Oxygen permeation in dense SrCo0.8Fe0.2O3 − δ membranes: Surface exchange kinetics versus bulk diffusion
Abstract Oxygen permeation measurements were made on dense discs of SrCo 0.8 Fe 0.2 O 3 − δ as a function of pressure gradient, 0.01 to 1 atm, temperature, 775 to 870 °C and disc thickness, 1 to 2.6 mm. Two different measuring configurations were used: with the pressure gradient applied parallel to the disc axis and with the pressure gradient applied between the edge and the two flat surfaces of the disc. This enabled us to take into account leakage effects due to the edge. A model is proposed for the dependence of the surface exchange current on the chemical potential drop at the gas-solid interface. Analysis of the pressure gradient and membrane thickness dependence of the permeation shows that the permeation is controlled by both bulk diffusion of oxide ions as well as exchange kinetics between gas-phase oxygen molecules and oxide ions. Values for the surface exchange rate coefficient k i 0 and the ambipolar diffusion coefficient D a are reported.