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| Hauptseite > Publikationsdatenbank > Joining and sealing technologies for asymmetric Ba0.5Sr0.5(Co0.2Fe0.8)0.97Zr0.03 O3-δ (BSCF-Zr) membranes for Oxy Combustion processes |
| Hauptseite > Publikationsdatenbank > Joining and sealing technologies for asymmetric Ba0.5Sr0.5(Co0.2Fe0.8)0.97Zr0.03 O3-δ (BSCF-Zr) membranes for Oxy Combustion processes |
| Conference Presentation (After Call) | FZJ-2015-05712 |
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2015
Abstract: Oxy combustion processes attracted great interest due to their potential role in decarbonisation of industrial processes. A key role plays the energy and cost efficient supply of pure oxygen. Ceramic oxygen transport membranes (OTM) are a promising alternative to the state-of-the-art separation processes. Mixed ionic-electronic conducting membranes (MIECs) are of interest due to their ability to transport oxygen via vacancies in the crystal lattice, resulting in a theoretical oxygen selectivity of 100%. One promising option is the high flux material Ba0.5Sr0.5Co0.2Fe0.8O3-δ (BSCF) stabilized with 3 mol% Zr on the B-site in order to suppress the formation of the undesired hexagonal polymorph. The resulting Ba0.5Sr0.5(Co0.2Fe0.8)0.97Zr0.03O3-δ (BSCF-Zr) can be operated in a 3-End mode, in which the feed air is compressed and the permeated oxygen is removed by a vacuum. In order to maximize the oxygen flux, the membrane was designed as thin film membrane consisting of a porous support and a thin membrane layer (~20 µm). This microstructure and the pressure difference at high application temperatures of about 850 °C impose challenging requirements for a gas tight sealing (e.g. dead end of the tube) and joining to the adjacent metallic components of the module. To solve these challenges, the following sealing/joining options were investigated:i) Reactive air brazing (RAB) with a silver/copper oxide brazeii) Metallic solder based on pure silveriii) Fully ceramic joining by garnishing techniqueWhile the high reactivity of RAB brazes is advantageous for monolithic BSCF tubes, the wettability causes problems for supported thin film membranes. The active element, i.e. copper oxide, tends to destroy the thin membrane layer and the high wettability leads to heavy infiltration into the support, causing failure of the entire component. A successful strategy to avoid the infiltration of the porous support and to ensure chemical compatibility the joining with pure silver via a liquid phase bonding was investigated. The green density of the brazing material was increased compared to standard pastes by the fabrication of silver foils by tape casting, sintering of the foil and a subsequent compression step in order to avoid pores or voids in the joining zone. Joining was performed at 960 °C (±5 °C). The plastic deformation of the thin metallic silver foil can partly buffer a mismatch in thermal expansion. Finally, a fully ceramic sealing procedure was developed. For this purpose thin (~100 µm) ceramic tapes from BSCF-Zr were fabricated via tape casting and placed between the components to be joint. By a load assisted sintering, a gas tight sealing could be achieved.Suitable for two ceramic joining partners is the garnishing technique as well as the use of silver solders. For ceramic-to-metal joining, the use of silver solder shows the most promising results.
Keyword(s): Materials Science (2nd)
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