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

4 Results and discussion
Abundance %
20
15
10
5
0
1 10 100 1000
Particle size in nm
51
A 28nm
B 26nm
Figure 23 Particle size distribution of Boehmite sol measured twice by means of Dynamic Light Scattering
The γ-Al2O3 layer obtained by dip coating is ~1 µm in thickness and can be increased to
approximately 3 µm by repeating the coating and firing steps (Figure 24-A).
Homogeneous γ-Al2O3 intermediate was obtained by means of spin-coating. The
thickness of the twice spin-coated γ-Al2O3 intermediate is ~3 µm (using 1000 or 3000
RPM), indicating that the layer thickness is more dependent on the concentration of the
Boehmite sol and the evaporation time than the actual spinning speed (Figure 24-B and
C). Raman or XRD analysis could not distinguish the γ from the α-Al2O3 phase of the
membranes. The γ-Al2O3 bulk material was analysed with XRD and gas physisorption
after drying and firing treatments.
γ-Al2O3
α- Al2O3
A B
γ-Al2O3
α- Al2O3
γ-Al2O3
α- Al2O3
2-3 µm
Figure 24 Cross section SEM images of γ-Al2O3 intermediate layers by dipcoating (single layer, A) or
spincoating at 1000 RPM (B) and 3000 RPM (C).
The γ-Al2O3 intermediate layer material calcined at 600ºC for 3 hours showed a type IV
isotherm indicating a mesoporous material. XRD pattern results confirm the presence of
pure γ-Al2O3 and the absence of α-Al2O3 and δ-Al2O3. The specific surface area is
derived from the Brunauer, Emmet and Teller (SBET) theory. 130 The Barret, Joyner and
Halenda (BJH) algorithm 130 is selected for estimating the pore size of mesoporous
material that presents type IV isotherms. The BET specific surface areas are in the range
C