Ceramic oxygen-permeable membranes are capable of efficiently separating oxygen from air. The separated oxygen can be fed directly to chemical reactions (membrane reactors). This combines the separation and reaction processes that are usually carried out separately (process intensification). In the context of the energy transition, such technologies offer very good prospects, as they can support the electrification of the chemical industry in addition to increasing efficiency.
The very stable perovskite SrTiO₃, which, however, is not O^2-permeable and therefore has to be functionalized by means of dopants, was the selected material in this work. By partially substituting Ti with 25% Fe (SrTi_0.75Fe_0.25O_3-δ, STF25), mixed ionic and electronic conductivity of the material is achieved.
A solid-state reaction route for powder synthesis was developed to receive homogeneous STF25 powder. Therefore, the reaction mechanism was investigated with DTA/TG to set the optimal parameters for heat treatment of the powder. However, sintering studies revealed that the densification of the stoichiometric STF25 composition is too low to achieve fully dense ceramic samples. Hence, a modification of the composition, an understoichiometric amount of Sr, was implemented to increase the densification successfully. Microstructural investigations with SEM showed that there is the possibility of secondary phase formation which can be overcome by choosing the right composition and sintering conditions. Finally, oxygen permeation was tested with different understoichiometric compositions showing a slight increase compared to the stoichiometric one provided that secondary phase formation is suppressed.