WO2022259803A1 - Nb3Sn超伝導線材とNbTi線材との超伝導接続構造体、その製造方法、および、それを用いた核磁気共鳴装置 - Google Patents
Nb3Sn超伝導線材とNbTi線材との超伝導接続構造体、その製造方法、および、それを用いた核磁気共鳴装置 Download PDFInfo
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- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 4
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- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims description 3
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- 238000005253 cladding Methods 0.000 claims 1
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Images
Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
- H02G1/00—Methods or apparatus specially adapted for installing, maintaining, repairing or dismantling electric cables or lines
- H02G1/14—Methods or apparatus specially adapted for installing, maintaining, repairing or dismantling electric cables or lines for joining or terminating cables
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F6/00—Superconducting magnets; Superconducting coils
- H01F6/06—Coils, e.g. winding, insulating, terminating or casing arrangements therefor
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
- H01R4/00—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation
- H01R4/58—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation characterised by the form or material of the contacting members
- H01R4/68—Connections to or between superconductive connectors
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
- H02G15/00—Cable fittings
- H02G15/34—Cable fittings for cryogenic cables
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N60/00—Superconducting devices
- H10N60/01—Manufacture or treatment
- H10N60/0184—Manufacture or treatment of devices comprising intermetallic compounds of type A-15, e.g. Nb3Sn
Definitions
- the present invention relates to a superconducting connection structure of a Nb 3 Sn superconducting wire and an NbTi wire, a method for producing the same, and an NMR spectrometer using the same.
- NbTi is a body-centered cubic Nb alloy in which Ti is dissolved in a solid solution, it is ductile and sticky, and it is known that it is possible to realize superconducting connections even by mechanical pressure welding.
- Patent Document 1 See, for example, Patent Document 1).
- Nb 3 Sn is an A15-type compound crystal composed of Nb atoms and Sn atoms at a ratio of 3:1, and is hard and brittle without ductility. Therefore, joining by a mechanical method was impossible.
- Patent Document 2 discloses superconducting connection technology using low-melting-point superconducting solder instead of mechanical joining.
- Patent Document 2 at the ends of the NbTi and Nb 3 Sn multifilamentary wires, the Cu matrix embedding the superconducting filaments is melted with molten Sn or Sn alloy, and the filaments are coated with Sn. Next, the ends of both wires are immersed in molten Pb--Bi to replace Sn with Pb--Bi.
- Non-Patent Document 1 describes a superconducting bonding technique using Wood metal (50% Bi-24% Pb-14% Sn-12% Cd), Pb-In, and Sn-In as another low melting point superconducting solder. Although disclosed, most of those having a relatively high critical magnetic field that can be used practically contain Pb and Cd, which are environmentally hazardous substances.
- Non-Patent Document 2 the Nb-4at%Ta-1at%Hf alloy with 1at% Hf and 4at% Ta was still dense even after heat treatment at 900 ° C. It is Furthermore, according to FIG. 2 of Non-Patent Document 2, when the recovery and recrystallization temperatures of an Nb—Hf alloy to which only Hf was added were examined, it was reported that the recovery temperature greatly exceeded 600°C. there is
- Non-Patent Document 2 is limited to a mere structure control study of Nb 3 Sn itself, and superconducting connections between dissimilar superconducting materials (for example, superconducting connections between Nb 3 Sn superconducting wires and NbTi wires). It did not provide any teaching or suggestion regarding conductive connection).
- An object of the present invention is to provide a completely new superconducting connection structure of a Nb 3 Sn superconducting wire and an NbTi wire that exceeds conventional ideas, a method for producing the same, and a core using the same, which does not contain substances of environmental concern such as Pb and Cd. It is to provide a magnetic resonance apparatus.
- the superconducting connecting structure of the present invention comprises a connecting strip having a Nb alloy strip to which an M element is added (here, the M element is an element that increases the recovery temperature and recrystallization temperature of Nb), Nb a Nb3Sn superconducting wire with a 3Sn superconducting core and a NbTi wire with a NbTi core , wherein one end of the connecting strip is connected to the Nb alloy strip and the Nb3Sn superconducting core. is connected to the Nb 3 Sn superconducting wire through the Nb 3 Sn superconducting layer, and the other end of the connecting strip is connected to the new surface of the Nb alloy strip and the NbTi core material.
- the M element may be at least one selected from the group consisting of hafnium (Hf), titanium (Ti), tantalum (Ta), zirconium (Zr), and tungsten (W).
- the Nb alloy strip may have any one shape selected from the group consisting of a core material, a sheet and a pipe.
- strip as used in the present application refers to a strip that is elongated, thin, and shaped like a core, sheet, pipe, or the like.
- the M element may be added in a range of 0.2 at % or more and 10 at % or less (here, at % means atomic % of the M element contained in the Nb alloy strip). .
- the portion where the Nb alloy strip and the Nb 3 Sn superconducting core material contact through the Nb 3 Sn superconducting layer, and the portion where the new surface of the Nb alloy strip and the new surface of the NbTi core material contact each other may each be covered with a crimp tube made of at least one material selected from the group consisting of tantalum (Ta), niobium (Nb), copper-nickel alloy (CuNi), and stainless steel.
- the length of the covered portion may have a length in the range of 10 mm to 30 mm.
- the connecting strip comprises the Nb alloy strip coated and/or embedded with a first stabilizing material
- the Nb 3 Sn superconducting wire comprises the Nb 3 Sn superconducting core as a second stabilizing material.
- the NbTi wire is formed by covering and/or embedding the NbTi core material with a third stabilizing material, and the first to third stabilizing materials are each , a copper metal, a copper alloy, a silver metal, and at least one metal selected from the group consisting of a silver alloy.
- the method for producing the above superconducting connection structure of the present invention is a connection strip having a Nb alloy strip to which an M element is added (wherein the M element is an element that increases the recovery temperature and recrystallization temperature of Nb).
- a) and a Nb 3 Sn superconducting wire having a Nb 3 Sn superconducting core, the other end of the connecting strip and the NbTi core a second step of connecting a NbTi wire having a NbTi wire, wherein the first connecting step includes exposing the Nb alloy strip from one end of the connecting strip; exposing the Nb core from one end of a Nb 3 Sn superconducting precursor wire embedded in a base material containing Sn; exposing the exposed Nb alloy strip; and exposing the Nb core.
- the second connecting step includes exposing the Nb alloy strip from the other end of the connecting strip; and exposing the NbTi strip from one end of the NbTi wire. exposing a core material, bundling the exposed Nb alloy strip and the exposed NbTi core material, and crimping the bundled Nb alloy strip and the NbTi core material, This solves the above problem.
- the step of exposing the Nb alloy strip in the first connecting step and the second connecting step may use chemical corrosion.
- the step of exposing the Nb core material in the first connecting step may use chemical corrosion.
- the step of exposing the Nb core material in the first connecting step may further perform mechanical polishing.
- the step of exposing the NbTi core material in the second connecting step may use chemical corrosion.
- the step of exposing the core material may each expose a length ranging from 10 mm to 30 mm.
- the crimping step in the first connecting step may expose new surfaces of the Nb alloy strip and the Nb core material, and bring the new surface of the Nb alloy strip and the new surface of the Nb core into close contact. .
- the step of crimping in the first connecting step includes forming the bound portion of the Nb alloy strip and the Nb core material from tantalum (Ta), niobium (Nb), copper-nickel alloy (CuNi), and stainless steel.
- the bundled Nb alloy strip and the Nb core may be covered with a crimp tube made of at least one material selected from the group consisting of the bundled Nb alloy strips and the Nb core material in a vertical direction to the longitudinal direction thereof.
- the pressure may range from 100 MPa to 1 GPa.
- the heat-treating step in the first connecting step includes heat-treating the connecting strip and the Nb 3 Sn superconducting precursor wire in a vacuum or an inert gas atmosphere at a temperature range of 600° C.
- the step of heat-treating in the first connecting step includes heating the connecting strip and the Nb 3 Sn superconducting precursor wire in a vacuum or inert gas atmosphere at a temperature range of 300° C. or higher and 500° C. or lower for 50 hours.
- a heat treatment may be performed for a time of 150 hours or less, and then a heat treatment in a temperature range of 600° C. or more and 800° C. or less for a time of 50 hours or more and 150 hours or less.
- the crimping step in the second connecting step may expose new surfaces of the Nb alloy strip and the NbTi core material, and bring the new surface of the Nb alloy strip and the new surface of the Nb core material into close contact. .
- the step of crimping in the second connecting step includes forming the bound portion of the Nb alloy strip and the NbTi core material from tantalum (Ta), niobium (Nb), copper-nickel alloy (CuNi), and stainless steel.
- a crimp tube made of a material selected from the group consisting of a crimp tube may be coated to apply pressure perpendicular to the longitudinal direction of the bundled Nb alloy strip and NbTi core. The pressure may range from 100 MPa to 1 GPa.
- the new surface in the present application means a metal surface in an active state that does not have an oxide film or the like and is not exposed to the atmosphere.
- a nuclear magnetic resonance apparatus of the present invention uses the superconducting connection structure described above (that is, the nuclear magnetic resonance apparatus of the present invention including the superconducting connection structure) to solve the above problems.
- the superconducting connection structure of the present invention uses an M element-added Nb alloy strip to connect a Nb 3 Sn superconducting wire and an NbTi wire.
- the addition of the M element increases the recovery and recrystallization temperature of Nb, so that the superconducting properties of the Nb alloy strip are not degraded even by the high temperature heat treatment (specifically, the heat treatment that produces the Nb 3 Sn layer).
- the high temperature heat treatment specifically, the heat treatment that produces the Nb 3 Sn layer.
- one end of the Nb alloy strip can be connected to the Nb 3 Sn superconducting wire through the newly formed Nb 3 Sn superconducting layer by diffusion bonding.
- the other end of the Nb alloy strip is mechanically connected to the NbTi wire, so that it can be connected to the NbTi without degrading the properties of the NbTi wire.
- the above-described method for manufacturing a superconducting connection structure of the present invention comprises: one end of a connection strip having a Nb alloy strip to which M element is added; and a Nb3Sn superconducting wire having a Nb3Sn superconducting core. and a second step of connecting the other end of the connecting strip and the NbTi wire with the NbTi core. Since the Nb alloy strip in which the recovery and recrystallization temperature of Nb are increased by the addition of the M element is used, the properties of the Nb alloy strip are not deteriorated even by heat treatment, and the Nb 3 Sn superconducting precursor wire is converted to superconducting Nb 3 Sn.
- a conductive wire can be produced, and the Nb alloy strip and the Nb 3 Sn superconducting wire can be joined through the Nb 3 Sn superconducting layer produced on the Nb alloy strip. Subsequently, the Nb alloy strip and the NbTi wire can be mechanically joined, so that the Nb 3 Sn superconducting wire and the NbTi wire can be superconductively joined without using environmentally hazardous substances such as Pb and Cd. can.
- FIG. 1 is a schematic diagram showing an exemplary morphology of a Nb alloy strip;
- FIG. 2(A) shows when the form of the Nb alloy strip is a core material
- FIG. 2(B) shows when the form of the Nb alloy strip is a sheet
- FIG. FIG. 4 is a schematic diagram of the alloy strip in the form of a pipe
- FIG. 2 is a diagram schematically showing a Nb 3 Sn superconducting wire and an NbTi wire
- FIG. 3A is a diagram schematically showing a cross section of the Nb 3 Sn superconducting wire
- FIG. 3B is a diagram schematically showing a cross section of the NbTi wire. It is a flowchart of the process of manufacturing the superconducting connection structure of the present invention.
- FIG. 2 is a diagram schematically showing an exemplary Nb 3 Sn superconducting precursor wire used for manufacturing the superconducting connecting structure of the present invention;
- FIG. 5A includes an Nb core material, a Cu—Sn base material (that is, a base material made of an alloy of Cu and Sn), a diffusion barrier layer, and a stabilizer, and the Nb core material is a Cu—
- FIG. 5(B) is an exemplary schematic diagram of a Nb 3 Sn superconducting precursor wire embedded in a Sn matrix, FIG. FIG.
- FIG. 2 is an exemplary schematic diagram of a Nb 3 Sn superconducting precursor wire provided with an encapsulant and a Nb core embedded only in a Cu matrix; 4 is a flow chart of a first connection process; It is the procedure of the first connection step. 10 is a flow chart of a second connection process; It is the procedure of the second connection step. It is a figure which shows the critical current characteristic before and behind the heat processing of NbTi wire (reference example).
- FIG. 3 is a graph showing critical current characteristics before and after heat treatment of an Nb--Ta--Hf wire (reference example);
- FIG. 3 is a view showing the results of electron microscope observation of a cross section of a joint portion between a connection strip of a superconducting connection structure and a Nb 3 Sn superconducting wire.
- FIG. 12(A) is a view showing the results of electron microscopic observation of the cross section of the connecting portion between the connecting strip (that is, the Nb--Ta--Hf wire) and the Nb 3 Sn superconducting core material.
- (B) is a diagram showing Nb mapping of the connection portion
- FIG. 12(C) is a diagram showing a backscattered electron image of the connection portion
- FIG. 12(D) is Sn mapping of the connection portion.
- FIG. 3 is a diagram showing critical current characteristics of the superconducting connection structure of Example 1.
- FIG. FIG. 10 is a diagram showing critical current characteristics of the superconducting connection structure of Example 2;
- FIG. 1 is a schematic diagram showing the superconducting connection structure of the present invention.
- a superconducting connection structure 100 of the present invention includes a connection strip 120 having an Nb alloy strip 110 to which the M element is added, a Nb 3 Sn superconducting wire 130 and an NbTi wire 140, and the Nb alloy strip 110 provides Nb 3 Sn superconducting wire 130 and NbTi wire 140 are connected.
- the Nb alloy strip 110 is characterized in that the addition of the M element increases the recovery temperature and recrystallization temperature of Nb.
- the degree of the increase is not particularly limited as long as the recovery temperature and recrystallization temperature of Nb are increased to the generation temperature of Nb 3 Sn (specifically, 600° C.) or higher.
- the Nb 3 Sn superconducting wire 130 has a Nb 3 Sn superconducting core 150 and the NbTi wire 140 has an NbTi core 160 .
- One end of the connecting strip 120 is connected to the Nb 3 Sn superconducting wire 130 by contacting the Nb alloy strip 110 and the Nb 3 Sn superconducting core 150 through the Nb 3 Sn superconducting layer 170 .
- the Nb 3 Sn superconducting layer 170 may be a layer forming the Nb 3 Sn superconducting core 150 or a layer formed on the surface of the Nb alloy strip 110 .
- the other end of the connecting strip 120 is connected to the NbTi wire rod 140 by bringing the new surface of the Nb alloy strip 110 and the new surface of the NbTi core material 160 into contact with each other.
- the nascent surface is intended to be a metal surface in an active state that does not have an oxide film or the like and is not exposed to the atmosphere, and contact between nascent surfaces can be evaluated from the critical current characteristics. can.
- the inventors of the present application have found that if the Nb alloy strip 110 with increased recovery temperature and recrystallization temperature is used, the superconducting connection structure 100 in which the Nb 3 Sn superconducting wire 130 and the NbTi wire 140 are connected by the manufacturing method described later. I have found that I can provide
- the M element is not particularly limited as long as it increases the recovery and recrystallization temperature of Nb, but preferably hafnium (Hf), titanium (Ti), tantalum (Ta), zirconium (Zr), and tungsten At least one element selected from the group consisting of (W). Among them, Hf is preferable. Since Hf can increase the recovery and recrystallization temperature of Nb by 200° C., it is advantageous in the manufacturing method described below.
- the amount of the M element added is not limited as long as it does not impair the superconducting properties of the Nb alloy, but is preferably 0.2 at% or more and 10 at% or less. If it is 0.2 at % or more, a critical magnetic field of 0.2 T or more can be obtained, which is advantageous for practical use, which is preferable. If it is 10 at % or less, it is possible to avoid difficulty in dissolving into the Nb alloy, which is preferable. From the viewpoint of recovery of Nb, increase in recrystallization temperature, and critical magnetic field, the amount of M element added is more preferably in the range of 1 at% to 6 at%, and more preferably 1.5 at% to 3 at%. Range. When the M element consists of a plurality of elements, the total addition amount of each element should be within the above range.
- the content of M element in the Nb alloy is measured by energy dispersive X-ray spectroscopy (EDS).
- the connecting strip 120 preferably comprises a first stabilizer 210 (FIG. 2) coating the Nb alloy strip 110 .
- the first stabilizing material is made of a normal-conducting metal material, and can easily divert the current and stabilize it even by thermal disturbance or the like.
- the first stabilizer 210 may preferably be made of a material selected from the group consisting of copper metal, copper alloy, silver metal, and silver alloy. All of these are known as normal-conducting metallic materials. Among them, copper metal is preferable from the viewpoint of price and workability.
- FIG. 2 is a schematic diagram showing an exemplary form of the Nb alloy strip.
- FIG. 2(A) shows a case where the form of the Nb alloy strip is the core material 110a, but the form of the Nb alloy strip is not limited to the core material (multifilamentary wire).
- the form of the Nb alloy strip may be a sheet 110b as shown in FIG. 2(B), and the form of the Nb alloy strip may be a pipe 110c as shown in FIG. 2(C).
- FIG. 2 shows how each shape (form) of Nb alloy strip is coated with a first stabilizer 210 .
- the form of the Nb alloy strip is the core material 110a, it is advantageous in suppressing a thermal runaway phenomenon peculiar to superconductors called magnetic flux jump.
- the form of the Nb alloy strip is a sheet 110b, the Nb core material that becomes the Nb 3 Sn superconducting core material 150 in the manufacturing process described later can be folded and bundled with the sheet 110b. It is advantageous because it can
- the form of the Nb alloy strip is a pipe 110c, the Nb core material that will become the Nb 3 Sn superconducting core material 150 in the manufacturing process described later can be bundled simply by passing it through the pipe 10c. It is advantageous because it can
- FIG. 3 is a diagram schematically showing a Nb 3 Sn superconducting wire and a NbTi wire.
- FIGS. 3A and 3B show cross sections of the Nb 3 Sn superconducting wire and the NbTi wire, respectively.
- the Nb 3 Sn superconducting wire 130 may have a multifilamentary Nb 3 Sn superconducting core 150 covered with and/or embedded in the second stabilizer 310 .
- the Nb 3 Sn superconducting wire 130 may be a commonly used Nb 3 Sn superconducting wire obtained by heat-treating a Nb 3 Sn precursor wire described later.
- the second stabilizing material 310 may comprise a normal metallic material, preferably a material selected from the group consisting of copper metal, copper alloys, silver metals and silver alloys.
- the Nb 3 Sn superconducting wire 130 may comprise a diffusion barrier layer 320 .
- the diffusion barrier layer 320 can prevent elemental diffusion during manufacture by heat treatment from the Nb 3 Sn precursor wire described below.
- Such diffusion barrier layers 320 may consist of tantalum (Ta), niobium (Nb), and alloys thereof. These materials more preferably suppress the diffusion of Sn and Nb.
- the NbTi wire 140 may have a multifilamentary NbTi core 160 covered with and/or embedded in the third stabilizer 330 .
- the third stabilizing material 330 may consist of a normal-conducting metallic material, preferably a material selected from the group consisting of copper metal, copper alloys, silver metals, and silver alloys. Note that the first to third stabilizers may be different or the same.
- NbTi core material 160 a commonly used and available NbTi core material can be adopted, but preferably the composition of Ti in the NbTi alloy satisfies the range of 8 at% or more and 90 at% or less. Within this range, wire drawing is possible and higher properties can be maintained.
- the composition of Ti in the NbTi alloy more preferably satisfies the range of 50 at % or more and 70 at % or less.
- the portion where the Nb alloy strip 110 and the Nb 3 Sn superconducting core material 150 contact through the Nb 3 Sn superconducting layer 170, and the Nb alloy strip A portion where the new surface of 110 and the new surface of the NbTi core material 160 contact each other may be covered with a crimp tube 180 as shown in FIG. This facilitates joining of the Nb alloy strip 110 and the Nb 3 Sn superconducting core material 150 and joining of the Nb alloy strip 110 and the NbTi core material 160 in the manufacturing method described later.
- the crimp tube 180 is not particularly limited as long as it has a Vickers hardness of 60 Hv or more, but examples include tantalum (Ta), niobium (Nb), copper-nickel alloy (CuNi), and stainless steel. consisting of a material selected from the group consisting of These materials have a Vickers hardness of 60 Hv or more and 300 Hv or less. Furthermore, in joining the Nb alloy strip 110 and the Nb 3 Sn superconducting core 150, in a situation where the crimp tube 180 and the Nb 3 Sn superconducting core 150 are in direct contact, reaction during heat treatment is suppressed. Therefore, tantalum (Ta) is desirable as the material for the crimp tube 180 .
- the length of the portion that is in contact and covered (specifically, the length of the crimp tube 180) is preferably in the range of 10 mm or more and 30 mm or less. Within this range, good superconducting properties can be obtained with sufficient contact.
- the lengths of the contacting and covered portions are more preferably in the range of 10 mm or more and 20 mm or less and in the range of 15 mm or more and 25 mm or less, respectively.
- the superconducting connection structure 100 of the present invention does not use environmentally hazardous substances such as Pb and Cd, and maintains a high critical current even in a magnetic field environment of 0.5 T to 1.0 T. Since the Nb 3 Sn superconducting wire 130 and the NbTi wire 140 are connected, it is also applicable to a high magnetic field nuclear magnetic resonance apparatus (NMR). In particular, since the superconducting connection structure 100 of the present invention does not use environmentally hazardous substances, there is no need to apply for exemption from the RoHS Directive (Restriction of Hazardous Substances Directive). Therefore, it is possible to significantly reduce the NMR manufacturing cost.
- the superconducting connection structure of the present invention preferably satisfies critical current characteristics of at least 50 A or more in a magnetic field environment of 0.6 T at 4.2K.
- FIG. 4 is a flowchart of steps for manufacturing the superconducting connecting structure of the present invention.
- Step S410 Connect one end of the connecting strip with the Nb alloy strip doped with M element and the Nb 3 Sn superconducting wire with the Nb 3 Sn superconducting core.
- Step S420 Connect the other end of the connecting strip with the NbTi wire with the NbTi core.
- the superconducting bonded structure 100 of the present invention is manufactured by the first connecting step of step S410 and the second connecting step of step S420.
- connection strip having the Nb alloy strip to which the M element is added and the NbTi wire rod having the NbTi core material have already been described with reference to FIG. 1, so description thereof will be omitted.
- a Nb 3 Sn superconducting wire can be produced from the Nb 3 Sn superconducting precursor wire (FIG. 5) described later, and the Nb alloy strip and Nb 3 Sn are connected via the Nb 3 Sn superconducting layer formed on the Nb alloy strip. A superconducting wire can be joined.
- the Nb alloy strip and the NbTi wire can be mechanically joined, so that the Nb 3 Sn superconducting wire and the NbTi wire can be connected without containing environmentally hazardous substances such as Pb and Cd. can be superconductingly bonded.
- a Nb 3 Sn superconducting precursor wire is used.
- the Nb 3 Sn superconducting precursor wire described above can be adopted, and such Nb 3 Sn superconducting precursor wire is commercially available.
- FIG. 5 is a diagram schematically showing an exemplary Nb 3 Sn superconducting precursor wire used for manufacturing the superconducting connecting structure of the present invention.
- the Nb core material 510 may be embedded in the Cu—Sn base material 520a.
- the Cu—Sn base material 520a is made of an alloy of Cu and Sn, and the Sn content preferably satisfies the range of 5 at % or more and 10 at % or less. Within this range, it reacts with the Nb core material 510 to form the Nb 3 Sn superconducting core material 150 (FIG. 1), which has wire workability.
- the Nb 3 Sn superconducting precursor wire 500a may preferably comprise a diffusion barrier layer 530 around the Cu—Sn matrix 520a.
- Diffusion barrier layer 530 may consist of tantalum (Ta), niobium (Nb), and alloys thereof.
- the Nb 3 Sn superconducting precursor wire 500a may preferably comprise a stabilizer 540 around the Cu—Sn matrix 520a.
- the stabilizing material 540 is the same material as the second stabilizing material 310 described above.
- the Nb 3 Sn superconducting precursor wire 500b shown in FIG. 5B is provided with a Cu base material 520b and a Sn base material 550 separately, and the Nb core material 510 is embedded only in the Cu base material 520b. , different from the Nb 3 Sn superconducting precursor wire 500a of FIG. 5(A).
- the base material in which the Nb core material is embedded is divided into a Cu base material and a Sn base material, the Nb core material is embedded in the base material containing Cu and Sn.
- the embodiment of "base material containing at least Cu and Sn" in the specification of the present application includes an embodiment containing at least Cu and Sn in the same base material (that is, containing Cu) as shown in FIG.
- the base material containing at least Cu and the base material containing Sn are separated. etc. are also included. Therefore, as a mode in which "the Nb core material is embedded in a base material containing at least Cu and Sn", as shown in FIG.
- the Nb core material is a Cu- In a mode embedded in a Sn base material, or in a base material in which a base material made of Cu and a base material made of Sn are separated as shown in FIG.
- the Sn base material 550 is preferably composed of the Cu base material 520 b and the Sn base material 550 .
- the Nb core material 510 satisfies the range of 10 at % or more and 60 at % or less with respect to the total of Within this range, it preferably reacts with the Nb core material 510 to form the Nb 3 Sn superconducting core material 150 (FIG. 1), which has wire workability.
- the Nb 3 Sn superconducting precursor wire 500b may comprise a stabilizer 540 around the Cu base material 520b, similar to the Nb 3 Sn superconducting precursor wire 500a.
- the Nb 3 Sn superconducting precursor wire shown in FIG. 5 is an example, and in addition to this, for example, Nb 3 Sn superconducting precursor wires described in WO2018/198515, WO2021/024529, etc. may also be applied. can be done.
- the Nb core material 510 may be embedded in a base material containing at least Cu and Sn, but the base material (Cu base material, Sn base material, or Cu—Sn base material) may further contain zinc (Zn), germanium (Ge), gallium (Ga), magnesium (Mg), aluminum (Al), titanium (Ti).
- FIG. 6 is a flow chart of the first connection process.
- FIG. 7 is the procedure of the first connecting step.
- Step S411 The Nb alloy strip 110a is exposed from one end of the connecting strip 120 covered with the first stabilizer 210 by the Nb alloy strip (core material) 110a.
- the method of exposing is not particularly limited, but chemical corrosion, mechanical polishing, or a combination of these may be used.
- the exposed length is preferably in the range of 10 mm or more and 30 mm or less. Within this range, when bundled with the Nb core material 510 to be described later, good superconductivity can be obtained due to sufficient contact.
- the exposed length is more preferably in the range of 10 mm or more and 20 mm or less.
- Step S412 The Nb core material 510 is exposed from one end of the Nb 3 Sn superconducting precursor wire 500a embedded in the base material (Cu—Sn base material 520a) in which the Nb core material 510 contains at least Cu and Sn.
- the method of exposing is not particularly limited, but may be chemical etching, mechanical polishing, or a combination thereof, preferably chemical etching and mechanical polishing in that order. This facilitates exposure even when the Nb 3 Sn superconducting precursor wire 500 a has a diffusion barrier layer 530 .
- the exposed length is preferably in the range of 10 mm or more and 30 mm or less.
- the exposed length is more preferably in the range of 10 mm or more and 20 mm or less. At this time, care should be taken not to completely remove the base material containing Cu and Sn. This is because the remaining Cu—Sn is indispensable for forming the Nb 3 Sn layer.
- Step S413 The exposed Nb alloy strip 110a and the exposed Nb core material 510 are bundled. There are no restrictions on the method of bundling, but it may be combined, twisted, entwined, or wound.
- Step S414 The Nb alloy strip 110a and the Nb core material 510 bundled in step S413 are crimped. Crimping is performed by applying pressure to the bundled Nb alloy strip 110a and the Nb core material 510, exposing their new surfaces, and bringing them into close contact. As a result, a Nb 3 Sn superconducting layer is formed on the new surface by heat treatment, which will be described later, and can be joined.
- the crimp tube 180 is as previously described with reference to FIG.
- the applied pressure range is preferably from 100 MPa to 1 GPa. Within this range, adhesion between the new surfaces can be promoted.
- the applied pressure range is more preferably 300 MPa or more and 500 MPa or less. Within this range, adhesion between new surfaces can be promoted without disconnection.
- Step S415 heat-treating the crimped Nb alloy strip and connecting strip 120 containing the Nb core and the Nb 3 Sn superconducting precursor wire 500a.
- the heat treatment may be a normal heat treatment for converting the Nb 3 Sn superconducting precursor wire 500a into a Nb 3 Sn superconducting wire.
- the Nb core material 510 reacts with the Cu—Sn base material 520a to become the Nb 3 Sn superconducting core material 150, and the Nb 3 Sn superconducting layer 170 is formed on the new surface of the bundled Nb alloy strip and the Nb core material. can be generated.
- the Nb alloy strip with increased Nb recovery temperature and recrystallization temperature due to the addition of the M element is used, the superconducting properties of the Nb alloy strip are not degraded even by the conventional heat treatment.
- the heat treatment conditions are preferably in a vacuum or an atmosphere of an inert gas such as argon (Ar) or helium (He) in a temperature range of 600° C. or more and 800° C. or less.
- an inert gas such as argon (Ar) or helium (He) in a temperature range of 600° C. or more and 800° C. or less.
- Ar argon
- He helium
- the heat treatment time varies depending on the length of the Nb 3 Sn superconducting precursor wire 500a and the number of multifilamentary wires, but is illustratively in the range of 5 hours or more and 300 hours or less.
- heat treatment conditions may be carried out in two stages within the above temperature range.
- the heat treatment conditions are as follows: in a vacuum or inert gas atmosphere, at a temperature range of 300° C. to 500° C. for 50 hours to 150 hours, and then in a temperature range of 600° C. to 800° C. The time may be 50 hours or more and 150 hours or less.
- Such a two-step heat treatment can promote the formation of a homogeneous Nb 3 Sn superconducting core 150 and a Nb 3 Sn superconducting layer 170 on the nascent surface while maintaining the high superconducting properties of the Nb alloy strip.
- step S411 and then step S412 are described in FIG. 6 as being performed in that order, step S412 and then step S411 may be performed in that order.
- FIG. 8 is a flow chart of the second connection process.
- FIG. 9 is the procedure of the second connection step.
- Step S421 expose the Nb alloy strip 110a from the other end of the connection strip 120 where the Nb alloy strip 110a is coated with the first stabilizer 210; Step S421 may be the same exposure method as step S411.
- the exposed length is preferably in the range of 10 mm or more and 30 mm or less. Within this range, when bundled with the NbTi core material 160 described later, good superconductivity can be obtained due to sufficient contact.
- the exposed length is more preferably in the range of 15 mm or more and 25 mm or less.
- the other end of the connection strip 120 is joined with the Nb 3 Sn superconducting wire 130 by the first connection process described above.
- Step S422 The NbTi core material 160 is exposed from one end of the NbTi wire material 140.
- the method of exposing is not particularly limited, but chemical corrosion, mechanical polishing, or a combination of these may be used.
- the exposed length is preferably in the range of 10 mm or more and 30 mm or less. Within this range, when bundled with the Nb alloy strip 110a exposed in step S421, good superconducting properties can be obtained due to sufficient contact.
- the exposed length is more preferably in the range of 15 mm or more and 25 mm or less.
- Step S423 The exposed Nb alloy strip 110a and the exposed NbTi core material 160 are bundled. There are no restrictions on the method of bundling, but it may be combined, twisted, entwined, or wound.
- Step S424 The Nb alloy strip and NbTi core material bundled in step S423 are crimped. Crimping is performed by applying pressure to the bundled Nb alloy strip 110a and the NbTi core material 160, exposing their new surfaces, and bringing them into close contact. As a result, the Nb alloy strip and the NbTi core material can be joined at the new surfaces.
- the applied pressure range is preferably from 100 MPa to 1 GPa. Within this range, adhesion between the new surfaces can be promoted.
- the applied pressure range is more preferably 300 MPa or more and 500 MPa or less. Within this range, adhesion between new surfaces can be promoted without disconnection. Thus, the superconducting connection structure 100 of the present invention is obtained.
- NbTi wire having a wire diameter of 0.5 mm and having 180 NbTi cores embedded in a Cu base material (National Bureau of Standards (NBS) standard sample) was examined for changes in critical current characteristics before and after heat treatment.
- the heat treatment conditions were 685° C. in vacuum for 100 hours.
- the Ti composition in the NbTi core material was 60 atomic %.
- the wire was immersed in liquid helium and the critical current was measured when an external magnetic field was applied. The results are shown in FIG.
- FIG. 10 is a diagram showing critical current characteristics before and after heat treatment of NbTi wire.
- the critical current of the NbTi wire before the heat treatment showed a high value.
- the current also decreased.
- the critical current of the NbTi wire after heat treatment was less than 100A even in a magnetic field of 0.2T. This is because the nanostructure such as dislocation cells in the NbTi core material disappears due to the heat treatment, and the nanoscale ribbon-like ⁇ -Ti that serves as the magnetic flux pinning point agglomerates, so that the magnetic flux pinning force is lost. As a result, the critical current is lowered.
- Nb alloy wires in which 19 Nb-2at%Hf cores and Nb-4at%Ta-1at%Hf cores are respectively embedded in a Cu base material with a linear length of 1mm is measured. Examined.
- a Nb alloy wire was manufactured as follows.
- the Nb-2at%Hf alloy and the Nb-4at%Ta-1at%Hf alloy melted by arc melting were processed into rods of slightly less than 6 mm by swaging, and each was made into a Cu tube with an outer diameter/inner diameter of 8 mm/6 mm. inserted. This was subjected to swaging and die wire drawing to produce a Cu/Nb--Hf single-filamentary wire and a Cu/Nb--Ta--Hf single-filamentary wire having an outer diameter of 1 mm.
- FIG. 11 is a diagram showing the critical current characteristics of Nb--Ta--Hf wire (Nb-4at% Ta-1at%Hf wire) before and after heat treatment.
- the Nb--Ta--Hf wire is referred to as Nb--4Ta--1Hf. Note that the critical current characteristics of the Nb—Hf wire before and after the heat treatment are not shown.
- the critical current of the Nb--Ta--Hf wire is only slightly reduced even after heat treatment above 600° C., which corresponds to the Nb 3 Sn formation temperature, and is still high at 0.5 T. maintained the current.
- the Nb--Hf wire maintained a high critical current at 0.8 T even after the heat treatment.
- the recovery temperature and recrystallization temperature of Nb are increased. It was found to maintain a high critical current. From this, it was shown that the Nb alloy to which the M element is added is effective for the connection strip with the Nb 3 Sn superconducting precursor wire.
- the connecting strip and the Nb 3 Sn superconducting precursor wire are connected (step S410), which requires heat treatment at a temperature equal to or higher than the Nb 3 Sn generation temperature, and then the connecting strip and the NbTi wire are connected. It has been shown that it is essential to perform the connection (step S420) in order.
- Example 1 In Example 1, the Nb--Ta--Hf (specifically, Nb-4at%Ta-1at%Hf) wire used in the reference example was used as the connecting strip, and the Nb 3 Sn superconductivity was obtained by the method shown in FIG. A superconducting joint structure was manufactured by joining a wire and a NbTi wire.
- Nb--Ta--Hf specifically, Nb-4at%Ta-1at%Hf
- Nb 3 Sn precursor wire As the Nb 3 Sn precursor wire, an Nb 3 Sn precursor wire having a structure in which 1045 Nb cores are embedded in a base material in which Cu and Sn are separated and arranged as shown in FIG. 5(B) is used. Got ready. A diffusion barrier layer made of Nb was provided between the region containing Cu, Sn, and Nb and the outermost Cu. The composition of Sn in the base material was 14 at %, the Nb core diameter was 11 ⁇ m, and the thickness of the diffusion barrier layer was 15 ⁇ m.
- the NbTi wire was the same as the NbTi wire used in the reference example.
- the Nb--Ta--Hf wire and the Nb 3 Sn superconducting wire were connected as connection strips (step S410 in FIG. 4). Specifically, the Nb--Ta--Hf wire was cut to a length of 8 cm, and the Nb--Ta--Hf core material was exposed as an Nb alloy strip from one end (step S411 in FIGS. 6 and 7). ). A 15 mm end portion of the Nb--Ta--Hf wire was immersed in nitric acid to remove the Cu (copper) base material of the stabilizing material. Next, the Nb core material was exposed from one end of the Nb 3 Sn superconducting precursor wire (step S412 in FIGS. 6 and 7).
- the exposed Nb--Ta--Hf core material and the exposed Nb core material were twisted and bundled so as to be entangled with each other (step S413 in FIGS. 6 and 7).
- the bundled portion was crimped (step S414 in FIGS. 6 and 7).
- the bundled portion was inserted into a tantalum (Ta) tube having an outer diameter/inner diameter of 3.6 mm/2.5 mm as a crimp tube, and a pressure of 400 MPa was applied using a hydraulic press.
- the Nb--Ta--Hf wire including the crimped portion and the Nb 3 Sn superconducting precursor wire were heat treated (step S415 in FIGS. 6 and 7).
- the heat treatment conditions were 390° C.
- the Nb 3 Sn superconducting wire is produced from the Nb 3 Sn superconducting precursor wire, and the Nb—Ta—Hf wire and the Nb 3 Sn superconducting wire are combined into an Nb 3 Sn superconducting layer. connected through
- the other end of the Nb--Ta--Hf wire was connected to the NbTi wire having the NbTi core (step S420 in FIG. 4).
- the Nb--Ta--Hf core was exposed from the other end of the Nb--Ta--Hf wire (step S421 in FIGS. 8 and 9).
- a 20 mm end portion of the Nb--Ta--Hf wire was immersed in nitric acid to remove the Cu base material (third stabilizer).
- the NbTi core was exposed from one end of the NbTi wire (step S422 in FIGS. 8 and 9).
- the Cu base material was removed with nitric acid from 20 mm of the end portion of the NbTi wire.
- the exposed Nb--Ta--Hf core material and the exposed NbTi core material were twisted and bundled so as to be entangled (step S423 in FIGS. 8 and 9).
- the bundled portion was crimped (step S424 in FIGS. 8 and 9).
- the bundled portion was inserted into a tantalum (Ta) tube having an outer diameter/inner diameter of 3.6 mm/2.5 mm as a crimp tube, and a pressure of 400 MPa was applied using a hydraulic press.
- Ta tantalum
- a pressure of 400 MPa was applied using a hydraulic press.
- the Nb--Ta--Hf wire rod and the NbTi wire rod were connected with each other's new surfaces in close contact with each other.
- a superconducting connection structure was obtained using the connection strip thus obtained.
- Example 1 The superconducting connection structure of Example 1 was observed using a scanning electron microscope (SEM, manufactured by JEOL Ltd.) equipped with an energy dispersive X-ray spectrometer (EDS) to investigate elemental mapping. The results are shown in FIG.
- FIG. 12 is a view showing the results of electron microscopic observation of a cross section of a joint portion between a connecting strip of a superconducting connecting structure and a Nb 3 Sn superconducting wire.
- the core material is in close contact with the connecting portion by crimping (step S414 in FIG. 6).
- the Nb 3 Sn superconducting core in the Nb 3 Sn superconducting wire is a multifilamentary wire and is in close contact with each other, and furthermore, the Nb--Ta--Hf core of the connecting strip. , and the Nb 3 Sn superconducting core material.
- the Nb—Ta—Hf core and the Nb 3 Sn superconducting core are Nb 3 Sn superconducting layers (referred to as Nb 3 Sn layers in the drawings). found to be in contact through
- FIG. 13 is a diagram showing critical current characteristics of the superconducting connecting structure of Example 1.
- the superconducting connecting structure (NbTi-Nb-4at%Ta-1at%Hf - Nb3Sn superconducting connecting structure) is referred to as the NbTi-Nb-4Ta-1Hf - Nb3Sn superconducting connecting structure. called.
- the superconducting connecting structure of Example 1 exhibited a high critical current exceeding 150 A even when 0.55 T was applied.
- Example 2 In Example 2, a superconducting joint structure was manufactured in the same manner as in Example 1 except that the Nb-Hf (Nb-2at%Hf) wires used in the Reference Example were used as the connecting strips. The superconducting joint structure of Example 2 was observed with an SEM to examine critical current characteristics. The results are shown in FIG.
- FIG. 14 is a diagram showing critical current characteristics of the superconducting connecting structure of Example 2.
- the superconducting connecting structure (NbTi-Nb-2at%Hf-Nb 3 Sn superconducting connecting structure) is referred to as NbTi-Nb-2Hf-Nb 3 Sn superconducting connecting structure.
- the superconducting connecting structure of Example 2 showed a high critical current exceeding 150 A even when a higher magnetic field (0.9 T) than that of the superconducting connecting structure of Example 1 was applied.
- SEM observation confirmed that the Nb—Hf core and the Nb 3 Sn superconducting core were in contact with each other via the Nb 3 Sn superconducting layer. From this, it was confirmed that a superconducting connection structure of a Nb 3 Sn superconducting wire and an NbTi wire, which maintains high superconducting properties without using environmentally hazardous substances such as Pb and Cd, can be provided. .
- Hf is preferable as the M element.
- the bonded structure of the Nb 3 Sn superconducting wire and the NbTi wire is connected without using environmentally hazardous substances such as Pb, Cd, etc., has excellent characteristics, and has a strength of 0.5T to 1.5T. It can be used in a magnetic field environment of 0 T, so it is applied as a superconducting connection for nuclear magnetic resonance apparatus (NMR) magnets.
- NMR nuclear magnetic resonance apparatus
- Reference Signs List 100 superconducting connection structure 110 Nb alloy strip 110a core 110b sheet 110c pipe 120 connection strip 130 Nb3Sn superconducting wire 140 NbTi wire 150 Nb3Sn superconducting core 160 NbTi core 170 Nb3Sn superconducting layer 180 Crimp tube 210 First stabilizer 310 Second stabilizer 320, 530 Diffusion barrier layer 330 Third stabilizer 500a, 500b Nb 3 Sn superconducting precursor wire 510 Nb core 520a Cu—Sn base material 520b Cu base material 540 Stabilizing material 550 Sn base material
Abstract
Description
また、非特許文献2は、Nb3Sn自体の単なる組織制御研究に留まるものでしかなく、異種超伝導材料間の超伝導接続(例えば、Nb3Sn超伝導線材とNbTi線材との間の超伝導接続)に関する教示や示唆を何ら与えるものでは無かった。
本発明の課題は、Pb、Cd等の環境負荷物質を有しない、従来発想を超える全く新しいNb3Sn超伝導線材とNbTi線材との超伝導接続構造体、その製造方法およびそれを用いた核磁気共鳴装置を提供することである。
前記M元素は、ハフニウム(Hf)、チタン(Ti)、タンタル(Ta)、ジルコニウム(Zr)、および、タングステン(W)からなる群から選択される少なくとも1種であってよい。
前記Nb合金ストリップは、芯材、シート、および、パイプからなる群から選択されるいずれか1種の形状であってよい。
なお、本願におけるストリップとは、帯状に長くて薄く、芯状やシート状やパイプ状などの形状にしたものである。
前記M元素は、0.2at%以上10at%以下の範囲(ここで、at%とは、前記Nb合金ストリップ中に含まれる前記M元素の原子%のことである。)で添加されていてよい。
前記Nb合金ストリップと前記Nb3Sn超伝導芯材とがNb3Sn超伝導層を介して接触する部分、および、前記Nb合金ストリップの新生面と前記NbTi芯材の新生面とが互いに接触する部分は、それぞれ、タンタル(Ta)、ニオブ(Nb)、銅ニッケル合金(CuNi)、および、ステンレスからなる群から選択される少なくとも1種の材料からなる圧着管で被覆されていてよい。
前記被覆されている部分の長さは、10mm以上30mm以下の範囲の長さを有してよい。
前記接続ストリップは、前記Nb合金ストリップが第1の安定化材で被覆および/または埋設されてなり、前記Nb3Sn超伝導線材は、前記Nb3Sn超伝導芯材が第2の安定化材で被覆および/または埋設されてなり、前記NbTi線材は、前記NbTi芯材が第3の安定化材で被覆および/または埋設されてなり、前記第1から前記第3の安定化材は、それぞれ、銅金属、銅合金、銀金属、および、銀合金からなる群から選択される少なくとも1種の金属であってよい。
本発明の上記超伝導接続構造体を製造する方法は、M元素が添加されたNb合金ストリップを有する接続ストリップ(ここで、前記M元素は、Nbの回復温度および再結晶温度を増大させる元素である)の一方の端部と、Nb3Sn超伝導芯材を有するNb3Sn超伝導線材とを接続する第1の接続工程と、前記接続ストリップのもう一方の端部と、NbTi芯材を有するNbTi線材とを接続する第2の工程とを包含し、前記第1の接続工程は、前記接続ストリップの一方の端部から前記Nb合金ストリップを露出させる工程と、Nb芯材が少なくともCuとSnを含有する母材中に埋設されたNb3Sn超伝導前駆体線材の一方の端部から前記Nb芯材を露出させる工程と、前記露出したNb合金ストリップと、前記露出したNb芯材とを束ねる工程と、前記束ねられた前記Nb合金ストリップおよび前記Nb芯材を圧着する工程と、前記圧着された前記Nb合金ストリップおよび前記Nb芯材を含む前記接続ストリップおよび前記Nb3Sn超伝導前駆体線材を熱処理する工程とを包含し、前記第2の接続工程は、前記接続ストリップのもう一方の端部から前記Nb合金ストリップを露出させる工程と、前記NbTi線材の一方の端部から前記NbTi芯材を露出させる工程と、前記露出したNb合金ストリップと、前記露出したNbTi芯材とを束ねる工程と、前記束ねられた前記Nb合金ストリップおよび前記NbTi芯材を圧着する工程とを包含し、これにより上記課題を解決する。
前記第1の接続工程および前記第2の接続工程における前記Nb合金ストリップを露出させる工程は、化学腐食を用いてもよい。
前記第1の接続工程における前記Nb芯材を露出させる工程は、化学腐食を用いてもよい。
前記第1の接続工程における前記Nb芯材を露出させる工程は、機械研磨をさらに行ってもよい。
前記第2の接続工程における前記NbTi芯材を露出させる工程は、化学腐食を用いてもよい。
前記第1の接続工程および前記第2の接続工程における前記Nb合金ストリップを露出させる工程、前記第1の接続工程における前記Nb芯材を露出させる工程、および、前記第2の接続工程における前記NbTi芯材を露出させる工程は、それぞれ、10mm以上30mm以下の範囲の長さを露出させてもよい。
前記第1の接続工程における前記圧着する工程は、前記Nb合金ストリップおよび前記Nb芯材のそれぞれの新生面を露出させ、前記Nb合金ストリップの新生面と前記Nb芯材の新生面とを密着させてもよい。
前記第1の接続工程における前記圧着する工程は、前記束ねられた前記Nb合金ストリップおよび前記Nb芯材の部分をタンタル(Ta)、ニオブ(Nb)、銅ニッケル合金(CuNi)、および、ステンレスからなる群から選択される少なくとも1種の材料からなる圧着管で被覆し、前記束ねられた前記Nb合金ストリップおよび前記Nb芯材の長手方向に対して垂直方向に圧力を印加してもよい。
前記圧力は、100MPa以上1GPa以下の範囲であってもよい。
前記第1の接続工程における前記熱処理する工程は、前記接続ストリップおよび前記Nb3Sn超伝導前駆体線材を、真空中または不活性ガス雰囲気中で600℃以上800℃以下の温度範囲で熱処理してもよい。
前記第1の接続工程における前記熱処理する工程は、前記接続ストリップおよび前記Nb3Sn超伝導前駆体線材を、真空中または不活性ガス雰囲気中で、300℃以500℃以下の温度範囲で50時間以上150時間以下の時間、次いで、600℃以上800℃以下の温度範囲で50時間以上150時間以下の時間、熱処理してもよい。
前記第2の接続工程における前記圧着する工程は、前記Nb合金ストリップおよび前記NbTi芯材のそれぞれの新生面を露出させ、前記Nb合金ストリップの新生面と前記Nb芯材の新生面とを密着させてもよい。
前記第2の接続工程における前記圧着する工程は、前記束ねられた前記Nb合金ストリップおよび前記NbTi芯材の部分をタンタル(Ta)、ニオブ(Nb)、銅ニッケル合金(CuNi)、および、ステンレスからなる群から選択される材料からなる圧着管で被覆し、前記束ねられた前記Nb合金ストリップおよび前記NbTi芯材の長手方向に対して垂直方向に圧力を印加してもよい。
前記圧力は、100MPa以上1GPa以下の範囲であってもよい。
なお、本願における新生面とは、後述のとおり、酸化被膜などを有さず、大気に触れていない、活性状態にある金属面のことである。
本発明の核磁気共鳴装置は、上記超伝導接続構造体を用い、これ(すなわち、上記超伝導接続構造体を含む本発明の核磁気共鳴装置)により上記課題を解決する。
M元素は、Nbの回復および再結晶温度を増大させるものであれば特に制限はないが、好ましくは、ハフニウム(Hf)、チタン(Ti)、タンタル(Ta)、ジルコニウム(Zr)、および、タングステン(W)からなる群から少なくとも1種選択される元素である。中でもHfが好ましい。Hfは、Nbの回復および再結晶温度を200℃増大させることができるため、後述する製造方法において、有利である。
図4は、本発明の超伝導接続構造体を製造する工程のフローチャートである。
ステップS420:接続ストリップのもう一方の端部と、NbTi芯材を有するNbTi線材とを接続する。
本発明の超伝導接続構造体100は、ステップS410の第1の接続工程とステップS420の第2の接続工程とによって製造される。
図6は、第1の接続工程のフローチャートである。
図7は、第1の接続工程のプロシージャである。
図9は、第2の接続工程のプロシージャである。
このようにして、本発明の超伝導接続構造体100が得られる。
線径0.5mm、Cu母材中に180芯のNbTi芯材が埋め込まれたNbTi線材(National Bureau of Standards(NBS)標準試料)の熱処理前後の臨界電流特性の変化を調べた。熱処理条件は、真空中、685℃で、100時間であった。NbTi芯材中のTi組成は60at%であった。線材を液体ヘリウムに浸漬し、外部磁場を印加した際の臨界電流を測定した。結果を図10に示す。
例1では、接続ストリップとして、参考例で用いたNb-Ta-Hf(具体的には、Nb-4at%Ta-1at%Hf)線材を用い、図4に示す方法によって、Nb3Sn超伝導線材とNbTi線材とを接合した超伝導接合構造体を製造した。
図13は、例1の超伝導接続構造体の臨界電流特性を示す図である。図13では、前記超伝導接続構造体(NbTi-Nb-4at%Ta-1at%Hf-Nb3Sn超伝導接続構造体)をNbTi-Nb-4Ta-1Hf-Nb3Sn超伝導接続構造体と称する。
図13によれば、例1の超伝導接続構造体は、0.55Tを印加しても、150Aを超える高い臨界電流を示した。このことから、Pb、Cd等の環境負荷物質を用いることなく、高い超伝導特性を維持した、Nb3Sn超伝導線材とNbTi線材との超伝導接続構造体が提供されることが確認された。
例2では、接続ストリップとして、参考例で用いたNb-Hf(Nb-2at%Hf)線材を用いた以外は例1と同様にして超伝導接合構造体を製造した。例2の超伝導接合構造体をSEM観察し、臨界電流特性を調べた。結果を図14に示す。
110 Nb合金ストリップ
110a 芯材
110b シート
110c パイプ
120 接続ストリップ
130 Nb3Sn超伝導線材
140 NbTi線材
150 Nb3Sn超伝導芯材
160 NbTi芯材
170 Nb3Sn超伝導層
180 圧着管
210 第1の安定化材
310 第2の安定化材
320、530 拡散バリア層
330 第3の安定化材
500a、500b Nb3Sn超伝導前駆体線材
510 Nb芯材
520a Cu-Sn母材
520b Cu母材
540 安定化材
550 Sn母材
Claims (22)
- M元素が添加されたNb合金ストリップを有する接続ストリップ(ここで、前記M元素は、Nbの回復温度および再結晶温度を増大させる元素である)と、
Nb3Sn超伝導芯材を有するNb3Sn超伝導線材と、
NbTi芯材を有するNbTi線材と
を備え、
前記接続ストリップの一方の端部は、前記Nb合金ストリップと前記Nb3Sn超伝導芯材とがNb3Sn超伝導層を介して接触することにより、前記Nb3Sn超伝導線材と接続されており、
前記接続ストリップの他方の端部は、前記Nb合金ストリップの新生面と前記NbTi芯材の新生面とが互いに接触することにより、前記NbTi線材と接続されている、超伝導接続構造体。 - 前記M元素は、ハフニウム(Hf)、チタン(Ti)、タンタル(Ta)、ジルコニウム(Zr)、および、タングステン(W)からなる群から選択される少なくとも1種である、請求項1に記載の超伝導接続構造体。
- 前記Nb合金ストリップは、芯材、シート、および、パイプからなる群から選択されるいずれか1種の形状である、請求項1または2に記載の超伝導接続構造体。
- 前記M元素は、0.2at%以上10at%以下の範囲で添加されている、請求項1~3のいずれかに記載の超伝導接続構造体。
- 前記Nb合金ストリップと前記Nb3Sn超伝導芯材とがNb3Sn超伝導層を介して接触する部分、および、前記Nb合金ストリップの新生面と前記NbTi芯材の新生面とが互いに接触する部分は、それぞれ、タンタル(Ta)、ニオブ(Nb)、銅ニッケル合金(CuNi)、および、ステンレスからなる群から選択される少なくとも1種の材料からなる圧着管で被覆されている、請求項1~4のいずれかに記載の超伝導接続構造体。
- 前記被覆されている部分の長さは、10mm以上30mm以下の範囲の長さを有する、請求項5に記載の超伝導接続構造体。
- 前記接続ストリップは、前記Nb合金ストリップが第1の安定化材で被覆および/または埋設されてなり、
前記Nb3Sn超伝導線材は、前記Nb3Sn超伝導芯材が第2の安定化材で被覆および/または埋設されてなり、
前記NbTi線材は、前記NbTi芯材が第3の安定化材で被覆および/または埋設されてなり、
前記第1から前記第3の安定化材は、それぞれ、銅金属、銅合金、銀金属、および、銀合金からなる群から選択される少なくとも1種の金属である、請求項1~6のいずれかに記載の超伝導接続構造体。 - M元素が添加されたNb合金ストリップを有する接続ストリップ(ここで、前記M元素は、Nbの回復温度および再結晶温度を増大させる元素である)の一方の端部と、Nb3Sn超伝導芯材を有するNb3Sn超伝導線材とを接続する第1の接続工程と、
前記接続ストリップのもう一方の端部と、NbTi芯材を有するNbTi線材とを接続する第2の工程と
を包含し、
前記第1の接続工程は、
前記接続ストリップの一方の端部から前記Nb合金ストリップを露出させる工程と、
Nb芯材が少なくともCuとSnを含有する母材中に埋設されたNb3Sn超伝導前駆体線材の一方の端部から前記Nb芯材を露出させる工程と、
前記露出したNb合金ストリップと、前記露出したNb芯材とを束ねる工程と、
前記束ねられた前記Nb合金ストリップおよび前記Nb芯材を圧着する工程と、
前記圧着された前記Nb合金ストリップおよび前記Nb芯材を含む前記接続ストリップおよび前記Nb3Sn超伝導前駆体線材を熱処理する工程と
を包含し、
前記第2の接続工程は、
前記接続ストリップのもう一方の端部から前記Nb合金ストリップを露出させる工程と、
前記NbTi線材の一方の端部から前記NbTi芯材を露出させる工程と、
前記露出したNb合金ストリップと、前記露出したNbTi芯材とを束ねる工程と、
前記束ねられた前記Nb合金ストリップおよび前記NbTi芯材を圧着する工程と
を包含する、請求項1~7のいずれかに記載の超伝導接続構造体を製造する方法。 - 前記第1の接続工程および前記第2の接続工程における前記Nb合金ストリップを露出させる工程は、化学腐食を用いる、請求項8に記載の方法。
- 前記第1の接続工程における前記Nb芯材を露出させる工程は、化学腐食を用いる、請求項8または9に記載の方法。
- 前記第1の接続工程における前記Nb芯材を露出させる工程は、機械研磨をさらに行う、請求項10に記載の方法。
- 前記第2の接続工程における前記NbTi芯材を露出させる工程は、化学腐食を用いる、請求項8~11のいずれかに記載の方法。
- 前記第1の接続工程および前記第2の接続工程における前記Nb合金ストリップを露出させる工程、前記第1の接続工程における前記Nb芯材を露出させる工程、および、前記第2の接続工程における前記NbTi芯材を露出させる工程は、それぞれ、10mm以上30mm以下の範囲の長さを露出させる、請求項8~12のいずれかに記載の方法。
- 前記第1の接続工程における前記圧着する工程は、前記Nb合金ストリップおよび前記Nb芯材のそれぞれの新生面を露出させ、前記Nb合金ストリップの新生面と前記Nb芯材の新生面とを密着させる、請求項8~13のいずれかに記載の方法。
- 前記第1の接続工程における前記圧着する工程は、前記束ねられた前記Nb合金ストリップおよび前記Nb芯材の部分をタンタル(Ta)、ニオブ(Nb)、銅ニッケル合金(CuNi)、および、ステンレスからなる群から選択される少なくとも1種の材料からなる圧着管で被覆し、前記束ねられた前記Nb合金ストリップおよび前記Nb芯材の長手方向に対して垂直方向に圧力を印加する、請求項14に記載の方法。
- 前記圧力は、100MPa以上1GPa以下の範囲である、請求項15に記載の方法。
- 前記第1の接続工程における前記熱処理する工程は、前記接続ストリップおよび前記Nb3Sn超伝導前駆体線材を、真空中または不活性ガス雰囲気中で600℃以上800℃以下の温度範囲で熱処理する、請求項8~16のいずれかに記載の方法。
- 前記第1の接続工程における前記熱処理する工程は、前記接続ストリップおよび前記Nb3Sn超伝導前駆体線材を、真空中または不活性ガス雰囲気中で、300℃以500℃以下の温度範囲で50時間以上150時間以下の時間、次いで、600℃以上800℃以下の温度範囲で50時間以上150時間以下の時間、熱処理する、請求項17に記載の方法。
- 前記第2の接続工程における前記圧着する工程は、前記Nb合金ストリップおよび前記NbTi芯材のそれぞれの新生面を露出させ、前記Nb合金ストリップの新生面と前記Nb芯材の新生面とを密着させる、請求項8~18のいずれかに記載の方法。
- 前記第2の接続工程における前記圧着する工程は、前記束ねられた前記Nb合金ストリップおよび前記NbTi芯材の部分をタンタル(Ta)、ニオブ(Nb)、銅ニッケル合金(CuNi)、および、ステンレスからなる群から選択される材料からなる圧着管で被覆し、前記束ねられた前記Nb合金ストリップおよび前記NbTi芯材の長手方向に対して垂直方向に圧力を印加する、請求項19に記載の方法。
- 前記圧力は、100MPa以上1GPa以下の範囲である、請求項20に記載の方法。
- 請求項1~7のいずれかに記載の超伝導接続構造体を含む、核磁気共鳴装置。
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