Microstructural evolution of mullite during the sintering of kaolin powder compacts

Kaolin particles are usually ̄aky in shape. In the present study, kaolin powder compacts were prepared by applying the diepressing technique. The kaolin ̄akes tend to lie down on the plane which is perpendicular to the die-pressing direction. The powder compact thus shows anisotropic shrinkage after ®ring. A series of phase transformations take place as the kaolin is ®red at elevated temperature. Mullite is ®rst formed at a temperature as low as 1100 C. If the ®ring temperature is higher than 1400 C, needleshaped mullite grains are formed. The size and the aspect ratio of the mullite grains increase with the increase of ®ring temperature. Furthermore, the long axes of the mullite needles tend to be perpendicular to the die-pressing direction. # 2000 Elsevier Science Ltd and Techna S.r.l. All rights reserved.