Plasma Synthesized Boron Nano-Sized Powder for MgB₂ Wires

J. V. Marzik¹, R. C. Lewis¹, M. R. Nickles¹, D. K. Finnemore²,
J. Yue³, M. Tomsic³, M. Rindfleisch³, M. D. Sumption⁴

¹Specialty Materials, Inc., Lowell MA, 01851, USA
²Iowa State University, Ames IA, 50011, USA
³Hyper Tech Research, Inc., Columbus OH, 43212, USA
⁴The Ohio State University, Columbus OH, 43210, USA

ABSTRACT - Plasma synthesized boron powder has been prepared under a variety of RF plasma conditions to examine the suitability of these powders for the preparation of powder-in-tube MgB₂ wire. Particle size emerging from the RF torch typically ranges from 5 nm to 200 nm and lattice imaging studies in a transmission electron microscope show large portions of both amorphous and beta rhombohedral crystalline material. In situ powder-in-tube wire that is made with a continuous tube filling and forming process consistently gives critical current densities ranging from 20,000 to 100,000 A/cm2 at 5 K and 5 Tesla for a powder containing about 4% carbon. As the temperature rises, the critical current density of 100,000 A/cm2 occurs at 4.3 T at 10 K, 3.5 T at 15 K, and 2.5 T at 20 K. In preparation for studies of an ex-situ powder-in-tube process, we have studied the size of reacted MgB₂ powder formed in a magnesium vapor. Reaction rates are much slower than for solid state diffusion in the in-situ process and care is needed to hold particle size under the micrometer range.

KEY WORDS: Superconductors, Nano-scale, Powders

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IEEE/CSC & ESAS EUROPEAN SUPERCONDUCTIVITY NEWS FORUM (ESNF), No. 10, October 2009.
On June 29, 2009, this manuscript was submitted for possible publication in “Advances in Cryogenic Engineering-Materials”