An Acoustic Emission Analysis of Glass-ceramic Sealants for Solid Oxide Fuel and Electrolysis Cells Exposed to Torsional Test: Room and High-temperature Experiments

The mechanical integrity of the sealant material is of key importance for the long-term, reliable operation of solid oxide fuel/electrolysis cell stacks. However, in-situ monitoring and detection of potential failures in sealing materials using classical electrochemical characterization techniques are difficult tasks. Therefore, in this work, the acoustic emission (AE) technique is applied to monitor and characterize the failure process of a glass-ceramic sealant exposed to torsional shear strength at both room and typical stack operation temperature (750 °C). Hourglass-shaped steel specimens are produced for the tests. A glass-ceramic material with two different porosities is used to join the specimens. The failure process is characterized in terms of AE peak amplitude, AE cumulative hits and AE energy, as well as the average frequency content of the signals. The results indicate that the degree of microscopic damage can be determined from the analysis of the AE energy and the fracture mechanisms can be found by statistical analysis of the average frequency of the signals. The fractured surfaces are visualized by optical microscopy to unveil that specimens with high porosity showed a fully cohesive fracture pattern, while specimens with low porosity showed a partially fracture pattern. As a result, AE method promises to be a potential in-operando technique for monitoring mechanical failure processes inside solid oxide cell stacks