A wide-temperature-range high-conductivity cable and its preparation method

Abstract

This invention belongs to the field of wire and cable technology, and discloses a wide-temperature-range high-conductivity cable and its preparation method. The cable includes at least one insulated core, a shielding layer (5), and an outer sheath (6). The insulated core includes a copper-silver-few-layer graphene nanocomposite conductor core (1) and a composite insulation layer (2). The mass percentages of copper, silver, and few-layer graphene with 2 to 10 layers in the conductor are 90% to 94%, 5% to 8%, and 1% to 3%, respectively. The conductor is formed by liquid-phase co-reduction, ultrasonic ball milling, spark plasma sintering, hot extrusion, continuous drawing, and low-temperature annealing. The composite insulation layer is formed by extrusion and electron beam irradiation crosslinking of fluororubber, thermoplastic aromatic polyimide, and nano-ceramic filler. This invention is used for cable transmission under wide-temperature-range conditions.

Description

Technical Field

[0001] This invention belongs to the technical field of wires and cables, composite conductors, and composite insulation materials, and specifically relates to a wide-temperature-range high-conductivity cable and its preparation method. Background Technology

[0002] Under special operating conditions such as high-load transmission, wide temperature range, corrosive media, or radiation, cables typically need to simultaneously meet requirements such as low conductor resistance, insulation temperature resistance, dielectric resistance, and structural stability. While traditional copper conductor cables have mature manufacturing processes, problems such as line loss, conductor heating, thermal aging, and strength degradation may still occur under long-distance or high-current-carrying conditions.

[0003] Existing silver-copper alloys or graphene-containing conductors can improve some electrical conductivity or mechanical properties. However, if only a broad composition is used, nano-silver and graphene are prone to agglomeration or segregation, making it difficult to form stable conductive channels in the copper matrix. When the content of the reinforcing phase is too low, the conductive channels are insufficient, and when the content is too high, it will reduce plasticity and increase porosity defects.

[0004] Existing cable insulation materials can be made of polyethylene, cross-linked polyethylene, ordinary rubber, silicone rubber, or fluororubber composites. These materials can meet the requirements under normal operating conditions, but in alternating temperature ranges of -60℃ to 250℃, irradiated environments, and corrosive media, they may still have problems such as insufficient thermal stability, low-temperature brittleness, poor interfacial compatibility, filler agglomeration, or decreased insulation strength.

[0005] Therefore, there is a need for a cable design that integrates conductor microstructure, conductor forming process, and insulation composite interface to improve conductor conductivity, mechanical strength, and insulation stability over a wide temperature range while maintaining processability. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a wide-temperature-range high-conductivity cable and its preparation method, so as to improve the problem that it is difficult to simultaneously achieve conductor conductivity, mechanical strength, insulation wide-temperature-range stability and processability in existing special working condition cables.

[0007] To address the aforementioned technical problems, this invention provides a wide-temperature-range high-conductivity cable. The cable includes at least one insulated core, a shielding layer covering the insulated core, and an outer sheath covering the shielding layer. The insulated core comprises a copper-silver-few-layer graphene nanocomposite conductor core and a composite insulation layer extruded over it. In a single-core cable, the shielding layer and outer sheath can be sequentially arranged outside the composite insulation layer; in a multi-core cable, multiple insulated cores can be twisted together to form a cable core, with a filling layer between the cores and a wrapping layer outside the cores.

[0008] The copper-silver-few-layer graphene nanocomposite conductor core, based on the mass percentages of copper, silver, and few-layer graphene in the final conductor, comprises 90%–94% copper, 5%–8% silver, and 1%–3% few-layer graphene, with the sum of the three mass percentages being 100%. The few-layer graphene has 2–10 layers and a thickness of 0.8–3.4 nm. Through liquid-phase co-reduction composite, ultrasonic ball milling dispersion, spark plasma sintering, hot extrusion drawing, and low-temperature annealing, the silver phase is distributed at the grain boundaries or particle boundaries of the copper matrix, and the few-layer graphene sheets are at least partially oriented and overlapped along the conductor axis.

[0009] The composite insulation layer comprises 60-70 parts fluororubber, 25-40 parts thermoplastic aromatic polyimide, and 5-15 parts nano-ceramic filler. The nano-ceramic filler is nano-alumina or nano-silicon nitride with a particle size of 30-80 nm. Through plasticizing, drying, internal mixing, twin-screw granulation, extrusion molding, and electron beam irradiation crosslinking, the flexibility and dielectric resistance of fluororubber, the heat resistance of polyimide, and the insulation reinforcement of nano-ceramic filler are synergistically combined.

[0010] The present invention also provides a method for preparing the above-mentioned cable, comprising: adding soluble copper salt, soluble silver salt and few-layer graphene according to the target mass ratio; preparing precursor composite powder by liquid phase co-reduction; obtaining copper-silver-few-layer graphene nanocomposite conductor core by ultrasonic ball milling, spark plasma sintering, hot extrusion drawing and low temperature annealing; and obtaining the cable by composite insulation particle preparation, extrusion, irradiation crosslinking, shielding layer setting and outer sheath extrusion.

[0011] Beneficial effects The beneficial effects of this invention are as follows: By controlling the ratio of copper, silver, and few-layer graphene at the conductor end, and through a continuous process of liquid-phase co-reduction, dispersion, discharge plasma sintering, and plastic processing, the silver phase boundary distribution and the axial overlapping structure of few-layer graphene are formed, thereby reducing the internal interfacial resistance of the conductor and improving the resistance stability after processing.

[0012] The copper matrix maintains the foundation for conductor plastic processing, while the silver phase and few-layer graphene provide conductive channels and participate in grain refinement and creep resistance, thus achieving a synergistic effect between conductivity, tensile strength, and drawability.

[0013] The fluororubber, thermoplastic aromatic polyimide and nano-ceramic filler in the composite insulation layer form a multiphase composite insulation system. After cross-linking by electron beam irradiation, it helps to reduce the impact of filler interface defects on breakdown strength and wide temperature range stability.

[0014] The shielding layer, outer sheath, filling layer, and wrapping layer work together with the aforementioned insulated cores to enable single-core or multi-core structures to be fabricated using conventional cable-making processes. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the cross-sectional structure of the multi-core cable of the present invention; Figure 2 This is a flowchart illustrating the preparation process of the copper-silver-few-layer graphene composite conductor of the present invention. Figure 3 This is a flowchart illustrating the preparation process of the composite insulating layer of the present invention.

[0016] Explanation of key figure labels: 1. Copper-silver-few-layer graphene nanocomposite conductor core; 2. Composite insulation layer; 3. High and low temperature resistant filling layer; 4. Wrapping layer; 5. Tinned copper wire braided shielding layer; 6. Modified fluororubber outer sheath. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described are for illustrative purposes and should not be construed as limiting the scope of protection. Without departing from the concept of the present invention, those skilled in the art can make conventional adjustments to the number of cable cores, cross-section, rated voltage, sheath thickness, and shielding method.

[0018] Unless otherwise stated, "parts" in this document refer to parts by weight; numerical ranges include endpoint values; IACS conductivity is based on volume resistivity at 20°C, with 100% IACS corresponding to a resistivity of 0.017241 Ω·mm at 20°C. 2 / m. In this article, D is the outer diameter of the cable core before the sheath, and TS is the nominal thickness of the sheath.

[0019] Structural composition like Figure 1 As shown, in the multi-core embodiment, each insulated core consists of a copper-silver-few-layer graphene nanocomposite conductor core 1 and a composite insulation layer 2. Multiple insulated cores are twisted together to form a cable core. The gaps between the cable cores are filled with a high- and low-temperature resistant filling layer 3, and a wrapping layer 4 is provided outside the cable core. A tinned copper wire braided shielding layer 5 is provided outside the wrapping layer 4, and a modified fluororubber outer sheath 6 is extruded outside the tinned copper wire braided shielding layer 5. In the single-core embodiment, the high- and low-temperature resistant filling layer 3 and the wrapping layer 4 can be omitted, and a shielding layer and an outer sheath are sequentially provided outside the composite insulation layer 2.

[0020] The specifications and functions of the main raw materials are shown in Table 1. The conductor preparation primarily follows a liquid-phase co-reduction route using soluble copper and silver salts. The copper and silver sources are added based on the target mass percentages of copper and silver in the final conductor. In one embodiment, copper nitrate and silver nitrate are used as the copper and silver sources, respectively, to maintain consistency in the conductor preparation route.

[0021] Table 1 Specifications and Functions of Main Raw Materials

[0022] As shown in Table 1, the key control points on the conductor side are the number of layers, thickness, sheet diameter, and oxygen-containing functional group content of few-layer graphene, while the key control points on the insulation side are the Mooney viscosity of fluororubber, the thermal properties of thermoplastic aromatic polyimide, and the particle size and surface treatment state of nano-ceramic fillers.

[0023] Preparation of copper-silver-few-layer graphene nanocomposite conductor core like Figure 2 As shown in Table 2, copper-silver-few-layer graphene nanocomposite conductor cores can be prepared using a continuous process involving co-reduction composite powder preparation, ultrasonic ball milling dispersion, spark plasma sintering, hot extrusion, continuous drawing, and low-temperature annealing. This process achieves simultaneous reduction of copper and silver and their bonding with graphene during the powder stage, obtains a sintered green body during the sintering stage, and induces the few-layer graphene sheets to align along the conductor axis during the plastic processing stage.

[0024] Table 2. Fabrication process of copper-silver-few-layer graphene nanocomposite conductor core

[0025] Table 2 shows that S2 to S6 constitute a continuous closed-loop process for conductor fabrication; among them, hot extrusion temperature, extrusion ratio, drawing passes, and low-temperature annealing window are related to conductor densification, axial orientation, and electrical stability.

[0026] Preparation of composite insulating layer like Figure 3 As shown in Table 3, the composite insulation layer uses fluororubber, thermoplastic aromatic polyimide, and nano-ceramic filler as the main raw materials. In this invention, thermoplastic aromatic polyimide is dispersed in the fluororubber matrix as a heat-resistant reinforcing phase in powder or granular form, and the composite insulation layer is formed through mixing, granulation, extrusion, and electron beam irradiation crosslinking. This description does not require the polyimide to form an independent molten continuous phase at the extrusion temperature.

[0027] Table 3. Preparation process of composite insulation layer

[0028] Table 3 shows the low-defect molding and irradiation crosslinking processes for forming composite insulation layers (T2 to T5). The thickness, eccentricity, and breakdown test conditions of the composite insulation layer can be determined according to product specifications.

[0029] Shielding layer, outer sheath and multi-core auxiliary structure The shielding layer adopts a tinned copper wire braided shielding structure with a braiding density of not less than 80%, and not less than 90% in one embodiment. The surface of the tinned round copper wire should be clean, continuous and free from mechanical damage that would affect the braiding; the nominal diameter of the tinned copper wire can be selected from 0.12 to 2.0 mm according to the outer diameter of the cable core before braiding, and the braiding angle can be 45°±10°.

[0030] For multi-core cables, the filler layer can be made of fiberglass rope, with filling and cable core cabling occurring simultaneously. The fiberglass rope can be dried at 80–100℃ for 4–6 hours before use; during cabling, the cores are cabled in a right-hand, untwisted manner, with a length of 25mm. 2 Cables of gauge 1 and below have a pitch ratio of 22 to 28 times, 35mm. 2 For cable gauges of 28 to 35, the section diameter ratio is 28 to 35. The size of the fiberglass rope is selected based on the actual outer diameter of the insulated core. After filling, the fiberglass tape is synchronously overlapped and wrapped around the outside of the cable core at a wrapping speed of 5 to 10 m / min, a wrapping tension of no more than 65 N, and an overlap rate of more than 30% to maintain the roundness of the cable core after cabling.

[0031] The outer sheath can be extruded from a modified fluororubber material. This modified fluororubber material can consist of fluororubber, reinforcing filler, wear-resistant filler, crosslinking agent, and processing aids. The reinforcing filler can be carbon black or fumed silica; the wear-resistant filler can be polytetrafluoroethylene powder, nano-silicon carbide, or modified montmorillonite; and the crosslinking agent can be a bisphenol-based vulcanizing agent or a peroxide vulcanizing agent. This outer sheath, in conjunction with the shielding layer, enhances the cable's resistance to dielectric and mechanical damage.

[0032] As a sheathing extrusion process, the single-screw extruder has a length-to-diameter ratio of 20:1 and a screw speed of 15–25 r / min. The barrel temperature zones from the hopper to the die head are 60–80℃, 100–120℃, 140–160℃, and 170–180℃, with the die head temperature not exceeding 185℃. The extrusion speed is 5–10 m / min, the water tank cooling temperature is 20–40℃, and the cooling length is not less than 5 m. The sheath thickness can be calculated as TS = 0.025D ​​+ 0.6 mm, where D is the outer diameter of the cable core before sheathing, and TS is the nominal sheath thickness. The minimum value of TS is not less than 0.8 mm, the average thickness is not less than the nominal value, and the thickness at the thinnest point is not less than 85% of the nominal value minus 0.1 mm.

[0033] Example 1: Universal wide temperature range cable The cable in this embodiment comprises, from the inside out, a copper-silver-few-layer graphene nanocomposite conductor core 1, a composite insulation layer 2, a tinned copper wire braided shielding layer 5, and a modified fluororubber outer sheath 6.

[0034] The copper-silver-few-layer graphene nanocomposite conductor core comprises 92% copper, 5% silver, and 3% few-layer graphene by final conductor mass percentage, with two layers of few-layer graphene. It is prepared using a process of liquid-phase co-reduction composite, ultrasonic ball milling dispersion, spark plasma sintering, hot extrusion, continuous drawing, and low-temperature annealing. Conductivity is converted to 20℃ IACS value according to GB / T 3048.2, and tensile strength is tested according to the corresponding tensile testing methods for metallic materials. The test results are shown in Table 4.

[0035] The composite insulation layer, by weight, comprises 65 parts of ethylene-vinylidene fluoride-hexafluoropropylene copolymer fluororubber, 30 parts of thermoplastic aromatic polyimide, and 5 parts of nano-alumina with a particle size of 50 nm. The composite insulation layer is formed through intensive mixing, twin-screw extrusion granulation, extrusion packaging, and electron beam irradiation crosslinking. Power frequency breakdown strength was tested according to GB / T 1408.1, and the test results are shown in Table 4.

[0036] The shielding layer uses a tin-plated copper wire braided structure with a braiding density of 92%; the outer sheath is made of modified fluororubber extruded. After evaluation by thermal aging, low-temperature bending, corrosion resistance, and withstand voltage according to the corresponding cable material test methods, the cable's appearance and insulation performance meet the design requirements for wide-temperature-range cables.

[0037] Example 2: Large cross-section transmission cable The cable structure in this embodiment is basically the same as that in Embodiment 1, except that the copper-silver-few-layer graphene nanocomposite conductor core is a multi-strand stranded composite conductor with a conductor cross-section of 300mm². 2 The final conductor contains 94% copper, 5% silver, and 1% graphene by mass, respectively.

[0038] In this embodiment, the conductor was tested according to GB / T 3048.2 and converted to the IACS value at 20℃. The tensile strength was tested according to the corresponding tensile test method for metallic materials. The test results are shown in Table 4.

[0039] The composite insulation layer is a three-layer co-extruded structure with a total thickness of 8 mm. Each layer adopts a fluororubber / thermoplastic aromatic polyimide / nano-silicon nitride composite system. The thickness of the inner, middle, and outer layers can be adjusted according to the electric field distribution and extrusion stability. By weight, the composite insulation layer comprises 70 parts fluororubber, 25 parts thermoplastic aromatic polyimide, and 5 parts nano-silicon nitride. Power frequency breakdown strength was tested according to GB / T 1408.1, and the test results are shown in Table 4.

[0040] Example 3: Radiation-resistant cable The cable structure in this embodiment is basically the same as that in embodiment 1, except that the copper-silver-few-layer graphene nanocomposite conductor core includes 90% copper, 8% silver and 2% few-layer graphene by the final conductor mass percentage.

[0041] The composite insulation layer comprises, by weight, 60 parts fluororubber, 35 parts thermoplastic aromatic polyimide, and 5 parts nano-alumina. The composite insulation layer is subjected to mixing, granulation, extrusion, and electron beam crosslinking according to the processes listed in Table 3, with an electron beam irradiation dose of 120–150 kGy. This embodiment, by increasing the silver phase ratio and employing a fluororubber / polyimide / nano-ceramic composite insulation system, is suitable for cable conditions requiring post-irradiation insulation retention evaluation.

[0042] Example Performance and Boundary Description The composition, structure, preparation conditions, and main evaluation results of the embodiments are shown in Table 4. The conductivity, tensile strength, and power frequency breakdown strength in Table 4 are used to illustrate the evaluation results of the conductor and composite insulation layer under the corresponding implementation conditions; the environmental adaptability item is used to illustrate that the cable can be evaluated according to the corresponding product requirements.

[0043] Table 4. Composition, structure, preparation conditions, and main evaluation results of the examples

[0044] To illustrate the boundary effects of the component distribution ratios in copper-silver-few-layer graphene nanocomposite conductors, while maintaining consistent preparation processes, only the mass percentages of copper, silver, and few-layer graphene in the final conductor can be changed, resulting in the comparison schemes listed in Table 5.

[0045] Table 5 Conductor Boundary Analysis

[0046] Table 5 illustrates from the perspective of conductor composition boundaries that the contents of copper, silver, and few-layer graphene are not arbitrary choices that are independent of each other, but rather a combination range that needs to take into account the formation of conductive channels, sintering densification, and continuous drawing processability.

[0047] To illustrate the boundary effects of component content and process window in composite insulation layers, the comparative schemes listed in Table 6 can be formed under the condition of fixed mixing, granulation, extrusion and irradiation crosslinking processes.

[0048] Table 6 Boundary Analysis of Composite Insulation Layer

[0049] Table 6 illustrates from the perspective of insulating composite systems that the range of fluororubber, thermoplastic aromatic polyimide, and nano-ceramic fillers needs to simultaneously meet the requirements of extrusion processing, interfacial compatibility, and insulation strength.

[0050] Test items and measurement methods The test items and measurement methods are shown in Table 7. The conductor conductivity is converted to IACS based on the volume resistivity at 20℃; the insulation strength, low temperature bending, high temperature aging, dielectric resistance and radiation resistance items can be selected according to the cable product specifications and the usage environment.

[0051] Table 7 Test Items and Measurement Methods

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. After reading this specification, any equivalent substitutions or conventional adjustments made by those skilled in the art to the material grade, number of cores, cross-section, rated voltage, sheath thickness, shielding structure, and process parameters without departing from the concept of the present invention should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A wide-temperature-range high-conductivity cable, characterized in that, The device comprises at least one insulated conductor, a shielding layer covering the at least one insulated conductor, and an outer sheath covering the shielding layer. Each insulated conductor comprises a copper-silver-few-layer graphene nanocomposite conductor core and a composite insulation layer extruded over the copper-silver-few-layer graphene nanocomposite conductor core. The copper-silver-few-layer graphene nanocomposite conductor core, based on the mass percentages of copper, silver, and few-layer graphene in the final conductor, comprises 90%–94% copper, 5%–8% silver, and 1%–3% few-layer graphene, with the sum of the mass percentages of the three being 100%. The copper-silver-few-layer graphene nanocomposite conductor core is co-reduced in a liquid phase using a copper source, a silver source, and few-layer graphene. The composite insulating layer is formed by composite, ultrasonic ball milling dispersion, spark plasma sintering, hot extrusion, continuous drawing and low temperature annealing. The silver phase is distributed at the grain boundaries or particle boundaries of the copper matrix, and the few-layer graphene sheets are at least partially oriented and overlapped along the conductor axis. The composite insulating layer includes 60-70 parts by weight of fluororubber, 25-40 parts of thermoplastic aromatic polyimide and 5-15 parts of nano-ceramic filler, wherein the nano-ceramic filler is nano-alumina or nano-silicon nitride with a particle size of 30-80 nm. The composite insulating layer is formed by extrusion molding and electron beam irradiation crosslinking. The shielding layer is a tin-plated copper wire braided shielding layer with a braiding density of not less than 80%. The outer sheath is a modified fluororubber outer sheath.

2. The wide temperature range high conductivity cable according to claim 1, characterized in that, The copper source is a soluble copper salt, and the silver source is a soluble silver salt. The copper source and the silver source are added according to the target mass percentage of copper and silver in the final conductor. The few-layer graphene has 2 to 10 layers, a thickness of 0.8 to 3.4 nm, a sheet diameter of 5 to 10 μm, a carbon content of not less than 99%, and an oxygen-containing functional group content of not more than 1%.

3. The wide temperature range high conductivity cable according to claim 1, characterized in that, The copper-silver-few-layer graphene nanocomposite conductor core is formed by sintering co-reduction composite powder into a sintered blank through spark plasma sintering, followed by hot extrusion, continuous drawing, and low-temperature annealing. In the co-reduction composite powder, few-layer graphene overlaps or coats the surface of copper-silver composite particles, and after hot extrusion and continuous drawing, at least some of the few-layer graphene sheets are oriented along the conductor axis.

4. The wide temperature range high conductivity cable according to claim 1, characterized in that, The copper-silver-few-layer graphene nanocomposite conductor core has a conductivity of not less than 100% IACS and a tensile strength of not less than 400 MPa at 20°C, as calculated by IACS. The conductivity is measured according to GB / T 3048.2 and corrected for temperature.

5. The wide temperature range high conductivity cable according to claim 1, characterized in that, The fluororubber is a vinylidene fluoride-hexafluoropropylene copolymer fluororubber with a volatile content not exceeding 0.5% and a Mooney viscosity ML(1+4) of 40-60 at 100℃; the thermoplastic aromatic polyimide is a powder or granule with a particle size of 200-300 mesh and a glass transition temperature not lower than 280℃; the purity of the nano-ceramic filler is not lower than 99.5%, and it is surface treated with a silane coupling agent.

6. The wide temperature range high conductivity cable according to claim 1, characterized in that, The irradiation dose for electron beam crosslinking is 120–150 kGy; the power frequency breakdown strength of the composite insulation layer is not less than 35 kV / mm, and the power frequency breakdown strength is determined according to GB / T 1408.

1.

7. The wide temperature range high conductivity cable according to claim 1, characterized in that, When the cable is a multi-core cable, multiple insulated cores are twisted together to form a cable core. A high and low temperature resistant filling layer is provided in the gaps between the cable cores. A wrapping layer is provided outside the cable core. The shielding layer covers the wrapping layer, and the outer sheath covers the shielding layer. The high and low temperature resistant filling layer is one or more of glass fiber filling layer, aramid fiber filling layer, polyimide fiber filling layer, or fluororubber elastic filling layer. The wrapping layer is one or more of glass fiber tape, polyimide tape, polytetrafluoroethylene tape, or mica tape. The nominal diameter of the tinned copper wire in the tinned copper wire braided shielding layer is 0.12 to 2.0 mm, the braiding angle is 45° ± 10°, and the braiding density is not less than 90%.

8. A method for preparing a wide-temperature-range high-conductivity cable as described in any one of claims 1 to 7, characterized in that, The process includes the following steps: S1, weighing and drying soluble copper salt, soluble silver salt, and few-layer graphene according to their mass percentages in the target conductor; S2, co-reducing and combining the soluble copper salt, soluble silver salt, and few-layer graphene in a liquid phase to obtain copper-silver-few-layer graphene precursor composite powder; S3, dispersing, drying, and sieving the precursor composite powder using ultrasonic ball milling; S4, subjecting the dispersed precursor composite powder to spark plasma sintering to obtain a sintered green body; S5, The sintered blank is subjected to hot extrusion, continuous drawing, and low-temperature annealing in sequence to obtain a copper-silver-few-layer graphene nanocomposite conductor core; S6, fluororubber, thermoplastic aromatic polyimide, and nano-ceramic filler are kneaded, blended, and granulated to obtain composite insulating particles; S7, the composite insulating particles are extruded onto the copper-silver-few-layer graphene nanocomposite conductor core and cross-linked by electron beam irradiation to form a composite insulating layer; S8, a shielding layer is provided on the outside of the composite insulating layer and an outer sheath is extruded to obtain the wide temperature range high conductivity cable.

9. The preparation method according to claim 8, characterized in that, In step S2, copper nitrate and silver nitrate are dissolved in deionized water to prepare a 0.5–1.0 mol / L metal salt mixed solution. A few-layer graphene ethanol dispersion is added dropwise to the metal salt mixed solution. Under nitrogen protection at 60–80°C, a 1.0–1.5 mol / L sodium borohydride reducing agent is added dropwise at a rate of 5–10 mL / min, with a stirring speed of 300–500 r / min. The reaction is carried out for 60–90 min, followed by centrifugation, washing, and drying at 60–80°C under a vacuum of not less than 0.095 MPa for 12–24 h. In step S3, anhydrous ethanol is used as the dispersion medium, and 0.5%–1% polyvinylpyrrolidone dispersant is added, with a pellet-to-material ratio of 15:1–20:

1. The ultrasonic power is 400-600W, the ball milling speed is 200-300r / min, the ball milling is intermittent for 4-6h, and the powder is dried and then passed through a 200-mesh sieve; in S4, the precursor composite powder is pre-pressed at 5-10MPa, and then held at a vacuum degree not exceeding 10Pa, a heating rate of 80-100℃ / min, a sintering temperature of 750-850℃, and a pressure of 30-50MPa for 10-15min; in S5, the hot extrusion temperature is 750-800℃, the extrusion ratio is 20:1-25:1, the extrusion speed is 2-4mm / s, the continuous drawing is performed for 12-16 passes, the single-pass surface reduction rate is 10%-15%, and then the powder is annealed at 220-250℃ under nitrogen protection for 60-90min.

10. The preparation method according to claim 8, characterized in that, S6 include: Fluororubber is plasticized at 60-70℃ for 10-15 min, and thermoplastic aromatic polyimide and nano-ceramic filler are vacuum dried at 80-90℃ for 4-6 h. The plasticized fluororubber is added to a mixer and mixed at 90-110℃ for 5-8 min. Then, thermoplastic aromatic polyimide and nano-ceramic filler are added, and the mixture is continued to be mixed at 30-40 r / min for 20-25 min with the temperature not exceeding 120℃ throughout. Subsequently, it is granulated by twin-screw extrusion to obtain composite insulating particles. In S7, the body temperature during extrusion molding is 180-200℃, the die head temperature is 210-220℃, the screw speed is 150-200 r / min, and the electron beam irradiation dose is 120-150 kGy.

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