Infrared evidence for the formation of an intermediate compound during thesynthesis of zeolite Na-A from metakaolin

Quantitative Infrared spectroscopy has been used to study the first step of the hydrothermal formation of zeolite Na-A from metakaolin. It is shown th at metakaolin reacts with aqueous NaOH solutions, at room temperature, to g ive an amorphous solid, characterised by its IR spectrum. This compound, th at has the same overall composition as zeolite Na-A must be regarded as the precursor of zeolite. At 60 degrees C, the IR spectra show that the precur sor is first synthesised and that zeolite Na-A is formed only when metakaol in has been totally transformed. The formation of the precursor corresponds to the induction period observed by several authors when X-ray diffraction is used to follow the synthesis. (C) 1999 Elsevier Science Ltd. All rights reserved.