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

4 Results and discussion
of hydrolysis solution acidity on the microstructure of the Ti0.5Zr0.5O2 bulk material was
studied with gas physisorption.
The fractal dimension of the 50 mol% TiO2 in ZrO2 sol is larger (1.29) with similar
particle size if H2O was used instead of 1 M HNO3 as hydrolysis solution.
Figure 58-A and B show a simultaneous decrease in the specific surface area (190 to
57 m 2 /g) and the relative microporous adsorbed volume (52 to 6%) as a result of a higher
pH of the hydrolysis solution. It should be noted that Spijksma et al. 80 reported results
for Ti0.66Zr0.34O2 calcined at 400ºC that show an inverse relation. In that particular work
an acidic hydrolysis solution resulted in a significant increase of both the average pore
size of the powder and the particle size of the sol.
V micro /V total [%]
Spec. Surface area [m 2 /g]
50
40
30
20
10
0
200
160
120
80
40
0
1 M HNO3 0.1 M HNO3 H2O
Figure 58 A) Relative micropore volume and B) Specific surface areas of powders calcined at 500ºC as a
function of the hydrolysis agent acidity.
DTA and XRD analysis are used to study the crystallisation temperature of the binary
oxides. All binary oxides containing 25 to 75 mol % TiO2 in ZrO2 are still XRD
amorphous at 500ºC and become nanocrystalline at 600ºC. 25 mol% TiO2 doped ZrO2
calcined at 600ºC possess a minor phase of highly disturbed monoclinic ZrO2 and a
higher ratio of tetragonality compared to the undoped ZrO2. The higher tetragonality can
be explained by the incorporation of titanium into the ZrO2 lattice (Figure 59-C). Clearly,
the monoclinic ZrO2 phase is suppressed by the addition of 25 mol% TiO2.
Ti0.5Zr0.5O2 crystallises between 550 and 600ºC (Figure 59-A) to a highly distorted and
disturbed orthorhombic phase similar to the orthorhombic TiZrO4 published in. 112
90
A
B