Yildirim, Erdem Kamil (2000) O-17 NMR studies of some silicate crystals and glasses. PhD thesis, University of Warwick.

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Abstract

Crystalline and glassy silicates were investigated by means of 17O NMR. The
dependence of the measured efg on the Si-O-Al bond angle was investigated in some
crystalline aluminosilicate sodalites and kalsilite. The results show that CQ increases
with increasing bond angle while 11 decreases with increasing bond angle and they both
follow a similar function to that found for the Si-O-Si bond angle. The cluster
calculations also confirm that the dependence of CQ and il on the Si-O-Al bond angle
is similar to that of one Si-O-Si linkage. The chemical shift decreases as the bond angle
increases. However this dependence does not seem to be monotonic.
The structural role of Al in aluminosilicate glasses was studied by means of 17O
3Q MAS NMR in sodium aluminosilicate glasses with Si/Al= 3,1.5,1,0.7.3Q MAS
NMR results showed the presence of Si-O-Si species as well as Si-O-Al species in
glasses with Si/Al>1. The 3Q MAS NMR spectrum of glass with Si/A1=0.7 displayed
the presence of Al-O-Al linkage as well as Si-O-Al. These results showed that as the
Si/Al ratio decreases from 3 to 0.7 Si-O-Si linkage is replaced by Al-O-AI linkage as
a result of addition of Al into the structure.
The structural role of Sn in tin-silicate glasses was also studied mainly by means
of 17O MAS NMR. The model developed from the 17O MAS NMR spectra of these
glasses showed the possible coexistence of two and three coordinated oxygen atoms in
the structure. Therefore some of the Sn has to be in three coordinated to oxygen for
charge balancing. The 17O MAS NMR spectra of a partially crystallised sample showed
three distinct sites which are assigned as Sn-O-Sn, Si-O-Sn, and Si-O-Si on the basis
of their chemical shift. The CQ values obtained from the simulations of these peaks
supports this assignment. The 29Si MAS NMR of the same sample showed two
crystalline and a glassy peaks which are fitted to two crystalline and two glassy sites.
The possible composition of this sample was calculated and found to be SiSn3O10.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Silicates -- Analysis, Nuclear magnetic resonance
Official Date:	March 2000
Dates:	Date Event March 2000 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Dupree, Ray
Sponsors:	Yükseköğretim Kurulu (Turkey) [Higher Education Council] ; Kirikkale University
Extent:	x, 149 p.
Language:	eng

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