JPH0799652B2 - Method for forming niobium-3 / tin superconductor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a niobium-3.tin superconductor having an improved current capacity and an improved niobium-3.tin tape.

[0002]

Superconductivity is the property of certain materials to carry current without resistance. A superconducting material exhibits this property only when its temperature is below the superconducting critical temperature of the material and the material does not experience a magnetic field greater than the material's superconducting critical magnetic field or a current greater than the material's superconducting critical current. Therefore, by making the temperature, the magnetic field, or the current that the superconducting element receives higher than the critical temperature, the magnetic field, or the current, the superconductivity is deactivated (quenched), that is, returned to the resistance state. Depending on the particular material, ie the relative width of its superconducting transition state with respect to temperature, magnetic field or current, the superconducting deactivation occurs rapidly or more slowly.

As is well known, the parent metal of choice, whether pure or containing small amounts of alloying elements (the latter being preferred), is reacted with other metals to give a large ampacity. A superconducting compound or alloy having can be formed. Parent metals such as niobium, tantalum, technetium and vanadium can be reacted or alloyed with reactive metals such as tin, aluminum, silicon and gallium to form superconducting alloys such as niobium 3 tin. The term "niobium 3 tin" used here
Is a superconducting alloy in the form of an intermetallic compound containing about 3 niobium atoms per tin atom. Niobium 3
Tin is a superconductor targeted by the present invention.

It is also known that niobium 3 tin can be improved. In the first method, the parent metal, that is, niobium, is added in a small amount of a solute metal having an atomic diameter larger than the diameter of the parent metal atom by 0.29 angstroms or more. Improves niobium-3 tin by alloying with. U.S. Pat. No. 3,429,032 discloses niobium containing about 25% or less zirconium by heating in the presence of excess tin and a non-metal selected from oxygen, nitrogen and carbon. It is disclosed that tin has an improved critical current. It is also known to alloy reactive metal tin with copper to improve niobium 3 tin.
J. S. Caslaw "Cryogenics" (Cryogenic)
s) (February 1971), pages 57-59, "Improvement of the critical current density in niobium-tin", by reacting niobium with a reactive metal consisting of up to about 45% by weight copper and the balance tin. , Niobium 3 · tin has improved the critical current density.

Niobium 3 tin alloys have been made in various forms, especially in the form of wires and tapes, for the purpose of making devices such as high field superconducting electromagnets. One method of continuously producing superconducting tape involves continuously passing a niobium or niobium alloy tape through a bath of molten reactive metal, such as tin or tin alloy. A thin film of reactive metal from the melting bath adheres to the tape, which is then heated in a reactor to promote the formation of a superconducting alloy on the surface of the parent metal tape.

Since the superconducting alloy formed on the tape is weak and brittle, the outer layer (lamina) of non-superconducting metal is laminated on the tape to form a laminated superconductor. This laminated superconductor is strong and can be wound into a coil without damaging the superconducting material. For example, a relatively thin tape of niobium foil is treated with tin to form a niobium 3 tin adhesion layer on both surfaces of the tape. Copper tapes of approximately the same width are soldered to each of the main surfaces of the superconducting tape to form a symmetrical laminated structure. Since there is a difference in the coefficient of thermal expansion between copper and niobium-niobium-3.tin tape, the brittle intermetallic compound remains under compression even at room temperature, and the risk of mechanical breakage during coil winding is reduced.

The copper outer layer serves several other important functions in the tape. When the current load on the superconducting tape exceeds the critical current density Jc, the tape is forced into a normal resistance state and a large amount of heat is generated, but if this heat is not dissipated quickly, the tape will be damaged. The outer layer of copper is niobium 3.
When tin becomes non-superconducting, it provides an alternative normal current path to reduce the heat generated. The copper outer layer also provides thermal cooling passages to lower the niobium-3.tin below the critical temperature of the superconductor. In order for the copper outer layer to exert such an effect on the superconducting tape, a strong and uniform bond between the niobium-3.tin and the copper outer layer is required.

[0008]

OBJECTS OF THE INVENTION It is an object of the present invention to provide a method for forming a niobium-3.tin superconductor having excellent current capacity. Another object of the invention is to provide good solder bonding between the non-superconducting outer layer and the niobium 3 tin inner layer of the laminated niobium 3 tin tin tape.

[0009]

SUMMARY OF THE INVENTION The method of the present invention forms a niobium 3 tin superconductor having excellent current carrying capacity. The superconducting niobium-3.tin tape is formed by coating the niobium tape with a tin bath and subjecting the coated tape to reaction annealing to form niobium-3.tin. In the method of this invention, the niobium tape is about 5-25% by weight lead, about 5-25%.
Coat with a tin bath consisting essentially of copper by weight and the balance tin. The lead-copper-tin alloy coating promotes rapid formation of particulate niobium 3 tin during the reactive annealing of the coated tape. The fine grain size of niobium 3 tin improves the current capacity of the superconducting tape. The lead-copper-tin alloy coating that remains on the niobium 3 tin after reaction annealing also improves the solder bonding of the non-superconducting outer layer to the niobium 3 tin.

[0010]

Detailed Description Niobium 3 tin tape is well known in the art, for example, IEE Transactions of Magnetics (IEE).
E. Transactions of Magnet
ics) MAG-2, No. 4, December 1966, pp.
760-764. Benz's paper "Superconducting properties of diffusion-treated niobium-tin tape" (Supercond)
uctingProperties of Diffu
sion Processed Niobium-Ti
n Tape).

A method for forming a continuous long niobium 3 tin tape is known, for example, British Patent Nos. 1,3.
42,726 and 1,254,542. This method will be described with reference to FIGS. Niobium tape 2 containing about 5 atomic% or less of a metal selected from the group consisting of zirconium, aluminum, hafnium, titanium and vanadium and about 5000 ppm or less of oxygen, and a molten tin bath containing about 45% by weight or less of copper. The film 4 is formed by bringing them into contact with each other. Alternatively, tin and copper may be separately deposited at least partially on the niobium wire or tape by plating. In addition, tin and copper may be applied electrolytically or chemically to the niobium wire or tape.

About 850-1 coated niobium tape 10
Reactive annealing at 100 ° C. reacts the niobium substrate with the coating to form niobium 3 tin layer 6 on both sides of niobium tape 2. As shown in FIG. 3, the excess film 4'is niobium 3.
Cover tin layer 6. The thickness of the remaining niobium tape 2'is
It is reduced by the reaction with the film forming the niobium 3 / tin layer 6. The non-superconducting outer layer 8 is bonded to the reacted tape, for example by soldering, to form a laminated niobium 3 tin tape 14 with improved strength and formability. For example, solder may be applied to the outer layer 8 and the niobium 3 tin tape 12
To the outer layer 8 and niobium 3 tin tape 12
And are heated to an appropriate soldering temperature to form a laminated niobium-3.tin tape 14.

The method of the present invention will be described with reference also to FIGS. 1-4. The present inventor
When coated to form a coating 4, preferably a tin bath consisting essentially of about 8-10 wt% lead, about 8-10 wt% copper and the balance tin, the coated tape is reactive annealed. It has been found that a niobium 3 / tin layer 6 having an improved current capacity can be formed. Lead on Niobium Tape 2 -Copper-
The tin alloy film 4 is uniform and continuous, and the coating amount is about 0.01
It is preferably −0.03 g / cm ² . Moreover, the residual (extra) coating 4'of the lead-copper-tin alloy remaining on the niobium 3 tin after reaction annealing is obtained by soldering the niobium 3 tin tape 12 to the outer layer 8 to form the laminated niobium 3 -Provides good solder joints when forming the tin tape 14.

The niobium tape 2 contains about 5 atomic% or less of a solute selected from the group consisting of zirconium, hafnium, molybdenum, uranium, rhenium and mixtures thereof, about 1
It is preferably composed of 0 atomic% or less of oxygen, the balance of niobium, and inevitable impurities. Niobium tape is about 1-2
It preferably contains at.% Solute and about 2-4 at.% Oxygen. Oxidation of the niobium tape surface and internal oxidation of the niobium tape is accomplished by conventional means known in the art.
This can be done, for example, as described in British Patent No. 1,342,726. Annealing in an inert atmosphere following anodic oxidation is a suitable means for introducing oxygen into the niobium tape. A suitable niobium tape 2 is about 10-50 microns thick and about 0.076-5 cm wide.

In a suitable anodization process, a conductor, ie niobium tape, is connected as an anode in a suitable electrolytic bath. As a result of electrolytic oxidation, niobium oxide Nb ₂ O ₅ is formed on the surface of the tape.
A film is produced. The tape holding the oxide film is heated in an inert atmosphere such as argon to diffuse oxygen into the tape. A desired concentration of oxygen, eg, about 10 atomic% or less, is diffused into the tape body, leaving the tape surface free of oxides. It is believed that oxygen combines with the solute elements in the tape.

To coat the niobium tape 2, the tape is passed through a molten tin bath of lead-copper-tin alloy. Preferably, the coating 4 is sufficiently thick so that it reacts with up to about 90% of the niobium tape, leaving the remaining (remaining) coating 4'on the niobium 3 tin 6. The coated tape 10 is heat treated in an inert atmosphere for a time sufficient to form the niobium-3.tin superconductor 6, eg, about 20-300 seconds. Preferably, before the niobium tape completely reacts, the reaction annealing is stopped to leave the niobium core 2'supporting the brittle niobium 3 and tin 6 on the niobium tape, and the remaining coating 4 '.
Cover niobium 3 and tin 6.

The reacted tape 12 is soldered between two non-superconducting outer layers 8 of a metal having a coefficient of thermal expansion greater than that of niobium-3.tin, preferably copper. The outer layer 8 is about the same width as the tape 12 and is about 75-150 μm thick. Solder bonding can be performed as shown in FIG. 5, for example. Niobium 3 tin tape 12 and two outer layers 8
Is introduced into the solder bath 20 heated to about 230-250 ° C. The alignment roller symmetrically aligns and contacts the tape 12 with the outer layer 8 in the bath 20. Roller wiper 2
2 to remove excess solder and tape 12
The outer layer 8 and the outer layer 8 are brought into close contact with each other under pressure to form a solder bond therebetween, thus forming a laminated niobium 3 / tin tape 14.

Returning again to FIGS. 3-4, preferably about 3
The outer layer 8 was made of niobium-3.tin tape 1 using a conventional lead-tin solder consisting of 7% by weight of lead and the balance of tin.
Combine to 2. The residual layer 4 ′ of the lead-copper-tin film achieves a good solder bond between the niobium 3 · tin tape 12 and the outer layer 8. The easiness of forming a solder bond and the uniformity and strength of the solder bond are improved by the residual film 4 ′ made of a lead-copper-tin alloy. For example, the use of a lead-copper-tin alloy residual coating 4'can form a solder bond at a lower temperature or in a shorter time than a tin or copper-tin alloy residual coating 4 '. it can. As a result, the outer layer 8 is maintained at a higher strength so that the niobium 3 tin 6 is maintained at a higher compression level, and the laminated niobium 3 tin tape 14 is better formable.

[0019]

Description of Embodiments Other features and effects of the method of the present invention will be shown in the following embodiments. The current densities of the niobium 3 tin tapes formed in the following examples are normal 4 well known in the art.
It was measured by a probe resistance measuring method. Briefly, two voltage probes were soldered to the superconducting tape a short distance apart. The current leads were soldered to the superconducting tape further away from each of the voltage probes.
The niobium 3 tin tape was cooled to 4.2K by cooling with liquid nitrogen and then liquid helium.
A magnet with a magnetic field of about 5 Tesla was positioned on the tape so that the magnetic field was perpendicular to the current path of the superconducting tape. A current was ramped through the tape and the voltage recorded from a probe on the tape. In this test, the critical current was defined as the current that produced a voltage difference of 0.2 μV between the probes.

[0020]

Example 1 A width of about 25 mm, a thickness of about 25 μm, and a thickness of about 1.
Niobium tape containing 0% by weight of zirconium was applied to Teledyne WahCh
ang, Albany, Oregon, USA). To anodize the niobium tape, the tape was passed through an aqueous bath containing about 7 g / liter sodium sulfate heated to about 90 ° C. A potential of 145 V was applied between the tape as the anode and the stainless steel cathode. In this way the tape is about 305 cm / min (10 ft / min) in the bath
Anodized at a rate of. Length of anodized tape about 9
Approximately for tube furnaces with a heating area of 1 cm / min (3 ft)
It was passed at a rate of 61 cm / min (2 ft / min) and heated to 1000 ° C in an argon atmosphere. Niobium oxide on the tape surface was decomposed to form a substantially oxide-free tape surface of metallic niobium and oxygen was diffused inside the tape.

A sample of the internal oxidation tape was used for about 16.6.
Contact was made with a tin bath consisting of copper by weight, balance tin and unavoidable impurities. The tin bath was heated to about 1050 ° C and the tape was placed in the bath at about 305 cm / min (10 ft / min).
Through at a rate of minute), about 0.03 g / cm on the tape surface
^A continuous tin-copper alloy film of 2 was produced. Put the tin coated tape in a tube furnace in an argon atmosphere at 1000-1.
Heat treatment was performed at a temperature in the range of 150 ° C. for various reaction times of 25-600 seconds. The reacted tape had about 2.6-10.8 μm niobium-3.tin reaction layer on each side of the tape and about 1-22 μm unreacted niobium on the core of the tape. Table I shows the measurement characteristics of the reaction temperature, the reaction time, the thickness of niobium-3.tin and the critical current, that is, the current density, for each tape sample.

[0022]

[Table 1] (Table I) Sample reaction temperature Reaction time Jc number (° C) (sec) Thickness (μm) (× 10 ⁵ A / cm ² ) 1 Nb ₃ Sn 5 Tesla 1 1000 150 2.6 7 0.012 1000 300 4.3 10.3 3 1000 500 8.1 9.5 9 4 1000 1000 600 9.7 8.76 5 1050 180 180 6.1 8.04 6 1150 25 2.6 6.25 7 1150 50 4.1 9.15 8 1150 75 75 8.1 6.74 9 1150 100 10.8 7.41

[0023]

Example 2 Niobium 3 was prepared in the same manner as in Example 1 except that the tin bath consisted of about 8.8% by weight copper, 8.8% by weight lead, balance tin and inevitable impurities. A sample of tin superconducting tape was formed. Reaction temperature, reaction time,
The thickness of niobium 3 tin and the measured properties are shown in Table II.

[0024]

(Table 2) (Table II) Sample reaction temperature Reaction time Jc number (° C) (sec) Thickness (μm) (× 10 ⁵ A / cm ² ) 10 1050 150 3.3 11 at Nb ₃ Sn 5 Tesla 0.47 11 1050 200 5.1 10.77 12 1050 250 6.8 11.84 Comparing the data in Tables I and II, the current density of niobium 3 tin formed from the lead-copper-tin alloy coating was found to be copper. It can be seen that it is larger than niobium 3 · tin formed from the tin coating. The excellent ampacity of the niobium 3 tin tape formed by the method of the present invention can be better understood with reference to FIGS. 6 and 7. FIGS. 6 and 7 show the relationship between the current density and the reaction time for the niobium 3 · tin tape formed by reacting the niobium tape coated with the copper-tin alloy and the niobium tape coated with the lead-copper-tin alloy, respectively. ₃ is a graph showing the relationship between the current density and the thickness of the Nb ₃ Sn layer.

Niobium 3 formed by the method of Example 1
The current densities of about 100 samples of tin tape were averaged to obtain the curves indicated by white circles in FIGS. 6 and 7. It can be seen that as the reaction time for the niobium to react with the copper-tin alloy coating increases, the crystal grain grows in the niobium-3.tin layer, so that the current density of niobium-3.tin decreases. But,
A niobium-3.tin superconductor formed by reacting niobium with a lead-copper-tin alloy coating maintains a fine grain size even if the reaction time increases, and has a current density of the conventional niobium-3.tin superconductor. It's getting better.

[Brief description of drawings]

FIG. 1 is a side view of a niobium tape.

FIG. 2 is a side view of a niobium tape coated with a tin alloy.

FIG. 3 is a side view of a reaction-annealed niobium-3.tin tape.

FIG. 4 is a side view of a structure in which a reaction-annealed niobium-3.tin tape is sandwiched between non-superconducting outer layers.

FIG. 5 is a diagram of a coating apparatus including a solder bath illustrating the method of the present invention.

FIG. 6 is a graph showing the relationship between the current density and the reaction time for niobium 3 tin superconductors formed from a niobium tape coated with a copper-tin alloy and a niobium tape coated with a lead-copper-tin alloy. .

FIG. 7 is a graph showing the relationship between the current density and the grain size of niobium 3 tin superconductors formed from a niobium tape coated with a copper-tin alloy and a niobium tape coated with a lead-copper-tin alloy. .

[Explanation of symbols]

 2 Niobium tape 2'Residual niobium tape 4 Coating 4'Residual coating 6 Niobium 3 tin 8 Outer layer 10 Coated niobium tape 12 Niobium 3 tin tape 14 Laminated niobium 3 tin tape 20 Solder bath 22 Roller wiper

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-62-139215 (JP, A) US Patent 3429032 (US, A) UK Patent 1254542 (GB, A) UK Patent 1342726 (GB, A)

Claims (5)

[Claims] 1. A coated niobium tape in tin bath, in triniobium tin superconducting tape forming method comprising the step of forming the coated by reacting tape triniobium tin, about 5-25 weight niobium tape % Tin, about 5-25% by weight copper and the balance tin, a coating of a tin bath consisting essentially of niobium 3 tin superconducting tape. 2. The niobium tape contains about 1-2 atomic% zirconium and about 2-4 atomic% oxygen.
The method for forming the niobium 3 tin superconducting tape according to 1. 3. A method of forming a niobium-3.tin superconducting tape according to claim 1, wherein the niobium-3.tin tape has an excess layer of tin bath coating, which comprises soldering it to a thin copper outer layer. . 4. A tin bath is coated with a niobium tape containing not more than about 5 atomic% of solute and not more than about 10 atomic% oxygen selected from the group consisting of zirconium, hafnium, molybdenum, uranium, rhenium or a mixture thereof. In a method for forming a niobium-3.tin superconducting tape, the method comprising reacting the coated tape to form niobium-3.tin, wherein the niobium tape comprises about 5-25 wt% lead, about 5-25 wt% copper and A method for forming a niobium-3.tin superconducting tape, which comprises coating with a tin bath which substantially consists of the balance of tin. 5. A method of forming a niobium-3.tin superconducting tape according to claim 4, wherein the niobium-3.tin tape has an excess layer of tin bath coating, which is soldered to a copper outer thin layer. .