Chemically-induced stresses in ceramic oxygen ion-conducting membranes

Many oxygen-ion conducting ceramics for potential application as membranes in solid oxide fuel cells, oxygen separators and partial oxidation reactors , suffer from a chemically-induced stress when subjected to a gradient in t he thermodynamic activity of oxygen. The relationships between the oxide pr operties, the membrane operating conditions, the membrane geometry and the resulting stresses are explored. Ceria and acceptor-doped lanthanum chromit e are given as typical examples for which relevant materials data have been published. Analysis of the experimental data shows that although the latti ce expansion on reduction, that gives rise to the stress, depends mainly on the deviation from stoichiometry in their oxide, the crystal structure and the dopant also have a significant influence. The induced stresses are pre dicted to be lowest for planar membranes that are free to bend in order to relax the stresses. However, the stresses in a planar membrane that is cons trained not to bend are predicted to be similar to those induced in a tubul ar membrane. (C) 2000 Elsevier Science B.V. All rights reserved.