High-thermal-conductivity niobium three-tin superconducting coil and manufacturing method thereofTechnical Field
The invention belongs to the field of superconducting materials, and particularly relates to a high-thermal-conductivity niobium three-tin superconducting coil and a manufacturing method thereof.
Background
The niobium tri-tin and niobium titanium superconducting material is representative of a low-temperature superconducting material, and compared with the niobium titanium superconducting material, the niobium tri-tin superconducting material has higher superconducting critical transition temperature, reaches more than 18K, has higher upper critical magnetic field, and can reach 25T at 4.2K. The niobium-three-tin superconducting coil is prepared by utilizing the high critical transition temperature and the high critical magnetic field of the niobium-three-tin superconducting material, can generate a higher magnetic field, and is one of the most ideal superconducting materials for generating a low-temperature strong magnetic field at present.
The niobium tri-tin has a crystal structure of an A15 ceramic phase, the formed niobium tri-tin wire has very poor mechanical properties, the superconducting performance of the niobium tri-tin phase can be damaged by small external mechanical interference, the whole niobium tri-tin coil is damaged, and the process is generally irreversible. Therefore, the preparation process of the niobium-tin superconducting coil is generally carried out by winding firstly and then carrying out heat treatment, firstly, a niobium-tin wire with certain mechanical ductility before heat treatment is wound on a framework to form a final coil shape, then the niobium-tin coil and the framework are carried out high-temperature heat treatment together, so that the niobium-tin wire carries out high-temperature diffusion reaction to generate a niobium-tin superconducting phase, and the niobium-tin superconducting coil is prepared.
The niobium-tin coil needs to be loaded with a certain pretightening force in the winding process to ensure that the niobium-tin wires are tightly arranged on the framework, so that the ampere-turns number of the coil is improved, the energizing current of the coil is improved, and the capability of the coil for generating a magnetic field is improved. The pretightening force in the winding process is gradually released in the heat treatment process of the coil, the heat treatment temperature of the niobium-three-tin coil is 600-700 ℃, and the stainless steel framework at the temperature can be softened, so that the cylindricity of the inner hole of the niobium-three-tin superconducting coil framework after temperature return is changed, and the inner diameter of the niobium-three-tin superconducting coil framework is reduced. This causes the shape of the niobium tri-tin superconducting coil to change as well, the field strength and shape of the resulting central magnetic field to change, which is very disadvantageous for high uniformity coils, and the process is difficult to repair. In the later coil assembly, the change of the inner hole of the coil can cause assembly errors for the radiation protection screen sleeved in the central hole, and the radiation protection screen with high cylindricity is greatly influenced.
The current carrying capacity of the niobium-tin coil has strong correlation with the temperature of the coil, the temperature of the coil firstly needs to be reduced below the superconducting critical temperature of the niobium-tin material to have superconducting performance, and when the temperature is lower, the larger the temperature margin is, the larger the current carrying capacity of the coil is, and the higher the magnetic field is generated. Therefore, in the manufacturing process of the niobium-tin superconducting coil, the coil must be sufficiently cooled, particularly, the current increasingly common conductive cold superconducting magnet is used for cooling the superconducting coil by using a refrigerator, and the cooling margin of the superconducting coil must be sufficiently considered for sufficiently cooling the superconducting coil.
Therefore, the shape and sufficient cooling of the coil are ensured in the coil manufacturing process, so that the coil manufacturing process is consistent with the design, and the coil manufacturing process is critical to successful manufacturing of the niobium three-tin coil. The framework of the niobium-tin coil is generally made of stainless steel metal materials, the heat conductivity of stainless steel is lower, compared with the niobium-titanium coil, aluminum alloy with high heat conductivity can be adopted, and the cooling capacity of the stainless steel framework on the niobium-tin coil is poorer. Meanwhile, in order to improve the current density of a limited space, the wall thickness of the stainless steel skeleton is generally thinner. Therefore, the thin-wall stainless steel skeleton can cause deformation problem due to high-temperature heat treatment in the manufacturing process of the niobium three-tin coil.
Disclosure of Invention
The invention aims to solve the problem that the cooling effect of a niobium three-tin superconducting coil wound by a stainless steel skeleton is poor due to the low heat conductivity of a stainless steel material in the prior art and the problem of deformation of the stainless steel skeleton during long-time high-temperature heat treatment, thereby providing a high-heat-conductivity niobium three-tin superconducting coil.
The aim of the invention is realized by the following technical scheme:
a high thermal conductivity niobium three-tin superconducting coil comprises a stainless steel skeleton, an insulating layer, a niobium three-tin superconducting coil, aluminum nitride, sodium chloride and a center support; the stainless steel framework is of a thin-wall structure, end plate flanges are welded at two ends, and a niobium three-tin superconducting coil formed by precisely arranging niobium three-tin wires is arranged in the middle of the end plate flanges at two ends; an insulating layer is arranged between the niobium three-tin superconducting coil and the stainless steel skeleton, the insulating layer is resistant to high-temperature heat treatment and low-temperature cooling, and the niobium three-tin superconducting coil is insulated from the stainless steel skeleton when being electrified and excited; a plurality of grooves are formed in the middle positions of the two end plate flanges of the stainless steel framework, and the grooves are filled with the aluminum nitride with high heat conductivity; and the gap between the stainless steel framework and the center support is filled with sodium chloride. The center support is inserted into the center hole of the stainless steel framework and has a solid structure so as to increase the rigidity and strength of the high-heat-conductivity niobium three-tin superconducting coil and reduce deformation.
Further, the grooves are uniformly distributed on the periphery of the stainless steel framework along the axial direction of the stainless steel framework, the width of each groove is 1-10mm, and the distance from the edge of each groove to the two end plate flanges is 5-10cm.
Further, aluminum nitride filled in the groove of the stainless steel skeleton is powder, and the grain size is 50 nanometers-100 micrometers.
Further, the width of the gap between the stainless steel framework and the center support is 0.5-5mm on one side.
The invention also provides a manufacturing method of the high-thermal-conductivity niobium three-tin superconducting coil, which is characterized by comprising the following steps of:
(1) The method comprises the steps that a stainless steel framework is made into a cylindrical structure with end plate flanges at two ends, the middle positions of the end plate flanges at the two ends are neutral surfaces, grooves are formed in two sides of the neutral surfaces, the width of each groove is 1-10mm, the length of each groove is determined according to the length of the stainless steel framework, and the distance from one edge of each groove to the two end plate flanges is 5-10cm;
(2) A solid heat-resistant steel is inserted into a central hole of the stainless steel framework to serve as a central support, and an assembly gap between the solid heat-resistant steel and the stainless steel framework is 0.5-5mm on one side, so that the solid heat-resistant steel can be easily inserted into the central hole of the stainless steel framework;
(3) Sodium chloride is added into a gap between the stainless steel framework and the center support, and the stainless steel framework and the center support are compacted from two sides;
(4) Adding high-thermal-conductivity aluminum nitride into a groove formed in a stainless steel framework, wherein the groove is powder; winding a stainless steel sheet on a stainless steel framework, hooping the stainless steel framework by using a clamp, compacting aluminum nitride to fill the groove of the stainless steel framework, and then taking down the clamp and the stainless steel sheet, wherein the aluminum nitride and the stainless steel framework are fully connected to form a cylindrical shape;
(5) Winding glass fiber cloth on a stainless steel skeleton to serve as an insulating layer of the niobium three-tin superconducting coil and the stainless steel skeleton, then precisely arranging wires on the insulated stainless steel skeleton, and carrying out vacuum heat treatment on the wound niobium three-tin superconducting coil to generate a niobium three-tin superconducting phase;
(6) After the heat treatment is finished, slowly adding boiled deionized water into sodium chloride between the stainless steel framework and the center support, gradually dissolving the sodium chloride, exposing a gap between the stainless steel framework and the center support, and slowly extracting the center support; then heating the niobium three-tin superconducting coil in vacuum to remove water vapor on the inner wall;
(7) And (3) carrying out vacuum impregnation of epoxy resin, wherein the epoxy resin is impregnated and permeated into the niobium three-tin superconducting coil from the outer surface and the central hole of the niobium three-tin superconducting coil, filling gaps of the niobium three-tin superconducting coil and aluminum nitride, and filling and curing the niobium three-tin superconducting coil, the stainless steel skeleton and the aluminum nitride into a whole to obtain the niobium three-tin superconducting coil with high heat conductivity.
The beneficial effects are that:
in order to reduce the influence of deformation of a stainless steel framework on a niobium three-tin coil, the invention provides a stainless steel framework structure, wherein the stainless steel framework is radially and distributively grooved at the middle position, high-density aluminum nitride powder is filled in the groove, a cylindrical solid heat-resistant steel is inserted into a central hole, the diameter of the heat-resistant steel is slightly smaller than the inner hole size of the stainless steel framework, and sodium chloride powder is added into a gap between the heat-resistant steel and the stainless steel to compact the powder. After the coil is tightly wound, the coil, the framework, the heat-resistant steel support at the center and the filled aluminum nitride and sodium chloride are subjected to high-temperature heat treatment. The stainless steel skeleton has flanges at its two ends to limit the deformation of the skeleton. The middle position is supported by sodium chloride and heat-resistant steel, so that radial deformation is inhibited, and the cylindricity and deformation of the whole stainless steel framework can be ensured.
After the coil is subjected to high temperature heat treatment, the niobium three-tin coil becomes very fragile and cannot withstand large mechanical vibration. Therefore, great care should be taken in the removal of the coil center support. The invention adopts sodium chloride for filling, the sodium chloride plays a good microscopic supporting role in gaps, the melting point of the sodium chloride is higher, the thermal stability at high temperature is high, the friction force between the powder is larger, and the radial shrinkage force of the stainless steel framework can be well resisted in the high-temperature treatment process. Meanwhile, after heat treatment, boiled deionized water is slowly added into sodium chloride, the intermediate sodium chloride filling layer is gradually removed by utilizing the dissolution of the deionized water to the sodium chloride, gaps between the stainless steel skeleton and the heat-resistant steel support are formed, and then the heat-resistant steel support is carefully taken out. And then heating the niobium three-tin coil to 120 ℃ under vacuum, removing water vapor in the coil, and ensuring the insulation strength of the coil. Finally, carrying out vacuum impregnation treatment on the heat-treated niobium three-tin coil, wherein epoxy resin is adopted as an impregnating material, enters inter-turn gaps of the coil and aluminum nitride powder, and finally, the niobium three-tin wire, the stainless steel framework and the aluminum nitride are solidified into a whole. Because the heat conductivity of the stainless steel is lower, the heat conduction capacity of the stainless steel skeleton can be increased by adopting aluminum nitride with high heat conductivity for filling, and meanwhile, the strength of the stainless steel skeleton is ensured.
The device has simple structure, can improve the refrigerating effect of the niobium-tin coil, can basically prevent the niobium-tin superconducting coil from deforming after long-time high-temperature heat treatment, can not cause mechanical damage to the coil in the coil support removal process, improves the manufacturing safety of the niobium-tin coil, and provides convenience for the later assembly process of the coil. Meanwhile, the device has simple structure and low cost, and is suitable for mass industrialized manufacture.
In summary, the high-thermal-conductivity niobium three-tin superconducting coil is adopted, and the mechanical supporting structure of the stainless steel is utilized, so that the high-thermal-conductivity performance of aluminum nitride is combined, the thin-wall stainless steel skeleton can be enabled to improve the cold-conducting effect, the problem of poor cooling capacity of the niobium three-tin coil is effectively solved, the refrigerating effect of the niobium three-tin coil is improved, the current carrying capacity of the niobium three-tin coil is improved, and the performance of the niobium three-tin superconducting coil is improved. Meanwhile, in order to solve the problem that the thin-wall stainless steel is easy to deform at high temperature, the central high-strength heat-resistant steel support is adopted, and in consideration of the characteristic of damage to the niobium three-tin coil after heat treatment, a gap between the stainless steel framework and the central heat-resistant steel support is filled with sodium chloride, so that radial shrinkage of the stainless steel at high temperature is effectively prevented, the sodium chloride can be removed only by dissolving the stainless steel in water after temperature return, and the central heat-resistant steel support is conveniently pulled out.
Drawings
FIG. 1 is a schematic view of a stainless steel former for winding a niobium three-tin superconducting coil of the present invention;
fig. 2 is a schematic diagram of a high thermal conductivity niobium three tin superconducting coil of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The invention is further described below with reference to the drawings and detailed description.
As shown in fig. 1-2, the high thermal conductivity niobium three-tin superconducting coil of the present invention comprises a stainless steel skeleton 1, an insulating layer 2, a niobium three-tin superconducting coil 3, aluminum nitride 4, sodium chloride 5 and a center support 6. The stainless steel skeleton 1 is of a thin-wall structure, end plate flanges 8 are welded at two ends of the stainless steel skeleton, and a niobium three-tin superconducting coil 3 formed by precisely arranging niobium three-tin wires is arranged between the two end plate flanges 8. The end plate flange 8 can play a role of reinforcing ribs on the cylindrical stainless steel skeleton 1, effectively prevent the stainless steel skeleton 1 from deforming, and limit and shape the niobium-three-tin superconducting coil 3. The insulating layer 2 is arranged between the niobium three-tin superconducting coil 3 and the stainless steel skeleton 1, and the insulating layer 2 can resist high-temperature heat treatment and low-temperature cooling and insulate the niobium three-tin superconducting coil 3 from the stainless steel skeleton 1 when the power is excited. The stainless steel framework 1 is characterized in that a plurality of grooves 7 are formed in the middle positions of two end plate flanges 8 of the stainless steel framework 1, the grooves 7 are uniformly distributed on the periphery of the stainless steel framework 1 along the axial direction of the stainless steel framework 1, the width of each groove 7 is 1-10mm, and the distance from the edge of each groove 7 to the two end plate flanges 8 is 5-10cm. Wherein the aluminum nitride 4 having high thermal conductivity fills the groove 7 to enhance the thermal conductivity of the stainless steel skeleton 1. The aluminum nitride 4 is filled into the powder, and the particle size is 50 nanometers-100 micrometers. The center support 6 is inserted into the center hole of the stainless steel framework 1, and the structure is a solid structure, so that the structural rigidity and strength of the center support 6 are increased, and the deformation is reduced. And the gap between the stainless steel framework 1 and the center support 6 is filled with sodium chloride 5 and compacted, and the width of the gap is 0.5-5mm on one side.
The manufacturing process of the high-thermal-conductivity niobium three-tin superconducting coil is as follows:
(1) The stainless steel framework 1 is made into a cylindrical structure with end plate flanges 8 at two ends, the middle positions of the end plate flanges 8 at two ends are neutral surfaces, a plurality of grooves 7 are formed in two sides of the neutral surfaces, the width of each groove 7 is 1-10mm, the length of each groove 7 is determined according to the length of the stainless steel framework, and the distance from one edge of each groove 7 to each end plate flange 8 is 5-10cm;
(2) A solid heat-resistant steel is inserted into a central hole of the stainless steel framework 1 to serve as a central support 6, and an assembly gap between the central support 6 and the stainless steel framework 1 is 0.5-5mm on one side, so that the central support 6 can be easily inserted into the central hole of the stainless steel framework 1; the center support 6 has a sufficiently high strength and resistance to deformation at high temperatures to provide sufficient mechanical support;
(3) Sodium chloride 5 is added into the gap between the stainless steel framework 1 and the center support 6, and the stainless steel framework and the center support are compacted from two sides;
(4) Adding high-thermal-conductivity aluminum nitride 4 which is powder into a groove 7 formed in the stainless steel skeleton 1; winding a stainless steel sheet on the stainless steel framework 1, hooping by using a clamp, compacting and filling aluminum nitride 4 into a groove 7 of the stainless steel framework 1, and then taking down the clamp and the stainless steel sheet, wherein the aluminum nitride 4 and the stainless steel framework 1 are fully connected to form a cylindrical shape;
(5) Winding glass fiber cloth on a stainless steel skeleton 1 to serve as a niobium three-tin superconducting coil 3 and an insulating layer 2 of the stainless steel skeleton 1, then precisely arranging wires on the insulated stainless steel skeleton 1, and carrying out vacuum heat treatment on the wound niobium three-tin superconducting coil 3 to generate a niobium three-tin superconducting phase;
(6) After the heat treatment is finished, slowly adding boiled deionized water into sodium chloride 5 between the stainless steel framework 1 and the center support 6, gradually dissolving the sodium chloride 5, exposing the gap between the stainless steel framework 1 and the center support 6, and slowly extracting the center support 6; then vacuum heating is carried out on the niobium three-tin superconducting coil 3 to remove water vapor on the inner wall; the step ensures the safety of the subsequent treatment process of the niobium-three-tin superconducting coil 3, and large mechanical interference is not introduced;
(7) And (3) carrying out vacuum impregnation of epoxy resin, wherein the epoxy resin is impregnated and permeated into the niobium three-tin superconducting coil 3 from the outer surface and the central hole of the niobium three-tin superconducting coil 3, filling gaps of the niobium three-tin superconducting coil 3 and aluminum nitride 4, and filling and curing the niobium three-tin superconducting coil 3, the stainless steel skeleton 1 and the aluminum nitride 4 into a whole to obtain the high-thermal-conductivity niobium three-tin superconducting coil. The tank 7 can enable epoxy resin to permeate outwards along the radial direction from the central hole in the vacuum impregnation process, so that the impregnation depth of the epoxy resin is increased, and the sufficient impregnation of the niobium-three-tin superconducting coil 3 is ensured. The epoxy resin further improves the heat conductance and strength of the niobium-three-tin superconducting coil 3, and improves the safety margin of the niobium-three-tin superconducting coil 3.
The following is a detailed description of two examples.
Embodiment one:
the stainless steel framework 1 is made into a cylindrical structure with end plate flanges 8 at two ends, the middle positions of the end plate flanges 8 at two ends are neutral surfaces, grooves 7 are formed in two sides of the neutral surfaces, the width of each groove 7 is 1mm, and the edge distance between the edges of each groove 7 and the end plate flanges 8 at two ends is 5cm. The solid heat-resistant steel is inserted into the central hole of the stainless steel framework 1 to serve as a central support 6, and the diameter of the central support 6 and the assembly gap of the stainless steel framework 1 are 5mm on one side, so that the solid heat-resistant steel can be easily inserted into the central hole of the stainless steel framework. Sodium chloride 5 is added into the gap between the stainless steel framework 1 and the center support 6, and is compacted from two sides. Adding high-heat-conductivity aluminum nitride 4 into a groove 7 formed in the stainless steel framework 1, winding a stainless steel sheet on the stainless steel framework 1, hooping by using a clamp, compacting and filling 500-nanometer aluminum nitride 4 into the groove 7 of the stainless steel framework 1. And then the clamp and the stainless steel sheet are taken down, and the aluminum nitride powder 4 and the stainless steel framework 1 are fully connected to form a cylindrical shape. An insulating layer 2 made of glass fiber cloth is wound on the stainless steel skeleton 1 for insulating the niobium three-tin superconducting coil 3 and the stainless steel skeleton 1, and then wires are precisely arranged on the insulated stainless steel skeleton 1. And then carrying out vacuum heat treatment on the wound niobium three-tin superconducting coil 3 to generate a niobium three-tin superconducting phase. After the heat treatment is completed, the boiled deionized water is slowly added into sodium chloride 5 between the stainless steel framework 1 and the center support 6, the sodium chloride 5 is gradually dissolved, a gap between the stainless steel framework 1 and the center support 6 is exposed, and the center support 6 is slowly pulled out. Then, the niobium three-tin superconducting coil 3 is vacuum heated to remove water vapor on the inner wall. Finally, the whole body is subjected to vacuum impregnation with epoxy resin, the epoxy resin is impregnated and permeated into the niobium three-tin superconducting coil 3 from the outer surface and the central hole of the niobium three-tin superconducting coil 3, the gaps of the niobium three-tin superconducting coil 3 and the aluminum nitride 4 are filled, the niobium three-tin superconducting coil 3, the stainless steel skeleton 1 and the aluminum nitride 4 are filled and solidified into a whole body, and finally the niobium three-tin superconducting coil 3 with high thermal conductivity is obtained.
Embodiment two:
the two sides of the neutral surface of the stainless steel skeleton 1 are provided with grooves 7, the width of each groove 7 is 10mm, and the edge distance between the grooves 7 and the two end plate flanges 8 is 10cm. The solid heat-resistant steel is inserted into the central hole of the stainless steel framework 1 to serve as a central support 6, the diameter of the central support 6 and the assembly gap of the stainless steel framework 1 are 0.5mm in a single side, and the heat-resistant steel can be easily inserted into the central hole of the stainless steel framework 1. Sodium chloride 5 is added in the gap between the stainless steel skeleton 1 and the center support 6, and compacted from both sides. Aluminum nitride 4 with high thermal conductivity is added into a groove 7 formed in the stainless steel framework 1, a stainless steel sheet is wound on the stainless steel framework 1, and the stainless steel framework 1 is tightly clamped by a clamp, so that the groove 7 of the stainless steel framework 1 is filled with 100 micrometers of aluminum nitride 4 in a compacting manner. And then the clamp and the stainless steel sheet are taken down, and the aluminum nitride powder 4 and the stainless steel framework 1 are fully connected to form a cylindrical shape. An insulating layer 2 made of glass fiber cloth is wound on the stainless steel skeleton 1 for insulating the niobium three-tin superconducting coil 3 and the stainless steel skeleton 1, and then wires are precisely arranged on the insulated stainless steel skeleton 1. And then carrying out vacuum heat treatment on the wound niobium three-tin superconducting coil 3 to generate a niobium three-tin superconducting phase. After the heat treatment is completed, the boiled deionized water is slowly added into sodium chloride 5 between the stainless steel framework 1 and the center support 6, the sodium chloride 5 is gradually dissolved, a gap between the stainless steel framework 1 and the center support 6 is exposed, and the center support 6 is slowly pulled out. Then, the niobium three-tin superconducting coil 3 is vacuum heated to remove water vapor on the inner wall. Finally, the whole body is subjected to vacuum impregnation with epoxy resin, the epoxy resin is impregnated and permeated from the outer surface of the niobium three-tin superconducting coil 3 and the niobium three-tin superconducting coil 3 in the two directions of the central hole, gaps of the niobium three-tin superconducting coil 3 and the aluminum nitride 4 are filled, the niobium three-tin superconducting coil 3, the stainless steel skeleton 1 and the aluminum nitride 4 are filled and solidified into a whole body, and finally the niobium three-tin superconducting coil 3 with high thermal conductivity is obtained.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.