Sintering behaviour of ammonium exchanged low silica zeolites synthesised by two different routes

Zeolites have been reported as novel precursors for aluminosilicate based ceramics. Even though the zeolites are conventionally synthesised from sodium aluminosilicate gel (gel route), kaolin is found to be an ideal raw material for the synthesis of low silica zeolites (clay route). The small amounts of ancillary minerals present in kaolin may affect the ion exchange and sintering behaviour of these zeolites. The present paper deals with the ammonium exchange of zeolites NaA and NaX synthesised by these two different routes and the sintering behaviour of these exchanged zeolites at different temperatures was studied by measuring the properties of the sintered products. The influence of the type of zeolite and the method of zeolite synthesis on the sintering behaviour of the exchanged zeolites was examined. The breakdown of zeolite structure was observed at a lower temperature for the gel route zeolites compared to the corresponding clay route zeolites. The final product of sintering in all cases was found to be a mullite-glass composite. Zero water absorption is achieved at a lower temperature of firing for zeolite NH4X compared to the zeolite NH(4)A. X-ray diffraction, thermal analysis and electron microscopic studies substantiated these findings. (C) 2001 Elsevier Science Ltd and Techna S.r.l. All rights reserved.