylong, and higher cutting speed can be can be used than in the case offull-sintered ceramics. The productivity of wet cutting is much higher than that ofdry cutting.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.858-864
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• 1995

A porous glass-ceramics body was prepared in the phosphate system. The glass composition of 47.2CaO-22.2TiO2-30.6P2O5 (mol%) containing a few weight percent of ZrO2 was suitable for a mother glass of a porous glass-ceramics. The dense glass-ceramics body was made by a two-step heat treatment of the mother glass. The crystalline phases of the glass-ceramics were $\beta$-Ca3(PO4)2 and CaTi4(PO4)6. The $\beta$-Ca3(PO4)2 phase could be selectively leached out with HCl solution and thus a crystalline $\beta$-Ca3(PO4)2 skeleton was remained. The dimension and shape of the porous glass-ceramics were nearly the same as the those of the first formed glass. The specific surface area and average proe radius of the porous glass-ceramics were 19$m^2$/g and 22 nm, respectively.

• Journal of the Korean Ceramic Society
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• v.43 no.12 s.295
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• pp.859-864
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• 2006

For the pressure compaction process of the ceramic powder, the green density is very different with both the ceramic body shape and the processing conditions. The density difference cause non-uniform shrinkages and deformations, and make cracks in the sintered ceramics. In this paper, Material properties of the alumina powder mixed with binder and the friction coefficient between the powder and the tool set were determined through the simple compaction experiments: Also the powder flow characteristics were simulated and the green density was analyzed during the powder compaction process with Finite Element Method (FEM). The results show that the density distributions of the green body were improved at the optimized processing condition and both the possibility of the farming crack generation and rho deformation of the sintered Alumina body were reduced.

• Journal of the Korean Ceramic Society
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• v.32 no.1
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• pp.113-119
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• 1995

The green body was fabricated by a new forming method, pressureless powder packaing forming method, and the characteristics of sintered specimen were investigated. It was found that alumina ceramics prepared by the present method showed porous structure with narrow pore size distribution, and in case of abrasive powder sintered body, compared with dry-pressed specimen, had the nearly same density. Especially, the specimen prepared with spray-dried granules showed the characteristic that granules were not either deformed or fractured during forming and sintering process. Therefore, it was found that this new forming method was effective method in fabrication of porous ceramics on account of easy control of porosity and pore size and its high thermal stability.

• The Korean Journal of Ceramics
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• v.5 no.3
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• pp.235-238
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• 1999

In a ceramic green body, some degree of nonuniformity in density always presents. These differences in green density will appear as nonuniform shrinkage after sintering takes place. For the complex ceramic bodies with various curves and angles, therefore, it is quite difficult to foresee the final dimensions precisely after sintering. This simulation study shows that, considering the sintering process as a thermal shrinkage phenomenon, the use of NASTRAN enables to predict the precise shape of a sintered body. Based on this result, 'the reverse engineering technique' has been developed that can unfold the exact dimensions of a green body to have the desired shape after sintering. This approach will provide a simple and useful tool for ceramic engineers to fabricate complicate bodies with tight dimensional tolerances.

• Journal of the Korean Ceramic Society
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• v.43 no.8 s.291
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• pp.458-462
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• 2006

A simple pressing process using a SiC powder, $Al_2O_3-Y_2O_3$ sintering additive, and polymer microbeads for fabricating cellular SiC ceramics is demonstrated. The strategy for making the cellular ceramics involves: (i) forming certain shapes using a mixture of a SiC powder, $Al_2O_3-Y_2O_3$ sintering additive, and polymer microbeads by pressing; (ii) heat-treatment of the formed body to burn-out the microbeads; and (iii) sintering the body. By controlling the microsphere content and sintering temperature, it was possible to adjust the porosity in a range of 16% to 69%. The flexural and compressive strengths of cellular SiC ceramics with $\sim$40% porosity were $\sim$60 MPa and $\sim$160 MPa, respectively.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.10
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• pp.81-86
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• 2020

A ceramic vacuum chamber feedthrough ceramic insulator is made of Al2O3; the manufacturing process involves filling alumina powder into a urethane mold and pressing it with a rubber press to produce a molded body. Thereafter, manufacturing is completed through primary shape processing, sintering, and secondary shape processing in the green body, which is a pressurized molding body, This work is intended to prevent defects in the first shape processing by improving the ceramic insulator in the green body, and to improve the productivity of the ceramic insulator by determining the optimal processing conditions.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.1
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• pp.27-32
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• 2020

The main cystal phases of traditional ceramics made of clay, quartz, and feldspar are mullite and cristobalite. Although mullite can provide strength to the ceramic body, it cannot be used for the heat resistant ceramics because the thermal expansion coefficient of it is relatively high as 5.3 × 10^-6/℃. In this study, development of lightweight heat resistant ceramics was tried by producing cordierite phase, of which the thermal expansion coefficient is 2.6 × 10^-6/℃, instead of forming mullite phase in the ceramic body by using Sanchung Kaolin and Jangsu gobdol sludge. It was concluded that ceramics having good heat resistant, bending strength, and refractoriness under load could be fabricated when 80 wt% of Sanchung Kaolin and 20 wt% of Jangsu gobdol sludge were used as raw materials. Also, the bulk specific gravity is 1.78, which is lighter than the existing Buncheong ware.