Degassing and tubing method for Bi-2212 precursor powder

Abstract

The invention relates to a degassing and tubing method for Bi-2212 precursor powder, and belongs to the technical field of powder tubing methods. The tubing method comprises the following steps: performing heat treatment on Bi-2212 precursor powder in air, naturally cooling, uniformly grinding, performing heat treatment in air, taking out, naturally cooling, and uniformly grinding to obtain powder I; then, the powder I is subjected to vacuum hot pressing sintering treatment and compressed into a bar; the bar is taken out under the condition of air isolation and is smashed and ground evenly, and powder II is obtained; and finally, the powder II is loaded into a silver tube under the vacuum condition through a vibration tube loading method, the two ends of the silver tube are sealed through silver plugs, and the Bi-2212 single-core rod is obtained. According to the method, the Bi-2212 precursor powder is subjected to hole-free treatment through a simple process, so that gas is prevented from remaining in particles, and then it can be guaranteed that impurity gas in a single-core rod or a single-core wire is greatly reduced after the precursor powder is filled into a tube.

Description

Technical Field

[0001] The invention belongs to the technical field of powder tube filling methods, and in particular relates to a degassing tube filling method for Bi-2212 precursor powder. Background Art

[0002] Bi-2212(Bi2Sr2CaCu2O x ) Superconducting materials have excellent current-carrying properties under high magnetic fields. Under liquid helium cooling (4.2K), its irreversible field can exceed 100T. Moreover, due to the texture characteristics of Bi-2212 during heat treatment, Bi-2212 becomes the only high-temperature superconducting material that can be made into isotropic round wires, which greatly facilitates the winding of magnet coils. It is precisely because of these characteristics that Bi-2212 is considered to be one of the superconducting materials with the most promising high-field applications, which is of great significance to the development of high-field magnets.

[0003] In mass production, the precursor of Bi-2212 is usually prepared by co-precipitation or spray pyrolysis, and then prepared into multi-core wires by powder in tube method (PIT), and the wires are heat treated.

[0004] The bubbles and holes in the core of Bi-2212 wire are one of the main current limiting factors of the wire. The bubbles and holes are mainly formed when the impurity gas in the core flows and gathers in the liquid phase during the partial melting heat treatment of the wire. The sources of the impurity gas are mainly the gas remaining in the pores within the powder particles in the precursor powder for tube loading of the single core rod (Bi-2212 precursor powder is generally a porous and loose ceramic powder), the gas between the powder particles, and the C and H elements remaining in the powder (the residual C and H elements will turn into CO2 and H2O gas during the partial melting heat treatment of the wire). It is relatively simple to remove or reduce the gas between the powder particles and the C and H elements remaining in the powder, but it is difficult to remove the gas within the powder particles, which becomes the source of bubble formation in the core, inhibiting the current carrying performance of the superconducting core of the wire. Summary of the invention

[0005] The purpose of the present invention is to provide a method for degassing and pipe-loading Bi-2212 precursor powder, which uses a simple process to perform a non-porous treatment on the Bi-2212 precursor powder to avoid gas retention inside the particles. This can ensure that after the precursor powder is pipe-loaded, 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 degassing and pipe-loading Bi-2212 precursor powder, comprising the following steps:

[0008] 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 powder I;

[0009] Step 2, subjecting the powder I obtained in step 1 to vacuum hot pressing and sintering treatment to compress the powder into a rod;

[0010] Step 3, taking out the rod obtained in step 2 under air-tight conditions and grinding it to an average particle size of 5 μm-15 μm to obtain powder II;

[0011] Step 4, the powder II obtained in step 3 is loaded into a silver tube by a vibration tube loading method under vacuum conditions, and both ends of the silver tube are sealed with silver plugs to obtain a Bi-2212 single core rod.

[0012] Preferably, the method further comprises step 5, wherein the Bi-2212 single core rod obtained in step 4 is rotary forged and drawn to form a single core wire.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] Preferably, in step 2, the vacuum hot pressing sintering temperature is 500°C-600°C, the holding time is 5h-8h, and the vacuum degree is better than 10 -2 Pa, pressure is 20T-30T.

[0017] Preferably, in step 4, the tube density of the powder II is 1.1-1.4 g / cm 3 .

[0018] The principle of the present invention is as follows: Bi-2212 precursor powder is a powder with a porous ceramic structure. After the powder is loaded into a tube, the air mainly remains in the holes inside the powder particles and in the gaps between the powder particles. When the powder after loading into a tube is degassed, only most of the gas between the particles can be extracted, but the gas inside the particles is difficult to remove and will always remain in the core wire of the wire. The present invention adopts a vacuum hot pressing sintering method to press the precursor powder into a rod with uniform density under high pressure, and performs a pore-free treatment to prepare a "pore-free solid" powder close to the theoretical density to avoid gas retention inside the particles. At the same time, it can also remove residual C and H elements by vacuum sintering. Afterwards, the rod is crushed and ground into a uniform powder. In this way, after the powder is loaded into a tube, since there are no pores and residual air inside the powder particles, and no residual C and H elements, the gas impurities in the single core rod can be greatly reduced. At the same time, the powder is transformed from a rod into powder and then loaded into a tube, so that there are vacuum gaps between the powders, the powder can be compressed, and the powder particles can also roll or slide between molecular layers, thus ensuring the good processability of the single core rod.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The degassing and tube-loading method of the Bi-2212 precursor powder of the present invention performs a non-porous treatment on the Bi-2212 precursor powder through a simple process to avoid gas retention inside the particles, and removes residual C and H elements at the same time. This ensures that after the precursor powder is loaded into the tube, the impurity gas in the single-core rod or single-core wire is greatly reduced, thereby improving the current-carrying performance of the single-core rod and single-wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 The morphology of the strip prepared from the Bi-2212 single core wire in Example 1 of the present invention after heat treatment;

[0023] Figure 2 This is the morphology of the strip prepared from the Bi-2212 single core wire in Comparative Example 1 of the present invention after heat treatment. DETAILED DESCRIPTION

[0024] 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.

[0025] The degassing and tube-loading method of Bi-2212 precursor powder of the present invention comprises the following steps:

[0026] 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 powder I, which is in a state of uniform particle size, loose and soft without hard particles;

[0027] Step 2, subjecting the powder I obtained in step 1 to vacuum hot pressing sintering, compressing the powder into a rod, wherein the rod is highly dense and the pores and C and H elements in the powder I are removed;

[0028] Step 3, taking out the rod obtained in step 2 under air-tight conditions and grinding it to an average particle size of 5 μm-15 μm to obtain powder II;

[0029] Step 4, the powder II obtained in step 3 is loaded into a silver tube by a vibration tube loading method under vacuum conditions, and both ends of the silver tube are sealed with silver plugs to obtain a Bi-2212 single core rod;

[0030] Step 5, forging and drawing the Bi-2212 single core rod obtained in step 4 to make a single core wire of required size.

[0031] 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.

[0032] In the above technical solution, in step 2, the temperature of vacuum hot pressing sintering is 500℃-600℃, and the holding time is 5-8h. The vacuum degree during vacuum hot pressing sintering is better than 10 -2 Pa, pressure is 20T-30T.

[0033] In the above technical solution, in step 4, the tube density of powder II is 1.1-1.4 g / cm 3 .

[0034] In the above technical solution, in step 5, during the rotary forging and drawing process, the Bi-2212 single core rod is first subjected to 2-3 rotary forging processes with a pass processing rate of 10%-15%, and then subjected to drawing process with a pass processing rate of 10%-20%.

[0035] The terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art, unless otherwise specified.

[0036] 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.

[0037] 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.

[0038] Example 1

[0039] The degassing and tube filling method of Bi-2212 precursor powder is as follows:

[0040] 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 I;

[0041] Step 2: subject the powder I obtained in step 1 to vacuum hot pressing sintering at a temperature of 500°C and a vacuum of more than 10 -2 Pa, pressure 30T, holding time 8h, and rods were obtained;

[0042] Step 3, taking out the rod obtained in step 2 under air-tight conditions and grinding it evenly to a particle size of 10 μm to obtain powder II;

[0043] Step 4: Powder II obtained in step 3 is loaded into a silver tube with an outer diameter of 21 mm and an inner diameter of 19 mm by a vibration loading method under vacuum conditions, and both ends of the silver tube after loading are sealed with silver plugs, and the loading density is 1.1 g / m 3 , and obtained the Bi-2212 single core rod.

[0044] Comparative Example 1

[0045] 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;

[0046] Step 2: The powder obtained in step 1 is loaded into a silver tube (outer diameter 21 mm, inner diameter 19 mm) by a vibration loading method under vacuum conditions, and both ends of the silver tube are sealed with silver plugs to obtain a Bi-2212 single core rod.

[0047] 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 1 is the morphology of strip 1 after heat treatment, Figure 2 is the morphology of the strip 2 after heat treatment. Figure 1 , Figure 2 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.

[0048] 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 degassing and pipe-loading Bi-2212 precursor powder, characterized in that: Here are the steps: 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 powder I; Step 2, subjecting the powder I obtained in step 1 to vacuum hot pressing and sintering treatment to compress the powder into a rod; Step 3, taking out the rod obtained in step 2 under air-tight conditions and grinding it to an average particle size of 5 μm-15 μm to obtain powder II; Step 4, the powder II obtained in step 3 is loaded into a silver tube by a vibration tube loading method under vacuum conditions, and both ends of the silver tube are sealed with silver plugs to obtain a Bi-2212 single core rod.

2. The degassing and pipe-loading method of Bi-2212 precursor powder according to claim 1, characterized in that: The method also includes step 5, wherein the Bi-2212 single core rod obtained in step 4 is rotary forged and drawn to form a Bi-2212 single core wire.

3. The degassing and pipe-loading method of Bi-2212 precursor powder according to claim 2, characterized in that: In step 5, during the rotary forging and drawing process, the Bi-2212 single core rod is first subjected to 2-3 rotary forging processes with a pass processing rate of 10%-15%, and then subjected to drawing process with a pass processing rate of 10%-20%.

4. The degassing and pipe-loading method of Bi-2212 precursor powder 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.

5. The degassing and pipe-loading method of Bi-2212 precursor powder according to claim 4, characterized in that: In step 1, 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.

6. The degassing and pipe-loading method of Bi-2212 precursor powder according to claim 1, characterized in that: In step 2, the vacuum hot pressing sintering temperature is 500°C-600°C, the holding time is 5h-8h, and the vacuum degree is better than 10 -2 Pa, pressure is 20T-30T.

7. The degassing and pipe-loading method of Bi-2212 precursor powder according to claim 1, characterized in that: In step 4, the tube density of the powder II is 1.1-1.4 g / cm 3 .

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