The enhancedJ_candB_irrofin situMgB₂wires and tapes alloyed with C₄H₆O₅(malic acid) after cold high pressure densification

Abstract

Cold high pressure densification, a method recently introduced at GAP in Geneva, was applied for improving the transport critical current density, Jc, and the irreversibility field, Birr, of monofilamentary in situ MgB2 wires and tapes alloyed with 10 wt% C4H6O5 (malic acid). Tapes densified at 1.48 GPa exhibited after reaction an enhancement of Jc from 2 to 4 × 104 A cm−2 at 4.2 K/10 T and from 0.5 to 4 × 104 A cm−2 at 20 K/5 T, while the Birr was enhanced from 19.3 to 22 T at 4.2 K and from 7.5 to 10.0 T at 20 K. Cold densification also caused a strong enhancement of B(104), the field at which Jc takes the value 1 × 104 A cm−2. For tapes subjected to 1.48 GPa, and at 4.2 K were found to increase from 11.8 and 10.5 T to 13.2 and 12.2 T, respectively. Almost isotropic conditions were obtained for rectangular wires with aspect ratios a/b<2 subjected to 2.0 GPa, where and T were obtained. At 20 K, the wires exhibited an almost isotropic behavior, with T and T, Birr(20 K) being ∼10 T. These values are equal to or higher than the highest values reported so far for isotropic in situ wires with SiC or other carbon based additives. Further improvements are expected on optimizing the cold high pressure densification process, which has the potential for fabrication of MgB2 wires of industrial lengths.

Drawing induced texture and the evolution of superconductive properties with heat treatment time in powder-in-tubein situprocessed MgB2strands

“…These can be accomplished through: (i) site-substitution into the Mg sublattice by Zr [21,22], Na [23], or similar-sized cations [24][25][26][27], (ii) site-substitution into the B sublattice by C [28][29][30][31][32] (with regard to which we note that it has been difficult to distinguish t-he influence of substitution from effect of possible C-induced lattice strain [33][34]), and (iii) increasing the connectivity between MgB 2 grains (or grain clusters) to increase the efficiency of supercurrent flow [35][36][37][38].…”

Technical aspects of cold high pressure densification (CHPD) on long lengths of In Situ MgB2 wires with enhanced Jc values

“…After densification, it was already reported in earlier articles [1,3,26] that no microcracks could be detected in the transition region between pressed and unpressed filament, neither by optical nor by SEM microscopy. This was also the case for repeated pressing steps on the same overlapping region.…”

“…The relative mass density inside MgB 2 filaments of in situ wires was enhanced from 48 to > 60 % for pressures well above 1 GPa, thus leading to strongly enhanced values of J c . The efficiency of densification was not only demonstrated for monofilamentary, binary in situ MgB 2 wires [1], but also for MgB 2 wires alloyed with SiC [24], C [25] and malic acid [24,26]. More recently, the CHPD process was successfully applied to a binary 18 filament MgB 2 wire [27].…”

Formation of High-Field Pinning Centers in Superconducting MgB2 Wires by Using High Hot Isostatic Pressure Process

“…Pure Mg has several advantages such as high ductility and malleability. These factors allow to form the structure of an unreacted MgB 2 wire by cold working, e.g., cold drawing [10], cold rolling [10], mechanical alloying [11], and cold isostatic pressure [12]. All these methods increase the density of the unreacted MgB 2 material and lead to an increase in critical current density.…”