A series of La0.6Sr0.4Co0.4Fe0.6O3-δ (LSCF) perovskite-type oxides were synthesized using a modified citrate process under various pH conditions (pH =1, 3, 5, 7, and 9, respectively). The effect of pH on the chelate process, crystal development, morphology, and oxygen permeability of LSCF oxides were investigated. FT-IR analysis showed that the chelate processes for pH = 1 and 3 were different from those for pH = 5, 7, and 9. XRD and SEM observations revealed that the crystal formation and morphology of LSCF oxides were dependent on the precursors with different pH conditions. The LSCF membranes derived from the precursors with lower pH values (pH = 1 and 3) exhibited larger apparent activation energy for oxygen permeation than the other samples (pH = 5, 7, and 9) in the range of 1073-1123K. This study indicated that properties such as crystallinity and oxygen permeability of LSCF oxide could be tailored by controlling the pH values in the synthesis process. © 2005 American Institute of Chemical Engineers AIChE J, 2006
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