Biomedical Engineering Reference
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-103 ppm
(a)
(b)
19
F
19
F
Tp2
LG26HT Tp2
Tp1+
2/2
-149 ppm
LG26HT Tp1
Tp1
LG26
LG120
ppm
ppm
-103 ppm
(c)
19
F
Tp2
Tp1+
2/2
Tp1
LG99
ppm
Figure 12.12.
19
F MAS-NMR spectra of some glasses based on 4.5SiO
2
-3Al
2
O
3
-1.5P
2
O
5
-(5-x)
CaO-xCaF
2
; A) LG120(
x
= 0.5), B) LG26(
x
= 2) and C) LG99(
z
= 3.0) heat treated to Tp1, Tp(1 + 2)/2
and Tp2 [67].
Ca(n) species corresponded to Al(IV) species; however, an increase in Al(VI) at
Tp2 indicated that there was an aluminium-silicon reach phase attributed to
mullite, considering that in
29
Si MAS-NMR spectra the change of the chemical
shift of the crystalline glass at Tp2 was due to the mullite formation of which alu-
minium is present as Al(VI).
12.7 CATION SUBSTITUTION IN IONOMER GLASSES
Often in dental and medical applications radiopacity is a very important aspect
for materials selection. In glass polyalkenoate cements, the ionomer glasses used
often contain strontium as a radiopaque agent [69]. Strontium has an ionic radius
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