Impurity gas removing method for Bi-2212 precursor powder

Abstract

The invention relates to a method for removing foreign gas from Bi-2212 precursor powder, which comprises the following steps: firstly, carrying out heat treatment and grinding on the Bi-2212 precursor powder in air, and then carrying out heat treatment and grinding to obtain powder; then pressing the powder into a uniform powder bar through a dry bag type cold isostatic pressing process; and then taking out the obtained powder bar under the condition of air isolation, putting the powder bar into a silver tube, and sealing the two ends of the silver tube by using silver plugs to obtain the Bi-2212 single-core bar. And performing rotary swaging and drawing on the Bi-2212 single-core rod to prepare the Bi-2212 single-core wire. 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 meanwhile, residual C and H elements are removed, so that impurity gas in a single-core rod or a single-core wire can be greatly reduced after the precursor powder is filled into a tube, and the current-carrying performance of the single-core rod or the single-core wire is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of impurity removal gas methods, and in particular relates to an impurity removal gas method for Bi-2212 precursor powder. Background Art

[0002] Bi-2212(Bi 2 Sr 2 CaCu 2 O x ) Superconducting materials have an irreversible field of more than 100 T at 4.2 K, and have a very high critical current density even at a magnetic field of 50 T. Therefore, after Bi-2212 is prepared into wire, it can be made into high-field magnets, which play an important role in the fields of science, engineering and industrial technology.

[0003] In the practical production of Bi-2212, its precursor powder is usually prepared by coprecipitation or spray pyrolysis. The prepared precursor powder is then processed and drawn into wire by the powder in tube method (PIT). During the processing of the wire, the air impurities and C and H elements remaining in the powder will form bubbles and holes in the subsequent heat treatment process, thereby hindering the flow of current in the wire, reducing the current carrying capacity or causing quenching. Therefore, in order to improve the current carrying performance and stability of the wire, it is necessary to reduce the impurity gas and C and H elements in the precursor powder as much as possible. It is relatively easy to remove the gas between the powder particles and the C and H elements remaining in the powder, but due to the loose and porous characteristics of Bi-2212 powder, the gas impurities in the powder particles are difficult to remove, becoming the source of bubble formation in the core wire, affecting the current carrying performance of the wire. Summary of the invention

[0004] The purpose of the present invention is to provide a method for removing impurity gases from 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 loaded into a tube, the impurity gas in a single core rod or a single core wire is greatly reduced.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows.

[0006] A method for removing impurity gas from Bi-2212 precursor powder, the steps are as follows:

[0007] 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;

[0008] Step 2, subjecting the powder obtained in step 1 to vacuum hot pressing and sintering to prepare a powder rod;

[0009] The powder rod is provided with a plurality of through holes along the axial direction, and the plurality of through holes are arranged in parallel;

[0010] Step 3, take out the powder rod obtained in step 2 under air-tight conditions and put it into a silver tube, and seal both ends of the silver tube with silver plugs, so that the two end surfaces of the powder rod are in contact with the inner surfaces of the two silver plugs respectively, to obtain a Bi-2212 single-core rod.

[0011] Preferably, the method further comprises step 4, wherein the Bi-2212 single core rod obtained in step 3 is subjected to rotary forging and drawing to form a Bi-2212 single core wire;

[0012] More preferably, the Bi-2212 single core rod is first subjected to 2-3 times of rotary forging, with a processing rate of 5%-10% per pass, and then subjected to drawing, with a processing rate of 10%-20% per pass.

[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 vacuum degree of the vacuum hot pressing sintering is better than 10 -2 Pa, temperature is 400℃-600℃, holding time is 5h-8h, pressure is 20T-30T.

[0016] Preferably, in step 2, the through holes in the powder rod are evenly distributed, and the total area of ​​the through holes accounts for 50%-60% of the cross-sectional area.

[0017] The principle of the present invention is as follows: Bi-2212 precursor powder is a powder of porous ceramic structure. After the powder is loaded into a tube, the air mainly remains in the holes inside the powder particles and the gaps between the powder particles. When the powder after loading into the 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 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 non-porous treatment to prepare a "non-porous solid" powder close to the theoretical density to avoid gas retention inside the particles, and at the same time, the residual C and H elements can be escaped by vacuum sintering. The gas impurities in the single core rod can be greatly reduced. At the same time, since the powder rod contains through holes, after 2-3 times of rotary forging, the powder rod is broken and fills the gaps of the through holes, and has a suitable porosity, so that the powder can be compressed in the subsequent drawing process, and the powder particles can also roll or slide between molecular layers, thereby ensuring the good processability of the single core rod.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The method for removing impurity gas from Bi-2212 precursor powder of the present invention performs a non-porous treatment on 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, so that after the precursor powder is loaded into a tube, the impurity gas in a single core rod or a single core wire is greatly reduced, thereby improving the current carrying performance of the single core rod and the single wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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.

[0021] Figure 1 A schematic diagram of the structure of the powder rod prepared by the present invention;

[0022] Figure 2 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 3 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 method for removing impurity gas from 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 a powder; the powder has a uniform particle size, is loose and soft, and has no hard particles;

[0027] Step 2, subjecting the powder obtained in step 1 to vacuum hot pressing and sintering to prepare a powder rod;

[0028] The powder rod is provided with a plurality of through holes along the axial direction, and the plurality of through holes are arranged in parallel; this can be achieved by prefabricating the plug rod;

[0029] During the vacuum hot pressing sintering process, the density of the powder rod can be made uniform, and the pores and C and H elements in the powder rod can also be removed;

[0030] Step 3, taking out the powder rod obtained in step 2 under air-tight conditions and loading it into a silver tube, and sealing both ends of the silver tube with silver plugs, so that the two end surfaces of the powder rod are in contact with the inner surfaces of the two silver plugs respectively, to obtain a Bi-2212 single-core rod;

[0031] Step 4, rotary forging and drawing the Bi-2212 single core rod obtained in step 3 to make a Bi-2212 single core wire.

[0032] 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.

[0033] In the above technical solution, in step 2, the vacuum degree of vacuum hot pressing sintering is better than 10 -2 Pa, temperature is 400℃-600℃, holding time is 5h-8h, and pressure is 20T-30T. The through holes in the powder rod are evenly distributed, and the total area of ​​the through holes accounts for 50%-60% of the cross-sectional area.

[0034] In the above technical solution, in step 4, the Bi-2212 single core rod is first subjected to 2-3 rotary forging processes with a processing rate of 5%-10% per pass, and then subjected to several drawing processes with a processing rate of 10%-20% per pass.

[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] A method for degassing and pipe-loading Bi-2212 precursor powder, comprising the following steps:

[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 a powder with uniform particle size, looseness, softness and no hard particles;

[0041] Step 2, subjecting the powder obtained in step 1 to vacuum hot pressing and sintering to prepare a powder rod;

[0042] The sintering temperature is 400℃ and the vacuum is better than 10 -2 Pa, pressure 30T, holding time 8h, total through-hole area 50% of the cross-sectional area of ​​the powder rod, powder rod diameter 18mm;

[0043] Step 3, the powder rod obtained in step 2 is placed in an airtight condition and loaded into a silver tube with an outer diameter of 21 mm and an inner diameter of 19 mm. Both ends of the silver tube are sealed with silver plugs. The two end surfaces of the powder rod are respectively in contact with the inner surfaces of the two silver plugs to obtain a 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 a powder with uniform particle size, looseness, softness and no hard particles;

[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 2 is the morphology of the strip 1 after heat treatment, Figure 3 is the morphology of the strip 2 after heat treatment. Figure 2 , Figure 3 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 removing impurity gas from Bi-2212 precursor powder, 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, subjecting the powder obtained in step 1 to vacuum hot pressing and sintering to prepare a powder rod; The powder rod is provided with a plurality of through holes along the axial direction, and the plurality of through holes are arranged in parallel; Step 3, take out the powder rod obtained in step 2 under air-tight conditions and put it into a silver tube, and seal both ends of the silver tube with silver plugs, so that the two end surfaces of the powder rod are in contact with the inner surfaces of the two silver plugs respectively, to obtain a Bi-2212 single-core rod.

2. The method for removing impurity gas from Bi-2212 precursor powder according to claim 1, characterized in that: The method also includes step 4, which involves rotary forging and drawing the Bi-2212 single core rod to form a Bi-2212 single core wire.

3. The method for preparing Bi-2212 single core wire according to claim 2, characterized in that: The Bi-2212 single core rod is first subjected to three rotary forging processes, with a processing rate of 5%-10% per pass, and then subjected to several drawing processes, with a processing rate of 10%-20% per pass.

4. The method for removing impurity gas from 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 method for removing impurity gas from 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 method for removing impurity gas from Bi-2212 precursor powder according to claim 1, characterized in that: In step 2, the vacuum degree of the vacuum hot pressing sintering is better than 10 -2 Pa, temperature is 400℃-600℃, holding time is 5h-8h, pressure is 20T-30T.

7. The method for removing impurity gas from Bi-2212 precursor powder according to claim 1, characterized in that: In step 2, the through holes in the powder rod are evenly distributed, and the total area of ​​the through holes accounts for 50%-60% of the cross-sectional area.

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