Perovskite-type oxides for high-temperature oxygen separation membranes

Oxygen permeation through dense ceramic membranes of perovskite-like SrCo0.9-xFe0.1CrxO3-delta (x = 0 01-0 05), Sr1-x-y Ln(x)CoO(3-delta)(Ln =La, Nd, Sm, Gd;x= 0.30-0.35;y = 0-0.10), SrCo1-xTixO3-delta (x= 0.05-0.20) and LaM1-xNixO3-delta (M = Ga, Co, Fe;x=0-0.6) was studied. The SrCoO3-delta-based solid solutions with cubic perovskite structure were found to exhibit highest permeation fluxes compared to other membranes. However, high thermal expansion coefficients and interaction with gas species such as carbon dioxide may complicate the employment of SrCoO3-delta membranes for oxygen separation membranes. Alternatively, the LaGa1-xNixO3-delta (x= 0.2-0.5) perovskites, having significant permeation fluxes as well as thermal expansion coefficients in the range of (10.8-11.6) x 10(-6) K-1, were demonstrated to be suitable as membrane materials at oxygen pressures from 1 x 10(-2) to 2 x 10(4) Pa. Testing oxygen permeation at oxygen partial pressures of 1-60 arm showed that only oxides with a high oxygen deficiency such as SrCo0.85Ti0.15F3-delta possess sufficient oxygen permeation fluxes. The oxygen permeability of perovskites on the basis of LaGaO3 and LaCoO3-delta was found to be negligible at oxygen pressures above 15 atm, caused by low oxygen vacancy concentration and ionic conductivity of such ceramic materials. (C) 1999 Elsevier Science B.V. All rights reserved.