Process for producing superconducting wires

A method for producing a superconducting rare earth barium copper oxide based wire exhibiting improved critical current density comprising the steps of:

• mixing a rare earth barium copper oxide based superconductor as a powder, silver or silver oxide as a powder in an amount of about 3-12 w/o of the total powder weight, and a binder as a melt at a solids loading of at least about 89% by weight to form a homogeneous extrudable powder/binder mixture, wherein said binder consists essentially of an ester wax with no more than about 0.25 weight percent extrusion-aiding additives, and said ester wax has the general formula RCOOR' with said R and said R' each being independently selected from the group consisting of long chain hydrocarbon groups of at least 6 carbons, and said ester wax has a melting point of about 40.degree.-100.degree. C. and a viscosity of about 94-2000 centipoise at its melting point;
• shaping said binder/powder mixture to form a shaped wire;
• heating said shaped wire in an oxidizing atmosphere at a heating rate of up to about 120.degree. C./hr to a binder removal temperature of about 500.degree.-600 .degree. C., and holding said wire in said oxidizing atmosphere at said binder removal temperature for a time sufficient to remove said binder from said wire and to form a green wire having a density of at least 50% of theoretical density;
• heating said green wire in said oxidizing atmosphere at a heating rate of about 50.degree.-130.degree. C./hr to about the incongruent melting temperature of said superconductor, and holding said green wire in said oxidizing atmosphere at said incongruent melting temperature for a time just sufficient to begin partial melting of at least one component in said superconductor;
• and
• cooling said partially melted wire in said oxidizing atmosphere at a rate below about 130.degree. C./hr to a consolidation temperature of about 940.degree.-969.degree. C., and holding said wire in said oxidizing atmosphere at said consolidation temperature for a time sufficient to consolidate said wire to a density of at least 90% of theoretical density and sufficient to achieve an average grain length of at least about 0.3 mm and grain alignment along the length of said wire;
• cooling said consolidated wire in said oxidizing atmosphere at a rate below about 130.degree. C./hr to a cooled temperature at or below about 550.degree. C.;
• and
• holding said cooled wire at an annealing temperature of about 450.degree.-550.degree. C. in an atmosphere of flowing oxygen for a time sufficient to convert the crystal structure of said wire to at least 50 v/o superconducting perovskite crystal.