ELEMENT DISTRIBUTION AND GROWTH-MECHANISM OF LARGE SAPO-5 CRYSTALS

The spatial distribution of silicon as T-atom substituent in large opt ically clear crystals with the AFI structure was studied by electron m icroprobing. The silicon concentration in the center of the crystals i s lower by a factor of two to three than in the other part of the crys tals. This is the second example of a microporous material, for which an inhomogeneous heteroelement distribution was observed. This corresp onds to the findings of our kinetic studies and previous findings conc erning the correlation between silicon content and crystal size. Durin g the early stages of AFI crystal growth we found 'pencil type' crysta ls which develop into hexagonal prisms by flattening of the tips durin g crystal growth. Increasing silicon content accelerates the morpholog ical change and inhibits lengthwise growth of the crystallites.