frequencies side and again towards the high frequencies side is connected with changes
in volume magnetic susceptibility of the sample while it is dehydrated and
dehydroxylated. Appearance of triplet at temperatures under 150°C and its
disappearance at 400°C are connected with changes in proton group structure of
zirconia when calcined.
Figure 2. NMR MAS
1
Н spectra of Zr
0,92
Sc
0,08
O(OH)
0,5
n
.
Н
2
О sample calcined
at temperatures,
º
C: 1 – 20; 2 – 150; 3 – 400; 4 – 500; 5 – 700
To evaluate the number of various proton groups, mass loss control had been
carried out in the whole temperature interval. Comparing NMR data and loss on
ignition it is possible to single out various groups and their thermal stability. So, most
of mass loss (29,56%) occurs at temperatures under 150° C which is connected with
desorption of water molecules from ZrО
2
nanocrystals surface.
On the other hand, in NMR
1
Н spectra shift of the line towards the high
frequencies side and their broadening were observed. This indicates the presence of
OH groups on the surface of the crystals and between these groups and water molecules
an intensive proton exchange is occurring which slows down when a significant
amount of water molecules is lost. Other proton groups are singled out at higher
temperatures in three stages: 150 – 400°С, 400 – 600°С and 600 – 800°С and amount
to 9,22, 2,42 and 0,82 mass % accordingly (Fig. 3). These three stages fully correlate
with three stages of change in proton spectra.
The appearance of a triplet while calcinating the sample under 150°C is quite
unusual. This indicates that on significant losses of water peculiar proton groups have
been formed in ZrO
2
which manifest themselves as a triplet in NMR spectrum.
∆ν, ppm
- 1404 -