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Article
Further studies of a simple atomistic model of silica: Thermodynamic stability of zeolite frameworks as silica polymorphs
Journal of Chemical Physics (2007)
  • Peter A Monson, University of Massachusetts - Amherst
  • S. M Auerbach
  • M. H Ford
Abstract
We have applied our previously reported model of silica based on low coordination and strong association [ J. Chem. Phys. 121, 8415 (2004) ], to the calculation of phase stability of zeolite frameworks SOD, LTA, MFI, and FAU as silica polymorphs. We applied the method of Frenkel and Ladd for calculating free energies of these solids. Our model predicts that the MFI framework structure has a regime of thermodynamic stability at low pressures and above ∼ 1400 K, relative to dense phases such as quartz. In contrast, our calculations predict that the less dense frameworks SOD, LTA, and FAU exhibit no regime of thermodynamic stability. We have also used our model to investigate whether templating extends the MFI regime of thermodynamic stability to lower temperatures, by considering templates with hard-sphere repulsions and mean-field attractions to silica. Within the assumptions of our model, we find that quartz remains the thermodynamically stable polymorph at zeolite synthesis temperatures ( ∼ 400 K) unless unphysically large template-silica attractions are assumed. These predictions suggest that some zeolites such as MFI may have regimes of thermodynamic stability even without template stabilization.
Disciplines
Publication Date
April, 2007
Publisher Statement
Copyright 2007 by The American Physical Society.
Citation Information
Peter A Monson, S. M Auerbach and M. H Ford. "Further studies of a simple atomistic model of silica: Thermodynamic stability of zeolite frameworks as silica polymorphs" Journal of Chemical Physics Vol. 126 Iss. 14 (2007)
Available at: http://works.bepress.com/peter_monson/2/