Abstract
Superconducting MgB2 fibers were synthesized through the reaction of liquid magnesium with 140 μm diameter boron fibers. Fiber reaction occurs by two concurrent mechanisms. First, concentric MgB2, MgB4 and MgB7 shells grow radially into the B fibers. Diffusion modeling provides rate constants and effective diffusion coefficients for the borides and their activation energies. Second, radial cracks form in the MgB4 or MgB7 shells, allowing for Mg ingress into the fibers and diffusional growth of MgB2 wedges in the radial and circumferential directions. Combining both shell and wedge MgB2 growth mechanisms into a single model provides predictions of overall MgB2 reaction kinetics as a function of time and temperature, which are in good agreement with in situ X-ray diffraction measurements performed at 885-1025 °C.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 5751-5763 |
| Number of pages | 13 |
| Journal | Acta Materialia |
| Volume | 56 |
| Issue number | 19 |
| DOIs | |
| State | Published - Nov 2008 |
Funding
This work was supported by the US National Science Foundation through Grant No. DMR-0319051. The authors thank Dr. J. Marzik of Specialty Materials, Inc. for providing boron fibers and Drs. J. Quintana, Q. Ma and D. Keane for help in performing the diffraction experiments at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT). DND-CAT is supported by E.I. DuPont de Nemours & Co., The Dow Chemical Company and the State of Illinois and is located at Sector 5 of the Advanced Photon Source which is supported by the US Department of Energy under Contract No. DE-AC02-06CH11357.
Keywords
- Chemical synthesis
- Magnesium diboride
- Superconductor
- Theory and modeling (kinetics, transport, diffusion)
- X-ray diffraction
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys