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Detailed Program
Paper Number : EF-I04
Time Frame : 16:30~16:55
Presentation Date : Friday, 28, November
Session Name : Electric Field Assisted Sintering
Session Chair 1# : Young-Hwan Han
Session Chair 2# : Koji Morita
Low-Temperature Spark Plasma Sintering of Transparent Alumina and Unusual Grain Growth
Byung-Nam KIM
National Institute for Materials Science
During spark plasma sintering of alumina at low temperatures, the effects of heating rate, pressure and loading schedule on the grain size are examined. When the alumina is densified at low temperatures, high heating rates accelerate grain growth, though the total heating time is reduced. The phenomena is unusual and cannot be explained by the common knowledge. The grain growth rate after full densification is also accelerated for high heating rates. The accelerated grain growth may result from the generation of defects during densification. The densification in the intermediate stage of sintering includes the deformation of powder particles, and the deformation of ceramics occurs mainly by grain-boundary sliding. The defects generated during grain-boundary sliding may enhance the grain-boundary mobility and accelerate the grain growth rate, that is the dynamic grain growth. It is considered, therefore, that the high deformation rate at high heating rates accelerates grain growth. The accelerated grain growth also appears for high-pressure sintering. The grain size after sintering increases with the applied pressure. High pressures lower the deformation temperature and increases the deformation rate. As a result, the higher deformation rate during heating may generate more defects and enhance the grain-boundary mobility. Lastly, the loading schedule during heating also affects the deformation and the grain growth. Applying pressure at lower temperatures may generate more defects and resultantly accelerate the grain growth. All the unusual grain growth observed during low-temperature sintering is explained by the model of grain-boundary sliding.
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