La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−α (LSCF) perovskite powders having a submicrometer size were synthesized by a sol−gel autocombustion method. From these powders, the gastight LSCF hollow-fiber membranes with a highly asymmetric structure comprising a dense layer of thickness ca. 88 μm integrated with a porous substrate were fabricated in a single step through a phase inversion/sintering technique with a mixture of N -methyl-2-pyrrolidone (NMP) and water as internal coagulant. Oxygen permeation fluxes through the obtained hollow-fiber membranes were measured under air/He gradients at different temperatures. The results indicate that the highly asymmetric hollow-fiber membranes possess an oxygen permeation flux of 0.11−2.19 mL cm −2 min −1 in the temperature range of 650−1000 °C, which is 2.6−10.5 times higher than that of the sandwich-structured hollow-fiber membranes. Oxygen permeation in the hollow-fiber membranes is limited primarily by the surface exchange reactions at lower temperatures, but ionic bulk diffusion will have a rate-limiting effect at temperatures higher than 900 °C.
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Wang et al. (2008) studied this question.
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