Publications (2)2.08 Total impact
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Article: A New Generation of In Situ Wires With Improved and Values Obtained by Cold Densification (CHPD)
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ABSTRACT: By means of Cold High Pressure Densification (CHPD), the critical current density, J <sub>c</sub>, of binary and alloyed MgB<sub>2</sub> wires has been enhanced by more than a factor 2 at 4.2 K and at fields up to 19 T. The relative MgB<sub>2</sub> mass density of binary MgB<sub>2</sub> wires was enhanced to ~ 54% after applying 2.5 GPa at 300 K before reaction. In C<sub>4</sub>H<sub>6</sub>O<sub>5</sub> (malic acid) alloyed wires, densification also caused the enhancement of B <sub>irr</sub>, as a consequence of a slightly enhanced C content, determined by X ray diffraction. Almost isotropic J <sub>c</sub> values were obtained for C<sub>4</sub>H<sub>6</sub>O<sub>5</sub> added wires of 1 × 0.6 mm<sup>2</sup> cross section, the values of J <sub>c</sub>(4.2 K)=1 × 10<sup>4</sup> A/cm<sup>2</sup> for parallel and perpendicular fields being obtained at 13.8 and 13.4 T, respectively (1 μV/cm criterion). The corresponding values for 20 K were both close to 6.2 T. The value of B <sub>irr</sub><sup>//</sup> at 20 K was 11 T. The positive effects of cold densification on J<sub>c</sub> and B <sub>irr</sub> on MgB<sub>2</sub> was also observed on 150 mm long wires alloyed with C<sub>4</sub>H<sub>6</sub>O<sub>5</sub> (malic acid) or with SiC, by the succession of 6 overlapping pressure steps. This process can be extended to long wire lengths: by means of a newly developed prototype machine with an automatic press/release/advance sequence, a first wire length of 1 m was densified at 1.5 GPa, yielding J<sub>c</sub>(4.2 K) = 1 x 10<sup>4</sup> A/cm<sup>2</sup> at 13.1 T. Further improvements are expected after optimization.IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor -
Article: Enhanced Connectivity and Percolation in Binary and Doped In Situ Wires After Cold High Pressure Densification
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ABSTRACT: The cold high pressure densification technique (CHPD) was recently developed in Geneva for improving the in-field critical current density J<sub>c</sub> of in situ binary and alloyed MgB<sub>2</sub> wires and tapes,. J<sub>c</sub> of CHPD treated square wires alloyed with malic acid (C<sub>4</sub>H<sub>6</sub>O<sub>5</sub>) was enhanced by a factor 2 at 10 T and 4.2 K. In order to understand the fundamental mechanism behind this strong improvement of J<sub>c</sub>, the properties of binary and alloyed MgB<sub>2</sub> wires have been investigated without and with CHPD, using resistivity and specific heat measurements in the temperature range from 5 to 35 K in magnetic fields up to 15 T. In particular, a deconvolution of the specific heat data was used to determine the distribution of T<sub>c</sub> in the samples. We have found that the effect of the densification process on the electrical and transport properties is related to the improved grain connectivity and percolation. By combining the results arising from the analysis of the T<sub>c</sub> distribution and those from resistivity measurements, it is concluded that the minimum superconducting volume fraction needed for the percolation of a superconducting path is strongly reduced in samples treated by CHPD.IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
