A substantial reduction in hydrogen permeation was
observed when comparing the membrane of Pd-1.0/HF-1300 to
the membrane of Pd-1.0/HF-1400.
As suggested before, the sintering temperature has limited impact towards the substrate permeability.
Therefore, the change in hydrogen permeation is associated with the formation of intermediate layer.
The analysis of MIP results (Fig. 4) of hollow fibre substrates sintered at 1300e1400 C revealed a significantdecrease in the porosity of the packed-pore network of the sponge-like layer.
Furthermore, an average pore size of approximately 0.18 and 0.22 mm was obtained for the spongelike
layer of HF-1300 and HF-1400, respectively.
This is in agreement with results reported in literature.
Due to the slightly bigger pore size of HF-1400, the penetration of Pd penetration in this substrate is easier to occur. Moreover, as the membrane of HFe1400 has lower porosity or higher densification than that of HFe1300, the impact of Pd penetration is more likely to reduce the porosity.
Thus, additional resistance from the intermediate layer compromises the hydrogen permeation flux measured under the same operating conditions.
This phenomenon can be further reinforced by comparison of the hydrogen permeation between the
membrane of Pd-1.0/HF-1400 and Pd-3.3/HF-1400 in which there is 1.5 times reduction in hydrogen permeation when the
membrane thickness is increased 3 times, suggesting that the adverse effect of the intermediate layer when the Pd layer becomes very thin.
The results shown in Table 3, in which thicker membranes presented similar or higher H2 permeation fluxes than that of thinner membranes , could then be explained by Pd penetration into the substrate, hence
the formation of the intermediate layer.