Inorganic Microporous Membranes for Gas Separation in Fossil Fuel ...

4 Results and discussion
significant weight loss is observed in the third step where the remaining organics are
combusted. The carbon content measurements at 140 to 600ºC are complementary to
these results (Figure 72).
Exo
uV/mg
0,3
0,2
0,1
0,0
-0,1
-0,2
-0,3
100 200 300 400 500 600 700
0
800
Temperature [ºC]
86
DTA
TG
Figure 53 DTA-TG curves of dried ZrO2 sol.
The DTA results (Figure 53) are complementary to the TG results. The exothermic peak
in the DTA plot at 308ºC suggests the removal of organic residues (Figure 53). More
organics remain in the ZrO2 microporous material in the temperature range of 140-600ºC
compared to TiO2 (Figure 72). The second exothermic peak at 358ºC might be related to
the formation of tetragonal ZrO2.
A combination of tetragonal and monoclinic ZrO2 (tetra/mono >>1) is formed when the
dried ZrO2 sol is calcined at 600ºC (Figure 54). No cubic ZrO2 could be observed as
expected from the mild temperature conditions and absence of a cubic phase stabilisator
such as Y2O3. Raman spectroscopy did observe only monoclinic and tetragonal ZrO2 on
the ZrO2 layers and will be discussed in the next section. The phase transformation from
tetragonal to monoclinic ZrO2 may form gradually in the temperature range of 450-
650ºC.
The gas physisorption, DTA and XRD results on ZrO2 DEA 2 wt% sols that are dried and
calcined at 140, 400, and 500ºC for 3 hours with a heating rate of 25ºC/hours suggest that
these materials might form microporous membranes with rather low permeability due to
the small specific surface areas.
120
100
80
60
40
20
weight loss %