THE INFLUENCE OF SURFACTANTS AND WATER-SOLUBLE POLYMERS ON THE CRYSTALLIZATION OF ZEOLITE NAA

The crystallization of zeolite NaA in the presence of various surfacta nts (sodium dodecyl sulfate, Aerosol OT, cetyltrimethylammonium bromid e, Nonidet P40) and of poly(ethylene glycol) was studied and compared to a control crystallization with no additive present. Crystalline-gro wth curves were determined by quantitative X-ray diffraction studies o f samples removed periodically from the hydrothermal system. Crystal-s ize distributions and linear crystal-growth rates were determined by s canning electron microscopy, and from these data, nucleation profiles were constructed. Changes in the concentrations of soluble aluminum an d silicon in the aqueous phase of the hydrothermal system during cryst allization were monitored by inductively coupled plasma atomic emissio n spectroscopy. The additives were shown to lengthen the prenucleation period, shorten the nucleation period, and increase the linear rate o f crystal growth. All but Aerosol OT increased the total number of nuc lei produced and gave crystals with a reduced mean size and narrower s ize distribution. These effects may be attributed to an effective redu ction in the water content of the hydrothermal system. Aerosol OT redu ced the number of nuclei produced and gave larger crystals, an effect that may be attributed to a specific interaction with aluminum species . In general, the aluminum concentration in the aqueous phase was foun d to decrease dramatically during the period of crystal growth.