Synchrotron Microtomography Investigation of the Filament Microstructure in Differently Processed Bi-2212 Wires

The Bi-2212 microstructure and porosity distribution in entire state-of-the-art multifilament wires was characterized by high-energy synchrotron X-ray absorption microtomography after meltprocessing at ambient pressure, at 100 bar overpressure, and at ambient pressure after prior cold isostatic pressing of initially identical as-drawn wires. Beyond the visualization of the Bi-2212 microstructure, the porosity distribution in the different filament bundles has been quantified. Spherical granulometry and finite percolation probability calculations have been performed in order to provide a measure for the porosity distribution and to compare filament connectivity in the axial wire direction. Possible artifacts of the microtomography (μ-CT) experiment and the possibility to estimate the effect of the Bi-2212 microstructure as seen in the μ-CT images on critical current density are discussed.