Method of producing high temperature superconductor wires

Abstract

A process for producing a superconductor wire by: A. coating the inner surface of a steel tube with a thin layer of silver metal; B. packing the tube with high temperature superconductor ceramic (HTSC) powder; C. sealing the tube; D. cold working the tube to reduce its diameter; E. etching or dissolving away the steel tube to leave a superconductor wire comprising the silver metal coating that was on the inner surface of the steel tube as a thin silver metal sheath which encapsulates the HTSC powder. The superconductor wire can be further treated by sintering or oxygenating the HTSC powder.

What is claimed is: 
     
       1. A method of producing a superconductor wire comprising: A. coating the inside surface of a cylindrical steel tube with a layer of silver metal;   B. packing the steel tube with a high temperature superconducting ceramic powder:   C. sealing the steel tube;   D. cold working the steel tube to reduce its inner diameter to the desired diameter of the superconductor wire; and   E. etching or dissolving away the steel tube with hydrochloric acid to leave a superconductor wire comprising the silver metal coating that was on the inside surface of the steel tube as a thin silver sheath encapsulating the high temperature superconductor ceramic powder.   
     
     
       2. The method of claim 1 wherein in step A the silver metal coating is formed on the inside surface of the steel tube by (1) coating the inside surface of the steel tube with molten AgNO 3  at a temperature above the melting point of AgNO 3  but below the decomposition temperature of AgNO 3  ;   (2) heating the steel tube and molten AgNO 3  coating to a temperature from above the decomposition temperature of AgNO 3  to about 700° C. to decompose the molten AgNO 3  and form a uniform thin layer of silver metal,   (3) repeating steps (1) and (2) until a uniform silver metal coating of the desired thickness is formed on the inside surface of the steel tube.   
     
     
       3. The method of claim 2 wherein the decomposition temperature in step (2) is from 450° C. to 550° C. 
     
     
       4. The method of claim 3 wherein the decomposition temperature in step (2) is from 450° C. to 500° C. 
     
     
       5. The method of claim 1 wherein in step D the inner diameter of the steel tube is reduced to a size that is from about 1/2 to about 1/20 of the original inner diameter. 
     
     
       6. The method of claim 5 wherein the inner diameter of the steel tube is reduced to a size that is from 1/10 to 1/20 of the original inner diameter. 
     
     
       7. The method of claim 1 wherein in step E the steel tube is etched away with concentrated hydrochloric acid. 
     
     
       8. The process of claim 1 wherein after step E the following step F is added F. sintering the high temperature superconductor ceramic powder in the thin silver metal sheathed superconductor wire produced in step E at a temperature of from about 800° C. to 930° C.   
     
     
       9. The process of claim 8 wherein the sintering takes place in pure oxygen. 
     
     
       10. The process of claim 8 wherein after the sintering step F the thin silver metal sheathed superconductor wire is heated at a temperature of from about 450° C. to about 700° C. in pure oxygen to restore the oxygen content of the high temperature superconductor ceramic material. 
     
     
       11. The process of claim 1 wherein after step E the thin silver metal sheathed superconductor wire is heated at a temperature of from about 450° C. to about 700° C. in pure oxygen to restore the oxygen content of the high temperature superconductor ceramic material. 
     
     
       12. The method of claim 2 wherein in step D the inner diameter of the steel tube is reduced to a size that is from about 1/2 to about 1/20 of the original inner diameter. 
     
     
       13. The method of claim 12 wherein the inner diameter of the steel tube is reduced to a size that is from 1/10 to 1/20 of the original inner diameter. 
     
     
       14. The method of claim 2 wherein in step E the steel tube is etched away with concentrated hydrochloric acid. 
     
     
       15. The process of claim 2 wherein after step E the following step F is added F. sintering the high temperature superconductor ceramic powder in the thin silver metal sheathed superconductor wire produced in Step E at a temperature of from about 800° C. to 930° C.   
     
     
       16. The process of claim 15 wherein the sintering takes place in pure oxygen. 
     
     
       17. The process of claim 15 wherein after the sintering step F the thin silver metal sheathed superconductor wire is heated at a temperature of from about 450° C. to about 700° C. in pure oxygen to restore the oxygen content of the high temperature superconductor ceramic material. 
     
     
       18. The process of claim 2 wherein after step E the thin silver metal sheathed superconductor wire is heated at a temperature of from about 450° C. to about 700° C. in pure oxygen to restore the oxygen content of the high temperature superconductor ceramic material.