Entropy of pure-silica molecular sieves

Patrick M. Piccione; Brian F. Woodfield; Juliana Boerio-Goates; Alexandra Navrotsky; Mark E. Davis

doi:10.1021/jp010491p

Entropy of pure-silica molecular sieves

Patrick M. Piccione, Brian F. Woodfield, Juliana Boerio-Goates, Alexandra Navrotsky, Mark E. Davis

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Abstract

The entropies of a series of pure-silica molecular sieves (structural codes *BEA, FAU, MFI, and MTT are obtained by calorimetric measurements of low-temperature heat capacity. The third-law entropies at 298.15 K are (on the basis of 1 mol of SiO₂): *BEA, 44.91 ± 0.11 J·K^-1·mol^-1; FAU, 44.73 ± 0.11 J·K^-1·mol^-1; MFI, 45.05 ± 0.11 J·K^-1·mol^-1; MTT, 45.69 ± 0.11 J·K^-1·mol^-1; while the corresponding entropies of transition from quartz at 298.15 K are *BEA, 3.4 J·K^-1·mol^-1; FAU, 3.2 J·K^-1·mol^-1; MFI, 3.6 J·K^-1·mol^-1; MTT, 4.2 J·K^-1·mol^-1. The entropies span a very narrow range at 3.2-4.2 J·K^-1·mol^-1 above quartz, despite a factor of 2 difference in molar volume. This confirms that there are no significant entropy barriers to transformations between SiO₂ polymorphs. Finally, the Gibbs free energy of transformation with respect to quartz is calculated for eight SiO₂ phases and all are found to be within twice the available thermal energy of each other at 298.15 K.

Original language	English (US)
Pages (from-to)	6025-6030
Number of pages	6
Journal	Journal of Physical Chemistry B
Volume	105
Issue number	25
DOIs	https://doi.org/10.1021/jp010491p
State	Published - Jun 28 2001
Externally published	Yes

ASJC Scopus subject areas

Physical and Theoretical Chemistry
Surfaces, Coatings and Films
Materials Chemistry

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@article{68384a2f80d8488b83a298b42513557a,

title = "Entropy of pure-silica molecular sieves",

abstract = "The entropies of a series of pure-silica molecular sieves (structural codes *BEA, FAU, MFI, and MTT are obtained by calorimetric measurements of low-temperature heat capacity. The third-law entropies at 298.15 K are (on the basis of 1 mol of SiO2): *BEA, 44.91 ± 0.11 J·K-1·mol-1; FAU, 44.73 ± 0.11 J·K-1·mol-1; MFI, 45.05 ± 0.11 J·K-1·mol-1; MTT, 45.69 ± 0.11 J·K-1·mol-1; while the corresponding entropies of transition from quartz at 298.15 K are *BEA, 3.4 J·K-1·mol-1; FAU, 3.2 J·K-1·mol-1; MFI, 3.6 J·K-1·mol-1; MTT, 4.2 J·K-1·mol-1. The entropies span a very narrow range at 3.2-4.2 J·K-1·mol-1 above quartz, despite a factor of 2 difference in molar volume. This confirms that there are no significant entropy barriers to transformations between SiO2 polymorphs. Finally, the Gibbs free energy of transformation with respect to quartz is calculated for eight SiO2 phases and all are found to be within twice the available thermal energy of each other at 298.15 K.",

author = "Piccione, {Patrick M.} and Woodfield, {Brian F.} and Juliana Boerio-Goates and Alexandra Navrotsky and Davis, {Mark E.}",

year = "2001",

month = jun,

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doi = "10.1021/jp010491p",

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journal = "Journal of Physical Chemistry B",

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T1 - Entropy of pure-silica molecular sieves

AU - Piccione, Patrick M.

AU - Woodfield, Brian F.

AU - Boerio-Goates, Juliana

AU - Navrotsky, Alexandra

AU - Davis, Mark E.

PY - 2001/6/28

Y1 - 2001/6/28

N2 - The entropies of a series of pure-silica molecular sieves (structural codes *BEA, FAU, MFI, and MTT are obtained by calorimetric measurements of low-temperature heat capacity. The third-law entropies at 298.15 K are (on the basis of 1 mol of SiO2): *BEA, 44.91 ± 0.11 J·K-1·mol-1; FAU, 44.73 ± 0.11 J·K-1·mol-1; MFI, 45.05 ± 0.11 J·K-1·mol-1; MTT, 45.69 ± 0.11 J·K-1·mol-1; while the corresponding entropies of transition from quartz at 298.15 K are *BEA, 3.4 J·K-1·mol-1; FAU, 3.2 J·K-1·mol-1; MFI, 3.6 J·K-1·mol-1; MTT, 4.2 J·K-1·mol-1. The entropies span a very narrow range at 3.2-4.2 J·K-1·mol-1 above quartz, despite a factor of 2 difference in molar volume. This confirms that there are no significant entropy barriers to transformations between SiO2 polymorphs. Finally, the Gibbs free energy of transformation with respect to quartz is calculated for eight SiO2 phases and all are found to be within twice the available thermal energy of each other at 298.15 K.

AB - The entropies of a series of pure-silica molecular sieves (structural codes *BEA, FAU, MFI, and MTT are obtained by calorimetric measurements of low-temperature heat capacity. The third-law entropies at 298.15 K are (on the basis of 1 mol of SiO2): *BEA, 44.91 ± 0.11 J·K-1·mol-1; FAU, 44.73 ± 0.11 J·K-1·mol-1; MFI, 45.05 ± 0.11 J·K-1·mol-1; MTT, 45.69 ± 0.11 J·K-1·mol-1; while the corresponding entropies of transition from quartz at 298.15 K are *BEA, 3.4 J·K-1·mol-1; FAU, 3.2 J·K-1·mol-1; MFI, 3.6 J·K-1·mol-1; MTT, 4.2 J·K-1·mol-1. The entropies span a very narrow range at 3.2-4.2 J·K-1·mol-1 above quartz, despite a factor of 2 difference in molar volume. This confirms that there are no significant entropy barriers to transformations between SiO2 polymorphs. Finally, the Gibbs free energy of transformation with respect to quartz is calculated for eight SiO2 phases and all are found to be within twice the available thermal energy of each other at 298.15 K.

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Entropy of pure-silica molecular sieves

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