Fabrication of superconducting wires and rods

Abstract

The fabrication of superconducting wires and rods having desired and consistent electrical and mechanical properties, in particular those based on Yttrium Barium Copper Oxide (YBCO) and Bismuth Strontium Calcium Copper Oxide (BSCCO), is disclosed. The first fabrication step is to form an extrudable paste by mixing YBCO or BSCCO superconducting powder with a set of organic additives, which include binder, plasticizers lubricant, dispersant, and a solvent. The following additional steps are performed on both YBCO and BSCCO based wires or rods: (i) using a piston extruder to extrude the superconducting wire or rod; (ii) drying the wire or rod to remove the solvent; and (iii) subjecting the wire or rod to a binder burn-out treatment to remove the remaining organic additives. In addition, YBCO wires and rods also require a sintering step, while BSCCO wires and rods also require cold isostatic pressing and heat treatment steps. The formation of cracks in thicker YBCO and BSCCO based rods during the drying and heating process steps is avoided by extruding hollow rods. The additives, processing parameters, and processing stages used to fabricate the superconducting wires and rods help achieve desired and consistent electrical and mechanical properties.

What is claimed is:  
     
         1 . An extrudable paste used in the fabrication of superconducting wires and rods, comprising: 
 (a) a superconducting powder;    (b) ethyl cellulose;    (c) glycerol;    (d) stearic acid;    (e) triolein; and    (f) a solvent.    
     
     
         2 . The extrudable paste of    claim 1   , wherein said superconducting powder is YBCO or BSCCO.  
     
     
         3 . The extrudable paste of    claim 1   , wherein said solvent is butyl carbitol, ethyl alcohol, or a mixture of butyl carbitol and ethyl alcohol.  
     
     
         4 . The extrudable paste of    claim 3   , wherein said superconducting powder is YBCO or BSCCO.  
     
     
         5 . The extrudable paste of    claim 1   , wherein said superconducting powder consists of particles having sizes of about 2 to 10 μm.  
     
     
         6 . The extrudable paste of    claim 2   , wherein said superconducting powder consists of particles having sizes of about 2 to 10 μm.  
     
     
         7 . The extrudable paste of    claim 3   , wherein said superconducting powder consists of particles having sizes of about 2 to 10 μm.  
     
     
         8 . The extrudable paste of    claim 4   , wherein said superconducting powder consists of particles having sizes of about 2 to 10 μm.  
     
     
         9 . An extrudable paste used in the fabrication of superconducting wire, comprising: 
 (a) superconducting powder;    (b) about 2 to 3 weight percent of ethyl cellulose;    (c) about 0.7 to 0.75 weight percent of glycerol;    (d) about 0.4 to 0.5 weight percent of stearic acid;    (e) about 0.1 weight percent of triolein; and    (f) about 15 to 18 weight percent of solvent.    
     
     
         10 . The extrudable paste of    claim 9   , wherein said superconducting powder is YBCO or BSCCO.  
     
     
         11 . The extrudable paste of    claim 9   , wherein said solvent is butyl carbitol, ethyl alcohol, or a mixture of butyl carbitol and ethyl alcohol.  
     
     
         12 . The extrudable paste of    claim 11   , wherein said superconducting powder is YBCO or BSCCO.  
     
     
         13 . The extrudable paste of    claim 9   , wherein said superconducting powder consists of particles having sizes of about 2 to 10 μm.  
     
     
         14 . The extrudable paste of    claim 10   , wherein said superconducting powder consists of particles having sizes of about 2 to 10 μm.  
     
     
         15 . The extrudable paste of    claim 11   , wherein said superconducting powder consists of particles having sizes of about 2 to 10 μm.  
     
     
         16 . The extrudable paste of    claim 12   , wherein said superconducting powder consists of particles having sizes of about 2 to 10 μm.  
     
     
         17 . An extrusion process for extruding superconducting wires and rods, comprising the steps of: 
 (a) providing a piston extruder comprising a die barrel, an extrusion nozzle, and a ram;    (b) closing said extrusion nozzle;    (c) loading extrudable paste in the form of granules into said die barrel, said extrudable paste comprising superconducting powder, a binder, a plasticizer, a lubricant, a dispersant, and a solvent;    (d) subjecting said die barrel to a vacuum of about 200 millitorr;    (e) compacting said extrudable paste by using said ram to apply a compaction stress of about 100 MPa;    (f) opening said extrusion nozzle; and    (g) extruding a wire or rod through said extrusion nozzle using said ram, said ram moving at a rate of about 0.02 to 0.1 inch/minute.    
     
     
         18 . The extrusion process of    claim 17   , further comprising the step of forming a hollow rod by attaching a mandrel to said ram.  
     
     
         19 . The extrusion process of    claim 17   , wherein said granules of extrudable paste are cubes having sides measuring about 2 to 3 mm.  
     
     
         20 . The extrusion process of    claim 18   , wherein said granules of extrudable paste are cubes having sides measuring about 2 to 3 mm.  
     
     
         21 . The extrusion process of    claim 17   , wherein said dispersant is triolein.  
     
     
         22 . The extrusion process of    claim 18   , wherein said dispersant is triolein.  
     
     
         23 . The extrusion process of    claim 19   , wherein said dispersant is triolein.  
     
     
         24 . The extrusion process of    claim 20   , wherein said dispersant is triolein.  
     
     
         25 . A method of drying a superconducting wire or rod, comprising the steps of: 
 (a) providing a superconducting wire or rod comprising at least superconducting powder, and a solvent;    (b) initially drying said wire or rod in still air at room temperature until about 20% of said solvent is removed; and    (c) subsequently drying said wire or rod in flowing air at a temperature of about 60° C. until all remaining solvent is removed.    
     
     
         26 . The extrusion process of    claim 17   , further comprising the steps of: 
 initially drying said wire or rod in still air at room temperature until about 20% of said solvent is removed; and    subsequently drying said wire or rod in flowing air at a temperature of about 60° C. until all remaining solvent is removed.    
     
     
         27 . The extrusion process of    claim 26   , further comprising the step of forming a hollow rod by attaching a mandrel to said ram.  
     
     
         28 . A method of removing organic additives from a superconducting wire or rod, comprising the steps of: 
 (a) providing a superconducting wire or rod comprising at least superconducting powder and organic additives;    (b) initially heating said wire or rod in flowing oxygen until a temperature of about 100° C. is reached;    (c) subsequently heating said wire or rod in flowing oxygen at a rate in the range of about 6 to 15° C./hour until a temperature of about 300° C. is reached; and    (d) thereafter heating said wire or rod in flowing oxygen at a rate of about 20° C./hour until a temperature of about 500° C. is reached.    
     
     
         29 . The method of    claim 28   , wherein in the temperature range of about 100 to 300° C., if said wire or rod has a diameter less than about 2 mm, said wire or rod is heated, in flowing oxygen, at a rate of about 15° C./hour, while if said wire or rod has a diameter equal to or greater than about 2 mm, said wire or rod is heated, in flowing oxygen, at a rate of about 6° C./hour.  
     
     
         30 . The method of    claim 28   , wherein said flowing oxygen has a flow rate of about 2 liters per minute for about 100 grams of said wire or rod being heated to a temperature of about 300° C., and a flow rate of about an additional 2 liters per minute for each additional 100 grams of said wire or rod being heated to about 300° C., and wherein said flowing oxygen has a flow rate of about 0.25 liters per minute for about 100 grams of said wire or rod being heated at a temperature above about 300° C., and a flow rate of about an additional 0.25 liters per minute for each additional 100 grams of said wire or rod heated about 300° C.  
     
     
         31 . The extrusion process of    claim 26   , further comprising the steps of: 
 initially heating said wire or rod in flowing oxygen until a temperature of about 100° C. is reached;    subsequently heating said wire or rod in flowing oxygen at a rate in the range of about 6 to 15° C./hour until a temperature of about 300° C. is reached; and    thereafter heating said wire or rod in flowing oxygen at a rate of about 20° C./hour until a temperature of about 500° C. is reached.    
     
     
         32 . The extrusion process of    claim 31   , further comprising the step of forming a hollow rod by attaching a mandrel to said ram.  
     
     
         33 . A process for fabricating superconducting wires and rods, comprising the steps of: 
 (a) providing a piston extruder comprising a die barrel, an extrusion nozzle, and a ram;    (b) closing said extrusion nozzle;    (c) loading extrudable paste in the form of granules into said die barrel, said extrudable paste comprising YBCO powder, a binder, a plasticizer, a lubricant, a dispersant, and a solvent;    (d) subjecting said die barrel to a vacuum of about 200 millitorr;    (e) compacting said extrudable paste by using said ram to apply a compaction stress of about 100 MPa;    (f) opening said extrusion nozzle;    (g) extruding a wire or rod through said extrusion nozzle using said ram, said ram extruding said wire or rod at a rate of about 0.02 to 0.1 inch/minute;    (h) initially drying said wire or rod in still air at room temperature until about 20% of said solvent is removed;    (i) subsequently drying said wire or rod in flowing air at a temperature of about 60° C. until all remaining solvent is removed;    (j) initially heating said wire or rod in flowing oxygen until a temperature of about 100° C. is reached;    (k) subsequently heating said wire or rod in flowing oxygen at a rate in the range of about 6 to 15° C./hour until a temperature of about 300° C. is reached;    (l) thereafter heating said wire or rod in flowing oxygen at a rate of about 20° C./hour until a temperature of about 500° C. is reached; and    (m) sintering said wire or rod at about 900° C. in an oxygen atmosphere for about 24 hours.    
     
     
         34 . The extrusion process of    claim 33   , further comprising the step of forming a hollow rod by attaching a mandrel to said ram.  
     
     
         35 . The process of    claim 33   , wherein said dispersant is-triolein.  
     
     
         36 . The process of    claim 33   , further comprising the step of exposing said wire or rod to an oxygen atmosphere at a temperature of about 500° C. for about 24 hours.  
     
     
         37 . A method of achieving a highly oriented, polycrystalline microstructure in superconducting wires or rods, comprising the steps of: 
 (a) providing a superconducting wire or rod;    (b) packing said wire or rod in a flexible container;    (c) placing said container in a support fixture;    (d) applying a first isostatic load to said container to densify said wire or rod;    (e) heating said wire or rod, in an atmosphere of about 9% oxygen and about 91% argon, at a temperature of about 830° C. for about 72 hours;    (f) applying a second isostatic load to said container to densify said wire or rod; and    (g) heating said wire or rod, in an atmosphere of about 9% oxygen and about 91% argon at 840° C. for about 72 hours.    
     
     
         38 . The method of    claim 37   , wherein said superconducting wires or rods comprise BSCCO.  
     
     
         39 . The method of    claim 37   , wherein said first isostatic load is about 40 Ksi, and said second isostatic load is about 60 Ksi.  
     
     
         40 . The method of    claim 38   , wherein said first isostatic load is about 40 Ksi, and said second isostatic load is about 60 Ksi.  
     
     
         41 . The method of    claim 37   , wherein if said superconducting wire or rod has a hollow center, further comprising the step of inserting a mandrel or rod into said hollow center prior to applying an isostatic load to said wire or rod.  
     
     
         42 . A process for fabricating superconducting wires and rods, comprising the steps of: 
 (a) providing a piston extruder comprising a die barrel, an extrusion nozzle, and a ram;    (b) closing said extrusion nozzle;    (c) loading extrudable paste in the form of granules into said die barrel, said extrudable paste comprising BSCCO powder, a binder, a plasticizer, a lubricant, a dispersant, and a solvent;    (d) subjecting said die barrel to a vacuum of about 200 millitorr;    (e) compacting said extrudable paste by using said ram to apply a compaction stress of about 100 MPa;    (f) opening said extrusion nozzle;    (g) extruding a wire or rod through said extrusion nozzle using said ram, said ram extruding said wire or rod at a rate of about 0.02 to 0.1 inch/minute;    (h) initially drying said wire or rod in still air at room temperature until about 20% of said solvent is removed;    (i) subsequently drying said wire or rod in flowing air at a temperature of about 60° C. until all remaining solvent is removed;    (j) initially heating said wire or rod in flowing oxygen until a temperature of about 100° C. is reached;    (k) subsequently heating said wire or rod in flowing oxygen at a rate in the range of about 6 to 15° C./hour until a temperature of about 300° C. is reached;    (l) thereafter heating said wire or rod in flowing oxygen at a rate of about 20° C./hour until a temperature of about 500° C. is reached;    (m) packing said wire or rod in a flexible container;    (n) placing said container in a support fixture;    (o) applying a first isostatic load to said container to densify said wire or rod;    (p) heating said wire or rod, in an atmosphere of about 9% oxygen and about 91% argon, at a temperature of about 830° C. for about 72 hours;    (q) applying a second isostatic load to said container to densify said wire or rod; and    (r) heating said wire or rod, in an atmosphere of about 9% oxygen and about 91% argon at about 840° C. for about 72 hours.    
     
     
         43 . The process of    claim 42   , wherein a mandrel is attached to said ram to form a wire or rod with a hollow center, and further comprising the step of inserting a mandrel or rod into said hollow center prior to applying an isostatic load to said wire or rod.  
     
     
         44 . The process of    claim 42   , wherein said dispersant is triolein.  
     
     
         45 . A superconducting wire or rod which is extruded by the steps of: 
 (a) providing a piston extruder comprising a die barrel, an extrusion nozzle, and a ram;    (b) closing said extrusion nozzle;    (c) loading extrudable paste in the form of granules into said die barrel, said extrudable paste comprising superconducting powder, a binder, a plasticizer, a lubricant, a dispersant, and a solvent;    (d) subjecting said die barrel to a vacuum of about 200 millitorr;    (e) compacting said extrudable paste By using said ram to apply a compaction stress of about 100 MPa;    (f) opening said extrusion nozzle; and    (g) extruding a wire: or rod through said extrusion nozzle using said ram, said ram moving at a rate of about 0.02 to 0.1 inch/minute.    
     
     
         46 . The superconducting wire or rod of    claim 45   , wherein said granules of extrudable paste are cubes having sides measuring about 2 to 3 mm.  
     
     
         47 . The superconducting wire or rod of    claim 45   , wherein said dispersant is triolein.  
     
     
         48 . A hollow superconducting wire or rod which is extruded by the steps of: 
 (a) providing a piston extruder comprising a die barrel, an extrusion nozzle, and a ram having a mandrel attached;    (b) closing said extrusion nozzle;    (c) loading extrudable paste in the form of granules into said die barrel, said extrudable paste comprising superconducting powder, a binder, a plasticizer, a lubricant, a dispersant, and a solvent;    (d) subjecting said die barrel to a vacuum of about 200 millitorr;    (e) compacting said extrudable paste by using said ram to apply a compaction stress of about 100 MPa;    (f) opening said extrusion nozzle; and    (g) extruding a hollow wire or rod through said extrusion nozzle using said ram, said ram moving at a rate of about 0.02 to 0.1 inch/minute.    
     
     
         49 . The hollow superconducting wire or rod of    claim 48   , wherein said granules of extrudable paste are cubes having sides measuring about 2 to 3 mm.  
     
     
         50 . The hollow superconducting wire or rod of    claim 48   , wherein said dispersant is triolein.  
     
     
         51 . A superconducting wire or rod which is fabricated by the steps of: 
 (a) providing a piston extruder comprising a die barrel, an extrusion nozzle, and a ram;    (b) closing said extrusion nozzle;    (c) loading extrudable paste in the form of granules into said die barrel, said extrudable paste comprising YBCO powder, a binder, a plasticizer, a lubricant, a dispersant, and a solvent;    (d) subjecting said die barrel to a vacuum of about 200 millitorr;    (e) compacting said extrudable paste by using said ram to apply a compaction stress of about 100 MPa;    (f) opening said extrusion nozzle;    (g) extruding a wire or rod through said extrusion nozzle using said ram, said ram extruding said wire or rod at a rate of about 0.02 to 0.1 inch/minute;    (h) initially drying said wire or rod in still air at room temperature until about 20% of said solvent is removed;    (i) subsequently drying said wire or rod in flowing air at a temperature of about 60° C. until all remaining solvent is removed;    (j) initially heating said wire or rod in flowing oxygen until a temperature of about 100° C. is reached;    (k) subsequently heating said wire or rod in flowing oxygen at a rate in the range of about 6 to 15° C./hour until a temperature of about 300° C. is reached;    (l) thereafter heating said wire or rod in flowing oxygen at a rate of about 20° C./hour until a temperature of about 500° C. is reached; and    (m) sintering said wire or rod at about 900° C. in an oxygen atmosphere for about 24 hours.    
     
     
         52 . The superconducting wire or rod of    claim 51   , wherein said wire or rod is fabricated in a hollow form by attaching a mandrel to said ram.  
     
     
         53 . The superconducting wire or rod of    claim 51   , wherein said dispersant is triolein.  
     
     
         54 . The superconducting wire or rod of    claim 51   , further comprising the fabrication step of exposing said wire or rod to an oxygen atmosphere at a temperature of about 500° C. for about 24 hours.  
     
     
         55 . A superconducting wire or rod which is fabricated by the steps of: 
 (a) providing a piston extruder comprising a die barrel, an extrusion nozzle, and a ram;    (b) closing said extrusion nozzle;    (c) loading extrudable paste in the form of granules into said die barrel, said extrudable paste comprising BSCCO powder, a binder, a plasticizer, a lubricant, a dispersant, and a solvent;,    (d) subjecting said die barrel to a vacuum of about 200 millitorr;    (e) compacting said extrudable paste by using said ram to apply a compaction stress of about 100 MPa;    (f) opening said extrusion nozzle;    (g) extruding a wire or rod through said extrusion nozzle using said ram, said ram extruding said wire or rod at a rate of about 0.02 to 0.1 inch/minute;    (h) initially drying said wire or rod in still air at room temperature until about 20% of said solvent is removed;    (i) subsequently drying said wire or rod in flowing air at a temperature of about 60° C. until all remaining solvent is removed;    (j) initially heating said wire or rod in flowing oxygen until a temperature of about 100° C. is reached;    (k) subsequently heating said wire or rod in flowing oxygen at a rate in the range of about 6 to 15° C./hour until a temperature of about 300° C. is reached;    (l) thereafter heating said wire or rod in flowing oxygen at a rate of about 20° C./hour until a temperature of about 500° C. is reached;    (m) packing said wire or rod in a flexible container;    (n) placing said container in a support fixture;    (o) applying a first isostatic load to said container to density said wire or rod;    (p) heating said wire or rod, in an atmosphere of about 9% oxygen and about 91% argon, at a temperature of about 830° C. for about 72 hours;    (q) applying a second isostatic load to said container to density said wire or rod; and    (r) heating said wire or rod, in an atmosphere of about 9% oxygen and about 91% argon at about 840° C. for about 72 hours.    
     
     
         56 . The superconducting wire or rod of    claim 55   , wherein said wire or rod is fabricated with a hollow center by attaching a mandrel to said ram, and further comprising the step of inserting a mandrel or rod into said hollow center prior to applying an isostatic load to said wire or rod.  
     
     
         57 . The superconducting wire or rod of    claim 55   , wherein said dispersant is triolein.