WO2001017036A2

WO2001017036A2 - Method of producing a superconducting tape

Info

Publication number: WO2001017036A2
Application number: PCT/DK2000/000368
Authority: WO
Inventors: Peder Skov-Hansen
Original assignee: Nordic Superconductor Technologies AS
Current assignee: Nordic Superconductor Technologies AS
Priority date: 1999-07-05
Filing date: 2000-07-05
Publication date: 2001-03-08
Anticipated expiration: 2002-01-05
Also published as: WO2001017036A3; AU5673900A

Abstract

Method of producing a superconducting wire/tape comprising the steps of placing a precursor powder in an Ag or Ag-alloyed tube to form a preform, drawing the preform into a wire, and surrounding the finished wire/tape by a nickel layer. One advantage of completely or partly using a nickel layer instead of a silver layer is that a nickel layer is stronger and thus may be made thinner than a silver layer. As a result the total thickness of the metal layer is reduced. Additionally, nickel is lower in cost than silver. The nickel layer may for instance have a thickness of 0.1 mm.

Description

Title: Method of producing a superconducting tape-

Technical Field

The invention relates to a method of producing a superconducting wire/tape comprising the steps of placing a precursor powder in an Ag or Ag-alloyed tube to form a preform, and drawing the preform into a wire.

Background Art

This method is known as the powder-in-tube method. By this method superconducting wires and tapes having excellent reproducible properties may be produced. A large potential market for Bi-based superconductors produced by the powder-in-mbe method is expected. Especially Bi-2223- and Bi-2212-based tapes have been used for obtaining high-temperature superconducting prototypes, eg for use in cables, magnets, engines, generators, fault current limiters , transformers, and as superconducting energy storage units.

However the cost/performance ratio must to be improved, if the products are to have any commercial interest. A high critical current density J_e (Ic A_(0tai) may improve this ratio. The J_c may be enhanced by increasing the J_c (I_c/A_0xιde) of the superconducting core or by reducing the matrix, in which a plurality of superconducting cores is inserted.

Brief Description of the Invention

The object of the invention is to provide a method for improving the strength properties of oxide superconductors and superconducting composites. Furthermore an oxide superconducting tape is provided having a higher critical current density J_e than hitherto known by reducing the amount of matrix material. A method of the above type is according to the invention characterised in that the finished wire/tape is surrounded by a metal layer stronger than silver and compatible therewith for increasing the mechanical strength. Thus the total thickness of the silver layer and the metal layer is reduced. As a result the J_e is increased at the same time.

In a particularly advantageous embodiment of the invention the wire is furthermore cut, bundled and processed to form a multi-filament before being surrounded by the said metal layer.

It is advantageous to use a metal layer which tolerates thermal stress without being oxidized. As a result the said metal layer may be applied before the heat treatment.

Furthermore according to the invention the used metal layer may be formed of Ni, steel, Cu or CuBe, preferably Ni, Ni tolerating thermal stress without being oxidized.

According to the invention the metal layer may be applied by plating, whereby the metal layer has a substantially uniform thickness.

The applied metal layer may according to the invention may have a thickness of 0.1 mm.

The invention further relates to a superconducting tape produced by the method according to the invention.

Moreover die invention relates to a cable comprising one or more superconducting tapes according to the invention.

The invention also relates to other methods of producing a superconducting tape including continuous methods and thick-film methods. In a particularly advantageous embodiment of the invention the cable according to the invention comprises a circular former to form a cooling duct for a through-flowing coolant, layers of superconducting tape being wound around said former and an inner and outer corrugated tube being arranged around the last layer of superconducting tape with spacers therebetween, the space between the tubes being evacuated to provide a thermal insulation of the superconducting tapes .

Brief Description of the Drawings.

The invention is explained in greater detail below with reference to the accompanying drawings, in which

Fig. 1 illustrates a method of producing a superconducting filament tape,

Fig. 2 is a cross-sectional view of a superconducting filament tape, and

2

Fig. 3 shows a cable, the superconducting filament tape forming part thereof.

Best Mode for Carrying Out the Inventioji

Fig. 1 is a flow chart of a method of producing a superconductor. The oxide precursor powder is fed into an Ag or an Ag-alloyed tube. The precursor powder consists of Bi-2212 and secondary phases. Individual filament wires are bundled to form a bundle. Such a bundling process is performed in a matrix 2 of pure Ag- The bundled wires are then placed in an Ag-alloyed tube 3 to form a bar. The bar is deformed by swaging, drawing or extrusion to form a wire. The wire may then be rolled into a tape, confer Fig. 2.

After the mechanical processing into a tape, a strong material is then either electrolytically or chemically deposited on the tape. The depositing may take place at any time after the processing. The additional outer sheath strengthens the oxide superconductor, whereby the total thickness of the metal layers is reduced and a higher critical current density J_e is obtained at the same time.

The following is an example of a process: A processed BSCCO tape is passed through a chemical bath or an electrolytic bath, in which a plating material, such as Ni, is deposited on the Ag surface. The Ni layer 4 may for instance have a thickness of 0.1 mm. Optionally steel, Cu or CuBe may be deposited. However, Ni is preferable, as it tolerates a subsequent annealing without being oxidized, whereas steel, Cu or CuBe have to be applied subsequent to heat treatment.

Another example is as follows: A green tape, which has not been annealed for conversion of the BSCCO powder into the Bi-2223 superconducting phase, is passed through a chemical or electrolytic bath for depositing of the plating material. The plating material may be deposited on the entire surface or on a portion thereof. The tape is then annealed to produce the finished tape. This method necessitates a plating material, such as Ni, which can tolerate the annealing process in such a manner that the superconducting properties of the tape are not impaired or destroyed. In both above examples the cross section of the finished tape is as shown in Fig. 2. The approximate tape dimensions are as follows: Total width: 4 mm, total thickness 0.25 mm, filament width: 0.2 mm, filament thickness: 0.2 mm and thickness of the outer plated sheath: 0.1 mm. The filament arrangement may be random or oriented in rows and columns. There are approximately 1-1000 filaments in the finished tape.

The superconducting tapes may for instance be used for producing a cable. Fig. 3 illustrates the composition of such a cable. Internally a circular cooling duct 11 is seen for a through-flowing coolant in form of liquid nitrogen. The duct 11 may for instance be formed of a circular former of a diameter of about 3 cm . The former may for instance be made of aluminium, steel, etc. Layers 12, optionally four layers, of superconducting tape are wound around the former. The tapes of each layer 12 are twisted, preferably alternately in opposite directions of each other. The twists render the cable more flexible. By twisting die tapes in different ways, the axial magnetic field is furthermore substantially eliminated. It is, however, not necessary to twist the tapes alternately in opposite directions. The three first layers 12 may for instance be twisted in one direction, while the fourth layer is twisted in the opposite direction. The superconducting tapes are wound so as to substantially abut each other. A minimal space between the adjacent tapes may, however, be present. A layer of plastics may optionally be inserted between the wound layers 12. An inner tube and an outer corrugated tube 14,15, respectively, are arranged after the last layer of superconducting tape. A vacuum is established in the space between the tubes 14, 15 to provide a thermal insulation of the layers 12 of superconducting tapes. The vacuum is maintained by means of pumps arranged along the cable at suitable intervals. Twisted spacers 16 are provided between the tubes 14, 15 to retain the space between said tubes 14, 15. The spacers 16 may be made of plastics. Layers 19 of aluminium film, eg. up 100 layers, are provided under die spacers 16. The corrugation of the tubes 14, 15 serves to render the finished cable more flexible. The tube 15 is provided with a dielectric layer 18 which is not cooled and thus has the same temperature as the surroundings. The dielectric layer 18 may for instance be made of polypropylene. The dielectric 18 is covered by a sheath 20 of copper or lead and yet another sheath 21 of polyethylene.

This cable is used as an underground cable, the space between the layers 14 and 15 being evacuated at suitable intervals. Furthermore, optionally in connection with each suction station, a pump station for the through-flowing liquid nitrogen is arranged at suitable intervals. In connection with the pump station a cooling unit ensures that the circulating liquid nitrogen has the correct temperature at all times.

The cable is for instance able to transmit a current of about 3kA.

Claims

1. Method of producing a superconducting wire/tape comprising the steps of: a) placing a precursor powder in an Ag or Ag alloyed tube to form a preform, b) drawing the preform into a wire, and possible processing of the wire into a tape, c) optionally heat-treating the wire/tape; d) surrounding the finished wire/tape by a metal layer stronger than silver and compatible with silver for increasing the mechanical strength.

2. Method according to claim 1, characterised in that the wire is cut, bundled and processed to form a multi -filament before being surrounded by die said metal layer.

3. A method according to claim 1 or 2, characterised in that a metal layer is used, which is able to withstand thermal stress without being oxidized.

4. Method according to claim 1-3, characterised in that die used metal layer is formed of Ni, steel, Cu or CuBe, preferably Ni, Ni tolerating thermal stress without being oxidized.

5. Method according to claims 1-4, characterised in that the metal layer is applied by plating.

6. Method according to claims 1-5, characterised in that the metal layer is applied in a thickness of about 0.1 mm.

7. Superconducting tape produced by the method according to one or more of the preceding claims.

8. Superconducting tape according to claim 7 used for producing a cable.

9. Cable comprising a circular former (11) for providing a cooling duct for a through-flowing coolant, layers (12) of superconducting tape being wound around said former (11) and an inner tube (14) and an outer corrugated tube (15) being arranged around the last layer of superconducting tape with spacers (16) therebetween, and the space between the tubes (14,15) being evacuated to provide a thermal insulation of the superconducting tape (12).

10. Cable according to claim 9, characterised in that the superconducting tapes in each layer (12) are twisted.

11. Cable according to claim 10, characterised in that the superconducting tapes in each layer (12) are twisted in opposite directions to substantially eliminate the magnetic fields therefrom.

12. Cable according to claims 9-11, characterised in that a layer of plastics is inserted between the wound layers (12) of the superconducting tapes.