Abd Karim, Mohd Mustamam (1995) A study of tin oxides in silicate based glasses. PhD thesis, University of Warwick.

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Abstract

The roles of tin in two silicate based glass systems have been investigated by
NMR and Môssbauer spectroscopies and by physical property measurements of the
glasses.
The first glass system investigated was the stannous silicate (binary SnO-Si02)
glass. Glasses with SnO contents ranging from 17 to 72 mol.% have been made by
melting pelleted powder in an alumina crucible. It was found that alumina crucibles are
unsuitable for making glass with <20 mol.% SnO because of attack on the crucible at the
high melting temperature (_>_1600°C). Silica crucibles will not withstand such high
temperature and tin will attack a platinum crucible. The ability of this system to form glass
past the orthosilicate composition has been discussed in terms of the polarizing power of
Sn2+ and the structure of SnO. The 119Sn NMR results did not give much structural
information due to the high chemical shift anisotropy of Sn 2+ site but they showed that
the glass also contains trace amounts of Sn4+species. The 29Si MAS NMR results
showed that SnO does not depolymerise the silicate network to the same extent as Na20
or even Pb0. Computer simulations of the 29 Si MAS NMR spectra showed that, for SnO
<-30 mol.%, the disposition of Qn species is consistent with the binary model, which
means that SnO is acting the role of modifier. For compositions > 30 mol.% SnO, the Qn
distribution follows the statistical model and this has been interpreted as SnO now acting
as an intermediate. The 119Sn MOssbauer results confirmed this interpretation. The Sn2+
isomer shift decreases with increase of SnO which is indicative of increasing covalent
character of the Sn—O bonds while the larger quadrupole splitting suggests distortion of
the SnO polyhedral structure in the glass. The relation of the Sn 2+ isomer shift to the
quadrupole splitting and the temperature dependence of the isomer shift of Sn2+ indicate
the formation of Si—O—Sn linkages at high SnO contents. The decrease of the viscosity
of the glass with increasing SnO is small when compared to the decrease of the viscosity
in alkali metal and alkaline-earth oxides silicates when the respective modifier oxide is
increased in those glasses. The variation of the density, thermal expansion and refractive
index with SnO content showed discontinuities in the region of 30-45 mol.% SnO. This
has been interpreted as being the point where SnO changes its role from that of modifier
to intermediate.
The results of differential thermal analysis and devitrification of SnO-Si02 glasses
showed that glass with 40 mol.% SnO can be heat treated in the temperature range of
570° to 680 °C to produce metastable SnSiO3 crystals. SnSiO 3 decomposed to
SnO + Si02 at temperatures above —700°C and, at temperatures greater than 720°C,
oxidation of SnO to Sn02 and Si02(glass) to Si02 (cristobalite) took place.
The second glass system is tin-doped float glass. This is glass of the float
composition remelted with tin(II) oxalate in silica crucibles under normal atmosphere
conditions. In this way it has been demonstrated that we can mimic the tin oxide
distribution found within the tin diffusion region in float glass. Synthesis of the glass has
shown that both Sn2+ and SO+ can be assimilated simultaneously in the glass but there is
a solubility limit for SO+. The 1195n Mbssbauer results showed that Sn2+ and SO+
played different structural roles in the glass. The environment of Sn2+ in glass is similar
to that in amorphous SnO while the SO + structure in glass does not change significantly
compared to crystalline Sn02. The Debye temperatures and recoil free fractions showed
that Sn2+ is less rigidly bound to the network modifier site while SO + is rigidly bound at
network former sites in the glass. The different structural roles of 5n 2+ and SO+ in the
glass were reflected in the some of the physical properties of the glasses.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Tin compounds, Glass
Official Date:	March 1995
Dates:	Date Event March 1995 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Holland, Diane
Sponsors:	Universiti Teknologi Malaysia ; Malaysia. Jabatan Perkhidmatan Awam [Public Services Dept.]
Extent:	xxiii, 240 leaves
Language:	eng

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