• Transactions of Materials Processing
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• v.19 no.7
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• pp.399-404
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• 2010

We propose an analysis model for simulating the detailed procedure of pore closing in open die forging of shafts. In the analysis model, an artificial symmetric plane is used, on which initial pores are located to be traced. The analysis model is employed to carry out three-dimensional simulation of pore closing in shaft free forging by both conventional free forging press and radial forging machine. With this result, two typical types of free forging equipment for manufacture of shafts are compared in detail. It has shown that the radial forging machine is much superior to the conventional open die forging press especially in pore closing under high hydrostatic pressure with sound strain.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.79-83
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• 2008

We carry out three-dimensional simulation of pore closing processes during upsetting in open die forging. Several pores on a plane section of a cylindrical material are traced at the same time and the results of hydrostatic pressure and effective strain are discussed to reveal the parameters affecting pore closing phenomena. Five different sizes of pores are also investigated by simulation to reveal the pore size effect in pore closing during upsetting. AFDEX 3D is employed for this study.

• Journal of the Korean Ceramic Society
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• v.37 no.7
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• pp.638-644
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• 2000

The sintering behaviors of the glass-alumina composites for low firing temperature were investigated as functiions of the volume fraction of alumina powder and the particle size with respect to porosity and pore shape. As the volume fraction of alumina powder was increased or the particle size of it was decreased, the sintering temperature of open pore-closing was raised. When the volume fractions of alumina which had 2.19$\mu\textrm{m}$ median diameter were increased with 20, 30, 40, and 50%, the sintering temperatures of open pore-closing were 425, 450, 475, and 500$^{\circ}C$. And when the median particle size of alumina was diminished from 2.19$\mu\textrm{m}$ to 0.38$\mu\textrm{m}$, the sintering temperature of open pore-closing was increased from 450$^{\circ}C$ to 475$^{\circ}C$. Especially, the sintering temperature, which showed maximum density, was corresponded with the stage of open pore-closing and after achieving maximum density over heating resulted in dedensification of specimen, so called, over-firing behavior.

• Journal of the Korean Ceramic Society
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• v.40 no.6
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• pp.572-576
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• 2003

Open/closed porosity, pore size and its distribution and pore type as a funtion of sintered density of UO$_2$-20 wt％CeO$_2$ pellets were investigated. Pore appeared almost closed-type with the density above 96％ of the theoretical density. Bimodal pore size distribution was observed regardless of the sintered density, but the number of pore decreased with increasing the sintered density. The shape of pore was changed from irregular shape to round type with increasing the sintered density.

• Journal of the Korean Ceramic Society
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• v.51 no.1
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• pp.11-18
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• 2014

Onggi, which is described as a breathing pottery, has strongly influenced the traditional food culture in Korea. In this study Onggi is compared to porcelains including celadon and white porcelain to analyze the sources of pore formation. The differences in starting materials are examined for chemical and mineralogical compositions, particle size and distribution. The gas permeability of the fired samples is correlated to the matrix microstructure. The broad particle size distribution and high iron oxide content of Onggi are revealed as the major cause for the pore formation. Open pores are formed with large particles in the Onggi body while closed pores have a high iron oxide concentration. The Onggi body with increased open pores leads to the high gas permeability.

• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.1044-1052
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• 1994

Tape casting technique was successfully applied to produce porous ceramics and multi-layered ceramics containing porous layers, where spherical hollow polymer particles were introduced as pore precursors. In the presence of extreme differences in density and size between Al2O3 and pore precursor particles, hindered settling was effective in preventing segregation of component particles and packing behavior of mixed powders was improved through bimodal packing. There were two transitions in packing behavior of mixed powders. The first transition took place at 40~50 vol% pore precursor addition, where majority of pores changed from close to open pore state. The other transition occured at 60~70 vol% pore precursor addition, where pore precursor particles formed a continuous network structure.

• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.957-968
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• 1994

Manufacturing process of porous glass by the filler method was studied. Commercial soda-lime-silicate glass powder was mixed with inorganic salt as the filler such as KCl, K2SO4, Na2SO4. Sintering shrinkages of mixed powders with the variation of sintering temperature were compared, and the effects of the fillers to shrinkages of mixed powder were increased in the order of Na2SO4${\mu}{\textrm}{m}$ of pore diameter were manufactured when the filler sizes 100~200 ${\mu}{\textrm}{m}$. The open pore volume of porous glass is determined by the quantity of filler and porous glasses having open pore volume between 30 and 70 vol% are available. Available sintering temperature range for preparation of porous glass is from the softening temperature of the glass powder to eutectic melting temperature of DTA curve of mixed powder.

• Nuclear Engineering and Technology
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• v.23 no.1
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• pp.49-55
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• 1991

The microstructure and pore characteristics have been studied on the sintered UO$_2$pellet which was made of the UO$_2$powder manufactured via AUC process. The open porosity decrease with the density and is nearly annihilated above the density of 10.45 g/㎤. The round pore smaller than 3 $\mu$m exist In all densities. The large and elongated pore appears additionally In low density The pore in low density is more elongated than the pore in high density The distribution of the pore area versus the pore size is monomodal and shows its peak on the pore size of 2 to 3 $\mu$m. As the density decreases, the related area of large pore Increases.

• Nuclear Engineering and Technology
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• v.35 no.1
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• pp.55-63
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• 2003

Threshold porosity above which fission gas release channels would be formed in the rim egion of high burnup UO$_2$ fuel was estimated by the Monte Carlo method and Hoshen-Kopelman algorithm. With the assumption that both rim pore and rim grain can be represented by cube, pore distribution in the rim was simulated 3-dimensionally by the Monte Carlo method according to porosity and pore size distribution. Then, using the Hoshen-Kopelman algorithm, the fraction of open rim pores interlinked to the outer surface of a fuel pellet was derived as a function of rim porosity. The simulation showed that porosity of 24-25% is the threshold above which the number of rim pores forming release channels increases very rapidly. On the other hand, channels would not be formed if the porosity is less than about 23.5%. This is consistent with the observation that, for porosity less than 23.5%, almost no fission gas is released in the rim. However, once the rim porosity reaches beyond 25%, extensive open paths would be developed and considerable fission gas release would start in the rim.

• Nuclear Engineering and Technology
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• v.31 no.6
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• pp.608-617
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• 1999

The powder mixture which has a bimodal size distribution, with a large mode corresponding to AUC-UO$_2$ powder and a small one corresponding to ADU-UO$_2$ powder, was prepared, pressed into compacts, and sintered at 1680t for 4 hours in hydrogen gas. The compact density of the powder mixture increases with increasing ADU-UO$_2$content within a content of 20 wt %, since small ADU-UO$_2$ particles can fill interstices between large AUC-UO$_2$particles. The UO$_2$ pellet made using the powder mixture has a lower open porosity than that made using AUC-UO$_2$ powder alone. The mechanism for the formation of a flake-like pore is proposed, and the decrease in open porosity may be ascribed to the decrease in the number of flake-like pores.