Mounting of the test object into the test system When mounting the test object into the test system some test-related factors should be considered in addition to the general safety precautions of the test system. When testing a single ceramic solid oxide cell, the cell is mounted within a cell test fixture, which provides gas connections and possible sensory connections similar to a stack assembly. When mounting a cell within a cell test fixture, some general considerations have to be made to assure that the influence of the test setup on the results is minimized: • Electrical contact to both the negative and positive electrodes has to be assured; this is done by ensuring actual mechanical contact of the cell to the contact components, and by having sufficient contact points to avoid current restrictions. • A well-defined or masked geometric area of an electrode has to be defined as the geometric cell area. • The cell has to be sufficiently leak-tight to avoid significant mixing of the test gases with other gases, before passing the negative or positive electrodes. • Any potential pollutants (sulphur, phosphorous, etc.) from components used in the cell test fixture have to be avoided. • Mechanical stresses from the cell test fixture components have to be avoided, to prevent any potential cracking of the cell during testing. • Furthermore, flow fields at the electrodes have to distribute the gas evenly, and without a potential turbulent flow, to avoid gas starvation and mass transport limitations at the electrodes. When the above mentioned considerations are adequately taken care of, the cell test fixture can be handled similar to a stack assembly. When the cell/stack assembly has to be mounted in the test setup, it has to be securely positioned, to avoid accidental movement during testing. Electrical connections have to be properly done and gas connections securely tightened, while sharp bends of the gas tubes should be avoided. Isolation resistances between the repeating units in the stack should be checked to avoid a short circuit. Gas tightness of the gas supply subsystem of the test station, of the stack itself and of the interface between stack and test station should also be checked. Furthermore, the gases fed into the cell test fixture/stack assembly have to be preheated to the ambient oven temperature, to avoid a significant temperature difference at the gas inlet. The mechanical load applied on the cell/stack should be uniform. In some cases, the compression mechanism required for stack t...
