A method for producing a superconducting target by a reaction sintering method

Abstract

This invention relates to a method for preparing superconducting targets using reaction sintering. The invention provides three reaction sintering processes for preparing superconducting targets, which can rapidly advance densification at ambient pressure and lower peak temperatures, avoiding the problems of excessive precipitation of Ba / Cu-rich liquid phase and insufficient densification caused by high temperature or high pressure. This achieves the preparation of high-density superconducting targets without Ba / Cu liquid phase precipitation and volatilization, and less prone to cracking, thereby improving the critical current density and other properties of the superconducting targets. Specifically, the low-temperature synthesis-pulverization process can prepare targets with higher density and better critical current density and other properties; the low-temperature synthesis-jaw crushing process can prepare high-density targets with a higher yield, better supporting mass production; and the low-temperature negative pressure synthesis-pressureless sintering process balances high density and yield, while eliminating high-pressure tooling, simplifying the sintering process, and reducing equipment wear.

Description

Technical Field

[0001] This invention belongs to the field of second-generation high-temperature superconducting technology and relates to a method for preparing superconducting targets by reaction sintering. Background Technology

[0002] Rare-earth barium copper-oxygen superconducting targets are core source materials for preparing functional thin films such as second-generation high-temperature superconducting coated conductors, superconducting quantum devices, and microwave components. The phase purity and oxidation stoichiometry of the target material are crucial. The critical current density (Jc) and microwave surface resistance of sputtered thin films are directly determined by factors such as δ), density, carbon impurity content, and microstructure uniformity.

[0003] Currently, the mainstream sintering methods for preparing rare-earth barium copper oxide ceramic targets in industry and laboratories include: atmospheric pressure sintering (pressureless sintering), hot pressing (HP), hot isostatic pressing (HIP), and spark plasma sintering (SPS). Each method has significant limitations, particularly in the prominent contradiction between density, purity, size, and cost. For example, while HP and SPS can achieve rapid densification and fine-grained structures, they generally rely on graphite mold systems. At high temperatures, carbon migration and diffusion easily occur at the interface between the graphite mold and the YBCO material, significantly increasing the carbon content of the target material. The presence of carbon impurities not only degrades the purity of the superconducting phase but also easily induces the formation of impurity phases such as BaCO3, deteriorating the sputtering stability and superconducting performance of the thin film. Furthermore, the equipment investment is large, mold consumption is high, and the size of the target material that can be prepared is severely limited by the mold and pressure chamber, making it difficult to meet the mass production needs of large-size (e.g., Φ > 150 mm) and elongated irregularly shaped targets. While hot isostatic pressing (HIP) can produce near-dense bulk materials, it requires encapsulation, which is a complicated process and expensive equipment. The encapsulation material and the sealing process pose a risk of introducing impurities, and the synergistic effect of high temperature and high pressure can easily exacerbate the local loss of volatile components such as Ba and Cu, leading to compositional deviations and uneven microstructure.

[0004] In contrast, atmospheric sintering (pressureless sintering) is simpler, lower in cost, and eliminates the risk of carbon pollution from molds. It naturally possesses low-carbon advantages and the potential for preparing large-size / irregularly shaped targets, making it a superior route for industrialization. However, this process lacks external driving forces, and densification relies entirely on the surface energy and diffusion mass transfer of the powder itself, thus placing stringent requirements on the activity of the precursor powder. Existing atmospheric sintering processes often face two dilemmas: Insufficient densification: If the sintering temperature is lowered to avoid the risk of high temperatures, it often results in low target density (<80%), high porosity, and easy generation of microparticles during sputtering, affecting the film quality and target lifespan; High-temperature liquid phase runaway: In pursuit of high density, the sintering temperature is often forced to be increased to near or into the BaO–CuO eutectic region (above 980℃). At this point, a large amount of Ba–Cu rich liquid phase appears, accompanied by significant volatilization of Ba and Cu components, causing local melting, abnormal grain growth, component segregation, and increased porosity, leading to increased target resistance and deterioration of superconducting performance. Existing processes struggle to achieve a balance between "dense firing" and "pure and uniform firing".

[0005] Existing attempts to improve the aforementioned processes still have shortcomings. For example, conventional improvements to increase the density of superconducting targets include: 1) increasing the pressing pressure to improve the green compact density, but this often increases the internal stress of the green compact, making it prone to cracking and spalling during sintering; 2) increasing the sintering temperature of the green compact to increase the target density, but for superconducting targets, excessively high sintering temperatures can produce a Ba / Cu liquid phase, easily generating a copper-rich phase inside, and may also cause Ba / Cu volatilization; 3) refining the grains by sand milling the superconducting powder, but this introduces a reaction with water, affecting the phase purity of the superconducting powder; 4) using dry methods such as air jet milling to refine the grains, but this can only break them down to the D50=5μm level, which improves the activity of the superconducting powder to a certain extent, but still carries the risk of overheating. In addition, some studies have improved phase purity through multi-step cyclic processes such as pre-sintering-crushing-re-forming, or introduced pore-forming agents to enhance atmosphere exchange and reduce carbon residue. However, the linkage problem of "highly active powder - low-temperature efficient densification - suppression of liquid phase volatilization" has not yet been systematically solved. Especially for large-size target blanks, if the particle size and morphology of the precursor powder are not well controlled, the sintering window is narrow, and density stratification and composition gradient caused by core-surface temperature difference are very likely to occur.

[0006] In summary, existing technologies suffer from the following core contradictions: While pressurization methods such as hot pressing and SPS achieve good densification, they result in heavy carbon pollution, high costs, and size limitations; while conventional pressureless sintering has low carbon content and low cost, it faces process dilemmas such as "insufficient temperature for densification and excessive liquid phase / volatilization at high temperatures," and is highly dependent on powder activity, making it difficult to stably obtain large-size superconducting targets with high density, low volatility, and uniform microstructure.

[0007] Therefore, there is an urgent need for a rare earth superconducting target preparation method that can achieve efficient densification at normal pressure and lower peak temperature, significantly suppress Ba / Cu liquid phase precipitation and volatilization, and maintain the advantages of low carbon / large size of pressureless sintering, so as to meet the demand of high-end sputtering coating for highly consistent targets. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a method for preparing superconducting targets using reaction sintering. The superconducting targets prepared by this invention exhibit high density, complete grain size, and composition consistent with the target values, resulting in excellent electrical properties. This invention provides three reaction sintering processes for preparing superconducting targets, enabling rapid densification at ambient pressure and lower peak temperatures. This avoids the problems of excessive precipitation of Ba / Cu-rich liquid phase and insufficient densification caused by high temperature or high pressure, achieving the preparation of high-density superconducting targets without Ba / Cu liquid phase precipitation and volatilization, and less prone to cracking at ambient pressure and lower peak temperatures, thereby improving the critical current density and other properties of the superconducting targets. Specifically, the low-temperature synthesis-pulverization process can prepare targets with higher density and better critical current density; the low-temperature synthesis-jaw crushing process can prepare high-density targets with a higher yield, better supporting mass production; the low-temperature negative pressure synthesis-pressureless sintering process balances high density and yield, while eliminating the need for high-pressure tooling, simplifying the sintering process, and reducing equipment wear.

[0009] The objective of this invention can be achieved through the following methods: In a first aspect, the present invention provides a method for preparing superconducting targets by reaction sintering, the method employing a low-temperature synthesis-pulverization process, specifically including the following steps: S1. After drying the slurry containing rare earth oxides, copper source and barium source, preheated air or oxygen is introduced and calcined at low temperature to obtain superconducting powder. The temperature for the low-temperature calcination is 880~920℃; S2. After being crushed, the superconducting powder is first molded to form a green body, and then the green body is sintered and densified to obtain the final product.

[0010] In one embodiment of the present invention, in step S1, the rare earth oxide includes one of europium oxide, gadolinium oxide, samarium oxide, and yttrium oxide; the copper source includes one of copper oxide and copper nitrate; and the barium source includes one of barium carbonate, barium oxide, and barium hydroxide.

[0011] As one embodiment of the present invention, in step S1, the molar ratio of the rare earth oxide, copper source and barium source is (0.5±0.05):(2±0.2):(3±0.3).

[0012] As one embodiment of the present invention, in step S1, the preparation method of the slurry containing rare earth oxides, copper source and barium source is as follows: weigh rare earth oxides, copper source and barium source as raw materials, and grind them to obtain slurry.

[0013] Furthermore, the ball mill used in the sand mill has a diameter of 0.2~0.5mm and is made of zirconium oxide.

[0014] Furthermore, the dispersion medium used in the sand milling includes ultrapure water, and the dispersant includes one or more of the following aqueous dispersants: ammonium polyacrylate, polyacrylic acid, polycarboxylate, alginate, etc.; the amount of the dispersant added is 0.2 wt.% to 2 wt.%.

[0015] Furthermore, the grinding time is 0.5 to 3 hours.

[0016] As one embodiment of the present invention, in step S1, the drying includes one of spray granulation and drying; wherein, in the spray granulation, the inlet air temperature is 200~250℃, the outlet air temperature is 90~120℃, and the rotation speed of the atomizer is 15000~24000RPM.

[0017] In one embodiment of the present invention, in step S1, the preheating temperature is 300~500℃.

[0018] In one embodiment of the present invention, in step S1, the flow rate of the air or oxygen is 100-1000 L / min.

[0019] As one embodiment of the present invention, in step S1, the air or oxygen is introduced by side diffusion.

[0020] In one embodiment of the present invention, in step S1, the calcination time is 10~40h.

[0021] This invention employs a low-temperature, one-step synthesis method to prepare powder with a superconducting phase content of approximately 93-97%. While achieving a certain degree of reaction, over-burning is avoided, thus maintaining a certain level of powder activity. This invention reduces the degree of reaction in the superconducting powder, effectively improving its reactivity. Highly active, fine-grained superconducting powder can be obtained using any method, such as ball milling, air jet milling, or dry sand milling. If the degree of reaction is too low, excessive CO2 emission during the molding and sintering process will lead to target material cracking; if the degree of reaction is too high, the superconducting powder will lack sufficient activity.

[0022] In this invention, if the calcination temperature is below 880℃, the carbon content of the synthesized powder is >2000ppm, which means that more CO2 needs to be discharged during the ceramic sintering process, easily increasing the risk of target material cracking. If the temperature is above 920℃, the carbon content of the synthesized powder is <1000ppm, the degree of reaction is greater than 95%, and the reactivity of the resulting powder is insufficient.

[0023] This invention achieves finer primary particles through low-temperature calcination, resulting in finer particles with a greater sintering driving force (related to 1 / R). Simultaneously, the fine particles fill the gaps between coarse particles, increasing the packing density, reducing the amount of mass migration required for sintering, and achieving significant grain boundary diffusion and viscous flow. Furthermore, the highly active fine particles can achieve earlier pore-closing shrinkage at lower temperatures, thereby advancing the densification temperature and reducing its overall densification level.

[0024] As one embodiment of the present invention, in step S2, the pulverization method includes one of ball milling, air jet milling, and dry sand milling.

[0025] In one embodiment of the present invention, in step S2, the particle size of the pulverized powder is 5~25μm.

[0026] In one embodiment of the present invention, in step S2, the pressure of the molding is 5~15 MPa and the time is 30~120 s.

[0027] In one embodiment of the present invention, in step S2, the sintering densification treatment is carried out at a temperature of 940~970℃ for a time of 10~40h. When the temperature is greater than 500℃, the heating rate is 0.1~2℃ / min. The present invention achieves densification under pressureless conditions.

[0028] Secondly, this invention provides a method for preparing superconducting targets by reaction sintering, wherein the method employs a low-temperature synthesis-jaw crushing process, specifically including the following steps: S1. After drying the slurry containing rare earth oxides, copper source and barium source, preheated air or oxygen is introduced and calcined at low temperature to obtain superconducting powder. The temperature for the low-temperature calcination is 880~920℃; S2. After being crushed and sieved, the superconducting powder is first molded to form a green body, and then the green body is sintered and densified to obtain the final product.

[0029] In one embodiment of the present invention, in step S1, the rare earth oxide includes one of europium oxide, gadolinium oxide, samarium oxide, and yttrium oxide; the copper source includes one of copper oxide and copper nitrate; and the barium source includes one of barium carbonate, barium oxide, and barium hydroxide.

[0030] As one embodiment of the present invention, in step S1, the molar ratio of the rare earth oxide, copper source and barium source is (0.5±0.05):(2±0.2):(3±0.3).

[0031] As one embodiment of the present invention, in step S1, the preparation method of the slurry containing rare earth oxides, copper source and barium source is as follows: weigh rare earth oxides, copper source and barium source as raw materials, and grind them to obtain slurry.

[0032] Furthermore, the ball mill used in the sand mill has a diameter of 0.2~0.5mm and is made of zirconium oxide.

[0033] Furthermore, the dispersion medium used in the sand milling includes ultrapure water, and the dispersant includes one or more of the following aqueous dispersants: ammonium polyacrylate, polyacrylic acid, polycarboxylate, alginate, etc.; the amount of the dispersant added is 0.2 wt.% to 2 wt.%.

[0034] Furthermore, the grinding time is 0.5 to 3 hours.

[0035] As one embodiment of the present invention, in step S1, the drying includes one of spray granulation and drying; wherein, in the spray granulation, the inlet air temperature is 200~250℃, the outlet air temperature is 90~120℃, and the rotation speed of the atomizer is 15000~24000RPM.

[0036] In one embodiment of the present invention, in step S1, the preheating temperature is 300~500℃.

[0037] In one embodiment of the present invention, in step S1, the flow rate of the air or oxygen is 100-1000 L / min.

[0038] As one embodiment of the present invention, in step S1, the air or oxygen is introduced by side diffusion.

[0039] In one embodiment of the present invention, in step S1, the calcination time is 10~40h.

[0040] In one embodiment of the present invention, in step S2, the particle size of the powder after jaw crushing is less than 38 μm.

[0041] In one embodiment of the present invention, in step S2, the mesh size of the sieve is 400 mesh.

[0042] In one embodiment of the present invention, in step S2, the pressure of the molding is 5~15 MPa and the time is 30~120 s.

[0043] In one embodiment of the present invention, in step S2, the sintering densification treatment is carried out at a temperature of 940~970℃ for a time of 10~40h. When the temperature is greater than 500℃, the heating rate is 0.1~2℃ / min. The present invention achieves densification under pressureless conditions.

[0044] This invention presents a "low-temperature synthesis-jaw crushing" scheme, which couples low-temperature synthesis with a jaw crushing and grading process. This synergistic approach, through powder activity regulation and particle size distribution formation mechanism, achieves efficient densification of the green body and effectively suppresses the precipitation of barium and copper liquid phases and component volatilization. The precursor powder obtained by low-temperature synthesis has a high degree of lattice distortion and abundant surface active sites, resulting in stronger atomic diffusion driving force during sintering, which is beneficial for low-temperature densification. Low-temperature synthesis can significantly reduce residual stress and lattice energy inside the powder, avoiding the problem of premature formation of Ba and Cu fusible phases that is prone to occur in high-temperature pre-synthesis, thus reducing liquid phase precipitation and high-temperature volatilization of elements from the source. The powder is broken up by jaw crusher to disperse hard agglomerates, and then screened to obtain spherical particles with a particle size of less than 38μm. The powder in this particle size range has excellent flowability and the particles are evenly stacked during molding and filling, which effectively eliminates the defects of local density stratification in the green body and greatly improves the uniformity of the density of the green body. At the same time, the spherical structure shrinks stably during the sintering and densification process, resulting in a yield of more than 90%. In the subsequent sintering stage, the shrinkage of the green body is synchronized and consistent, without local liquid phase enrichment or element volatilization imbalance. Finally, a superconducting target material with uniform composition and low density dispersion is obtained.

[0045] Thirdly, this invention provides a method for preparing superconducting targets by reaction sintering, wherein the method employs a low-temperature negative pressure synthesis-pressureless sintering process, specifically including the following steps: S1. After drying the slurry containing rare earth oxides, copper source and barium source, it is subjected to low temperature negative pressure treatment to obtain superconducting powder. The pressure of the low-temperature negative pressure treatment is 200~10000Pa, and the temperature is 650~750℃; S2. After being crushed and molded, the superconducting powder is sintered without pressure to obtain the superconducting target material.

[0046] In one embodiment of the present invention, in step S1, the rare earth oxide includes one of europium oxide, gadolinium oxide, samarium oxide, and yttrium oxide; the copper source includes one of copper oxide and copper nitrate; and the barium source includes one of barium carbonate, barium oxide, and barium hydroxide.

[0047] As one embodiment of the present invention, in step S1, the molar ratio of the rare earth oxide, copper source and barium source is (0.5±0.05):(2±0.2):(3±0.3).

[0048] As one embodiment of the present invention, in step S1, the preparation method of the slurry of rare earth oxide, copper source and barium source is as follows: weigh rare earth oxide, copper source and barium source as raw materials, and grind them to obtain slurry.

[0049] Furthermore, the ball mill used in the sand mill has a diameter of 0.2~0.5mm and is made of zirconium oxide.

[0050] Furthermore, the dispersion medium used in the sand milling includes ultrapure water, and the dispersant includes one or more of the following aqueous dispersants: ammonium polyacrylate, polyacrylic acid, polycarboxylate, alginate, etc.; the amount of the dispersant added is 0.2 wt.% to 2 wt.%.

[0051] Furthermore, the grinding time is 0.5 to 3 hours.

[0052] As one embodiment of the present invention, in step S1, the drying includes one of spray granulation and drying; wherein, in the spray granulation, the inlet air temperature is 200~250℃, the outlet air temperature is 90~120℃, and the rotation speed of the atomizer is 15000~24000RPM.

[0053] In one embodiment of the present invention, in step S1, the time for the low-temperature negative pressure treatment is 2 to 20 hours.

[0054] As one embodiment of the present invention, in step S2, the pulverization method includes one of ball milling, air jet milling, and dry sand milling.

[0055] In one embodiment of the present invention, in step S2, the particle size of the pulverized powder is 5~25μm.

[0056] In one embodiment of the present invention, in step S2, the pressureless sintering temperature is 920~950 ℃ and the time is 4~12h.

[0057] This invention presents a "low-temperature negative pressure synthesis-pressureless sintering" scheme, which couples low-temperature negative pressure synthesis with pressureless sintering. Utilizing the intrinsic properties of the powder and the synergistic mechanism of atmosphere control, it achieves efficient densification while simultaneously suppressing the precipitation of Ba and Cu liquid phases and component volatilization. Submicron-sized spherical superconducting powders are synthesized under low-temperature negative pressure. The fine grains introduce numerous lattice defects and surface active sites, significantly reducing the atomic diffusion activation energy. On one hand, the spherical particles exhibit excellent flowability and uniform packing during molding, resulting in low density dispersion in the green blank. On the other hand, mass migration can be completed at a relatively mild temperature during sintering, achieving efficient densification. Furthermore, low-temperature negative pressure synthesis avoids the premature formation of Ba-rich and Cu-rich low-melting-point impurities from the high-temperature reaction of precursors, reducing liquid phase precipitation during sintering from the source. The pressureless sintering process involves a gradual heating process, which, combined with the high activity of the powder, achieves low-temperature densification, shortens the high-temperature holding time, and significantly mitigates the high-temperature loss of volatile Ba and Cu components. Ultimately, a superconducting target material with stable composition, high density, and uniform structure is obtained.

[0058] This solution utilizes spherical powders with excellent flowability, resulting in uniform packing during molding. The green body shrinks synchronously during sintering, effectively avoiding defects such as cracking, delamination, and impurities caused by localized liquid phase enrichment and uneven component volatilization. This significantly improves the target material yield and processing efficiency. The high activity of the submicron powders themselves can lower the sintering densification temperature, reduce the precipitation of Ba and Cu liquid phases and element volatilization, ensuring uniform and stable target material composition and density. At the same time, pressureless sintering eliminates the need for high-pressure tooling, simplifies the sintering process, and reduces equipment wear.

[0059] Fourthly, the present invention provides a superconducting target material prepared by the method described above.

[0060] Compared with the prior art, the present invention has the following beneficial effects: 1. The "low-temperature synthesis-pulverization" scheme of this invention, by reducing the calcination temperature, results in insufficient grain growth, higher specific surface area and surface energy, and obtains highly active powder with a reaction degree of approximately 93-97%. This highly active powder, on the one hand, facilitates diffusion and bonding at the particle contact points in the early stages of sintering, enabling rapid densification under normal pressure and lower peak temperatures; on the other hand, the anisotropy of the interfacial energy is controllable during sintering, and the grain boundary diffusion path is more consistent, which is beneficial for densification and maintaining the continuity of the superconducting phase. Thus, it is possible to prepare high-density superconducting targets without Ba / Cu liquid phase precipitation and volatilization and less prone to cracking under normal pressure and lower peak temperatures (below 980℃), thereby improving the critical current density and other properties of the superconducting target.

[0061] 2. The target material prepared by this method has a higher density and better performance such as critical current density.

[0062] 3. The present invention can also select the "low temperature synthesis-jaw crushing" scheme. The powder is broken up by jaw crushing and hard agglomerates, and then screened by sieve to obtain spherical particles with a particle size of less than 38μm. The powder in this particle size range has excellent flowability and the particles are evenly stacked and arranged during molding and filling, which effectively eliminates the defects of local density stratification in the green body and greatly improves the uniformity of the density of the molded green body. At the same time, the spherical structure shrinks stably during the sintering and densification process, resulting in a yield of more than 90%.

[0063] 4. In this solution, because the spherical structure is maintained, a more uniform green body with fewer defects can be obtained during the molding process, and a ceramic block with more uniform density can be obtained during the sintering process. At the same time, due to its more uniform shrinkage, the yield is also higher, which can better support mass production.

[0064] 5. Alternatively, this invention can employ a "low-temperature negative pressure synthesis-pressureless sintering" method. Submicron-sized spherical superconducting powder is synthesized under low-temperature negative pressure. The fine grains introduce numerous lattice defects and surface active sites, significantly reducing the atomic diffusion activation energy. On one hand, the spherical particles exhibit excellent flowability and uniform packing during molding, resulting in low density dispersion in the green blank. On the other hand, mass migration can be completed at a relatively mild temperature during sintering, achieving efficient densification. Furthermore, low-temperature negative pressure synthesis avoids the premature formation of Ba-rich and Cu-rich low-melting-point impurity phases from the high-temperature reaction of the precursor, reducing liquid phase precipitation during sintering from the source.

[0065] 6. This solution balances high density and yield, while pressureless sintering eliminates the need for high-pressure tooling, simplifies the sintering process, and reduces equipment wear. Attached Figure Description

[0066] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of air being introduced via a side-diffuse airflow method. Figure 2 Here is a photograph of the target material in Example 2; Figure 3 This is a SEM image showing the complete grain growth of the target material in Example 2; Figure 4 These are microscopic morphology images of the superconducting powders in Examples 2, 4, and 5. Figure 5 The images show the XRD patterns of the superconducting powders in Examples 2, 4, and 5. Figure 6 The image shows an electron microscope image of the target material in Comparative Example 2. Figure 7 The image shows the actual target material for Comparative Example 2. Figure 8 Here is a picture of the actual target material for Comparative Example 3; Figure 9The image shows the microstructure of the superconducting powder in Example 9. Figure 10 The image shows the XRD pattern of the superconducting powder in Example 9. Figure 11 The image shows the microstructure of the spherical superconducting powder in Example 10. Figure 12 The image shows the XRD pattern of the superconducting powder in Example 10. Detailed Implementation

[0067] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0068] Example 1 This embodiment provides a method for preparing superconducting targets by reaction sintering, including the following steps: S1. Weigh europium oxide, copper oxide and barium carbonate as raw materials, mix the raw materials and grind them in a sand mill for 1 hour to obtain a slurry; wherein the molar ratio of europium oxide, copper oxide and barium carbonate is 0.5:2:3; Among them, the sand milling is carried out by using a zirconia ball mill with a diameter of 0.2 mm, using ultrapure water as the dispersion medium, the solid content of the slurry is 55 wt.%, and using a peristaltic pump to add ammonium polyacrylate as a dispersant at a uniform rate, with a final addition amount of 1 wt.%, and the sand milling time is 1 h. S2. After spray granulation of the slurry, it is introduced through side dispersion (e.g.) Figure 1 As shown in the figure, air preheated at 300℃ (flow rate of 800 L / min) is introduced and calcined at 900℃ for 20 h to obtain superconducting powder with a C content of 1500 ppm; The inlet air temperature for spray granulation is 200℃, the outlet air temperature is 80℃, and the atomizer speed is 20000RPM. S3. After ball milling, the superconducting powder was pulverized to obtain powder with a D50 of 12.6 μm. It was first molded using a press (10 MPa, 60 s) to form a green body. The green body was then sintered and densified under normal pressure (950℃, 20 h) to obtain the superconducting target material with a density of 6.16 g / cm³. 3 .

[0069] Example 2 This embodiment provides a method for preparing superconducting targets by reaction sintering, including the following steps: S1. Weigh europium oxide, copper oxide and barium carbonate as raw materials, mix the raw materials and grind them in a sand mill for 1 hour to obtain a slurry; wherein the molar ratio of europium oxide, copper oxide and barium carbonate is 0.5:2:3; Among them, the sand milling is carried out by using a zirconia ball mill with a diameter of 0.2 mm, using ultrapure water as the dispersion medium, the solid content of the slurry is 55 wt.%, and using a peristaltic pump to add ammonium polyacrylate as a dispersant at a uniform rate, with a final addition amount of 1 wt.%, and the sand milling time is 1 h. S2. After spray granulation of the slurry, air preheated at 300℃ (flow rate of 800 L / min) is introduced by side diffusion, and calcined at 900℃ for 20h to obtain superconducting powder with a C content of 1500ppm. The inlet air temperature for spray granulation is 200℃, the outlet air temperature is 80℃, and the atomizer speed is 20000RPM. S3. After being pulverized by an air jet mill, superconducting powder with a D50 of 11.3 μm was obtained. This powder was then molded using a press (10 MPa, 60 s) to form a green body. The green body was then sintered and densified under normal pressure (950℃, 20 h) to obtain the superconducting target material with a density of 6.11 g / cm³. 3 .

[0070] Example 3 This embodiment provides a method for preparing superconducting targets by reaction sintering, including the following steps: S1. Weigh europium oxide, copper oxide and barium carbonate as raw materials, mix the raw materials and grind them in a sand mill for 1 hour to obtain a slurry; wherein the molar ratio of europium oxide, copper oxide and barium carbonate is 0.5:2:3; Among them, the sand milling is carried out by using a zirconia ball mill with a diameter of 0.2 mm, using ultrapure water as the dispersion medium, the solid content of the slurry is 55 wt.%, and using a peristaltic pump to add ammonium polyacrylate as a dispersant at a uniform rate, with a final addition amount of 1 wt.%, and the sand milling time is 1 h. S2. After spray granulation of the slurry, air preheated at 300℃ (flow rate of 800 L / min) is introduced by side diffusion, and calcined at 900℃ for 20h to obtain superconducting powder with a C content of 1500ppm. The inlet air temperature for spray granulation is 200℃, the outlet air temperature is 80℃, and the atomizer speed is 20000RPM. S3. After dry sand milling, superconducting powder was obtained with a D50 of 12.1 μm. This powder was first molded using a press (10 MPa, 60 s) to form a green body. The green body was then sintered and densified (950℃, 20 h) to obtain the superconducting target material with a density of 6.21 g / cm³. 3 .

[0071] Example 4 The preparation method in this embodiment is basically the same as that in Example 2, except that the calcination temperature in step S2 is replaced with 880℃, and the density of the resulting superconducting target is 6.35 g / cm³. 3 .

[0072] Example 5 The preparation method in this embodiment is basically the same as that in Example 2, except that the calcination temperature in step S2 is replaced with 920℃, and the density of the resulting superconducting target is 6.06 g / cm³. 3 .

[0073] Example 6 The preparation method in this embodiment is basically the same as that in embodiment 2, except that europium oxide in step S1 is replaced with gadolinium oxide.

[0074] Example 7 The preparation method in this embodiment is basically the same as that in Example 2, except that europium oxide in step S1 is replaced with samarium oxide.

[0075] Example 8 The preparation method in this embodiment is basically the same as that in Example 2, except that europium oxide in step S1 is replaced with yttrium oxide.

[0076] Figure 2 The image shows the actual target material of Example 2. Its surface is intact, and the dimensional shrinkage after sintering can be clearly observed from the white powder underneath. Figure 3 This is a SEM image of the target material with complete grain growth in Example 2.

[0077] Figure 4 These are microscopic morphology images of the superconducting powders in Examples 2, 4, and 5. Figure 5 The XRD patterns of the superconducting powders in Examples 2, 4, and 5 are shown. It can be seen that the powder synthesized at 880℃ is clearly a mixed phase, and the (003) peak has a significantly larger half-width at half-maximum (WHM) of 0.197, indicating weaker crystallinity and, conversely, stronger activity. The powder synthesized at 900℃ is still a mixed phase, and the (003) peak has a WHM of 0.159. Compared to the powder synthesized at 880℃, the crystallinity is slightly improved, and the activity is slightly decreased. The powder synthesized at 920℃ is essentially a superconducting phase, but the measured C content is around 900 ppm, and the (003) peak has a WHM of 0.118, indicating slightly stronger crystallinity and slightly weaker activity.

[0078] Example 9 This embodiment provides a method for preparing superconducting targets by reaction sintering, including the following steps: S1. Weigh europium oxide, copper oxide and barium carbonate as raw materials, mix the raw materials and grind them in a sand mill for 1 hour to obtain a slurry; wherein the molar ratio of europium oxide, copper oxide and barium carbonate is 0.5:2:3; Among them, the sand milling is carried out by using a zirconia ball mill with a diameter of 0.2 mm, using ultrapure water as the dispersion medium, the solid content of the slurry is 55 wt.%, and using a peristaltic pump to add ammonium polyacrylate as a dispersant at a uniform rate, with a final addition amount of 1 wt.%, and the sand milling time is 1 h. S2. After spray granulation of the slurry, it is introduced through side dispersion (e.g.) Figure 1 As shown in the figure, air preheated at 300℃ (flow rate of 800 L / min) is introduced and calcined at 900℃ for 20 h to obtain superconducting powder with a C content of 1500 ppm; The inlet air temperature for spray granulation is 200℃, the outlet air temperature is 80℃, and the atomizer speed is 20000RPM. S3. After being crushed by a jaw crusher and classified through a 400-mesh sieve, superconducting powder with a D50 of 35 μm was obtained. This powder was first molded using a press (10 MPa, 60 s) to form a green body. The green body was then sintered and densified under normal pressure (950℃) to obtain the superconducting target material with a density of 5.5 g / cm³. 3 .

[0079] Figure 9 The image shows the microstructure of the superconducting powder. Figure 10 The image shows the XRD pattern of the superconducting powder. It can be seen that the superconducting powder prepared by the "low-temperature synthesis-jaw crushing" method has strong activity and a high yield.

[0080] Example 10 This embodiment provides a method for preparing superconducting targets by reaction sintering, including the following steps: S1. Weigh europium oxide, copper oxide and barium carbonate as raw materials, mix the raw materials and grind them in a sand mill for 1 hour to obtain a slurry; wherein the molar ratio of europium oxide, copper oxide and barium carbonate is 0.5:2:3; Among them, the sand milling is carried out by using a zirconia ball mill with a diameter of 0.2 mm, using ultrapure water as the dispersion medium, the solid content of the slurry is 55 wt.%, and using a peristaltic pump to add ammonium polyacrylate as a dispersant at a uniform rate, with a final addition amount of 1 wt.%, and the sand milling time is 1 h. S2. After spray granulation of the slurry, it is subjected to low-temperature negative pressure treatment (pressure of negative pressure of 800 Pa, temperature of 750℃, time of 4 h) to obtain superconducting powder with a C content of 600 ppm. The inlet air temperature for spray granulation is 200℃, the outlet air temperature is 80℃, and the atomizer speed is 20000RPM. S3. After being crushed by a jaw crusher, superconducting powder is obtained as spherical powder with a D50 of 40 μm. This powder is then subjected to pressureless sintering (at 940℃ for 6 hours) to obtain the superconducting target material with a density of 6.2 g / cm³. 3 .

[0081] Figure 11 The image shows the microstructure of spherical superconducting powder. Figure 12 The image shows the XRD pattern of the superconducting powder. It can be seen that the superconducting powder prepared by the "low-temperature negative pressure synthesis-pressureless sintering" method has strong activity and high density.

[0082] Comparative Example 1 This embodiment provides a method for preparing superconducting targets by reaction sintering, including the following steps: S1. Weigh europium oxide, copper oxide and barium carbonate as raw materials, mix the raw materials and grind them in a sand mill for 1 hour to obtain a slurry; wherein the molar ratio of europium oxide, copper oxide and barium carbonate is 0.5:2:3; Among them, the sand milling is carried out by using a zirconia ball mill with a diameter of 0.2 mm, using ultrapure water as the dispersion medium, the solid content of the slurry is 55 wt.%, and using a peristaltic pump to add ammonium polyacrylate as a dispersant at a uniform rate, with a final addition amount of 1 wt.%, and the sand milling time is 1 h. S2. After spray granulation of the slurry, preheated air at 300℃ (flow rate of 800 L / min) is introduced by side diffusion, and calcined at 960℃ for 20h to obtain superconducting powder with a C content of 495ppm. The inlet air temperature for spray granulation is 200℃, the outlet air temperature is 80℃, and the atomizer speed is 20000RPM. S3. After being pulverized by an air jet mill, superconducting powder with a D50 of 12.6 μm was obtained. This powder was then molded using a press (10 MPa, 60 s) to form a green body. The green body was then sintered and densified (950℃, 20 h) to obtain the superconducting target material with a density of 5.11 g / cm³. 3 It has a low density.

[0083] Comparative Example 2 This embodiment provides a method for preparing superconducting targets by reaction sintering, including the following steps: S1. Weigh europium oxide, copper oxide and barium carbonate as raw materials, mix the raw materials and grind them in a sand mill for 1 hour to obtain a slurry; wherein the molar ratio of europium oxide, copper oxide and barium carbonate is 0.5:2:3; Among them, the sand milling is carried out by using a zirconia ball mill with a diameter of 0.2 mm, using ultrapure water as the dispersion medium, the solid content of the slurry is 55 wt.%, and using a peristaltic pump to add ammonium polyacrylate as a dispersant at a uniform rate, with a final addition amount of 1 wt.%, and the sand milling time is 1 h. S2. After spray granulation of the slurry, preheated air at 300℃ (flow rate of 800 L / min) is introduced by side diffusion, and calcined at 960℃ for 20h to obtain superconducting powder with a C content of 495ppm. The inlet air temperature for spray granulation is 200℃, the outlet air temperature is 80℃, and the atomizer speed is 20000RPM. S3. After being pulverized by an air jet mill, the superconducting powder was further crushed to obtain powder with a D50 of 12.6 μm. This powder was first molded using a press (10 MPa, 60 s) to form a green body. The green body was then subjected to high-temperature sintering and densification treatment (980℃, 20 h) to obtain the superconducting target material with a density of 5.56 g / cm³. 3 .

[0084] from Figure 6 In the SEM image of the target material in Comparative Example 2, some rounded regions are clearly visible, indicating formation by liquid phase flow. The corresponding EDS image clearly shows Cu-rich regions, while lacking Ba and Eu, indicating formation by copper oxide liquid phase flowing to the grain boundary interstices at high temperatures. Figure 7 As can be seen from the actual image of the target material in Comparative Example 2, liquid phase is precipitated at the bottom.

[0085] Comparative Example 3 This embodiment provides a method for preparing superconducting targets by reaction sintering, including the following steps: S1. Weigh europium oxide, copper oxide and barium carbonate as raw materials, mix the raw materials and grind them in a sand mill for 1 hour to obtain a slurry; wherein the molar ratio of europium oxide, copper oxide and barium carbonate is 0.5:2:3; Among them, the sand milling is carried out by using a zirconia ball mill with a diameter of 0.2 mm, using ultrapure water as the dispersion medium, the solid content of the slurry is 55 wt.%, and using a peristaltic pump to add ammonium polyacrylate as a dispersant at a uniform rate, with a final addition amount of 1 wt.%, and the sand milling time is 1 h. S2. After spray granulation of the slurry, preheated air at 300℃ (flow rate of 800 L / min) is introduced by side diffusion, and calcined at 860℃ for 20h to obtain superconducting powder with a C content of 3000ppm. The inlet air temperature for spray granulation is 200℃, the outlet air temperature is 80℃, and the atomizer speed is 20000RPM. S3. After being pulverized by an air jet mill, superconducting powder with a D50 of 10.11 μm was obtained. This powder was then molded using a press (10 MPa, 60 s) to form a green body. The green body was then sintered and densified (950℃, 20 h) to obtain the superconducting target material with a density of 6.35 g / cm³. 3 .

[0086] from Figure 8 As can be seen from the actual target material of Comparative Example 3, due to its excessively high C content, more CO2 needs to be discharged during the sintering process, resulting in cracking.

[0087] Performance testing The targets prepared in Examples 1-10 and Comparative Examples 1-3 were used to prepare superconducting tapes with a superconducting film thickness of 1 μm using pulsed laser deposition. The target composition was measured by inductively coupled plasma atomic emission spectrometry after calibration, and the results are shown in Table 1. It should be emphasized that for REBCO, the critical transition temperature Tc increases almost linearly with the increase of the ionic radius r, and the critical current Ic at 77 K is affected by its Tc, increasing with the increase of the RE ionic radius. That is, the Ic of YBCO is relatively lower than that of SmBCO, EuBCO, and GdBCO.

[0088] Table 1

[0089] It is evident that if the target density is too low, there will be more pores, making it easier to introduce defects during the coating process and thus reducing the critical current temperature of the superconducting tape at 77K. At the same time, the lower the target density, the more easily the plasma plume becomes unstable due to the instability of the target surface during the coating process, thereby affecting the quality of the tape film.

[0090] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing superconducting targets by reaction sintering, characterized in that, The method employs a low-temperature synthesis-pulverization process, specifically including the following steps: S1. After drying the slurry containing rare earth oxides, copper source and barium source, preheated air or oxygen is introduced and calcined at low temperature to obtain superconducting powder. The temperature for the low-temperature calcination is 880~920℃; S2. After being crushed, the superconducting powder is first molded to form a green body, and then the green body is sintered and densified to obtain the final product.

2. The method according to claim 1, characterized in that, In step S1, the preparation method of the slurry containing rare earth oxides, copper source, and barium source is as follows: rare earth oxides, copper source, and barium source are weighed as raw materials and milled to obtain a slurry; the molar ratio of rare earth oxides, copper source, and barium source is (0.5±0.05):(2±0.2):(3±0.3); the rare earth oxide includes one of europium oxide, gadolinium oxide, samarium oxide, and yttrium oxide; the copper source includes one of copper oxide and copper nitrate; the barium source includes one of barium carbonate, barium oxide, and barium hydroxide; the diameter of the ball mill used for milling is 0.2~0.5mm, and the material includes zirconium oxide; the milling time is 0.5~3h.

3. The method according to claim 1, characterized in that, In step S1, the preheating temperature is 300~500℃; the air or oxygen flow rate is 100-1000 L / min; the air or oxygen is introduced by side diffusion; and the calcination time is 10~40h.

4. The method according to claim 1, characterized in that, In step S2, the pulverization method includes one of ball milling, air jet milling, and dry sand milling; the particle size of the pulverized powder is 5~25μm.

5. The method according to claim 1, characterized in that, In step S2, the pressure of the molding is 5~15 MPa and the time is 30~120 s; the temperature of the sintering densification treatment is 940~970℃ and the time is 10~40 h.

6. A method for preparing superconducting targets by reaction sintering, characterized in that, The method employs a low-temperature synthesis-jaw crushing process, specifically including the following steps: S1. After drying the slurry containing rare earth oxides, copper source and barium source, preheated air or oxygen is introduced and calcined at low temperature to obtain superconducting powder. The temperature for the low-temperature calcination is 880~920℃; S2. After being crushed and sieved, the superconducting powder is first molded to form a green body, and then the green body is sintered and densified to obtain the final product.

7. The method according to claim 6, characterized in that, In step S2, the particle size of the powder after jaw crushing is less than 38 μm; the sieve mesh number is 400 mesh.

8. A method for preparing superconducting targets by reaction sintering, characterized in that, The method employs a low-temperature negative pressure synthesis-pressureless sintering process, specifically including the following steps: S1. After drying the slurry containing rare earth oxides, copper source and barium source, preheated air or oxygen is introduced and subjected to low temperature negative pressure treatment to obtain superconducting powder. The pressure of the low-temperature negative pressure treatment is 200~10000Pa, and the temperature is 650~750℃; S2. After being crushed and molded, the superconducting powder is sintered without pressure to obtain the superconducting target material.

9. The method according to claim 8, characterized in that, The pressureless sintering temperature is 920~950 ℃, and the time is 4~12h.

10. A superconducting target prepared by the method according to any one of claims 1-9.

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