Gas-phase plasma synthesis methods were used to prepare nano-scale particles of C-doped B powder that were very suitable for the powder-in-tube fabrication of superconducting wire. Mixtures of H2, BCl3, and CH4 gas were injected into an induction plasma where doped B powder was formed and collected on a stainless steel screen. The particles were typically about 20nm in size and collected into lacy agglomerates in the 1 to 50μm size-range. Pressed pellets of these powders, heated in a Mg atmosphere, were transformed into the MgB2 phase at 600 to 1200C. The critical current densities at 5K ranged from about 106A/cm2 at self-field to 4 x 104A/cm2 at 7T. At 20K, JC ranged from 5 x 105A/cm2 in self-field to about 104A/cm2 at 3T. Samples of pure B powder and B with 7.4%C powder were prepared as powder-in-tube wires having a combination of an Fe inner jacket and a cupro-nickel outer jacket. These powder-in-tube JC values were lower than, but comparable to, those of pressed-pellet values. The powder-in-tube samples could be reacted in times of the order of 10min, and still exhibited values greater than 105A/cm2 at 5K and 2T.

Plasma Synthesized Doped B Powders for MgB2 Superconductors. J.V.Marzik, R.J.Suplinskas, R.H.T.Wilke, P.C.Canfield, D.K.Finnemore, M.Rindfleisch, J.Margolies, S.T.Hannahs: Physica C, 2005, 423[3-4], 83-8