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arXiv · 0712.2056

Nanoscale grains, high irreversibility field, and large critical current density as a function of high energy ball milling time in C-doped magnesium diboride

B. J. Senkowicz·R. J. Mungall·Y. Zhu·J. Jiang·P. M. Voyles·E. E. Hellstrom·D. C. Larbalestier
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Abstract

Magnesium diboride (MgB2) powder was mechanically alloyed by high energy ball milling with C to a composition of Mg(B0.95C0.05)2 and then sintered at 1000 C in a hot isostatic press. Milling times varied from 1 minute to 3000 minutes. Full C incorporation required only 30-60 min of milling. Grain size of sintered samples decreased with increased milling time to less than 30 nm for 20-50 hrs of milling. Milling had a weak detrimental effect on connectivity. Strong irreversibility field (H*) increase (from 13.3 T to 17.2 T at 4.2 K) due to increased milling time was observed and correlated linearly with inverse grain size (1/d). As a result, high field Jc benefited greatly from lengthy powder milling. Jc(8 T, 4.2 K) peaked at > 80,000 A/cm2 with 1200 min of milling compared with only ~ 26,000 A/cm2 for 60 min of milling. This non-compositional performance increase is attributed to grain refinement of the unsintered powder by milling, and to the probable suppression of grain growth by milling-induced MgO nano-dispersions.

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B. J. Senkowicz, R. J. Mungall, Y. Zhu, J. Jiang, P. M. Voyles, E. E. Hellstrom, D. C. Larbalestier. 2007-12-12. Nanoscale grains, high irreversibility field, and large critical current density as a function of high energy ball milling time in C-doped magnesium diboride. https://doi.org/10.1088/0953-2048%2F21%2F3%2F035009

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