A Macroscopic Model of the Thermo-Chemo-Mechanical Behaviour of Mixed Ionic and Electronic Conductors

This paper suggests a macroscopic model describing the thermo-chemo-mechanical behaviour of ceramic dense membrane for oxygen separation application. This work takes in account to oxygen permeation and strain induced by stoichiometry variation with working conditions. This model, developed within the traditional framework of phenomenological approach, is based on the assumption of strain partitions and requires only three state variables: oxygen activity, temperature and total strain. Oxygen bulk diffusion and surface exchanges are described thanks to the thermodynamic approach developed by Onsager. While many works focused on semi-permeation induced strain, the proposed model also includes the temperature effect on chemical expansion. Strains predicted by the proposed model are validated thanks to experimental test on La_0.8Sr_0.2Fe_0.7Ga_0.3O_3−δ. Implemented in F.E.A code Abaqus, this model permits studying the design and the process management effects such as chemical shocks on the membrane reliability.