MICRO-GRATING OF PSEUDOMORPHIC AMORPHOUS PHASE AND MICRO-CUBIC CRYSTALLINE PHASE OBTAINED BY ALKALI DISSOLUITON OF ISOTHERMAL TREATED NH₄-ZEOLITE A

Abstract

Ammonium exchanged zeolites A were isothermally treated at 400-1000°C for durations up to 100min in the air, and then were leached in 1M NaOH solution at 70°C. The products were characterized by XRD, SEM, ICP-AES and ATR-FTIR. The results from isothermal treatments confirmed that the pseudomorphic transformations took place through the formations of an amorphous phase with the tweed-like patterns on the surface of the cubic solid and a subsequent recrystallization to a cubic-shaped composite of mullite and amorphous material. These characterizations supported the existence of a thin surface layer of zeolite crystals acting as a microvessel, which was consistent with a previous hypothesis. After leaching by hot alkali solution, micrograting patterns appeared on the surfaces of the pseudomorphic amorphous phase which exhibited the tweedlike patterns. A cubic solid with fine voids were obtained from a composite of mullite and an amorphous phase. The observed differences in the surface morphology are closely related to the investigated solids.