to achieve electric neutrality, this is compensated by substitution of ОН
-
for О
2-
in the
anionic part of zirconium dioxide structure. This assumption is also confirmed by the
data obtained for ZrO
2
with СеО
2
additive.
To check the assumption for presence of bridge-type OH groups in ZrO
2
with Sc
additive static NMR of
45
Sс nuclei spectra were recorded (Fig. 4).
Figure 4. NMR
45
Sc spectra of Zr
0,92
Sc
0,08
O(OH)
0,5
nН
2
О samples
calcined at temperatures,
о
С: 1 – 20; 2 – 150; 3 – 400; 4 – 700; 5 – 900
Spectrum of the original sample is made up of a single component with width at
half height ∆ν
1/2
-226-ppm shifted towards high frequencies area at δ =126 ppm relative
to Larmor frequency (97.199 MHz) (Fig. 4). Calcination of the sample at temperatures
150, 400 and 700°C i.e. at temperatures when surface water, pore water and OH groups
are practically completely separated proved the following: when heated up to 1200°C
the parameters of the narrow component remained practically unchanged and in the
spectrum of the sample calcined at 150°C, first, broader (-1000 ppm) component is
identified which intensity relative to the narrow component increased along with
temperature increasing and was 1:2 at 700°C and remained unchanged up to 1200°C
(Fig. 4). Its breadth increased to 3000 ppm while heating to 700°C and remained
unchanged during further heating. Further increase in calcination temperature has not
revealed marked changes in NMR
45
Sс spectrum. Annealing at 700° C led to shifting
of the broad component into high frequencies area at δ =500 ppm. Further calcination
showed practically no changes in chemical shift.
The obtained NMR
45
Sс spectra in ZrO
2
connected with central lines, are specified
by two nonequivalent positions of scandium ions.
Comparing NMR data on protons and scandium (Fig. 5) the narrow component in
scandium spectrum can be rated among purely oxygen environment of these ions inside
ZrO
2
crystal structure. This follows from the fact that heating to 1200°C does not effect
∆ν, ppm
- 1406 -