Figure 3. (Н
2
О+ОН
-
) total loss in: 1 – Zr
0,92
Sc
0,08
O(OH)
0,5
n
.
Н
2
О;
2 – Zr
0,92
Y
0,08
O(OH)
0,5
n
.
Н
2
О samples depending on calcination temperature
In our opinion multiplet structure in NMR spectra results from separate lines that
represent water molecules localized in open mezopores of various diameter. Intensity
of high frequency component at δ=85 ppm shows the number of smaller pores and
component intensity at δ =83 and 82 ppm reflects the number of water molecules in
micropores. It follows that in micropores water molecules are more strongly connected
to the surface which means that protons are more strongly shielded by zirconium oxide
electrons. The openness of pores results from an intensive proton exchange between
various proton groups and from mixing of water molecules at open surface and in the
mezopores.
The first stage of water loss in temperature interval between 150 and 400°C is
connected with water release from mezopores and amounts to 9.22 weight %.
The second stage of water release corresponds to temperature interval 400-600°C
and manifest itself in two weakly resolvable components at = 84.2 and 83.0 ppm in
NMR spectra. Component with less chemical shift was put into OH groups localized
at ZrO
2
particles surface, and that with big shift into OH groups that are located inside
crystal structure (particle).
The third stage of water release corresponds with temperature interval 600-800°C
and manifests itself in a single component at = 84.2 ppm and width ∆ν
1/2
=3.2 ppm in
NMR spectra of both samples. This component ranks among structural OH groups.
Their number is approximately the same in both samples and amounts to 0.8%, i.e. it
correlates with the number of additive ions Sс
3+
and Y
3+
. This indicates that in
heterovalent isomorphism according to a scheme Zr
4+
– Ме
3+
the charge is insufficient
0
5
10
15
100
200
300
400
500
600
700
800
m , %
H
2
O
T,
o
C
1
2
- 1405 -