2
9
changes to the Si MAS NMR spectra, it produces little change in
the Ga or Al environments, which remain in four-fold coordination
with oxygen.
Conclusions
Gallium silicate analogues of aluminosilicate inorganic polymers
were successfully synthesised by a combination of sol–gel and
solid-state techniques. The same method could also be used to
produce compounds with a range of Al-for Ga substitutions.
The optimum composition of these compounds was SiO
2
:(Ga
2
O
3
+
Al ) = 7; samples in which this ratio was greater or less
2
O
3
than 7 either separated into layers and cracked, or were weak
and in some cases did not set. The cured and hardened prod-
ucts all showed typical inorganic polymer characteristics, being
X-ray amorphous with the Al and Ga shown by MAS NMR
2
9
spectroscopy to be in solely tetrahedral coordination. Si MAS
NMR and electron microscopy showed that although the Ga,
Al and Si was homogeneously distributed in the products, they
contained some unreacted silica.
Fig. 7 SEM micrograph of a potassium gallium aluminium silicate
inorganic polymer, Ga : Al = 50 : 50. Arrows indicate unreacted spherical
silica particles.
Thermal treatment of these compounds results in an over-
◦
lapping two-stage endothermic water loss at about 75 C and
◦
◦
1
60 C followed by a broad exothermic event at about 950 C
corresponding to crystallization of the amorphous compound.
◦
The gallium end-member crystallises to KGaSi
2
O
6
above 800 C,
whereas compounds containing Al never fully crystallise but melt
◦
at 1200 C to an X-ray amorphous product. Thermal treatment
causes the unreacted silica in all these compounds to fully react,
2
9
as evidenced by the disappearance of the characteristic Si NMR
resonance at -108 ppm.
Acknowledgements
This work was partly funded by the MacDiarmid Institute
for Advanced Materials and Nanotechnology, and by contract
C08 ¥ 0302 from the NZ Foundation for Research Science
and Technology, as a subcontract from Industrial Research Ltd.
ATD acknowledges financial support from a William Georgetti
Scholarship, the Todd Foundation, a J.L Stewart Scholarship,
Freemasons NZ University Scholarship and a Curtis–Gordon
Scholarship. We are indebted to D. Flynn for assistance with the
electron microscopy.
Fig. 8 Thermogram of potassium gallium silicate inorganic polymer.
2
9
The Si NMR spectrum of the 50 : 50 Ga : Al silicate inorganic
◦
polymer fired at 1200 C (Fig. 4E) shows that all the unreacted
silica (the resonance at -108 ppm in the original compound) has
reacted, forming a single resonance, the position of which suggests
a change of Si(3Al) and Si(3Ga) in the original inorganic polymer
to Si(1Al) and Si(1Ga) in the fired product. The position of this
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