Abstract
Amorphous alumino-silicates of different compositions were aged at 175° C under acid and basic conditions. At high pH, crystallization of two zeolites, phillipsite and chabazite, was recorded. Under acid or neutral conditions, a demixing into boehmite and a more stable alumino-silicic gel has been observed.These results are discussed in relation to the affinity of silica for alumina.