Thesis (M.Sc.)--Chulalongkorn University, 2005

The perovskite oxides of La[subscript 0.3]Sr[subscript 0.7]Al[subscript 0.2]Fe[subscript 0.8]O[subscript 3-delta] (LSAF), Ba[subscript 0.5]Sr[subscript 0.5]Co[subscript 0.8]Fe[subscript 0.2]O[subscript 3-delta] (BSCF), La[subscript 0.6]Sr[subscript 0.4]Co[subscript 0.delta]Fe[subscript 0.2] O[subscript 3-delta] (LSCF) and Lo[subscript 0.6]Srsubscript 0.4]Co[subscript O3-delta] (LSC) were synthesized by a modified citrate method and solution method. The crystal structure of single-phase perovskite power was characterized by X-ray diffraction (XRD0. LSAF-BSCF, LSAF-LSCF and LSAF-LSC dual-phase membranes were prepared by mixing the powder of LSAF with BSCF, LSCF and LSC, respectively with ratio 12:1-12:4 by weight. The dual-phase membranes were sintered around 1,200-1,400 C for 5-10 hours. The XRD analysis showed the formation of cubic perovskite phase. Influence of sintering time, sintering temperature and amount of BSCF, LSCF and LSC on the morphology of dual-phase membranes were examined by using scanning electron microscopy (SEM). The result exhibited that the grain size of the dual-phase membranes after sintering at 1,400 C for 6 hours is larger than that of the other conditions. All dual-phase perovskites with ratio 12:4 had the largest grain size. The oxygen desorption property of dual-phase perovskite was investigated by thermogravimetric analysis (TGA) and temperature program desorption of oxygen (O[subscript 2]-TPD). TGA results demonstrated that the amount of oxygen desorption of LSAF-LSC dual-phase with ratio 12:4 by weight had higher value compared to those of LSAF and the other ratios of dual-phase of LSAF-BSCF and LSAF-LSCF. The O[subscript 2]-TPD data revealed the total amount of oxygen liberated from composite LSAF-BSCF is less than the pure phase of LSAF. The LSAF-LSCF with ratio 12:2 and LSAF-LSC with ratio 12:4 showed the high oxygen desorption than those of the other ratios. Therefore, the oxygen permeation flux of LSAF could be increased by mixing LSAF with LSCF and LSC.