Three-Dimensional Analysis of MgB2 Wire by use of X-ray Micro-Tomography

For the further development of MgB2 wires, investigation of 3-D structures for MgB2 filaments and sheath materials is important. However, typical cross-sectional observation such as optical microscopy and scanning electron microscopy are essentially 2-D, therefore, not enough to understand the 3-D filament structures. In this paper, we have adopted X-ray microtomography and carried out a 3-D analysis for MgB2 wire. X-ray microtomography (Skyscan 1172, Bruker) allows us to visualize the internal filament structure of a centimeter-long MgB2 wire with a high spatial resolution of 1.1 mu m, with a nondestructive manner. We investigated the boundary between the sheath material and the MgB2 filament of an internal Mg-diffusion-processed MgB2 wire. Furthermore, by improving the signal-to-noise ratio for the X-ray microtomography, we have also identified the boundary between the MgB2 filament and the hole (air) in spite of the low X-ray absorption coefficient for boron and magnesium. From the 3-D analysis, we can reveal the shape and area of MgB2 filament quantitatively and also their statistical distribution.