437 research outputs found
Influence of mechanical reinforcement of MgB2 wires on the superconducting properties
Monofilamentary MgB2-wires with a mechanical tough Nb/Cu/steel or Fe/steel
sheath were prepared and characterized. The steel content was varied to
investigate the reinforcement effect and the consequences for the
superconducting properties of the wires, which were heat treated to achieve
dense and homogeneous filaments. The use of Nb as first sheath layer, having a
smaller thermal expansion coefficient than MgB2, requires the application of
higher amounts of steel to achieve compressive pre-stress on the filament in
comparison to Fe as first wall material. With raised steel content in the
sheath the critical transport currents show field dependent significant
critical current and irreversibility field degradations. First Ic vs. axial
stress and strain experiments confirmed this observation of pre-stress induced
degradations. Consequences for improved wires and for future applications will
be discussed.Comment: 14 pages, 7 figures, 1 table; Submitted to Physica C; presentation at
ISS-2001, Kobe Japa
High transport currents in mechanically reinforced MgB2 wires
We prepared and characterized monofilamentary MgB2 wires with a mechanically
reinforced composite sheath of Ta(Nb)/Cu/steel, which leads to dense filaments
and correspondingly high transport currents up to Jc = 10^5 A/cm^2 at 4.2 K,
self field. The reproducibility of the measured transport currents was
excellent and not depending on the wire diameter. Using different precursors,
commercial reacted powder or an unreacted Mg/B powder mixture, a strong
influence on the pinning behaviour and the irreversibility field was observed.
The critical transport current density showed a nearly linear temperature
dependency for all wires being still 52 kA/cm^2 at 20 K and 23 kA/cm^2 at 30 K.
Detailed data for Jc(B,T) and Tc(B) were measured.Comment: 21 pages, 13 figures, revised version, to be published in Supercond.
Sci. Techno
Influence parameters of impact grinding mills
Significant parameters for impact grinding mills were investigated. Final particle size was used to evaluate grinding results. Adjustment of the parameters toward increased charge load results in improved efficiency; however, it was not possible to define a single, unified set to optimum grinding conditions
Mechanically reinforced MgB2 wires and tapes with high transport currents
Monofilamentary MgB2-wires with a 2- or 3-component sheath containing
mechanical reinforcing stainless steel (SS) were prepared and characterized. In
direct contact to the superconductor Nb, Ta or Fe was used. For a selection of
samples with a Fe and Fe/SS sheath, we investigated the transport critical
current behaviour in magnetic fields changing systematically the geometrical
shape from a round wire to a flat tape. A strong increase of the current
densities in flat tapes was observed and possible reasons for this are
discussed. Reinforcing the sheath in the outer layer with different amounts of
stainless steel leads to a systematic field dependent decrease of the transport
critical current density with increasing steel amount. This is an indication
for a pre-stress induced degradation of the critical currents in MgB2 wires and
first Ic-stress-strain experiments seem to confirm this observation and
interpretation.Comment: 12 pages, 5 figures. Submitted to Physica C (Proceedings of EUCAS
2001
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