Large critical current density improvement in Bi-2212 wires through groove-rolling process

Recently the interest about Bi-2212 round wire superconductor for high magnetic field use has been enhancing despite the fact that an increase of the critical current is still needed to boost its successful use in such applications. Recent studies have demonstrated that the main obstacle to current flow, especially in long wires, is the residual porosity inside these Powder-In-Tube processed conductors which develops in bubbles-agglomeration when the Bi-2212 melts. Through this work we tried to overcome this issue acting on the wire densification by changing the deformation process. Here we show the effects of groove-rolling versus drawing process on the critical current density JC and on the microstructure. In particular, groove-rolled multifilamentary wires show a JC increased by a factor of about 3 with respect to drawn wires prepared with the same Bi-2212 powder and architecture. We think that this approach in the deformation process is able to produce the required improvements both because the superconducting properties are enhanced and because it makes the fabrication process faster and cheaper

Groove-rolling as an alternative process to fabricate Bi-2212 wires for practical applications

Bi2Sr2CaCu2O8+x (Bi-2212) superconducting long-length wires are mainly limited in obtaining high critical currents densities (JC) by the internal gas pressure generated during the heat treatment, which expands the wire diameter and dedensifies the superconducting filaments. Several ways have been developed to increase the density of the superconducting filaments and therefore decreasing the bubble density: much higher critical currents have been reached always acting on the final as-drawn wires. We here try to pursue the same goal of having a denser wire by acting on the deformation technique, through a partial use of the groove-rolling at different wire processing stages. Such technique has a larger powders compaction power, is straightforwardly adaptable to long length samples, and allows the fabrication of samples with round, square or rectangular shape depending on the application requirements. In this paper we demonstrate the capability of this technique to increase the density in Bi-2212 wires which leads to a three-fold increase in Jc with respect to drawn wires, making this approach very promising for fabricating Bi-2212 wires for high magnetic field magnets, i.e. above 25 T

Magnetic alignment of carbon nanofibers in polymer composites and anisotropy of mechanical properties

Engineering applications of carbon nanofibers and nanotubes require their alignment in specific directions. Single-walled carbon nanotubes can be aligned in a magnetic field due to the presence of small amounts of catalyst elements, such as Ni and Co. However, for carbon nanofibers, their extremely low magnetic susceptibility is not sufficient for magnetically induced alignment. We present a method of solution-coating of NiO and CoO onto the surface of the carbon nanofibers. Due to the NiO- and CoO-coating, these nanofibers can be well aligned in the polymer composites under moderate magnetic field (3 T). Both transmission electron microscopy and scanning electron microscopy results show the well-aligned nanofibers in a polymer matrix. Mechanical testing shows a pronounced anisotropy in tensile strength in directions normal (12.1 MPa) and parallel (22 MPa) to the applied field, resulting from the well-aligned nanofibers in the polymer matrix. The mechanism of magnetic alignment due to coating of NiO and CoO on the nanofiber surface is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87644/2/064312_1.pd

Growth of YBCO single domains through an array of holes for FCL c-axis superconducting elements

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High field Ic characterizations of commercial HTS conductors

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Thin-Wall Bulk High Temperature Superconductor as a Permanent Cryomagnet

International audienceThin-wall single domains with artificial patterned holes are highly interesting for stimulating superconducting and mechanical properties of bulk YBCO materials. YBCO single domains were successfully grown from multiple holes preforms by using TSIG or TSMG techniques. The thin-wall configuration enables a remarkable improvement in flux trapping and superconducting properties whatever the used growth process. Progressive oxygenation under high pressure associated to the large specific areas was shown to boost the material performances. A trapped field maximum of 0.84 T was recorded at 0.2 mm above the top surface of a 16 mm thin wall pellet at 77 K. Such complex geometry can be easily and abundantly produced by using an extrusion process. We report for the first time to our knowledge the growth of a single domain from an extruded preform. Thin-wall samples were then impregnated by resign/alloy for mechanical reinforcement

Extruded YBCO HTS Single Domain Bulk Materials for Permanent Magnets

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Thin-Wall Bulk High Temperature Superconductor as a Permanent Cryomagnet

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Bulk YBCO growth monitored by in situ high-temperature magnetic susceptibility

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