Coarsening and Spinodal Decomposition of Zeolite Linde Type A Precursor Gels Aged at Low Temperatures

Abstract

We monitored the effect of different gel aging temperatures (from −20 to 40 °C) and gel aging times (from 7 to 21 days) on the particle size and crystalline structure of template-free Linde type A zeolites through scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. We demonstrate the synthesis of zeolite LTA with average particle sizes of 0.45 ± 0.07 μm by preliminary heat treatment of the precursor gel at −8 °C followed by crystallization at 100 °C. Here, we found that aging the precursor gels for 2 weeks at 40 °C decreases the size of particles by 59% compared with particles formed from unaged gels, and aging gels for 2 weeks at −8 °C results in particles that have a 95% smaller diameter compared with particles formed from the unaged gel. We hypothesize that decreasing the precursor aging temperature below 0 °C leads to the occurrence of spinodal decomposition at which the nucleation barrier vanishes. Consequently, a very large number of nuclei form...