Formation of bismuth strontium calcium copper oxide superconductors

Patent metadata

Field	Value
Publication number	US-9773962-B2
Application number	US-201314433986-A
Country	US
Kind code	B2
Filing date	Oct 8, 2013
Priority date	Oct 8, 2012
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

A BÏ2212 article may be formed by mixing metallic precursor powders including bismuth, strontium, calcium and copper in an oxygen-free atmosphere, mechanically alloying the metallic precursor powders in an oxygen-free atmosphere, and heating the metallic precursor alloy according to a temperature profile. The profile may include a ramp-up stage during which the alloy is heated to a peak temperature in an oxygen-free atmosphere, a dwell stage during which the alloy is held at the peak temperature for a dwell time, and a ramp-down stage during which the alloy is cooled from the peak temperature. During at least a portion of the dwell stage, the oxygen-free atmosphere is switched to an oxygen-inclusive atmosphere, wherein the alloy is oxidized to form a superconducting oxide, which may be sintered during or after oxidation. The alloy may be formed into a shape, such as a wire, prior to oxidizing.

First claim

What is claimed is:

1. A method for forming a Bi2212 article, the method comprising:
mixing a plurality of metallic precursor powders comprising bismuth, strontium, calcium and copper in an oxygen-free atmosphere;
mechanically alloying the metallic precursor powders in an oxygen-free atmosphere to form a metallic precursor alloy;
heating the metallic precursor alloy according to a temperature profile comprising a ramp-up stage during which the metallic precursor alloy is heated to a peak temperature in an oxygen-free atmosphere, a dwell stage during which the metallic precursor alloy is held at the peak temperature for a dwell time, and a ramp-down stage during which the metallic precursor alloy is cooled from the peak temperature; and
during at least a portion of the dwell stage, switching the oxygen-free atmosphere to an oxygen-inclusive atmosphere, wherein the metallic precursor alloy is oxidized to form a superconducting oxide,
wherein at least a portion of the temperature profile during oxidation or following oxidation is effective for sintering the superconducting oxide.

2. The method of claim 1 , wherein mechanically alloying is done under an operating condition sufficient to form one or more intermetallic compounds in the metallic precursor alloy.

3. The method of claim 2 , wherein the operating condition is selected from the group consisting of slurry milling with mineral oil, dry powder milling under an oxygen-free atmosphere, cryogenically, and high-energy ball milling.

4. The method of claim 2 , wherein the one or more intermetallic compounds comprise a bismuth-inclusive pre-alloy.

5. The method of claim 2 , wherein the one or more intermetallic compounds are selected from the group consisting of bismuth-strontium, bismuth-calcium, and both bismuth-strontium and bismuth-calcium.

6. The method of claim 1 , comprising integrating a ceramic powder into the metallic precursor alloy.

7. The method of claim 6 , wherein integrating comprises performing a step selected from the group consisting of: mixing the ceramic powder with the metallic precursor powders, followed by mechanically alloying the ceramic powder together with the metallic precursor powders; and after mechanically alloying the metallic precursor powders to form the metallic precursor alloy, mechanically alloying or grinding the ceramic powder with the metallic precursor alloy.

8. The method of claim 6 , wherein the ceramic powder is selected from the group consisting of zirconia, alumina, silicon nitride, magnesium oxide, and a combination of two or more of the foregoing.

9. The method of claim 6 , wherein, after integrating, the amount of the ceramic in the metallic precursor alloy ranges from 1 to 20% molar fraction.

10. The method of claim 1 , comprising integrating a noble metallic dopant into the metallic precursor alloy.

11. The method of claim 10 , wherein integrating comprises performing a step selected from the group consisting of: mixing the noble metallic dopant with the metallic precursor powders, followed by mechanically alloying the noble metallic dopant together with the metallic precursor powders; and after mechanically alloying the metallic precursor powders to form the metallic precursor alloy, mechanically alloying or grinding the noble metallic dopant with the metallic precursor alloy.

12. The method of claim 10 , wherein the noble metallic dopant is selected from the group consisting of silver, gold, platinum, palladium, and a combination of two or more of the foregoing.

13. The method of claim 10 , wherein, after integrating, the amount of the noble metallic dopant in the metallic precursor alloy ranges from 1 to 50% by weight.

14. The method of claim 1 , wherein the temperature profile comprises a first ramp-up stage during which the metallic precursor alloy is heated to an intermediate temperature, and a first dwell stage during which the metallic precursor alloy is held at the intermediate temperature, and a second ramp-up stage following the first dwell stage during which the metallic precursor alloy is heated from the intermediate temperature to the peak temperature, and wherein the during which the metallic precursor alloy is held at the peak temperature is a second dwell stage.

15. The method of claim 14 , comprising initiating oxidation occurs during the first dwell stage.

16. The method of claim 1 , comprising, before oxidizing, forming the metallic precursor alloy into a shape.

17. The method of claim 16 , wherein forming the metallic precursor alloy into the shape comprises extruding or drawing the metallic precursor alloy into a wire.

18. The method of claim 17 , wherein the density of the metallic precursor alloy in the wire is 90% of theoretical density or greater.

19. The method of claim 17 , wherein the wire has a diameter ranging from 0.5 mm to 3 mm.

20. The method of claim 17 , wherein forming the metallic precursor alloy into the shape comprises packing the metallic precursor alloy into a sheath comprising silver or a silver alloy, and extruding the metallic precursor alloy and the sheath into a composite wire comprising a core of the metallic precursor alloy and a cladding of the silver or the silver alloy.

21. The method of claim 17 , wherein forming the metallic precursor alloy into the shape comprises drawing the metallic precursor alloy into a monofilament rod, cutting the monofilament rod into a plurality of shorter-length rods, packing a parallel arrangement of the shorter-length rods into a sheath comprising silver or a silver alloy, and extruding the metallic precursor alloy and the sheath into a composite wire comprising a core of the metallic precursor alloy and a cladding of the silver or the silver alloy.

22. The method of claim 16 , wherein forming the metallic precursor alloy into the shape is done in an oxygen-free atmosphere.

23. The method of claim 16 , wherein forming the metallic precursor alloy into the shape comprises forming the metallic precursor alloy into a plate, a tape, a film, a rod, a wire having a round cross-section, or a wire having a polygonal cross-section.

24. The method of claim 1 , wherein the metallic precursor powders have a characteristic dimension ranging from 0.1 μm to 1000 μm.

25. The method of claim 1 , comprising, prior to mixing, grinding the strontium powders to reduce a characteristic dimension thereof.

26. The method of claim 1 , wherein the oxygen-free atmosphere has a composition selected from the group consisting of a noble gas, nitrogen, helium, or a combination of two or more of the foregoing.

27. The method of claim 1 , wherein mechanically alloying comprises ball milling or high-energy ball milling.

28. The method of claim 1 , wherein mechanically alloying comprises loading the metallic precursor powders into a ball mill vial, and vibrating the ball mill at a rate ranging from 850 cycles/minute to 1100 cycles/minute for a duration ranging from 10 hours to 50 hours.

29. The method of claim 1 , wherein mechanically alloying is done at a temperature ranging from 77 K to 320 K.

30. The method of claim 1 , wherein mixing and mechanically alloying comprises mechanically alloying two or more of the bismuth, strontium, calcium and copper powders to form an intermetallic compound, mixing the intermetallic compound with the other metallic precursor powders, and mechanica

Assignees

• Univ North Carolina State

Inventors

• Schwartz Justin
• Koch Carl C
• Zhang Yun
• Liu Xiaotao

Classifications

• B22F2009/044

  by jet milling · CPC title

• B22F5/12

  of wires {(of tubes B22F5/10)} · CPC title

• B22F2009/041

  by mechanical alloying, e.g. blending, milling · CPC title

• B22F2999/00

  Aspects linked to processes or compositions used in powder metallurgy · CPC title

• B22F9/04

  starting from solid material, e.g. by crushing, grinding or milling ({C22C1/1084 takes precedence}; crushing, grinding or milling, in general, see the relevant subclasses, e.g. B02C) · CPC title