Thermal collapse and hierarchy of polymorphs in a faujasite-type zeolite and its analogous melt-quenched glass.
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.
Otto Schott Institute of Materials Research, University of Jena, 07743 Jena, Germany.
Theresia
T
Palenta
Otto Schott Institute of Materials Research, University of Jena, 07743 Jena, Germany.
Sindy
S
Fuhrmann
Department of Materials Science and Metallurgy, University of Cambridge, CB3 0FS Cambridge, United Kingdom.
G Neville
GN
Greaves
Department of Chemical and Bioengineering, University of Erlangen-Nuremberg, 91058 Erlangen, Germany.
Wilhelm
W
Schwieger
Otto Schott Institute of Materials Research, University of Jena, 07743 Jena, Germany.
Lothar
L
Wondraczek