Mechanical reliability and oxygen permeation of Ce0.8Gd0.2O2-δ-FeCo2O4 dual phase membranes

Dual phase oxygen transport membranes, consisting of ionic and electronic conducting phases, exhibit great potential in high-purity oxygen generation due to their high stability under harsh application atmospheres. Oxygen-ion conductive fluorite oxides (e.g. Ce0.8Gd0.2O2-δ) and electron conductive spinel phases (e.g. FeCo2O4) are promising material candidates for such a dual phase oxygen transport membrane. Mechanical properties (e.g. elastic modulus, hardness, strength and subcritical crack growth behaviour) and oxygen permeation of the membrane are important parameters regarding reliability for future applications. These parameters have close relationships with composition and microstructural characteristics, like grain size, phase distribution and defects (e.g. microcracks). However, these relationships are currently not fully understood. Therefore, in this thesis, the influence of composition, grain size and microstructural defects on mechanical properties are investigated for Ce0.8Gd0.2O2-δ-FeCo2O4 membranes. Milling procedures during powder fabrication and ceramic sintering profiles are optimized to overcome the formation of unfavorable microstructural defects. Furthermore, the effects of grain size and phase distribution on oxygen permeation are discussed for a 85 wt% Ce0.8Gd0.2O2-δ-15 wt% FeCo2O4 membrane.