Thermal collapse and hierarchy of polymorphs in a faujasite-type zeolite and its analogous melt-quenched glass

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 HDAcollapse is generated through an order-disorder transition from the original zeolite via a low density phase LDAcollapse, at around 790 °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 = Si(4+), Al(3+)) rings at the expense of 4-membered rings. The HDAamorph transforms into crystalline nepheline, though, through an intermediate metastable carnegieite phase. In comparison, the melt-derived glass of similar composition, HDAMQ, crystallizes directly into the nepheline phase without the occurrence of intermediate carnegieite. This is attributed to the higher structural order of the faujasite-derived HDAcollapse which prefers the re-crystallization into the highly symmetric carnegieite phase before transformation into nepheline with lower symmetry.

3D-printed zeolite 13X-Strontium chloride units as ammonia carriers

“…The 13X showed moisture removal below 200 °C and an exothermic peak at 907 °C possibly due to phase transformation [ 29 ]. At high temperatures, typically above 800 C, the crystalline 13X zeolite transforms into an amorphous aluminosilicate, and the amorphous phase recrystallizes into a nepheline phase by releasing the energy with the temperature increase [ [30] , [31] , [32] ]. The bentonite showed two peaks apart from free moisture loss below 200 °C.…”

The Effect of Thermal Treatment on the Physicochemical Properties of Minerals Applied to Heterogeneous Catalytic Ozonation

“…Upon heating, zeolites undergo a series of chemical and structural changes until they are eventually largely converted to an amorphous material [23].Similar observations have been reported by Christidis et al [24], where a Greek zeolite collapses after heating at 450 °C. Clinoptilolite dehydrates at temperatures up to 300 °C and dehydroxylates at temperatures up to 800 °C, while at even higher temperatures, it decomposes and transforms into amorphous Al-Si and Si glasses [25].Figure 2a shows the initial raw zeolite containing clinoptilolite (card PDF 01-089-7539) as its major crystalline phase, accompanied by orthoclase (card PDF 01-086-0437), anorthoclase (card PDF 01-075-1634) and quartz (card PDF 01-079-1910). The same structure was presented by the respective calcined material at 300 °C.…”

Kinetics of Decelerated Melting

“…b) Structural location of the lattice planes used for evaluation. [32]. d) φ data fit to the kinetic model (Equation (2)), displaying individual fractions of LSX and LDA for melting at 780 °C.…”

“…The darker‐shaded area in (f) indicates the experimental occurrence of carnegieite recrystallization according to ref. .…”