Failure analysis of electrolyte-supported solid oxide fuel cells

High temperature mechanical properties of zirconia tapes used for electrolyte supported solid oxide fuel cells

“…Taking the strength data of the dull sides (side of the cast tape which was opposite to the support foil) of commercial 3YSZ, 6ScSZ and 10Sc1CeSZ tapes from a previous study [13], given in Table 3, the influence of temperature and SCCG can be quantitatively assessed for a given system and its respective load environment. To give an example how these different dependencies influence the strength, the load environment of the m-CHP (small scale combined heat and power plant) Galileo 1000 N of Hexis AG (Winterthur, Switzerland) [31] is considered for further discussion, which has been described in a previous study [27]. At T ¼ 850 C it is assumed that the peak loads are caused by thermal stresses, which effectively load a surface area S of approximately 10 cm 2 of the total cell area of 200 cm 2 .…”

“…8YSZ on the other hand appears to be the weakest of the common zirconia. Comparing the strength to the magnitude of thermal stresses which are expected to rise due a generally given inhomogeneous temperature distribution throughout the cell and which are typically in the range of 50e60 MPa [16,27,33,34], it is revealed that 8YSZ is not suited for the application in electrolyte supported fuel cells.…”

“…Next to thermal stresses the electrolyte is also subjected to stresses due to the clamping, as the contact between the metallic interconnect (MIC) and the cell is never perfectly flat and leads to local bending, and residual stresses due to thermal mismatch of the cell components. The residual stresses are small at operating temperatures, while they increase if the cell is cooled down to RT, putting the electrolyte under a slight compressive load (~20 MPa) [27,35]. Hence the residual stresses can be neglected for further discussion.…”

“…Hence the residual stresses can be neglected for further discussion. Stresses due to clamping on the other hand can become significant and might lead to local damage [27]. Fig.…”

“…[23]. to thermal mismatch strains and local stresses due to an uneven clamping of the cell [27]. Since clamping loads can become significant in magnitude and are present from RT to operating temperature, the temperature behaviour of the biaxial fracture strain (ε frac,biax ¼ s frac,biax (1 À n)/E) is considered as well and shown in Fig.…”