High Temperature Superconducting Wires

Ceramic superconductor (e.g., YBa2Cu3O7_x) wires have been fabricated via binder-assisted extrusion (Ref 8, 9, 18, 19, 31, 32). Both solvent-based and polymer binders have been used, and extrusions have been made at room and elevated temperatures. For solvent-based binder systems, care must be taken to select a solvent that does not contaminate the ceramic superconducting powders. A binder system that has been used in the extrusion of YBa2Cu3O7_x powders at room temperatures is (Ref 19): ethyl cellulose as the organic binder, glycerol as the solvent, and stearic acid as a lubricant. Other solvents that are compatible with YBa2Cu3O7-x powders include methylethylketone, methanol, and xylene (Ref 32). Polymers, such as polyethylene, polystyrene, and waxes, have been used as binders for hot extrusion of the YBa2Cu3O7-x powders (Ref 9, 18, 19). Wires with diameters of between 0.2 and 20 mm, with lengths well over 15 m, have been produced by binder-assisted extrusion. Because the extruded wire is flexible prior to binder removal, coils can be made by wrapping the wire around a mandrel.

With YBa2Cu3O7_x powders that possess a platelike morphology, the apparent viscosity of the feedstock can significantly influence the critical current density for superconductivity (Ref 19). This is shown in Fig. 16, where the platelike particles align unidirectionally during the extrusion process as a result of the high apparent viscosity of the mixture.

Fig. 16 Influence of feedstock viscosity on the critical current density (Jc) for and bulk density for binderassisted extruded superconducting wires. Source: Ref 19

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