Chemistry Reference
In-Depth Information
The observed weight losses are in agreement with the theoretical ones. Indeed, in a first
step, a complete loss of OH groups (as 0.75 H
2
O) corresponds to a theoretical weight loss
of 15 wt. %. In a second step, the decomposition of Ti-based fluoro-species (as 0.375 TiF
4
)
is associated with a theoretical weight loss of 52 wt. %, slightly higher than the observed 45
wt. % weight loss. The small discrepancies reported previously could be explained by a
more complex decomposition scheme, assuming a simultaneous departure of OH groups
and fluorine as HF.
This decomposition scheme is also in agreement with the ex situ annealing of
Ti
0.75
(OH)
1.5
F
1.5
during 4 hours under N
2
atmosphere. The evolution of the X-ray
powder pattern is reported in Figure 8.22. After the first weight loss, the XRD pattern of
101
Ti
0.75
(OH)
1.5
F
1.5
ReO
3
Thermal decomposition - 350°C
Thermal decomposition - 600°C
*
Al sample-holder
**
WL
α
h' k' l'- TiO
2
Anatase
2
0
0
h k l - Ti
0.75
(OH)
1.5
F
1.5
0
0
4
105
2
11
2
0
4
215
301
103
112
11
6
220
2
2
4
008
213
*
*
*
110
111
200
210
2
1
1
220
30
310
222
100
20
30
40
50
60
70
80
90
2-Tetha
λ
CuK
α
(°)
Figure 8.22 XRD patterns of ReO
3
-derived Ti hydroxyfluoride annealed under N
2
during 4 h
at various temperatures (T¼350
C, T¼600
C). Reproduced with the permission of ACS or
American Chemical Society
the sample annealed at 350 C exhibits mainly Bragg peaks corresponding to TiOF
2
(ICDD 08-0060)
27
Bragg peaks corresponding to TiO
2
anatase can also be noted
(ICDD 21-1272)
64
. Finally, after the second weight loss, XRD pattern of sample annealed
at 600 C shows only the presence of Bragg peaks indexed with the TiO
2
anatase structure.
8.4 UV Shielding Properties of Divided Oxyfluorides
Diffuse reflectance measurements were carried out in the UV-visible range from 200 to
800 cm
1
on a Cary spectrophotometer at room temperature in order to illustrate the
UV-shielding properties of such compounds.
