Preparation method of high-purity bi-2212 superconducting material precursor powder

Abstract

The application discloses a preparation method of high-purity Bi-2212 superconducting material precursor powder, which comprises the following steps: S1, accurately weighing required raw materials according to a certain stoichiometric ratio, preparing a Bi-2212 precursor solution, and then preparing high-uniformity and high-activity Bi-2212 precursor powder; S2, performing high-pressure die compaction densification on the precursor powder prepared in S1 to form a dense green body; S3, performing high-temperature sintering on the dense green body obtained in S2 to obtain low-Bi-2201 phase high-purity Bi-2212 tube-packed powder; S4, preparing Bi-2212 superconducting wire using the tube-packed powder obtained in S3 by a PIT method; and S5, performing high-pressure sintering treatment on the superconducting wire obtained in S4, and finally obtaining Bi-2212 superconducting wire with high current-carrying performance. According to the application, the precursor powder is pre-densified by high-pressure tabletting, and then high-temperature sintering is performed, so that Bi element high-temperature volatilization is inhibited, element microscopic component segregation is weakened, and the Bi-2201 phase content in the Bi-2212 matrix is effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of Bi-2212 high-temperature superconducting material preparation technology, specifically relating to a method for preparing high-purity Bi-2212 superconducting material precursor powder. Background Technology

[0002] Bi₂Sr₂CaCu₂O 8+δ Bi-2212 (Bi-2212) high-temperature superconducting materials possess high critical temperatures and excellent strong magnetic field current-carrying characteristics, making them irreplaceable in core equipment such as high-field superconducting magnets, particle accelerator magnets, and nuclear fusion superconducting coils. Bi, an element in Bi-based superconductors, exhibits strong high-temperature reactivity, readily undergoing surface evaporation and grain boundary diffusion within the conventional sintering temperature range of 850–875℃. Conventional precursor powder preparation processes involve loosely spreading the powder and directly sintering it, resulting in a loose packing structure with numerous interconnected pores and a large specific surface area, providing ample channels for Bi diffusion.

[0003] After a large amount of Bi volatilizes and diffuses, the local elemental ratio in the powder becomes unbalanced, forming Bi-rich and Ca-deficient micro-regions, which readily nucleate and precipitate Bi₂Sr₂CuO. 6+δ (Bi-2201) phase. Bi-2201 is a non-superconducting impurity phase with a low critical temperature. It not only disrupts the crystal matching between Bi-2212 matrix grains, but also induces weak grain boundary connectivity, significantly reducing the critical current density of the material and deteriorating its superconducting transport properties and structural thermal stability.

[0004] Existing research mainly focuses on sintering temperature, oxygen partial pressure control, and elemental doping modification. It has not yet addressed the issue of densification of precursor powder to fundamentally block Bi volatilization channels, suppress microscopic component segregation, and reduce Bi-22O1 phase formation, thereby improving the purity of Bi-2212 superconducting material precursor powder. Therefore, developing a simple, industrially adaptable, and effective densification sintering process that significantly reduces Bi-22O1 phase content and improves precursor powder purity has significant engineering value. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high-purity Bi-2212 superconducting material precursor powder. The precursor powder is pre-densified by high-pressure pressing and then sintered at high temperature, thereby suppressing the high-temperature volatilization of Bi element, reducing the segregation of elemental microstructure, and effectively reducing the content of Bi-2201 phase in Bi-2212 matrix.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing high-purity Bi-2212 superconducting material precursor powder includes the following steps: S1. Accurately weigh the required raw materials according to a certain stoichiometric ratio to prepare a Bi-2212 precursor solution, and then prepare a highly uniform and highly active Bi-2212 precursor powder. S2, the precursor powder prepared in S1 is densified by high-pressure molding to form a dense green body; S3, the dense green body obtained in S2 is sintered at high temperature to obtain high-purity Bi-2212 tube powder with low Bi-2201 phase. S4. The tube-packed powder obtained in S3 was used to prepare Bi-2212 superconducting wire using the PIT method. S5. The superconducting wire obtained in S4 is subjected to high-pressure sintering to finally obtain Bi-2212 superconducting wire with high current carrying capacity.

[0007] Preferably, in step S1, the Bi-2212 precursor solution is prepared by a nitrate mixing method, wherein the atomic ratio of Bi, Sr, Ca, and Cu is 2.17 : 1.94 : 0.89 : 2.00, and the error of the content of each element in the obtained precursor solution does not exceed 3%.

[0008] Preferably, in S1, the precursor powder is prepared using spray pyrolysis technology.

[0009] Preferably, in step S2, the specific steps of step S2 are as follows: the precursor powder from step S1 is loaded into a cemented carbide mold and prepared by a unidirectional compression molding process, with the pressure controlled at 15-35 MPa and the holding time at pressure at 3-10 min; the molding process parameters are adjusted so that the relative density of the resulting sheet-like or columnar green body is maintained at 80%-90%, forming a dense green body structure with tightly packed particles and high pore closure.

[0010] Preferably, in S3, the high-temperature sintering process specifically includes: sintering twice; each time, the temperature is raised to 830-860°C at a uniform rate of 5-10°C / min and held for 10-12 hours; after sintering, the furnace is cooled to room temperature; and the sintering atmosphere for each sintering is air or oxygen.

[0011] Preferably, in step S4, the PIT method specifically involves loading the powder obtained in step S3 into a silver tube of a certain size under vacuum and sealing both ends of the silver tube. Combined with multiple drawing and assembly processes, a Bi-2212 superconducting wire with excellent and uniform superconducting properties is prepared.

[0012] The beneficial effects of this invention are as follows: 1. This invention pre-densifies the precursor powder by high-pressure pressing, blocking the channels for Bi element volatilization and diffusion. This overcomes the shortcomings of existing loose powder sintering processes, such as well-developed internal interconnected pores, large specific surface area, and easy gas-phase escape of Bi atoms along the particle surface and pore channels at high temperatures. After high-pressure pressing, the particle interfaces are tightly bonded, large open pores and interconnected pores are largely closed, and the specific surface area is significantly reduced, thereby significantly reducing the volatilization and diffusion paths of Bi element and effectively suppressing the loss of Bi element due to high-temperature volatilization.

[0013] 2. This invention pre-densifies the precursor powder by high-pressure pressing, which suppresses the high-temperature diffusion and escape of Bi element, while weakening the micro-component segregation inside the powder. It effectively eliminates the Bi-rich and Ca-deficient micro-segregation region in the system, inhibits the nucleation process of the Bi-2201 phase from the composition source level, significantly reduces the content of the Bi-2201 non-superconducting phase in the precursor powder, and improves the purity of the Bi-2212 phase.

[0014] 3. This invention reduces the Bi-2201 phase content in the precursor powder by pre-densifying the powder under high pressure, thereby improving the crystallinity and lattice integrity of Bi-2212 grains in the microstructure, effectively weakening the weak grain boundary connection effect, reducing the tendency of Bi-2212 layered lattice to become unstable at high temperature and to decompose into Bi-2201 phase, maintaining the structural stability of the target superconducting phase, and thus improving the low-temperature current carrying capacity of the superconducting material to a certain extent.

[0015] 4. The precursor powder compaction densification process of the present invention does not require vacuum or special protective atmosphere, nor does it require additional doping modification. Second phase suppression can be achieved simply by molding and high-temperature sintering. It has strong equipment adaptability, simple process, low cost, and is suitable for industrial mass production. It is of great significance for accelerating the engineering application of Bi-2212 superconducting materials in high-field magnets. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0018] like Figure 1 As shown, a method for preparing high-purity Bi-2212 superconducting material precursor powder includes the following steps: S1. Accurately weigh the required raw materials according to a certain stoichiometric ratio to prepare a Bi-2212 precursor solution, and then prepare a Bi-2212 precursor powder with high uniformity and high activity.

[0019] The Bi-2212 precursor solution was prepared using a nitrate mixing method, wherein the atomic ratio of Bi, Sr, Ca, and Cu was 2.17:1.94:0.89:2.00, and the error in the content of each element in the obtained precursor solution did not exceed 3%.

[0020] The precursor powder is prepared using spray pyrolysis technology. This invention prepares Bi-2212 precursor powder using spray pyrolysis technology. The prepared precursor powder exhibits higher reactivity, lower element loss rate, and smaller particle size, resulting in a more uniform critical current distribution in the superconducting material.

[0021] S2, the precursor powder prepared in S1 is densified by high-pressure molding to form a dense green body.

[0022] The precursor powder in S1 is loaded into a cemented carbide mold and prepared by unidirectional compression molding process. The pressure is controlled at 15-35 MPa and the holding time is 3-10 min. The molding process parameters are adjusted to maintain the relative density of the obtained sheet or columnar green body at 80%-90%, forming a dense green body structure with tightly packed particles and high pore closure.

[0023] S3, the dense green body obtained in S2 is sintered at high temperature to obtain high-purity Bi-2212 tube powder with low Bi-2201 phase.

[0024] The high-temperature sintering process specifically involves two sintering cycles; each cycle involves uniformly raising the temperature to 830–860°C at a rate of 5–10°C / min and holding for 10–12 hours; after sintering, the furnace is cooled to room temperature; the first sintering atmosphere is air, and the second sintering atmosphere is oxygen. This invention obtains highly active and highly uniform packaged powders by controlling the high-temperature sintering process parameters.

[0025] S4. The tube powder obtained in S3 is used to prepare Bi-2212 superconducting wire using the PIT method.

[0026] The specific steps of the PIT method are as follows: the powder obtained in S3 is packed into a silver tube of a certain size under vacuum and the two ends of the silver tube are sealed. Combined with multiple drawing and assembly processes, Bi-2212 superconducting wire with excellent and uniform superconducting properties is prepared.

[0027] S5. The superconducting wire obtained in S4 is subjected to high-pressure sintering to finally obtain Bi-2212 superconducting wire with high current carrying capacity.

[0028] This invention first prepares Bi-2212 precursor powder, and then prepares a densified green body by pressing the precursor powder into tablets, thus blocking the channels for Bi volatilization and diffusion. Loose powder has well-developed interconnected pores and a large specific surface area, making it easy for Bi atoms to escape into the gas phase along the particle surface and pore channels at high temperatures. After high-pressure pressing and densification, the particle interfaces are tightly bonded, large open pores and interconnected pores are largely closed, and the specific surface area is significantly reduced, thereby significantly reducing the volatilization and diffusion paths of Bi and effectively suppressing Bi volatilization losses at high temperatures.

[0029] This invention effectively suppresses the diffusion and escape of Bi element by densifying the precursor powder through pelleting, weakens the micro-segregation of the powder's internal microstructure, and effectively eliminates the Bi-rich and Ca-deficient micro-segregation regions within the system. It cuts off the nucleation driving force of the Bi-2201 phase at its compositional source, resulting in a purer phase composition of the precursor powder after sintering. Pelletizing ensures uniform stress at the powder particle contact interface, significantly improving the diffusion rate and uniformity of elements during sintering. Furthermore, the reduced formation of the Bi-2201 phase at grain boundaries stabilizes the Bi-2212 layered crystal structure, improves weak connections between grain boundaries, reduces the tendency for high-temperature instability of the Bi-2212 layered lattice and its phase transformation into the Bi-2201 phase, and maintains the structural stability of the target superconducting phase.

[0030] This invention prepares Bi-2212 precursor powder through spray pyrolysis, and then prepares a high-density powder green body by limiting the molding parameters of the precursor powder. Combined with a high-temperature solid-state sintering process, it achieves the suppression of high-temperature volatilization of Bi element, uniform solid-state diffusion of elements, and elimination of Bi-rich and Ca-deficient micro-regions. It suppresses the nucleation and growth of the Bi-2201 non-superconducting phase from both the physical structure and composition levels, thereby improving the purity of the Bi-2212 phase, the integrity of crystal crystallization, and the high-field superconducting current-carrying performance.

[0031] The present invention will be further described in detail through the following embodiments.

[0032] Example 1 This embodiment includes the following steps: S1, a precursor solution with an atomic ratio of Bi, Sr, Ca, and Cu of 2.17 : 1.94 : 0.89 : 2.00 was prepared using a nitrate mixing method, and Bi-2212 precursor powder was prepared using a spray thermal decomposition process; S2, the Bi-2212 precursor powder prepared in S1 is loaded into a cemented carbide mold and prepared by unidirectional compression molding process. The pressure is set to 25MPa and the holding time is 5min, and a dense green blank with a relative density of 82% is obtained. S3: The densified green blank prepared in S2 is placed in a three-temperature zone tube furnace for high-temperature sintering, and the sintering is performed twice. The temperature is raised from room temperature to 830°C at a uniform rate of 10°C / min and held for 12 hours. The sintering atmosphere is air. After sintering, the furnace is cooled to room temperature. Then, the temperature is raised from room temperature to 860°C at a uniform rate of 10°C / min and held for 12 hours. The sintering atmosphere is oxygen. After sintering, the furnace is cooled to room temperature to obtain the tube-packed powder. S4. The tube-packing powder prepared in S3 is packed into a silver tube under vacuum, and Bi-2212 superconducting wire with excellent and uniform superconducting properties is prepared by PIT method. S5. The superconducting wire obtained in S4 is subjected to high-pressure sintering to finally obtain Bi-2212 superconducting wire with high current carrying capacity.

[0033] Testing revealed that the Bi-2201 phase content in the Bi-2212 tube powder prepared in this embodiment was 1.4%, and the Bi element volatility was 2.3%. The prepared Bi-2212 superconducting wire exhibited a critical current density of 6200 A / mm² under conditions of 4.2 K and 12 T. 2 .

[0034] Comparative Example 1 This comparative example includes the following steps: S1, a precursor solution with an atomic ratio of Bi, Sr, Ca, and Cu of 2.17 : 1.94 : 0.89 : 2.00 was prepared using a nitrate mixing method, and Bi-2212 precursor powder was prepared using a spray thermal decomposition process; S2, the loose Bi-2212 precursor powder prepared in S1 is placed in a three-temperature zone tube furnace for high-temperature sintering, and the sintering is performed twice. The temperature is raised from room temperature to 830℃ at a uniform rate of 10℃ / min and held for 12 h. The sintering atmosphere is air. After sintering, the furnace is cooled to room temperature. Then the temperature is raised from room temperature to 860℃ at a uniform rate of 10℃ / min and held for 12 h. The sintering atmosphere is oxygen. After sintering, the furnace is cooled to room temperature to obtain the tube-packed powder. S3, the tube-packing powder prepared in S2 is packed into a silver tube under vacuum, and Bi-2212 superconducting wire is prepared by PIT method; S4. The superconducting wire obtained in S3 is subjected to high-pressure sintering.

[0035] Testing revealed that the Bi-2212 tube powder prepared in this embodiment contained 7.5% Bi-2201 phase and had a Bi volatilization rate of 8.8%. The prepared Bi-2212 superconducting wire exhibited a critical current density of 4150 A / mm² under conditions of 4.2 K and 12 T. 2 .

[0036] By comparing Example 1 and Comparative Example 1, it can be seen that the densification and sintering of Bi-2212 precursor powder has a significant effect on reducing the content of Bi-2201 phase, increasing the purity of Bi-2212 phase, and improving the superconducting performance of wire. Specifically: (1) The volatility of Bi element is significantly reduced: The volatility of Bi element in the precursor powder in Example 1 is significantly lower than that in Comparative Example 1. High-pressure pre-densification blocks the channels for the volatilization and diffusion of Bi element, effectively suppressing the loss of Bi volatilization at high temperature. At the same time, it also weakens the micro-component segregation inside the powder and effectively eliminates the micro-segregation region rich in Bi and lacking in Ca in the system. (2) The content of Bi-2201 phase is significantly reduced: The content of Bi-2201 phase in the precursor powder in Example 1 is significantly lower than that in Comparative Example 1. Densification fundamentally suppresses the nucleation process of Bi-2201 phase and improves the purity of Bi-2212 phase. (3) Significantly improved superconducting current carrying capacity: The critical current density of the superconducting wire in Example 1 under the conditions of 4.2K and 12T is about 50% higher than that of Comparative Example 1. The compaction effectively weakens the weak grain boundary connection effect, maintains the structural stability of the target superconducting phase, significantly improves the current carrying capacity of the wire, and provides strong support for the development of high temperature superconducting technology.

[0037] Example 2 This embodiment includes the following steps: S1, a precursor solution with an atomic ratio of Bi, Sr, Ca, and Cu of 2.17 : 1.94 : 0.89 : 2.00 was prepared using a nitrate mixing method, and Bi-2212 precursor powder was prepared using a spray thermal decomposition process; S2, the Bi-2212 precursor powder prepared in S1 is loaded into a cemented carbide mold and prepared by unidirectional compression molding process. The pressure is set to 25MPa and the holding time is 8min, and a dense green blank with a relative density of 86% is obtained. S3: The densified green blank prepared in S2 is placed in a three-temperature zone tube furnace for high-temperature sintering, and the sintering is performed twice. The temperature is raised from room temperature to 830°C at a uniform rate of 10°C / min and held for 12 hours. The sintering atmosphere is air. After sintering, the furnace is cooled to room temperature. Then, the temperature is raised from room temperature to 860°C at a uniform rate of 10°C / min and held for 12 hours. The sintering atmosphere is oxygen. After sintering, the furnace is cooled to room temperature to obtain the tube-packed powder. S4. The tube-packing powder prepared in S3 is packed into a silver tube under vacuum, and Bi-2212 superconducting wire with excellent and uniform superconducting properties is prepared by PIT method. S5. The superconducting wire obtained in S4 is subjected to high-pressure sintering to finally obtain Bi-2212 superconducting wire with high current carrying capacity.

[0038] Testing revealed that the Bi-2201 phase content in the Bi-2212 tube powder prepared in this embodiment was 1.2%, and the Bi element volatility was 2.0%. The prepared Bi-2212 superconducting wire exhibited a critical current density of 6400 A / mm² under conditions of 4.2 K and 12 T. 2 .

[0039] Example 3 This embodiment includes the following steps: S1, a precursor solution with an atomic ratio of Bi, Sr, Ca, and Cu of 2.17 : 1.94 : 0.89 : 2.00 was prepared using a nitrate mixing method, and Bi-2212 precursor powder was prepared using a spray thermal decomposition process; S2, the Bi-2212 precursor powder prepared in S1 is loaded into a cemented carbide mold and prepared by unidirectional compression molding process. The pressure is set to 20MPa and the holding time is 5min to prepare a dense green blank with a relative density of 80%. S3: The densified green blank prepared in S2 is placed in a three-temperature zone tube furnace for high-temperature sintering, and the sintering is performed twice. The temperature is raised from room temperature to 830°C at a uniform rate of 10°C / min and held for 12 hours. The sintering atmosphere is air. After sintering, the furnace is cooled to room temperature. Then, the temperature is raised from room temperature to 860°C at a uniform rate of 10°C / min and held for 12 hours. The sintering atmosphere is oxygen. After sintering, the furnace is cooled to room temperature to obtain the tube-packed powder. S4. The tube-packing powder prepared in S3 is packed into a silver tube under vacuum, and Bi-2212 superconducting wire with excellent and uniform superconducting properties is prepared by PIT method. S5. The superconducting wire obtained in S4 is subjected to high-pressure sintering to finally obtain Bi-2212 superconducting wire with high current carrying capacity.

[0040] Testing revealed that the Bi-2201 phase content in the Bi-2212 tube powder prepared in this embodiment was 1.8%, and the Bi element volatility was 2.6%. The prepared Bi-2212 superconducting wire exhibited a critical current density of 5950 A / mm² under conditions of 4.2 K and 12 T. 2 .

Claims

1. A method for preparing high-purity Bi-2212 superconducting material precursor powder, characterized in that, Includes the following steps: S1. Accurately weigh the required raw materials according to a certain stoichiometric ratio to prepare a Bi-2212 precursor solution, and then prepare a Bi-2212 precursor powder with high uniformity and high activity. S2, the precursor powder prepared in S1 is densified by high-pressure molding to form a dense green body; S3, the dense green body obtained in S2 is sintered at high temperature to obtain high-purity Bi-2212 tube powder with low Bi-2201 phase; S4. The tube-packed powder obtained in S3 is used to prepare Bi-2212 superconducting wire using the PIT method; S5. The superconducting wire obtained in S4 is subjected to high-pressure sintering to finally obtain Bi-2212 superconducting wire with high current carrying capacity.

2. The method for preparing high-purity Bi-2212 superconducting material precursor powder according to claim 1, characterized in that, In S1, the Bi-2212 precursor solution is prepared by nitrate mixing method, wherein the atomic ratio of Bi, Sr, Ca and Cu is 2.17 : 1.94 : 0.89 : 2.00, and the error of the content of each element in the obtained precursor solution does not exceed 3%.

3. The method for preparing high-purity Bi-2212 superconducting material precursor powder according to claim 1, characterized in that, In S1, the precursor powder is prepared using spray pyrolysis technology.

4. The method for preparing high-purity Bi-2212 superconducting material precursor powder according to claim 1, characterized in that, In S2, the specific steps of S2 are as follows: the precursor powder in S1 is loaded into a cemented carbide mold and prepared by unidirectional compression molding process, with the pressure controlled at 15-35 MPa and the pressure holding time at 3-10 min. By adjusting the molding process parameters, the relative density of the resulting sheet-like or columnar green body is maintained at 80% to 90%, forming a dense green body structure with tightly packed particles and high porosity.

5. The method for preparing high-purity Bi-2212 superconducting material precursor powder according to claim 1, characterized in that, In S3, the high-temperature sintering process specifically includes: sintering twice; each time the temperature is raised to 830-860℃ at a uniform rate of 5-10℃ / min and held for 10-12 hours; after sintering, the furnace is cooled to room temperature; and the sintering atmosphere is air or oxygen each time.

6. The method for preparing high-purity Bi-2212 superconducting material precursor powder according to claim 1, characterized in that, In step S4, the specific steps of the PIT method are as follows: the powder obtained in step S3 is loaded into a silver tube of a certain size under vacuum and the two ends of the silver tube are sealed. Combined with multiple drawing and assembly processes, Bi-2212 superconducting wire with excellent and uniform superconducting properties is prepared.

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