Creep behaviour of tubular Ba0.5Sr0.5Co0.8Fe0.2O3−δ gas separation membranes

The creep behaviour of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) membrane material was investigated in the temperature range 600–950 °C using tubular specimens. Oxygen partial pressure (4 and 2 × 10−6 mbar), as well as compressive stress (20–63 MPa) were varied. The steady state strain rates from compressive creep tests under axial loading were described by a standard creep equation considering as exponential fitting parameters the influence of temperature, stress, oxygen partial pressure and grain size. Differences in activation energy in the low and high temperature regime appeared to be associated with the disappearance of a second phase. After the creep tests, no significant changes in grain morphology were observed. In addition to the compressive tests, C-ring shaped specimens were machined from the tubes and deformed at 900 °C in a combined tensile-compressive creep mode that revealed the formation of pores along grain boundaries normal to the local tensile stresses that ultimately might lead to creep rupture.