Influence of the milling energy transferred to the precursor powder on the microstructure and the superconducting properties of MgB₂wires

Abstract

A systematic study of the influence of the milling energy of the precursor powder on the microstructure and the superconducting properties of MgB 2 bulk samples and wires, and, in addition, the deformation behavior of the wires is presented. An explicit approximate formula for the energy transferred to the powder sample during milling and its dependence on the parameters of the milling process is developed and used for the data analysis. For higher milling energies the amount of the reacted MgB 2 -phase shows a strong increase. The transport critical current density of wires can be enhanced by using precursor powder milled with higher energy. Because the deformation properties are degraded to some extent, one has to find a compromise of the preparation parameters between current density and deformation behavior.

Enhanced upper critical field in Co-doped Ba122 superconductors by lattice defect tuning

“…where c is the dimensionless constant of the order of 0.1,  is the mass ratio of balls to the powder, p is the angular frequency, rp is the revolution radius, rv is the rotation radius, and t is the ball-milling time 28 . The milled powders were pressed into disk-shaped pellets with a diameter and thickness of 7 and 1.2 mm, respectively.…”

Increased critical current density of in-situ MgB2 wires by Mg deficiency

“…7 the field dependence of the critical current densities of multi-core wires with stoichiometric and Mg-deficient precursor (x = 0.85) and for each case 3 different milling energies (7 Á 10 7 J/kg, 1 Á 10 9 J/kg, 5 Á 10 9 J/kg [8]) is compared. There it is clearly visible that the dependence of j e on the milling energy can be found at samples with non-stoichiometric precursor like at stoichiometric ones [8] as well. In Fig.…”

“…Mechanical alloying was done using a Retsch PM 4000 planetary ball mill with tungsten-carbide vials and balls under inert argon atmosphere (milling energy between 6 Á 10 7 J/kg and 5 Á 10 9 J/kg [8] …”

Effect of Ball Milling and Fatty Acid Addition on the Properties of <inline-formula> <tex-math notation="TeX">$\hbox{MgB}_{2}$</tex-math></inline-formula> Wires

“…RAIN REFINEMENT [1]- [3] and carbon doping [4]- [7] are two processes widely used to improve the J c (B) performance of metal composite MgB 2 wires and tapes. Ball milling of MgB 2 precursor powders may produce very fine and well mixed precursors with higher reactivity, yielding ex-situ tapes with small grains and improved density of grain boundaries, without introducing additional magnetic flux pinning mechanisms [1], [2].…”