FIGURE 1: MgB2 dispersed within Mg matrix
FIGURE 2: 140 mm diameter MgB2 fiber in magnesium matrix under cross-polarized light. Metallographic preparation and image copurtesy Buehler Ltd. (Lake Bluff, IL)
John DeFouw is working on the synthesis of superconducting magnesium diboride (MgB2) composites. Magnesium diboride is a superconductor with a critical temperature around 39 K. While this is not as high as the high-temperature cuprate superconductors (Tc well above 100 K) it is higher than other intermetallic superconductors such as the workhorse Nb3Sn that is used in magnetic resonance imaging (MRI) components. Wires of MgB2 would allow practical application near 20 K, which can be achieved with conventional refrigeration techniques and would not require the expensive liquid He that Nb3Sn requires. However, MgB2 is a brittle ceramic and wires cannot be drawn as with a ductile metal. For this reason, practical wires of MgB2 must be in combination with a ductile metal phase.
We have produced metal matrix composites with a continuous phase of MgB2 through two routes involving liquid metal infiltration. In one route, we produce an isotropic composite through the infiltration of a high density preform of MgB2 powders with Mg or Al.
Through infiltrating a preform of boron powders or boron fibers with liquid magnesium followed by heat treatment, we form MgB2 within an Mg matrix. Magnetometer measurements show the superconducting transition temperature at 39 K with a critical current density of 360 kA/cm2 at 5 K under self-field.
We are currently studying the reaction kinetics of the formation of MgB2 from Mg and B precursors using synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory as well as the processing history’s effect on the microstructure and mechanical and superconducting properties.
Related Publications
- D.C. Dunand. “Synthesis of Superconducting Mg/MgB2 Composites”, Applied Physics Letters, 79, 25, 4186-4188 (2001).
PDF - J. DeFouw, D.C. Dunand. “In-situ Synthesis of Superconducting MgB2 Fibers within a Magnesium Matrix”, Applied Physics Letters, 83, 1, 120-122 (2003).
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Financial Support
This research is funded by the National Science Foundation.
