| Popis: |
The perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) is a mixed ionic electronic conductive ceramic and can be used as oxygen transport membrane (OTM) material for oxygen supply in high-temperature applications. For BSCF, reactive brazing in air atmosphere (RAB) is the only technical applicable solution for a heat resistant and gas tight sealing to metals. As a consequence of brazing BSCF to the heat resistant austenitic steel AISI 314 a change in microstructure in the BSCF appears at the interface due to reactions with the copper oxide (CuO) from the AgCu braze alloy. After aging for 500 h at 850 °C in air atmosphere, a further change in the microstructure appears, which is characterized by an additional increase of porosity in the interface area between ceramic and braze. Also, a needle shaped phase at the grain boundaries in the ceramic can be observed. This kind of structure is known as product phase of a transformation of cubic BSCF into hexagonal perovskite. Mechanical tests with the BSCF/AISI 314-joints show a decrease of the room temperature strength after aging. |
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