SINTERING AND CRYSTALLIZATION OF MULLITE IN DIPHASIC GELS

Diphasic monolithic mullite gel of stoichiometric composition shows a multiple aggregation of colloidal SiO2 (similar to 12 nm) and AIOOH (s imilar to 10 nm) particles. The identity of the colloidal particles is retained up to the crystallization of mullite at a temperature of 124 0 degrees C in unpressed or 1220 degrees C in gels cold-isostatically pressed at 1.5 GPa. Intensive sintering is closely followed by crystal lization of mullite. Both sintering and crystallization are apparently related with the formation of a silica continuum. Nucleation of mulli te appears to occur at points of contact (interface) of SiO2/delta-Al2 O3 particles.