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Further studies of a simple atomistic model of silica: Thermodynamic stability of zeolite frameworks as silica polymorphs
 

Summary: Further studies of a simple atomistic model of silica: Thermodynamic
stability of zeolite frameworks as silica polymorphs
Matthew H. Ford
Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts 01003
Scott M. Auerbach
Department of Chemical Engineering and Department of Chemistry, University of Massachusetts, Amherst,
Massachusetts 01003
P. A. Monsona
Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts 01003
Received 1 November 2006; accepted 6 February 2007; published online 9 April 2007
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

  

Source: Auerbach, Scott M. - Department of Chemistry, University of Massachusetts at Amherst

 

Collections: Chemistry