Flexibility of the framework structure in highly crystalline silicalite during the reversible monoclinic/orthorhombic solid state polymorphic phase transition
Highly crystalline silicalite ( Si Al >5000 ) obtained by hydrothermal dealumination of a ZSM-5 material ( Si Al =132 ) has been investigated at several temperatures by X-ray powder diffraction. Interpretation of the step-scanned XRD profiles by the Rietveld structure refinement code (DBW) shows...
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Published in | Materials research bulletin Vol. 28; no. 10; pp. 1017 - 1024 |
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Main Authors | , |
Format | Journal Article |
Language | English |
Published |
London
Elsevier Ltd
01.10.1993
Amsterdam Elsevier Science |
Subjects | |
Online Access | Get full text |
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Summary: | Highly crystalline silicalite (
Si
Al
>5000
) obtained by hydrothermal dealumination of a ZSM-5 material (
Si
Al
=132
) has been investigated at several temperatures by X-ray powder diffraction. Interpretation of the step-scanned XRD profiles by the Rietveld structure refinement code (DBW) shows that the displacive
P2
1
n·1·1(
M
)
⇆
Pnma (
O1) polymorphic phase transition occurs between 77 and 90°C (≈83°C). On heating (20–127°C temperature range) the minor and major axis-directions of the
elliptical D10R (double ten-ring) pore-openings corresponding to the straight-channels (
8.50×7.95
and
8.55×7.98
A
̊
at 20°C)
progressively change and are finally inverted (
7.99×
8.52
A
̊
at 90°C). At the same time, the elliptical D10R sections of the zig-zag channels (
8.68×8.06
and
8.51×7.69
A
̊
at 20°C) become more circular (
8.35×8.13
and
8.43×7.96
A
̊
at 90°C). |
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ISSN: | 0025-5408 1873-4227 |
DOI: | 10.1016/0025-5408(93)90139-5 |