Synthesis of dense perovskite membrane (La, Ba)[subscript 1-x]Sr[subscript x]Co[subscript 1-y]Fe[subscript y]O[subscript 3-delta] and their oxygen permeation property

Abstract

La[subscript 1-x]Sr[subscript x]Co[subscript 1-y]Fe[subscript y]O[subscript 3-delta] (LSCF) and Ba[subscript 1-x]Sr[subscript x]Co[subscript 1-y]Fe[subscript y]O[subscript 3-delta] (BSCF), where x = 0.2-0.5; y = 0.1-0.5, have been prepared by citrate and modified citrate methods, respectively. They were the candidate materials for oxygen permeation membrane for air separation. The membranes were prepared by pressing the perovskite powder using a uniaxial peressing machine and sintering around 1,100-1,300 ํC for 10 hours. LSCF and BSCF perovskite oxides were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Oxygen permeation property was determined by thermogravimetric analysis (TGA) and oxygen temperature-programmed desorption (O[subscript 2]-TPD). XRD patterns revealed the presence of a single phase of LSCF for substitutions 0.2 [is less than or equal to] x [is less than or equal to] 0.3. SrCO[subscript 3] was observed for x > 0.3, however it disappeared after sintering at 1,300 ํC. For BSCF series, the XRD analysis shows BaFeO[subscript 2.9] phase when y [is less than or equal to] 0.2. The results indicated that low amount of Sr and Co in the matrix of LSCF and BSCF caused the formation of single rhombohedral and cubic structure, respectively. The dense membranes were obtained from the suitable of the preparation methods and sintering temperature. From TGA, it can be inferred that the oxygen deficiencies increased with increasing Sr content but Fe contents did not affect the oxygen vacancies in LSCF system. On the other hand, the substitution of Sr in BSCF systems did not cause the oxygen deficiency but the oxygen vacancies increased with decreasing the Fe contents. Experimental results of O[subscript 2]-TPD in range of 500-800 ํC indicated that the amount of oxygen desorbed from LSCF8264 is far bigger than BSCF8264