Fig. 3 and Table 2 show the SEM images and properties of Al2O3
hollow fibres sintered at 1300 C and 1400 C.
The Al2O3 hollow fibres presented an asymmetric structure composed by a thin
outer sponge-like layer and a plurality of self-organised
micro-channels, as can be seen in Fig. 3 A1 and B1.
The overall morphology of the fibre was well retained when the
sintering temperature was increased from 1300 C to 1400 C,which suggests a uniform shrinkage of the substrate as reinforced by the similarity in the extent of the micro-channel
(approximately 88e89%).
The thin outer sponge-like layer,shown in Fig. 3
A2 and B2, presents all the requirements (e.g. small pore size and reduced roughness) for direct deposition
of Pd membranes.
Meanwhile, the widely open microchannels at the inner surface, shown in Fig. 3 A3 and B3,
lead to a lower mass transfer resistance across the substrate.
In contrast to previous hollow fibre substrates with multiple
sponge-like layers, the use of a solvent-based internal coagulant
in this study allowed the micro-channels to initiate fromthe outer surface and grow continuously until penetrating
through the inner surface, creating a significant number of
openings.
Therefore, the formed hollow fibre presents only
one outer thin sponge-like layer of approximately 10% of
cross-sectional area, which significantly reduces the mass
transfer resistance of the structure.
Although similar methodologies have been used for developing capillary solid oxide
fuel cells , dense hollow fibre membranes for oxygen
separation and hollow fibre membranes for microfiltration
this type of structures has not been used for
developing highly permeable substrate for composite Pd
membranes.