X-ray tomography has proven to be a powerful tool in the characterisation of electrochemical devices, particularly, when inspecting the structural alterations caused by degradation mechanisms [4]. Additionally, in combination with techniques such as digital volume correlation (DVC), strain and material displacement can be mapped in three dimensions with trajectory information [5], improving understanding of material migration under operationally relevant conditions.
This work presents the microstructural developments at interfacial regions within a solid oxide half-cell exposed to varying degrees of thermal shock, similar to that which would be expected in operational conditions. The microstructure is analysed with use of lab-based X-ray tomography achieving statistically relevant data with sub-micron resolutions while preserving macroscopic mechanical influence via large sample volumes, ca. 5 x107 μm3. By imaging the same volume sequentially using the authors were able to correlate the structural dynamics within the volume using computational DVC analysis.
Figure 1 presents the change in electrolyte angle of an anode supported solid oxide-half cell through increased thermal shock. Various degrees of thermal ramp-rate are examined via X-ray tomography slices and phase percolation network lengths. Decreased connectivity in the electrochemical activity maps within the anode is observed with the increasing electrolyte bowing, resulting in a reduction in the percolated triple phase boundary (TPB) reaction site density. The results here present enhance insight into the real-world mechanical influence of expansion gradients between neighbouring layers during operational thermal cycling.
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Figure 1
Electrolyte bowing observed in an anode supported Ni-YSZ/YSZ solid oxide half-cell captured using X-ray computed tomography: a) profiles for the four thermal cycles at successively increasing ramp rates of 3, 10, 20 and 30 ᴼC/min, with accompanying single tomograph slices from the b) pre and ci) post-cycling tomograms, cii) magnified electrolyte bowing from the post-cycling tomogram, and d) Ni percolation mapping where white and red paths represent segments longer and shorter than 10 μm respectively.