Preparation and oxygen permeation of SrCo_0.4Fe_0.4 Zr_0.2O_3-δ mixed-conducting hollow fibre membrane

SrCo_0.4Fe_0.4 Zr_0.2O_3-δ (SCFZ) mixed conducting hollow fibre membranes were prepared by a dry-wet spinning technology based on the phase separation theory combined with subsequent sintering process. XRD, SEM, thermal expansion technique and oxygen permeation test were utilized to characterize the crystal phase structures, microstructures, sintering behavior and oxygen permeation flux of SCFZ powder and/or hollow fibre membranes. XRD patterns show that the crystal phase of SCFZ hollow fibre membranes are composed of perovskite main phase, SrZrO₃ and Co₃O₄ impurity phases. The content of SrZrO₃ increases with increasing the sintering temperature. The SEM images demonstrate that fingerlike pores exist adjacent to the inner and outer skin layer of membrane wall. Meantime, sponge-like pores appear in the middle zone of wall. This kind of morphology is caused by the immersion phase separation process. From the gastight, mechanical strength, sintering behavior, XRD and SEM results, the optimum sintering temperature of the green membranes is considered to be 1240°C. The SCFZ hollow fibre membranes are obtained under the optimum sintering schedule. The sintered SCFZ membranes exhibit high mechanical strength and the fracture strength reaches 74.19 MPa. At 850°C, the oxygen permeation flux of the membrane is 2.9×10^-7 mol/(cm²·s) under air/He gradient, and the flux is stable during the test for more than 160 h.