Bent, Julian Francis (1999) An experimental study of some silicate based glasses. PhD thesis, University of Warwick.

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Abstract

TOF neutron diffraction and multinuclear MAS NMR data are combined to
investigate the local structure of three silicate based glass forming systems. The
effects of experimental resolution on the structural parameters obtained from neutron
diffraction data are considered using simulated correlation functions.
The Gaussian fit parameters to a peak in T(r) report a smaller peak width and area
than that of the Gaussian broadening. This is due to the contribution of the realspace
resolution function. This effect is most dramatic for small values of (u 2) 1/2
and Qmax but is negligible for typical values.
The experimental uncertainty in measuring Q is considered for TOF neutron
diffraction data. ΔQ is considered constant for data measured at several scattering
angles. Some of the scattering intensity is transferred to a tail on the low r side of
each peak, the magnitude of which increases with ΔQ. The peak fit parameters
(position, width and area) change with increasing ΔQ, both before and after
removing the gradient at low r. The Q-space resolution at a fixed scattering angle is
considered by broadening i(Q) with a Gaussian of width ΔQ/Q=constant. The peak
fit parameters change with increasing ΔQ/Q but not significantly at the resolution
quoted for the high angle detectors on LAD.
The interpretation of experimental data in terms of glass structure is greatly
dependant upon an accurate knowledge of the glass composition. It is considered
necessary to determine the concentration of all the cation species by a single or
combination of techniques.
TOF neutron diffraction and 170 MAS NMR data are reported for several
(SnO)x(Si02)1-x glasses and a partially crystallised (SnO)(Si02) sample. 29Si, 119Sn
MAS NMR and a powder X-ray diffraction data are also presented for the partially
crystallised sample. The tin is present as Sn2+ and is three co-ordinated to oxygen at
all compositions. The (SnO)x(Si02)1-x glasses are thought to consist of a network of
Sn03/3 and Si04/2 polyhedra. The tin polyhedra may form pairs or chains. The local
order in the crystalline phase is thought to be similar to that in the glasses. There are
two tin and two silicon sites in the crystal phase of approximate composition
(SnO)4(Si02). It has not been possible to refine the crystal structure.
29Si MAS NMR data are presented for (Li20)x(SnO)1-x(Si02), (Na20)x(SnO)1-x
(Si02) and (K20)x(SnO)1-x(Si02) glasses and TOP neutron diffraction data for
(K20)x(SnO)1-x(Si02). The tin is present as Sn2+ and is three co-ordinated at all
compositions. Replacing the tin with modifier oxide reduces the 29Si NMR chemical
shift. The modifier cation is thought to depolymerise the tin silicate network,
associating with the tin to maintain charge neutrality.
29Si and 31p MAS NMR and TOP neutron diffraction data are presented for (K20-
4Si02)x(P205)1-x, (K20-2Si02)x(P205)1-x and (Si02)x(P205)1-x glasses. Each glass
contains SiIV and SiVI species, the potassium tetrasilicate-Pjt), glasses also contain
SiV species. The proportion of silicon species changed with thermal history. Each
glass is thought to consist of a modified phospho silicate network. The potassium
disilicate-Pjo, glasses are thought to consist of a continuous network of
Si(OP)3(OSi), Si(OP)4(OSi)2, (p-Q2)- and (P-Q4)+ species. The alkali-free
phosphosilicate and potassium tetrasilicate-P2O5, glasses are thought to have similar
structures but it is not possible to define the phosphate species. It was not possible to
distinguish the different species by neutron diffraction. The phosphosilicate network
is thought to be more disordered than modified phosphate and modified silicate
networks.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Glass -- Research, Physics -- Mathematical models
Official Date:	June 1999
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Holland, Diane ; Hannon, Alex C.
Sponsors:	Engineering and Physical Sciences Research Council (Great Britain) ; Rutherford Appleton Laboratory
Extent:	xx, 177 leaves
Language:	eng

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