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Investigations on the Growth of the Zeolite Type NaY
Investigations on the Growth of the Zeolite Type NaY Hartmut Kacirek and Hans Lechert* Institute of Physical Chemistry of the University of Hamburg, 2 Hamburg 13, West Germany (Received December 13, 1974)
Publication costs assisted by the Institute of Physical Chemistry of the University of Hamburg
In the hydrothermal system Na20/Al203/Si02/H20 we have studied the growth of faujasite crystals with varying Si/Al ratios using seed crystals of the zeolite NaX and a water glass solution as the silica source. The kinetics of the process of growth of the faujasite from amorphous alumosilicate gel has been investigated and procedures for the synthesis of faujasites with varying but definite silicon contents are described. It can be shown that the growing of faujasite crystals from nuclei is possible in concentration ranges where nucleation of this or other species is negligible. In a wide range of crystallization, the growth obeys a kinetic law of the order 2/3.
Introduction Until now kinetic studies of zeolite growth have been carried out mostly for A-type zeolites. Kerr1,2 and Ciric3 found that the growing of A- and X-type zeolites has to be regarded as an autocatalytic process which is in agreement with results received by Breck and Flanigen4 and Mirskii and Pirozhkov12 showing that the formation of zeolites is accelerated by nuclei already present. Detailed studies of Zhdanov5 deal with the influence of liquid and solid phases of the hydrothermal system taking also into account the crystal size in his kinetic considerations. Following the arguments of Zhdanov,5 Meise and Schwochow6 were able to study nucleation and growth of the crystals of A-type zeolites separately, analyzing distribution curves of the particle size and the crystallization curves. Using nuclei for their experiments, they were able to show that the growth can be regarded as a reaction of first order, whereas the nucleation reaction of higher order. Investigations of Culfaz and Sand7 deal with the influence of nuclei on the formation of mordenite. In their experiments, nuclei showed only slight influence on the crystallization of A-type and no influence on the crystallization of X-type zeolites. Besides the composition of the batch, formation of the zeolites are influenced by a number of parameters, e.g., the kind of starting material, the age of the gel, stirring, etc., which have been investigated in various papers.4-6’8’9 In order to keep these influences low, studies on the growth of the zeolites were carried out after a concentration equilibrium had been established between the solid and the liquid is
tered, washed, dried, and analyzed quantitatively by X-ray phase analysis. The Si/Al ratio was determined by X-ray fluorescence analysis. For some samples, we have carried out an analysis of the particle size distribution. This analysis proved to be necessary for the investigation of the kinetics but also for an exact X-ray phase analysis. To obtain the particle size electron micrographs were produced. The distribution curve was derived by counting the particles of different size. For this procedure, one obtains the curve of the distribution density representing the number qo(r) of particles with radii between r and r + dr present in the sample. For qo(r) holds q0{r) dr
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