Study of the crystallization of zeolite NaA by quasi-elastic light-scattering spectroscopy and electron microscopy

Abstract

A study of the crystallization of the molecular sieve zeolite NaA from clear aluminosilicate solutions is reported. It was determined by powder X-ray diffraction that zeolite NaA was the only phase in the solid precipitate. The syntheses were monitored in situ by quasi-elastic light scattering spectroscopy. Characteristics of the products were examined by scanning and transmission electron microscopy. Our data show that nuclei formed from the clear aluminosilicate solution, that crystal growth occurred from the solution, that crystal growth was accelerated at elevated temperatures, and that aging the solution at room temperature before raising the synthesis temperature increased both the number of nuclei that formed and also the crystal growth rate for aging times up to a limit. Adding crushed seed crystal fragments to an unaged synthesis solution produced similar results to aging the solution, including reduced induction times, increased crystal growth rates, and polycrystalline product formation.