Influence of microstructure on oxygen transport in perovskite type membranes

The influence of bulk microstructure (grain size distribution, grain boundary length) on the oxygen transport properties of permeation membranes has been investigated. For this purpose, La0.5Sr0.5FeO3-delta samples with different microstructures were prepared by varying sintering time and temperature. Average grain sizes, which ranged from 0(.)20 to 1(.)43 mum, were determined by SEM analysis. The oxygen transport properties of the samples were characterised by permeation measurements (is a function of temperature it? an air/argon oxygen partial pressure gradient. The fluxes presented a change in activation energy, which was attributed to a change in the rate limiting step diffusion (it lower temperature (<850degreesC) to from bulk dif surface limitation at higher temperature (>900degreesC). Only transport through the bulk was influenced by the microstructure, with the highest flux for the smallest grains. At 800degreesC, the fluxes were respectively 0.06, 0.03 and 0.01 mumol cm(2) s(-1) through approximate to1 nun thick samples with average grain sizes of 0.20, 0.63 and 1.43 pin respectively. This would imply that oxygen transport occurs more rapidly along grain boundaries than through the bulk.. Grain boundary structure and composition were analysed by TEM.