The increase of sintering temperature from 1300 C to
1400 C lead to a reduction of 13% and 6% in the outer and
inner diameter of the hollow fibre substrate, respectively,
which suggests a greater densification at a higher sintering
temperature.
In order to evaluate the impact of such densification
in the substrate morphology, a detailed assessment of
the pore structure was performed by mercury intrusion
porosimetry and summarised in Fig. 4 and Table 2.
As can be seen in Fig. 4, the peak between 5 and 20 mm, which representsthe pore size of the micro-channels entrances, was little affected by the sintering temperature.
In contrast, the intensity of the peak corresponding to the packed-pore network
of the sponge-like layer, located between 0.1 and 0.3 mm, was
substantially reduced when the sintering temperature was
increased from 1300 to 1400 C.
Since this peak represents both the outer sponge-like layer and the wall between microchannels,
the decrease in peak intensity and area indicates a significant reduction in porosity.
The increase in sintering temperature leads to a reduction of the overall porosity from
64% to 54% and, consequently, an increase of mechanical
strength from 41 to 74 MPa (Table 2).