Reaktives Löten als Verbindungstechnologie für die SOFC

Solid oxide fuel cells (SOFC) consist of ceramic and metallic components which have to be joined and sealed for operation at high temperatures up to 850°C in dual atmospheres. Appropriate sealing materials have to match the CTE of these materials, must withstand the harsh chemical environment and must show good long term stability under operating conditions. Glasses and glass-ceramics are widely used to fulfil these requirements. Nevertheless they are afflicted with several drawbacks which can be avoided in case of active brazing process. The conventional brazing technologies are not suitable to join ceramics. Therefore active brazes containing an additional reactive phase which realizes the adhesion to the ceramic surface by an oxidation reaction should be used. In comparison with glass seals, which show viscous flow under operating conditions, brazes are solid and a more rigid joining can be achieved. One approach is given by the reactive air brazing process where components like Cu, Cu2O or CuO act as active phases. Furthermore, with these compositions the brazing process can be conducted in air in contradiction to the standard active brazes having additions of Ti. The investigation of long-term stability and thermal cylcability performed with copper containing brazes and their interaction with metallic and ceramic parts shows a good potential for their application as joining materials.