A NEW CLASS OF OXYGEN SELECTIVE CHEMICALLY DRIVEN NONPOROUS CERAMIC MEMBRANES .1. A-SITE DOPED PEROVSKITES

The transport properties of a new class of inorganic nonporous membranes based on mixed-conducting perovskites were measured by a solid state electrochemical technique. Since oxygen is the only ionic species that is transported, these membranes provide absolute selectivity for oxygen. The chemical diffusion coefficient of oxygen in (La0.79Sr0.20)MnO3-delta and (La0.50Sr0.50)MnO3-delta was found to be of the order of 10(-8) to 10(-6) cm2/sec between 700-degrees-C and 860-degrees-C. Such high transport rates open up exciting opportunities for chemically driven membrane applications for the selective separation or purification of oxygen. The oxygen permeation rates calculated for modest oxygen pressure differential values across 1 mm thick (La0.79Sr0.20)MnO3-delta membranes are about 10(-11) mol/sec-cm2 at 700-degrees-C and close to 10(-9) mol/sec-cm2 at 860-degrees-C. These values provide an attractive alternative to polymeric and porous ceramic membranes, all of which have only limited oxygen selectivity.