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SUMMARY:The structural mechanics of crystals - Dr Simon Guest\, CUED
DTSTART:20120302T140000Z
DTEND:20120302T150000Z
UID:TALK35729@talks.cam.ac.uk
CONTACT:Ms Helen Gardner
DESCRIPTION:Zeolites are microporous aluminosilicate minerals.  A zeolite 
 can be simply modelled as a set of vertex-pinned rigid tetrahedra: typical
 ly a silicon atom and four surrounding Oxygen atoms form a relatively stif
 f tetrahedron\, with each Oxygen atom common to two tetrahedra.  The Oxyge
 n acts as a spherical joint\, as the Si-O-Si bond angle is relatively flex
 ible.  The tetrahedra can be connected together in many different ways to 
 give zeolites with various voids and channels\, and this structure is esse
 ntial to their important uses as molecular sieves and catalysts.\n\nThe in
 teresting structural characteristic of zeolite frameworks is the equality 
 between the number of rigid-body freedoms of the tetrahedra\, and the numb
 er of constraints at the hinges.  In fact this implies that there must be 
 at least three inextensional deformation modes for the framework\, and the
  presence of symmetry may increase this number.  This insight may have rel
 evance to understanding why there are a relatively small number of actual 
 zeolites (around 200)\, compared with the several million hypothetical str
 uctures that have been found.
LOCATION:Oatley Seminar Room\, Department of Engineering
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