Studies on the Densification Process of Kaolin Bodies

Abstract

Densification processes and microstructural changes of kaolin bodies during firing were examined and their co-relations were discussed.From the results of the firing shrinkage, bulk density and apparent porosity measurements, following results were obtained. Degree of densification increased with the temperature. The longer the grinding time of the kaolin, the lower the densification of the bodies when fired at 1000°C. However, when fired at temperatures higher than 1100°C, the effect of grinding time on the densification of kaolin resulted inversely.Shrinkage behaviours were also examined kinematically, and the following results were inferred. The kaolin body shrank at about 500°C, 900°C and 1100°C. Shrinkage occurred at about 900°C might be due to the diffusion sintering process of metakaolin grains. Shrinkage occurred at slightly lower temperatures than 1100°C might be attributed to the viscous flow mechanism and partly diffusion process in the spinel intermediate phase.Microstructural changes of the fired bodies were also examined by means of X-ray diffraction, polarizing microscope and scanning electron microscope. Further, it was shown that the densification processes and accompanied phenomena of the fired bodies were clearly explained by these microstructural observations.