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Diffusion In Porous Solids : Void Disorder, Orientation And Rotation, Reaction And Separation, And Levitation Effect

Electronic Theses of Indian Institute of Science

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Title Diffusion In Porous Solids : Void Disorder, Orientation And Rotation, Reaction And Separation, And Levitation Effect
 
Creator Anil Kumar, A V
 
Subject Physical Chemistry
Levitation
Diffusion
Zeolite
Diffusion Coupling
Translational-Orientational Coupling
Blow-torch Effect
 
Description Diffusion in bulk has been well studied and our understanding may be said to be adequate if not complete. Similarly, surface diffusion has been investigated by a number of workers and a fair understanding of it has emerged. When guest particles are confined within the micropores of solids such as zeolites, the resulting phase is neither bulk nor an adsorbed phase but something in between. Properties of such a phase have not been understood sufficiently. Such phase found within these porous solids display rich variety in their property. In part, such a variety arises from the large number of factors that determine their properties. Present thesis attempts to study the relationship of some of these factors, viz., the pore size and the disorder in the pore sizes, the sorbate sizes, the role of orienta-tional motion, the inhomogeneities in temperature etc. to diffusion of the guest molecules in porous solids.

Chapter 1 gives a brief overview of the literature and the present understanding in the field of diffusion of spherical atoms and small molecules in microporous materials with special attention to zeolites.,The discussion is focussed on the experimental, theoretical and computer simulation results reported in the last few years.

In chapter 2 an analytic expression is derived for the diffusion coefficient of a sorbate in a crystalline porous solid with bottlenecks. This is done by assuming a situation of quasiequi-Hbrium and by applying some elementary results of kinetic theory of gases. The diffusion coefficients obtained from the analytic expression is found to agree well with the molecular dynamics results. Further, it is found to reproduce the diffusion anomaly and its temperature dependence for different zeolites such as Y, A and p. The present calculations provide a strong theoretical support for the levitation effect obtained so far purely from molecular dynamics calculations. The computational effort involved in evaluating the derived expression is at least an order of magnitude less as compared to the molecular dynamics simulations.

Levitation effect is found to exist in crystalline porous solids, irrespective of the geometry and topology of the void network of the host - the zeolite. Does levitation effect exist in non-crystalline porous solids where a distribution of pore sizes is seen instead of a single size? Chapter 3 attempts to answer this question via detailed molecular dynamics simulations on zeolite Y whose perfectly crystalline pore structure has been modified by introducing disorder. A normal distribution characterized by its width
 
Publisher Indian Institute of Science
 
Contributor Yashonath, S
 
Date 2006-12-12T10:23:02Z
2006-12-12T10:23:02Z
2006-12-12T10:23:02Z
2001-12
 
Type Electronic Thesis and Dissertation
 
Format 7297027 bytes
application/pdf
 
Identifier http://etd.iisc.ernet.in/handle/2005/248
null
 
Language en
 
Rights I grant Indian Institute of Science the right to archive and to make available my thesis or dissertation in whole or in part in all forms of media, now hereafter known. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation.