Abstract
We examine the route of structural collapse and re-crystallization of faujasite-type (Na, K)-LSX zeolite. As the first step, a rather stable amorphous high density phase HDA(collapse) is generated through an order-disorder transition from the original zeolite via a low density phase LDA(collapse), at around 790 degrees C. We find that the overall amorphization is driven by an increase in the bond angle distribution within T-O-T and a change in ring statistics to 6-membered TO4 (T = Si4+, Al3+) rings at the expense of 4-membered rings. The HDA(amorph) transforms into crystalline nepheline, though, through an intermediate metastable carnegieite phase. In comparison, the melt-derived glass of similar composition, HDA(MQ), crystallizes directly into the nepheline phase without the occurrence of intermediate carnegieite. This is attributed to the higher structural order of the faujasite-derived HDA(collapse) which prefers the re-crystallization into the highly symmetric carnegieite phase before transformation into nepheline with lower symmetry. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.