Degradation of Ba0.5Sr0.5Co0.8Fe0.2O3-δ Membrane Material in CO2-containing Atmosphere

Annett Moebius ,  Torsten Markus 

Forschungszentrum Jülich, Institute of Energy Research IEF (FZJ-IEF), Leo-Brandt-Strasse, Jülich 52425, Germany

Abstract

Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF5582) is a mixed ionic and electronic conductor which could be used for oxygen separation. The thermochemical behavior of the material is a main factor in the selection of the material for membrane technology. In this work the degradation and the reversibility of degradation is investigated.
It is known from literature that BSCF5582 forms (Ba,Sr)CO3 if it is annealed in CO2-containing atmosphere.1 Hence, annealing experiments in 20% CO2 in air are conducted. Samples are heated up to 800°C and dwelled for 200h. The microstructure is investigated by SEM+EDX. In Fig. 1A a SEM image of the annealed sample is shown. As can be seen a carbonate layer (3.5μm) is formed on the surface. Below the layer needle-like structures occurred (16μm). The reversibility of the degradation is checked by further annealing. As-annealed samples are then annealed in synthetic air at 800°C for 200h. As can be seen in Fig. 1B the carbonate layer is decomposed and SrO is formed. The needle-like structures are partially destroyed.

Fig. 1: SEM images of BSCF5582 annealed in 20% CO2 in air (A) and in 20% CO2 in air, afterwards annealed in synthetic air (B)

The tendency of BSCF5582 to react with CO2 and the reversibility of the formation of carbonates is investigated by DTA measurements. Therefore, samples are heated up to 1100°C and cooled down in air, heated up to 1100°C and cooled down in 20% CO2 in air, and heated up to 1100°C and cooled down in air again. Fig. 2 shows the normalized mass change. After heating up and cooling down in 20% CO2 in air there is an enduring increase in weight. Anyway, after heating up and cooling down in air again the origin is reached. Hence, it could be assumed that the formation of carbonates is reversible. Our results are in good agreement with literature.2

Fig. 2: Normalized mass change of BSCF5582 with and without CO2


References

1 Arnold et al., J. Membr. Sci. 293 (2007) 44–52

2 Bucher et al., J. Electrochem. Soc. 155 (2008) B1218–B1224

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Presentation: Poster at E-MRS Fall Meeting 2009, Symposium G, by Annett Moebius
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-13 13:43
Revised:   2009-06-07 00:48
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