Draft: 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 Onsager approach. 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 La0.8Sr0.2Fe0.7Ga0.3O3.. Implemented in F.E.A code Abaqus, this model permits studying the design and the process management effects on the membrane reliability. NOMENCLATURE Oxygen activity Surface oxygen activity Coefficient of thermal expansion Thermal chemical expansion coefficient Chemical expansion coefficient “intrinsic” oxygen diffusivity Total strain tensor Chemical strain Chemical strain induce by the temperature change Maximum chemical strain amplitude Elastic strain Thermal strain Second rank identity tensor Bluk density of oxygen flux Oxygen flux through surfaces Surface exchange coefficient Four rank Hooke tensor