This paper describes the design and development of a composite seal for SOFC to produce a hermetic joint between the ceramic and metallic components of the SOFC stacks. The composite seal was designed to be chemical compatible with the ceramic electrolyte (YSZ) and the interconnect (AISI 430), to have suitable thermo-mechanical properties (T g , thermal expansion coefficient, TEC), and good wettability with them. The reinforcing phase (alumina) was chosen to increase the seal viscosity at the SOFC working temperature (about 800 • C), to improve the thermal shock resistance of the seal and to match the thermal expansion coefficient of the components to be joined.
The seal was morphological and thermo-mechanical characterized by scanning electron microscopy, SEM, energy dispersive spectroscopy, EDS, thermo-mechanical analysis, TMA, X-ray diffraction, XRD and differential thermal analysis, DTA.
The joining process between YSZ and AISI 430 was optimized taking into account that the maximum process temperature should be around 1000 • C. Joined samples were preliminary submitted to H 2 -3% H 2 O atmosphere exposure at 800 • C for 200 h.