Bi-2212 single-core rod as well as preparation method and application thereof

Abstract

The invention relates to a Bi-2212 single-core rod as well as a preparation method and application thereof. Bi-2212 precursor powder is firstly subjected to heat treatment and grinding in air and then subjected to heat treatment and grinding, and powder is obtained; then pressing the powder into a uniform powder bar through a dry bag type cold isostatic pressing process; then the powder bar is loaded into a silver tube, one end of the silver tube is welded and sealed through a silver plug, and the other end of the silver tube is welded and sealed through a silver plug with a suction nozzle; then the single-core rod is placed in a tubular furnace with flowing oxygen atmosphere, a suction nozzle extends out of the tubular furnace and is connected with a vacuum pump, and the single-core rod in the silver tube is vacuumized and subjected to heat treatment at the same time; and finally, sealing the suction nozzle, stopping vacuumizing and heat treatment, cooling the furnace to room temperature, and taking out to obtain the single-core rod. And performing rotary swaging and drawing on the single-core rod to prepare a single-core wire. According to the method, precursor powder is treated through a simple process, so that the precursor powder is kept uniform and consistent in density after being filled into a tube, and impurity gas in a single-core rod or a single-core wire is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of single core rods, and in particular relates to a Bi-2212 single core rod and a preparation method and application thereof. Background Art

[0002] Bi-2212(Bi2Sr2CaCu2O x ) Superconducting materials have an irreversible field of more than 100 T at 4.2 K, and can carry high current even in a magnetic field of 50 T. Moreover, due to its texture characteristics, Bi-2212 is the only high-temperature superconducting material that can be made into isotropic round wires, which is convenient for winding magnet coils. Therefore, Bi-2212 is considered to be one of the ideal materials for preparing future high-field magnets.

[0003] In industry, the precursor powder of Bi-2212 is usually prepared by coprecipitation or spray pyrolysis, and then prepared into multi-core superconducting round wire by powder in tube method (PIT), and finally the wire is heat treated.

[0004] In the process of preparing Bi-2212 wire by PIT method, the precursor powder is usually loaded into the silver tube by vibration tube loading method to prepare a single core rod. Since the precursor powder after tube loading by vibration tube loading method is unevenly distributed and the density is inconsistent, the wire uniformity is poor, and the degassing effect of this method is poor. During the partial melting heat treatment of the wire, the impurity gas in the core wire (in addition to the residual impurity gas, the residual C and H elements will become impurity gas of CO2 and H2O during the partial melting heat treatment of the wire) flows and gathers in the liquid phase to form bubbles and holes, reducing the current carrying performance of the wire. Summary of the invention

[0005] The purpose of the present invention is to provide a Bi-2212 single core rod and a preparation method and application thereof. The method processes the precursor powder through a simple process so that the precursor powder remains uniform and has a consistent density after being loaded into a tube, and the impurity gas in the single core rod or single core wire is greatly reduced.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows.

[0007] A method for preparing a Bi-2212 single core rod, the steps are as follows:

[0008] Step 1, heat-treating the Bi-2212 precursor powder in air at 810°C-820°C for 10h-12h, grinding it evenly after natural cooling, and then heat-treating it in air at 850°C-860°C for 20h-22h, taking it out, and grinding it to an average particle size of 4μm-8μm after natural cooling to obtain powder;

[0009] Step 2, pressing the powder obtained in step 1 into a uniform powder rod by a dry bag cold isostatic pressing process;

[0010] Step 3, putting the powder rod obtained in step 2 into a silver tube, welding and sealing one end of the silver tube with a silver plug, and welding and sealing the other end with a silver plug with a suction nozzle, the two end surfaces of the powder rod are in contact with the inner surfaces of the two silver plugs respectively, and the inner diameter of the silver tube is 1mm-1.5mm larger than the diameter of the powder rod;

[0011] Step 4, placing the silver tube containing the powder rod obtained in step 3 into a tubular furnace in a flowing oxygen atmosphere, extending the suction nozzle out of the tubular furnace and connecting a vacuum pump to evacuate the powder rod in the silver tube and perform heat treatment at the same time;

[0012] Step 5, seal the nozzle, stop vacuuming and heat treatment, cool the furnace to room temperature, take it out, and obtain a Bi-2212 single core rod.

[0013] Preferably, in step 1, the Bi-2212 precursor powder is prepared by spray pyrolysis, and the purity of the Bi-2212 precursor powder is ≥99%, and the average particle size is 4 μm-8 μm.

[0014] More preferably, the reaction solution of the spray thermal decomposition method is a mixture of Bi nitrate, Sr nitrate, Ca nitrate and Cu nitrate solutions, in which the molar ratio of Bi:Sr:Ca:Cu is 2.17:1.94:0.89:2 and the total cation concentration is 1 mol / L.

[0015] Preferably, in step 2, the pressure of the dry bag cold isostatic pressing is 30 MPa-40 MPa.

[0016] Preferably, in step 3, the wall thickness of the silver tube is 1 mm-1.5 mm.

[0017] Preferably, in step 4, the heat treatment temperature is 600°C-650°C, the heat treatment time is 10h-20h, and the vacuum degree is better than 10 -3 Pa, the pressure of the flowing oxygen atmosphere is 0.2Mpa-0.4Mpa.

[0018] The present invention also provides a Bi-2212 single core rod prepared by the preparation method of the Bi-2212 single core rod.

[0019] The present invention also provides a method for preparing a Bi-2212 single core wire by using the Bi-2212 single core rod, wherein the Bi-2212 single core rod is rotary forged and drawn to prepare the Bi-2212 single core wire.

[0020] More preferably, during the rotary forging and drawing process, the Bi-2212 single core rod is first subjected to 2-3 rotary forging processes with a processing rate of 10%-15% per pass, and then subjected to drawing process with a processing rate of 10%-20% per pass.

[0021] The present invention also provides a Bi-2212 single-core wire prepared by the preparation method of the Bi-2212 single-core wire.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The single core rod and single core wire prepared by the preparation method of the present invention have high uniformity, uniform internal powder distribution, and consistent density.

[0024] (2) The preparation method of the present invention adopts the method of evacuating and performing heat treatment at the same time. When heating and evacuating, the impurity gas in the powder rod only needs to diffuse radially to the surface of the powder rod and can be quickly drawn out from the gap between the surface of the powder rod and the inner surface of the silver tube. The impurity gas can be easily diffused and removed.

[0025] (3) The preparation method of the present invention heats a single core rod in a flowing oxygen atmosphere. When there is a pressure difference and concentration difference inside and outside the silver tube after vacuuming, since oxygen atoms can freely penetrate through the silver tube, a small amount of oxygen atoms will penetrate into the tube and "wash away" the impurity gas that cannot be completely pumped out and remains, playing a role of washing. Although a very small amount of oxygen molecules will remain in the tube, since oxygen atoms can freely penetrate in the silver, they will diffuse out during the subsequent heat treatment process of the preparation, and will not form bubbles or holes, so the degassing effect is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the specific implementation modes of the present invention, the drawings required for use in the specific implementation modes will be briefly introduced below. Obviously, the drawings described below are only some specific implementation modes of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 It is a process schematic diagram of step 3 in the method for preparing a Bi-2212 single core rod of the present invention;

[0028] Figure 2 It is a process schematic diagram of step 4 in the method for preparing a Bi-2212 single core rod of the present invention;

[0029] Figure 3 The morphology of the strip prepared from the Bi-221 single core wire in Example 1 of the present invention after heat treatment;

[0030] Figure 4This is the morphology of the strip prepared from the Bi-221 single core wire in Comparative Example 1 of the present invention after heat treatment. DETAILED DESCRIPTION

[0031] In order to further understand the present invention, preferred embodiments of the present invention are described below. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0032] The preparation method of the Bi-2212 single core rod of the present invention comprises the following steps:

[0033] Step 1, heat-treating the Bi-2212 precursor powder at 810°C-820°C in air for 10h-12h, grinding it evenly after natural cooling, and then heat-treating it at 850°C-860°C in air for 20h-22h, taking it out, and grinding it to an average particle size of 4μm-8μm after natural cooling to obtain a powder with uniform particle size, loose and soft and without hard particles;

[0034] Step 2, pressing the powder obtained in step 1 into a uniform powder rod by a dry bag cold isostatic pressing process;

[0035] Step 3, put the powder rod obtained in step 2 into a silver tube, weld one end of the silver tube with a silver plug and seal it, weld the other end with a silver plug with a nozzle, the two end surfaces of the powder rod are in contact with the inner surfaces of the two silver plugs respectively, and the inner diameter of the silver tube is 1mm-1.5mm larger than the diameter of the powder rod, such as Figure 1 As shown;

[0036] Step 4, placing the silver tube containing the powder rod obtained in step 3 into a tubular furnace in a flowing oxygen atmosphere, extending the suction nozzle out of the tubular furnace and connecting a vacuum pump, evacuating the powder rod in the silver tube and performing heat treatment at the same time, such as Figure 2 As shown;

[0037] Step 5, clamp the nozzle to seal, stop vacuuming and heat treatment, cool the furnace to room temperature, take it out, and obtain a Bi-2212 single core rod.

[0038] In the above technical solution, in step 1, the Bi-2212 precursor powder is a prior art and can be prepared by spray pyrolysis. The purity of the Bi-2212 precursor powder is ≥99% and the average particle size is 4μm-8μm. The reaction solution of the spray pyrolysis method is a mixture of Bi nitrate, Sr nitrate, Ca nitrate and Cu nitrate solutions. In the mixture, the molar ratio of Bi:Sr:Ca:Cu is 2.17:1.94:0.89:2, and the total cation concentration is 1 mol / L.

[0039] In the above technical solution, in step 2, the pressure of the dry bag cold isostatic pressing is 30Mpa-40Mpa.

[0040] In the above technical solution, in step 3, the wall thickness of the silver tube is 1 mm-1.5 mm.

[0041] In the above technical solution, in step 4, the heat treatment temperature is 600°C-650°C, the heat treatment time is 10h-20h, and the vacuum degree is better than 10 -3 Pa, the pressure of the flowing oxygen atmosphere is 0.2Mpa-0.4Mpa.

[0042] The Bi-2212 single core rod prepared by the preparation method of the Bi-2212 single core rod of the present invention can be made into a Bi-2212 single core wire by rotary forging and drawing.

[0043] In the above technical solution, during the rotary forging and drawing process of the Bi-2212 single core rod, it is preferred to first perform 2-3 rotary forging processes with a pass processing rate of 10%-15%, and then perform drawing process with a pass processing rate of 10%-20%.

[0044] The terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art, unless otherwise specified.

[0045] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with embodiments.

[0046] In the following examples, various processes and methods not described in detail are conventional methods known in the art. Unless otherwise specified, the materials, reagents, devices, instruments, equipment, etc. used in the following examples can be obtained from commercial sources.

[0047] Example 1

[0048] The preparation method of Bi-2212 single core rod and Bi-2212 single core wire comprises the following steps:

[0049] Step 1, heat-treating 400 g of Bi-2212 precursor powder prepared by spray pyrolysis in air at 820° C. for 10 h, grinding it evenly after natural cooling, and then heat-treating it in air at 850° C. for 20 h, taking it out, and grinding it to an average particle size of 4 μm after natural cooling to obtain powder;

[0050] Step 2, the powder obtained in step 1 is processed by dry bag cold isostatic pressing process, and pressed into uniform powder rods with a diameter of 19 mm at a pressure of 30 MPa;

[0051] Step 3, the powder rod obtained in step 2 is loaded into a silver tube, one end of the silver tube is sealed by welding with a silver plug, and the other end is sealed by welding with a silver plug with a suction nozzle, and the two end surfaces of the powder rod are respectively in contact with the inner surfaces of the two silver plugs, the inner diameter of the silver tube is 1 mm larger than the diameter of the powder rod, and the wall thickness is 1 mm;

[0052] Step 4, placing the silver tube containing the powder rod obtained in step 3 into a tubular furnace in a flowing oxygen atmosphere, extending the suction nozzle out of the tubular furnace and connecting a vacuum pump to evacuate the powder rod in the silver tube and perform heat treatment at the same time;

[0053] The vacuum degree is 5×10 -4 Pa, the pressure of flowing oxygen atmosphere in the tubular furnace is 0.2Mpa, the heat treatment temperature is 600℃, and the holding time is 15h;

[0054] Step 5, seal the nozzle, stop vacuuming and heat treatment, cool the furnace to room temperature, take it out, and obtain a Bi-2212 single core rod.

[0055] Comparative Example 1

[0056] Step 1, heat-treating 400 g of Bi-2212 precursor powder prepared by spray pyrolysis in air at 820° C. for 10 h, grinding it evenly after natural cooling, and then heat-treating it in air at 850° C. for 20 h, taking it out, and grinding it to an average particle size of 4 μm after natural cooling to obtain powder;

[0057] Step 2, the powder obtained in step 1 is placed in a silver tube with an inner diameter of 20 mm and a wall thickness of 1 mm by vibrating the tube, one end of the silver tube is sealed by welding with a silver plug, and the other end is sealed by welding with a silver plug with a suction nozzle;

[0058] Step 3: vacuumize the silver tube and perform heat treatment at the same time, with a vacuum degree of 5×10 -4 Pa, furnace heat treatment temperature is 600℃, holding time is 15h;

[0059] Step 4, clamp the nozzle tightly and seal it, stop vacuuming and heat treatment, cool the furnace to room temperature, take it out, and obtain a Bi-2212 single core rod.

[0060] In order to verify the degassing effect, the Bi-2212 single core rod prepared in Example 1 and Comparative Example 1 was first subjected to two rotary forging processes, with a processing rate of 10%, and then drawn into a single core wire of 1.5 mm in diameter at a processing rate of 15%, and then rolled into a strip with a thickness of 0.3 mm at a processing rate of 20%, respectively recorded as Strip 1 and Strip 2. Strip 1 and Strip 2 were subjected to normal pressure heat treatment in a heat treatment furnace together, and the heat treatment process was first heated to 890°C at a rate of 160°C / h, kept warm for 15 minutes, then cooled to 880°C at a rate of 10°C / h, and then cooled to 836°C at 2.5°C / h, kept warm for 30 hours, and finally cooled to room temperature in the furnace. Figure 3 is the morphology of the strip 1 after heat treatment, Figure 4 is the morphology of the strip 2 after heat treatment. Figure 3 , Figure 4 By comparison, it can be seen that the strip obtained by the method of the present invention has no bubbling phenomenon, which proves that the degassing effect is good and the impurity gas is small.

[0061] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a Bi-2212 single core rod, characterized in that: Here are the steps: Step 1, heat-treating the Bi-2212 precursor powder in air at 810°C-820°C for 10h-12h, grinding it evenly after natural cooling, and then heat-treating it in air at 850°C-860°C for 20h-22h, taking it out, and grinding it to an average particle size of 4μm-8μm after natural cooling to obtain powder; Step 2, pressing the powder obtained in step 1 into a uniform powder rod by a dry bag cold isostatic pressing process; Step 3, putting the powder rod obtained in step 2 into a silver tube, welding and sealing one end of the silver tube with a silver plug, and welding and sealing the other end with a silver plug with a suction nozzle, the two end surfaces of the powder rod are in contact with the inner surfaces of the two silver plugs respectively, and the inner diameter of the silver tube is 1mm-1.5mm larger than the diameter of the powder rod; Step 4, placing the silver tube containing the powder rod obtained in step 3 into a tubular furnace in a flowing oxygen atmosphere, extending the suction nozzle out of the tubular furnace and connecting a vacuum pump to evacuate the powder rod in the silver tube and perform heat treatment at the same time; Step 5, seal the nozzle, stop vacuuming and heat treatment, cool the furnace to room temperature, take it out, and obtain a Bi-2212 single core rod.

2. The method for preparing a Bi-2212 single core rod according to claim 1, characterized in that: In step 1, the Bi-2212 precursor powder is prepared by spray pyrolysis, and the purity of the Bi-2212 precursor powder is ≥99%, and the average particle size is 4 μm-8 μm.

3. The method for preparing a Bi-2212 single core rod according to claim 2, characterized in that: The reaction solution of the spray thermal decomposition method is a mixture of Bi nitrate, Sr nitrate, Ca nitrate and Cu nitrate solutions, in which the molar ratio of Bi:Sr:Ca:Cu is 2.17:1.94:0.89:2, and the total cation concentration is 1 mol / L.

4. The method for preparing a Bi-2212 single core rod according to claim 1, characterized in that: In step 2, the pressure of the dry bag cold isostatic pressing is 30Mpa-40Mpa.

5. The method for preparing a Bi-2212 single core rod according to claim 1, characterized in that: In step 3, the wall thickness of the silver tube is 1 mm-1.5 mm.

6. The method for preparing a Bi-2212 single core rod according to claim 1, characterized in that: In step 4, the heat treatment temperature is 600°C-650°C, the heat treatment time is 10h-20h, and the vacuum degree is better than 10 -3 Pa, the pressure of the flowing oxygen atmosphere is 0.2Mpa-0.4Mpa.

7. A Bi-2212 single core rod prepared according to the preparation method according to any one of claims 1 to 6.

8. A method for preparing a Bi-2212 single core wire using the Bi-2212 single core rod according to claim 7, characterized in that: The Bi-2212 single core rod is rotary forged and drawn to produce the Bi-2212 single core wire.

9. The method for preparing Bi-2212 single core wire according to claim 8, characterized in that: During the rotary forging and drawing process, the Bi-2212 single core rod is firstly subjected to 2-3 rotary forging processes with a processing rate of 10%-15% and then subjected to drawing process with a processing rate of 10%-20%.

10. The Bi-2212 single core wire prepared by the method for preparing the Bi-2212 single core wire according to claim 8.

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