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A nuclear magnetic resonance investigation of the structure of some alkali silicate glasses
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Mortuza, Muhammad Golam (1989) A nuclear magnetic resonance investigation of the structure of some alkali silicate glasses. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b1455407~S1
Abstract
The potential
for the use of MAS
and static
NMR in the
investigation of alkali silicate and alkali phosphosilicate glasses and
glass ceramics
is the main theme of this thesis. MAS NMR of binary
lithium silicate glasses containing
24-29
mol%
Li20 shows that their
structure
follows the constrained
distribution
model.
However
addition
of
Li20 in
excess of
29
mol% causes
deviation from the model and a
concentration
dependent disproportionation
of Q3 to Q4+Q2 occurs. This
is observable
from MAS NMR in
combination with static
NMR results. The
devitrification of these glasses produces two polymorphs of
lithium
disilicate. The
structural changes
during heat treatment occur aNve
the glass transition temperature and are observed
from the Si
chemical shift and
full
width at
half
maximum.
The static
Li
spectra
for the crystallised samples exhibit a
Pake doublet indicative
of the
presence of
Li
pairs.
The effect of paramagnetic
impurity from 0-0.8
mol% on the
29Si
T1
relaxation
times in Na20.2SiO2 base
glasses
is discussed.
The heat treatment of the sodium
disilicate
glasses shows a -,
ß-,
Y- and
6- Na2Si2O5 as the devitrification
products
depending
upon
heat treatment. A
way of estimating the unknown
Si-O-Si
mean
bond
angle of the polymorphs
is
presented.
The effect of the addition of
0-70
moll
P205 to alkali
disilicate
glasses
is described. Small
amounts of P205 (1-10
mol%)
in the glasses
results
in the scavenging of alkali metal
ions by
phosphate groups.
In
sodium and potassium
disilicates
the phosphate groups resemble
orthophosphate and pyrophosphate
but
only orthophosphate
like
units are
formed in lithium disilicate
glasses. As
a consequence of the
scavenging,
the silicate network partially repolymerises.
A
structural
model
for the disilicates
with
(1-10)
moll
P2OS is presented.
For
larger concentrations of P205 (>10
mol%)
in
sodium
disilicate
glasses
only metaphosphate species are observed and phosphorus occurs as next
nearest neighbour of silicon. However this arrangement gradually
changes
to Si-O-Si bond
with
-
25
moll
P 05
and the length of
metaphosphate chain
increases. On
addition oft greater
than about
30
mol%
P205 some of the network silicon changes radically
from its
conventional
four
coordination to six coordination.
Both the
tetrahedral and octahedral environments of silicon at these
concentrations are characteristic of mainly Si-O-P bonds. The six
coordinated silicon occupies a
SiPZO7 like
environment.
The
proportion
of
"SiP2O7" depends
upon the alkali content and the cooling rate.
The
cooling rates cause structural relaxation and are used to measure
fictive temperature. This
gives an estimate of the change of enthalpy
for the conversion of one mole of six coordinated silicon
from four
coordinated silicon.
The
29Si
T1
relaxation times in
alkali silicate glass, glass
ceramics and alkali phosphosilicates are presented.
The T1 in
sodium
disilicate glasses as a
function
of MnO
content
is
a single exponential
but a two component
T1 is
observed after
heat treatment. The
single
component relaxation times for the disilicate
composition range
becomes
two component as the Na20
content is
reduced. The Tl values
in
all the
lithium silicate glasses, glass ceramics and alkali phosphosilicate
systems are two component. The
conversion of single component
exponential
to two component because
of
heat treatment or
Na20
content
could
be due to either nucleation or glass-in-glass phase separation.
Thus the possibilities
for
obtaining new
information
about phase
separation
in glasses are also briefly discussed
with the help
of
TEM
micrographs.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics | ||||
Library of Congress Subject Headings (LCSH): | Magnetic resonance, Nuclear magnetic resonance , Nuclear physics, Soluble glass, Silicates | ||||
Official Date: | September 1989 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Dupree, Raymond ; Holland, Diane | ||||
Sponsors: | Commonwealth Scholarship Commission in the United Kingdom (CSCUK) | ||||
Extent: | xvii, 298 leaves | ||||
Language: | eng |
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