Porous Fe21Cr7Al1Mo0.5Y metal supports for oxygen transport membranes: Thermo-mechanical properties, sintering and corrosion behaviour

• Porous Fe21Cr7Al shown to be suitable support for thin oxygen transport membranes.
• Microstructure, porosity and pre-oxidation controlled simultaneously in-situ during sintering.
• Oxidation of porous supports showed optimal porosity > 30%, pore size ≫ maximum scale thickness.
• Alloy lifetimes modelled with respect to operation temperature, Al-content and surface area.
• Operation of device at 750 °C recommended to achieve lifetime > 30 000 h with low enough creep rate.

An Fe21Cr7Al1Mo0.5Y alumina-forming stainless steel is designed and evaluated as a material for porous supports for oxygen transport membranes. The thermal expansion coefficient, elastic modulus and creep rates of the alloy are presented. The microstructure, porosity and pre-oxidation conditions are optimised simultaneously in-situ during sintering by controlling the growth rate of the oxide scale. Oxidation of metal supports with 20–40% porosity at 850 °C and oxygen partial pressure of 10− 11 kPa showed sub-parabolic kinetics and stability over 3000 h. The FeCrAl steel shows vastly superior oxidation resistance compared with an FeCr steel of similar composition and porosity. Modelling of the alloy lifetime as a function of surface area and Al-content was performed, and lifetimes over 30 000 h are predicted for a metal support with 30% porosity operating at a temperature of 750 °C, where the oxidation and creep rates are sufficiently low. Ceramic interlayers with graded porosity and pore-size were applied and co-fired with the metal supports, producing substrates that were shown to be viable for a 3 μm dense Ce0.8Gd0.2O1.9 − δ oxygen transport membrane deposited using sputtering.