1-s2.0-092765139400087C-main

ELSEVIER Micropo rous Materials 4 ( 1995 ) 239-242 MICROPOROUS MATERIALS Short communication ole of hom ogeneous nucleation in the formation of primary zeolite particles J. Bronid, B. Subotid Ruder Bogkovik Institute Bijeni6ka 54 P.O. Box 1016 41001 Zagreb Croatia Received 4 July 1994; accepted 4 Novem ber 1994 Abstract Different mechanisms of nucleation in the liquid phase, such as homogeneous, heterogeneous, secondary and autocatalytic nucleation, were assumed in the literature as the dom inant processes of the form ation of primary zeolite particles. Since just homogeneous nucleation was very frequently pointed out as possible process of the formation of primary zeolite particles, the possibility of the occurrence of homogeneous nucleation during zeolite crystallization from aluminosilicate gels was analyzed in accordance with the classical theory of homogeneous nucleation. Analysis of three different crystallizing systems show that the rate of homogeneous nucleation is extremely low under the given synthesis conditions, so the other nucleation processes must be considered relevant for the formation of primary zeolite particles. Keywords: Zeolites; Homogeneous nucleation; Heterogeneous nucleation; Rate of nucleation; Crystallization 1 Introduction Various nucleation mechanisms have been pro- posed for the formation of zeolite particles, and the controversy over the mechanism of zeolite nucleation is persisting. Today's prevalent opinion is that the formation of primary zeolite particles can occur by homogeneous [1-4], heterogeneous [5,6] and secondary [1,7,8] nucleation in the liquid phase supersaturated with soluble silicate, alumi- nate and aluminosilicate species, or by heterogeneous nucleation at the liquid-solid interface of the gel [9]. Crystallization of various types of zeolites from clear solutions [2,10-12] has undoubtedly demonstrated that nucleation may * Corresponding author 0927-6513/ 95/ 9.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0927-6513(94)00087-5 occur in the liquid phase, in the absence of a solid precursor (gel). Homogeneous nucleation [1-4,13] was frequently assumed as a possible process for the formation of primary zeolite particles in the liquid phase. Thus, the objective of this work is to elucidate the real role of hom ogeneous nucleation in the formation of primary particles of zeolites during their hydrothermal synthesis. For this reason we analyzed the possibility of the occurrence of homogeneous nucleation during three different zeolite syntheses. 2 Theory of homogeneous nucleation According to the classical theory of homogeneous nucleation [14 16], it can occur only in a

1-s2.0-092765139400087C-main

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