Oxygen permeation in Co-containing perovskites: surface oxygen exchange vs bulk oxygen diffusion

摘要

The oxygen permeation fluxes of Co-containing ceramic membranes with perovskite structure were measured by Gas Chromatography as functions of oxygen chemical potential gradient, temperature and thickness. A power index n>0 is obtained when J_(o2) vs Po_2'~n-Po_2"~n is plotted as a straight-line in conditions of 950 deg C >= T >= 810 deg C, 0.21 atm >= Po_2" >= 3x10~(-3) atm and membrane thickness 2.5 mm >= L >= 0.50mm. The results indicate an overall permeation process controlled by both surface oxygen exchange and bulk oxygen diffusion. The mechanism of the surface exchange is discussed and an analytic expression that agrees well with the experimental results is obtained. The determination of oxygen-vacancy conductivity across a perovskite membrane by measurement of oxygen permeation where ther is no reactant on the reducing side can be misleading.