Experimental evidence of the "memory" effect of amorphous aluminosilicate gel precursors

The principle of the "memory" effect of amorphous aluminosilicate gel precursors, namely that crystal size distribution in the crystalline end product depends exclusively on the number and distribution of nuclei in the get matrix, previously evidenced theoretically by simulation of zeolite crystallization under various conditions, was evaluated experimentally by analysis of the data obtained from specially designed kinetic experiments of zeolite crystallization. It was found that particulate properties (specific number of crystals, crystal size distribution, size of the largest zeolite crystals) considerably depend on the conditions of gel preparation, and thus on the specific number of nuclei and their distribution in the gel matrix. On the other hand, despite considerable differences in the rates of nucleation and crystal growth during crystallization from appropriate precursor, the particulate properties of the crystalline end products as well as number and distribution of nuclei in the gel matrix are not affected, or are affected very slightly by the crystallization condition, and thus by the rates of the relevant critical process (gel dissolution, nucleation, crystal growth). Hence, it was shown that invariability of the size distribution of zeolite crystals in the crystalline end products (zeolite) crystallized from the amorphous alummosilicate precursors prepared in the same way, but differently treated prior and during crystallization is a consequence of the constancy in the number and distribution of nuclei in the matrix of appropriate gel precursor. This result is in accordance with the result obtained previously by simulation, and thus the principle of the "memory" effect of amorphous aluminosilicate gel precursors was evidenced not only theoretically but also experimentally. (C) 2003 Elsevier Inc. All rights reserved.