Shape, size and composition of mullite nanocrystals from a rapidly sintered kaolin

The characteristics of mullite crystallites from a kaolin raw material were determined at the early stage of crystallisation by X-ray diffractometry. The equipment was a Debye-Scherrer system equipped with a curved position s ensitive detector. We measured the size and shape of mullite crystallites i n relation to the temperature (1100-1150 degreesC) and the temperature rate (3-20 degreesC/min). In particular, a temperature rate influence was found on crystallites anisotropy. This result was satisfactorily correlated with TEM observations of sintered materials. The mullite cells constants were a lso measured, they vary significantly with sintering conditions. Cell const ants were correlated with mullite stoechiometry using the Cameron relations hip. Results indicated a narrow composition domain (62-65% Al2O3) for all t hermal cycles. In each case, the orthorhombic phase was identified, in spit e of the low temperature range studied and the relatively high alumina cont ent. (C) 2001 Elsevier Science Ltd. All rights reserved.