Reinvestigation of the Permeation Behaviour of a Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ) Perovskite-type Membrane

摘要

A Perovskite-type Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(0.3-δ)(designed as BSCFO) with mixed electronic and oxygen ionic conductivity at high temperatures was used as an oxygen permeable membrane. BSCFO powder was successfully made by the citrate- ethylenediamine tetra acetic acid complexing method. Disk shape membranes were prepared under a hydraulic pressure of 2×10~8 Pa and sintered at 1373 K for 3.6×10~4 sec. After polishing the membranes to the thickness of interest, oxygen permeation flux of air as feed was determined in permeation side at different temperatures of 923, 1073 and 1223 K, feed flow rates between 1.67×10~(-6) and 3.33×l0~(-6) nrVsec and helium flow rates between 0.67×10~(-6) and 1.33×10~(-6) m~3/sec, respectively.rnIt was found that increasing helium flow rate increases oxygen permeation flux of the membranes and this is due to the fact that oxygen partial pressure decreases in the permeate side with increasing helium flow rate. However, it was also found out that oxygen permeation flux could also be affected by air flow rate in the feed side. At air flow rates higher than 2.5×10~(-6) m~3/sec, sensitivity of oxygen permeation flux is much less than that at lower air flow rates. Scanning electron microscope (SEM) pictures of the used membranernsurfaces exposed to air and helium were also compared with SEM picture of the fresh membrane surface.rnAlthough results of energy dispersive spectroscopy (EDS) analysis show that surface of the BSCFO membrane exposed to helium for 2.7×10~5 sec is almost similar to the surface of the fresh membrane, X-ray diffraction (XRD) analysis and SEM pictures show that those are different in crystalline form.rnThe comparison of SEM pictures shows that ceramic grains on the membrane surface exposed to helium were extremely fine and much coalesced, comparing with the other surfaces.