A nano-composite protective agent for repairing arc ablation of 10kV vacuum circuit breaker contacts, and a preparation method and application thereof

Abstract

This invention belongs to the technical field of power equipment repair materials, specifically relating to a nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts, its preparation method, and its application. The method includes: drying core-shell structured nano-metal powder, mixing it with γ-aminopropyltriethoxysilane, polyethylene glycol, and deionized water to prepare a coupling agent treatment solution; then adding quaternary transition metal boron carbonitride nanoclusters, polyvinylpyrrolidone, and acetic acid, ultrasonically dispersing, and filtering to obtain the product. The core-shell structured nano-metal powder is prepared via a two-step hydrazine hydrate reduction method: first, copper nitrate and chromium nitrate are reduced to form a copper-chromium alloy core, and then silver nitrate is reduced to form a silver shell. The quaternary transition metal boron carbonitride nanoclusters are prepared by reacting hafnium tetrachloride, zirconium tetrachloride, and sodium borohydride under anhydrous and oxygen-free conditions, followed by high-temperature treatment with ammonia and methane. The protective agent prepared by this invention reduces contact resistance and improves arc erosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of power equipment repair materials technology, specifically relating to a nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts, its preparation method, and its application. Background Technology

[0002] Vacuum circuit breakers, as indispensable control and protection devices in medium- and high-voltage power grids, rely heavily on the vacuum interrupter, whose contact performance directly determines the breaking capacity and operational reliability of the circuit breaker. During the breaking process, the contacts must withstand multiple challenges, including high-temperature arc erosion, mechanical impact, and current-induced thermal effects. Currently, copper-chromium alloys have become the mainstream material for vacuum interrupter contacts due to their excellent electrical and thermal conductivity and resistance to welding. However, with the development of power systems towards higher voltage, larger capacity, and the integration of new energy sources, vacuum circuit breakers need to frequently interrupt fault currents and even cope with complex operating conditions such as high-frequency harmonics. Under the high temperature of the arc, the contact surface melts, sputters, and evaporates, leading to material loss, surface roughening, and crack formation. In severe cases, this can cause contact welding or termination of electrical life. Research shows that copper particles cause severe erosion of the contacts under the action of an arc, and the erosion depth and mass loss increase significantly with increasing power density. Therefore, improving the arc erosion resistance of contact materials or effectively repairing eroded contacts has become a pressing technical challenge in the field of vacuum circuit breakers.

[0003] To address the aforementioned issues, scholars both domestically and internationally have conducted extensive research from the perspective of material modification. In alloying, the addition of high-melting-point metals such as tungsten and molybdenum to dope and strengthen copper-chromium contact materials has yielded results, with copper-chromium-molybdenum alloys showing a significant improvement in arc erosion resistance. Regarding surface modification, forming a nanocrystalline layer on the surface of microcrystalline copper-chromium alloys can improve contact erosion behavior without affecting the overall contact performance. Furthermore, optimizing the grain size and distribution of the chromium phase in copper-chromium alloys and improving the magnetic field type of the vacuum interrupter have also been proven to be effective ways to reduce contact erosion. However, existing technologies largely focus on improving the preparation process of the contact material itself or developing new contact materials. For in-service contacts that have already suffered erosion damage, there is still a lack of effective on-site repair methods. Traditional contact replacement methods require disassembling the circuit breaker and vacuuming, which are time-consuming and costly, failing to meet the needs of rapid power restoration in power systems. Existing surface coating repair technologies, such as plasma spraying or cold spraying, often require specialized equipment and are difficult to achieve uniform coverage in a vacuum environment. The repaired coating has insufficient bonding strength with the substrate and is prone to peeling off again during subsequent fracture processes.

[0004] Therefore, developing a technical solution for in-situ repair of ablated contacts without disassembling the circuit breaker has significant engineering application value. Simultaneously, this technical solution must meet the following stringent requirements: the repair material must be compatible with the vacuum environment and must not release volatile substances that affect the vacuum level; the repair layer must possess good conductivity and resistance to secondary ablation; and the construction process should be simple and quick, and can be implemented through the inspection hole of the vacuum interrupter. However, no solution has yet been found in the existing technology that simultaneously meets all of the above requirements. How to design a composite protection system that can be sprayed at room temperature and pressure, forms a reinforcing layer in situ under low current conditions, and does not affect the original insulation performance of the vacuum circuit breaker is a long-standing technical problem that those skilled in the art have long sought to solve but have yet to succeed in. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts, its preparation method, and its application.

[0006] In a first aspect, the present invention provides a method for preparing a nanocomposite protective agent for arc erosion repair of contacts in a 10kV vacuum circuit breaker, comprising the following steps: S1. By weight, place the core-shell structured nano-metal powder in a vacuum drying oven and dry it at 60-80℃ to obtain the dried core-shell structured nano-metal powder; dissolve 2-6 parts of γ-aminopropyltriethoxysilane in 21-30 parts of polyethylene glycol, add 0.5-1.0 parts of deionized water, and stir at 28-32℃ under nitrogen protection to obtain the coupling agent treatment solution; S2. Add 35-55 parts of dried core-shell structured nano-metal powder to the coupling agent treatment solution and stir under nitrogen protection; add 1-4 parts of quaternary transition metal boron carbonitride nanoclusters, 0.5-3 parts of polyvinylpyrrolidone and 0.1-0.5 parts of acetic acid, and disperse by ultrasonication to obtain a slurry; filter the slurry.

[0007] In this invention, the preparation of a nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts involves three key processes: coupling agent hydrolysis, nanoparticle surface modification, and multi-component composite dispersion. First, γ-aminopropyltriethoxysilane is dissolved in polyethylene glycol, and a trace amount of deionized water is added. At room temperature, the ethoxy groups of the silane undergo hydrolysis to generate silanol groups. These silanol groups have high reactivity and can condense with the hydroxyl groups on the surface of the nanoparticles to form silicon-oxygen covalent bonds, thereby forming an organic coating layer on the surface of the nanoparticles. This coating layer prevents nanoparticle aggregation through steric hindrance, and its terminal amino groups can form hydrogen bonds or coordination bonds with other components. The coupling treatment is carried out under nitrogen protection to avoid interference from moisture and oxygen in the air. Then, the dried core-shell structured nanoparticles are added to the coupling agent treatment solution, and under high-speed shear dispersion, the coupling agent uniformly coats the surface of each nanoparticle. Next, quaternary transition metal boron carbonitride nanoclusters, polyvinylpyrrolidone (PVP), and acetic acid are added. PVP, acting as a suspension stabilizer, adsorbs onto the nanoparticle surface through coordination between its carbonyl groups and metal atoms, providing both steric hindrance and electrostatic repulsion stabilization. Acetic acid, as a trace activator, slightly etches the oxide layer on the contact surface, promoting the bonding of the subsequent repair layer to the substrate. During ultrasonic dispersion, high-frequency sound waves generate cavitation, forming localized high-temperature, high-pressure microjets that break up the aggregated nanoparticles. Simultaneously, multiple hydrogen bonds form between the amino end groups of the quaternary transition metal boron carbonitride nanoclusters and the amino or silanol groups in the coupling agent coating layer, while the amino groups form coordination bonds with silver atoms on the surface of the nanoparticle metal powder, achieving a uniform composite of the two nanocomponents. Finally, trace agglomerates are removed by filtration, yielding a stable nanocomposite protective agent slurry. After subsequent spraying and low-current aging treatment, the protective agent causes the nano-silver shell to melt and spread, exposing the copper-chromium core and metallurgically bonding it with the substrate. At the same time, the quaternary transition metal boron carbonitride nanoclusters decompose to produce a high-melting-point ceramic phase that is pinned into the repair layer, forming a dense and reinforced ablation-resistant surface.

[0008] According to a preferred embodiment of the present invention, in step S1, the drying time at 60-80°C is 2-4 hours.

[0009] According to a preferred embodiment of the present invention, in step S2, the ultrasonic dispersion time is 45-60 min.

[0010] According to a preferred embodiment of the present invention, the preparation method of the core-shell structured modified nano-metal powder includes: A1. Under argon protection, 150-250 parts of deionized water are added to a reaction vessel, along with 5-7 parts of copper nitrate and 0.08-0.12 parts of chromium nitrate, and 0.3-0.8 parts of polyvinylpyrrolidone. The mixture is stirred and heated at room temperature to obtain a metal salt solution; 0.8-1.2 parts of hydrazine hydrate are dissolved in 15-25 parts of deionized water, and the pH is adjusted to 10.0-12.0 with 1-3 parts of ammonia to obtain a reducing agent solution; the reducing agent solution is added dropwise to the metal salt solution. In step A1, after the addition is complete, the mixture is stirred at 78-82℃ to obtain a Cu-Cr alloy nanoparticle suspension. In step A2, 1.5-1.7 parts of the Cu-Cr alloy nanoparticle suspension prepared in step A1 are added to a solution of 1.5-2.0 parts silver nitrate dissolved in 8-12 parts deionized water. Stirring continues, followed by the addition of a reducing solution containing 0.6-1.0 parts hydrazine hydrate and 8-12 parts deionized water. The mixture is stirred at 78-82℃ to obtain a suspension. The suspension is naturally cooled to room temperature, centrifuged, and the precipitate is collected. The precipitate is washed with deionized water and anhydrous ethanol and then vacuum dried.

[0011] In this invention, the preparation of core-shell structure modified nano-metal powder is divided into two stages: first, a copper-chromium alloy core is prepared, and then a nano-silver shell is coated on its surface. In the first stage, under inert gas protection, divalent copper ions and trivalent chromium ions are dissolved in deionized water, and polyvinylpyrrolidone is added as a dispersant and stabilizer to form a homogeneous metal salt solution. Subsequently, a reducing agent solution is prepared: hydrazine hydrate is dissolved in deionized water, and the pH of the system is adjusted to a strongly alkaline range using ammonia water, making the solution strongly alkaline. Under alkaline conditions, the reducing power of hydrazine hydrate is significantly enhanced. The reaction formula is: hydrazine hydrate loses electrons in an alkaline environment to generate nitrogen gas and water, while simultaneously releasing electrons. Each hydrazine hydrate molecule can provide multiple electrons. When the reducing agent solution is slowly added dropwise to the metal salt solution, divalent copper ions gain electrons and are reduced to zero-valent copper, and trivalent chromium ions gain electrons and are reduced to zero-valent chromium. Since the standard electrode potential of copper is positive and that of chromium is negative, the reduction of chromium requires stronger reducing conditions. The alkaline environment not only increases the reduction potential of hydrazine hydrate but also causes trivalent chromium ions to form chromium hydroxide colloids, which are more easily adsorbed onto the surface of copper particles and simultaneously reduced, thus forming a copper-chromium solid solution or intermetallic compound. The reaction temperature is controlled within an appropriate high-temperature range, and continuous stirring for a sufficient time allows for sufficient nucleus growth, ultimately yielding a suspension of copper-chromium alloy nanoparticles with a nanoscale particle size. In the second stage, silver nitrate solution is added to the suspension, and silver ions are adsorbed onto the surface of the copper-chromium alloy particles. Subsequently, a reducing solution containing hydrazine hydrate is added dropwise. Under alkaline conditions, silver ions gain electrons and are reduced to zero-valent silver, preferentially undergoing heterogeneous nucleation on the surface of the alloy particles, depositing a continuous and dense silver layer. Because the standard electrode potential of silver is much higher than that of copper and chromium, silver ions are easily reduced. By controlling the amount of silver nitrate, the thickness of the silver shell is controlled within the nanoscale range. After the reaction is complete, centrifugation, washing, and vacuum drying yield modified nano-metal powder with a complete core-shell structure, its core being a copper-chromium alloy and its outer shell a nano-silver layer with extremely high silver coverage.

[0012] According to a preferred embodiment of the present invention, in step A1, the stirring reaction time at 78-82°C is 1-2 hours.

[0013] According to a preferred embodiment of the present invention, in step A2, the temperature of vacuum drying is 58-62°C.

[0014] According to a preferred embodiment of the present invention, the preparation method of the quaternary transition metal boron carbonitride nanoclusters includes: B1, under anhydrous and oxygen-free conditions, dissolving 3.0-3.5 parts of hafnium tetrachloride and 2.2-2.5 parts of zirconium tetrachloride in 40-60 parts of anhydrous ethanol, and reacting at room temperature with stirring to obtain a hafnium-zirconium mixed chloride solution; dissolving 1.0-1.3 parts of sodium borohydride in 25-35 parts of ethylene glycol, and stirring under ice-water bath cooling to obtain a sodium borohydride ethylene glycol solution; adding the hafnium-zirconium mixed chloride solution to the sodium borohydride ethylene glycol solution with stirring, and continuing to stir the reaction in an ice-water bath after the addition is complete to obtain... The reaction mixture was allowed to stand and age at room temperature, then evaporated in a water bath at 78-82℃ to obtain the product. The product was transferred to a tube furnace and heated to 345-355℃ under an argon atmosphere. A mixture of ammonia and methane was introduced, and the temperature was raised to 795-805℃ and held. The methane and ammonia were then turned off, and the mixture was allowed to cool naturally to room temperature under a pure argon atmosphere to obtain the crude product. B2. The crude product was dispersed in 80-120 parts of anhydrous ethanol, and 0.3-0.8 parts of polyvinylpyrrolidone were added. The mixture was ultrasonically dispersed, centrifuged, and the precipitate was collected. The precipitate was washed with anhydrous ethanol and dried under vacuum at 58-62℃.

[0015] In this invention, the preparation of the quaternary transition metal boron carbonitride nanoclusters is divided into two stages: low-temperature reduction and high-temperature carbonitride. The first stage is carried out under strictly anhydrous and oxygen-free conditions to prevent the hydrolysis of hafnium tetrachloride and zirconium tetrachloride. Hafnium tetrachloride and zirconium tetrachloride are dissolved in anhydrous ethanol to form a hafnium-zirconium mixed chloride solution. Simultaneously, sodium borohydride is dissolved in ethylene glycol and kept at a low temperature under ice-water bath cooling. Sodium borohydride is a strong reducing agent, and each borohydride ion can provide multiple electrons. The hafnium-zirconium mixed chloride solution is slowly added dropwise to the sodium borohydride ethylene glycol solution, and the temperature is controlled within a low range to prevent local overheating that could lead to product agglomeration. Under these conditions, tetravalent hafnium and zirconium ions are reduced by sodium borohydride, while boron participates in the reaction to form hafnium-zirconium-boron ternary metal boride nanocrystals. This process involves complex electron transfer and atomic rearrangement, with boron atoms from sodium borohydride entering the metal lattice to form a boride phase with a high melting point. The reaction mixture was aged at room temperature for a sufficient time to allow the crystal nuclei to grow and mature further. The solvent was then evaporated in a water bath at an appropriate temperature to remove the solvent, yielding a brownish-black viscous substance. In the second stage, the product was transferred to a tube furnace and heated to a suitable temperature under argon protection for a period of time to remove residual organic matter. The temperature was then increased to a high temperature range, and a mixture of ammonia and methane was introduced. At the high temperature, ammonia decomposed into active nitrogen atoms and hydrogen, and methane decomposed into active carbon atoms and hydrogen. These active nitrogen and carbon atoms diffused to the surface of the hafnium-zirconium-boron nanocrystals, reacting with the hafnium and zirconium on the surface to form a hafnium-zirconium carbonitride solid solution shell. Simultaneously, some nitrogen atoms grew outward in the form of amino groups, forming a dendritic structure. Finally, quaternary transition metal boron carbonitride nanoclusters were obtained.

[0016] According to a preferred embodiment of the present invention, the holding time for heating to 795-805°C is 2-4 hours.

[0017] A second aspect of the present invention provides a nanocomposite protective agent for arc erosion repair of contacts of a 10kV vacuum circuit breaker, prepared according to the method described above.

[0018] A third aspect of the present invention provides the application of the nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts in the arc erosion repair of 10kV vacuum circuit breaker contacts.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention achieves efficient in-situ repair of ablated contact surfaces, significantly reducing contact resistance and restoring electrical contact performance. The core-shell structured nano-metal powder in this protective agent has a low-melting-point nano-silver outer shell and a high-melting-point copper-chromium alloy core. When the protective agent is sprayed onto the contact surface and subjected to low-current aging treatment, the outer shell nano-silver preferentially melts and spreads, filling the micropores, microcracks, and ablation pits on the contact surface to form a continuous conductive channel; subsequently, the core copper-chromium alloy is exposed and forms a metallurgical bond with the contact substrate, ultimately forming a dense and reinforced layer on the contact surface. At the same time, the functional dispersion medium in this protective agent is polyethylene glycol, which has a moderate evaporation rate and a very low residual rate at room temperature for a short time after spraying, which will not affect the vacuum degree of the arc-extinguishing chamber, thereby ensuring that the insulation performance of the circuit breaker after repair meets the operating requirements.

[0020] (2) The quaternary transition metal boron carbonitride nanoclusters synthesized for the first time in this invention, in synergy with core-shell structured nano-metal powder, significantly enhance the resistance to secondary ablation and the interfacial bonding strength of the repair layer. These nanoclusters possess a unique "core-shell-claw" three-layer structure: the core is hafnium-zirconium-boron ternary metal boride nanocrystals, the middle shell is hafnium-zirconium carbonitride solid solution, and the outer shell is dendritic amino-terminal groups. During the aging process, the boride core is partially transformed into high-melting-point hafnium boride and zirconium boride ceramic phases, anchoring themselves in the microcracks and pores on the contact surface, forming an "anchoring effect" that effectively inhibits subsequent arc ablation damage to the repair layer. Simultaneously, the amino-terminal groups of the outer shell form multiple hydrogen bonds and coordination bonds with the surface of the nano-metal powder treated with the coupling agent, achieving uniform composite at the nanoscale, significantly improving the density and uniformity of the repair layer. Microhardness testing shows that the surface hardness of the contact treated with the protective agent of this invention is significantly higher than that of the untreated contact, resulting in a substantial improvement in arc ablation resistance. In addition, the free nitrogen atoms in the nanoclusters form copper-nitrogen coordination bonds with the copper substrate of the contact, which further enhances the interfacial bonding between the repair layer and the substrate, solving the problem of easy peeling of the repair layer in existing surface coating technologies.

[0021] (3) The preparation method of this invention has mild process conditions, is suitable for industrial production, and the protective agent can be sprayed on-site through the inspection hole without disassembling the circuit breaker, which has extremely high engineering practical value. In the preparation process, the formation of the core-shell structure is precisely controlled by a two-step hydrazine hydrate reduction method: the first step is to reduce copper nitrate and chromium nitrate under alkaline conditions to form a nanoscale copper-chromium alloy core; the second step uses the alloy core as a template to reduce silver nitrate to form a silver shell with a nanoscale thickness. The silver layer coverage is extremely high, ensuring the integrity and consistency of the core-shell structure. At the same time, the preparation of the quaternary transition metal boron carbonitride nanoclusters adopts sodium borohydride reduction under anhydrous and oxygen-free conditions combined with high-temperature ammonia methane treatment. The product has uniform particle size, large specific surface area, and exhibits excellent dispersion stability in ethanol. In the preparation of the protective agent, γ-aminopropyltriethoxysilane hydrolyzes in the presence of trace amounts of deionized water to form silanol, which condenses with the hydroxyl groups on the surface of the nano metal powder to form an organic coating layer, effectively preventing the agglomeration of nanoparticles. Therefore, this invention not only achieves a breakthrough in contact repair performance, but also demonstrates significant advantages in manufacturing process and ease of application, providing an economical, efficient, and reliable solution for the ablation repair of vacuum circuit breaker contacts. Detailed Implementation

[0022] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention. Example

[0023] This embodiment provides a method for preparing a nanocomposite protective agent for arc erosion repair of contacts in a 10kV vacuum circuit breaker, comprising the following steps: S1. Place 45g of core-shell structured nano-metal powder in a vacuum drying oven and dry at 70℃ for 3h to obtain dried core-shell structured nano-metal powder; Dissolve 4g of γ-aminopropyltriethoxysilane (kH-550) in 25.5g of polyethylene glycol 400 (PEG-400), add 0.75g of deionized water, and stir in a 30℃ water bath for 30min under nitrogen protection to obtain coupling agent treatment solution; S2. Slowly add 45g of dried core-shell structured nano-metal powder to the coupling agent treatment solution. Under nitrogen protection, disperse at a high speed of 1500r / min for 2h to ensure the coupling agent fully coats the surface of the nanoparticles. Then add 2.5g of quaternary transition metal boron carbonitride nanoclusters (TMB-CN-NC), 1.75g ​​of polyvinylpyrrolidone (PVPk30), and 0.3g of acetic acid. Transfer to an ultrasonic dispersion device and ultrasonically disperse at 20kHz frequency and 500W power for 52.5min. Control the temperature not to exceed 40℃ during dispersion to allow the dendritic "claw" structure of TMB-CN-NC to form multiple hydrogen bonds and coordination bonds with the coupling agent layer on the surface of the nano-metal powder, achieving a uniform nanoscale composite of inorganic modified compound and nano-metal powder. The dispersed slurry is then filtered through a 1μm pore size filter membrane to remove any possible agglomerated particles, yielding the final product. The finished product is packaged in brown glass bottles, protected with nitrogen, and stored in a cool, dry place.

[0024] The preparation method of core-shell structure modified nano-metal powder includes the following steps: A1. Under argon protection, 200g of deionized water was added to a reaction vessel, along with 6g of copper nitrate and 0.1g of chromium nitrate, and 0.55g of polyvinylpyrrolidone. The mixture was stirred at 300r / min for 30min at room temperature, and then heated to 80℃ to obtain a metal salt solution. 1.0g of hydrazine hydrate (85wt%) was dissolved in 20g of deionized water, and the pH was adjusted to 11.0 with 2g of ammonia (25wt%) to obtain a reducing agent solution. The reducing agent solution was added dropwise to the metal salt solution at a rate of 0.5mL / min. During the addition, the solution color gradually changed from blue to reddish-brown. After the addition was complete, the mixture was stirred at 400r / min at 80℃ for 1.5h to obtain a Cu-Cr alloy nanoparticle suspension with a particle size of 35±5nm. A2. The 1.6g Cu-Cr alloy nanoparticle suspension prepared in step A1 was added to a solution of 1.75g ​​silver nitrate dissolved in 10g deionized water. The mixture was stirred at 80℃ for 10min to allow Ag⁺ to be uniformly adsorbed onto the surface of the alloy nanoparticles. Then, a reducing solution containing 0.8g hydrazine hydrate (85wt%) and 10g deionized water was added dropwise at a rate of 0.2mL / min. The mixture was stirred at 80℃ for 30min to obtain a suspension. The suspension was naturally cooled to room temperature and centrifuged at 8000r / min for 15min to collect the precipitate. The precipitate was washed three times alternately with 25g deionized water and 25g anhydrous ethanol. Finally, it was dried at 60℃ under a vacuum of ≤-0.08MPa for 4h to obtain a core-shell structure modified nano-metal powder. The core is a Cu-Cr alloy with a Cr content of 0.8% (particle size 35±5nm), and the outer shell is a nano-silver layer (thickness 7±2nm) with a silver layer coverage of ≥95%.

[0025] The preparation method of quaternary transition metal boron carbonitride nanoclusters includes the following steps: B1. Under strictly anhydrous and oxygen-free conditions (high-purity argon protection), weigh 3.25g of hafnium tetrachloride and 2.35g of zirconium tetrachloride, mix them, and dissolve them in 50g of anhydrous ethanol (dried by molecular sieve). React at room temperature for 30min under magnetic stirring to form a hafnium-zirconium mixed chloride solution. Simultaneously, dissolve 1.15g of sodium borohydride in 30g of ethylene glycol (dried), and stir for 15min under ice-water bath cooling to form a sodium borohydride ethylene glycol solution. Under vigorous stirring, add the hafnium-zirconium mixed chloride solution dropwise to the sodium borohydride ethylene glycol solution at a rate of 1mL / min, keeping the reaction temperature below 5℃ throughout the addition. After the addition is complete, continue stirring in an ice-water bath for 2h to allow hafnium and zirconium ions to be reduced by sodium borohydride to form Hf-Zr-B ternary metal boride nanocrystals. After the reaction is complete, The reaction mixture was allowed to stand at room temperature for 4 hours, and then heated in an 80°C water bath to evaporate most of the solvent, yielding a brownish-black viscous substance. Next, the brownish-black viscous substance was transferred to a tube furnace and heated to 350°C at a heating rate of 5°C / min under an argon atmosphere, and held for 1 hour to remove residual organic matter and volatile byproducts. Then, it was heated to 800°C at a heating rate of 10°C / min. At this temperature, a mixed gas of ammonia (flow rate 50 mL / min) and methane (flow rate 20 mL / min) was introduced and held for 3 hours to allow active nitrogen and carbon atoms to diffuse to the surface of the nanocrystals and react with Hf and Zr on the surface to form an Hf-Zr-CN solid solution carbonitride shell. After the holding period, the methane and ammonia gas were turned off, and the mixture was naturally cooled to room temperature under a pure argon atmosphere to obtain a grayish-black crude TMB-CN-NC product. B2. The crude product was dispersed in 100g of anhydrous ethanol, and 0.55g of polyvinylpyrrolidone (PVPk30) was added. The mixture was ultrasonically dispersed at 40kHz and 300W for 30min. The precipitate was then collected by centrifugation at 8000r / min for 15min, washed three times with 25g of anhydrous ethanol, and dried in a vacuum drying oven at 60℃ for 12h to obtain quaternary transition metal boron carbonitride nanoclusters. Example

[0026] The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts, the steps of which include: S1. Place the core-shell structured nano-metal powder in a vacuum drying oven and dry it at 60℃ for 2 hours to obtain the dried core-shell structured nano-metal powder; dissolve 2g of γ-aminopropyltriethoxysilane in 21g of polyethylene glycol, add 0.5g of deionized water, and stir at 28℃ for 30 minutes under nitrogen protection to obtain the coupling agent treatment solution.

[0027] S2. Add 35g of dried core-shell structured nano-metal powder to the coupling agent treatment solution and stir at 1200r / min for 1.5h under nitrogen protection. Add 1g of quaternary transition metal boron carbonitride nanoclusters, 0.5g of polyvinylpyrrolidone and 0.1g of acetic acid, and ultrasonically disperse at 20kHz and 500W for 45min to obtain a slurry. Filter the slurry through a 1μm filter membrane to obtain the product.

[0028] Preparation of core-shell structure modified nano-metal powder: A1. Under argon protection, 150g of deionized water was added to a reaction vessel, along with 5g of copper nitrate and 0.08g of chromium nitrate, and 0.3g of polyvinylpyrrolidone. The mixture was stirred at room temperature for 30min and then heated to 78℃ to obtain a metal salt solution. 0.8g of hydrazine hydrate was dissolved in 15g of deionized water, and the pH was adjusted to 10.0 with 1g of ammonia to obtain a reducing agent solution. The reducing agent solution was added dropwise to the metal salt solution at 0.5mL / min. After the addition was complete, the mixture was stirred at 78℃ for 1h to obtain a Cu-Cr alloy nanoparticle suspension.

[0029] A2. Add the 1.5g Cu-Cr alloy nanoparticle suspension prepared in step A1 to a solution of 1.5g silver nitrate dissolved in 8g deionized water, and continue stirring for 10min. Then, add a reducing solution containing 0.6g hydrazine hydrate and 8g deionized water dropwise, and continue stirring at 78℃ for 30min to obtain a suspension. Cool the suspension naturally to room temperature, centrifuge at 8000r / min for 15min, and collect the precipitate. Wash the precipitate three times alternately with 20g deionized water and 20g anhydrous ethanol, and vacuum dry at 58℃ for 4h to obtain core-shell structure modified nano-metal powder.

[0030] Preparation of quaternary transition metal boron carbonitride nanoclusters: B1. Under strictly anhydrous and oxygen-free conditions (glove box, high-purity argon), dissolve 3.0 g of hafnium tetrachloride and 2.2 g of zirconium tetrachloride in 40 g of anhydrous ethanol and react at room temperature for 30 min with stirring to obtain a hafnium-zirconium mixed chloride solution; dissolve 1.0 g of sodium borohydride in 25 g of ethylene glycol and stir for 15 min under ice-water bath cooling to obtain a sodium borohydride ethylene glycol solution; under vigorous stirring, add the hafnium-zirconium mixed chloride solution dropwise to the sodium borohydride ethylene glycol solution at a rate of 1 mL / min, maintaining the temperature ≤5℃ during the addition, and continue stirring in an ice-water bath after the addition is complete. The reaction mixture was stirred for 2 hours to obtain a reaction mixture. The reaction mixture was allowed to stand at room temperature for 4 hours, and then most of the solvent was evaporated in a water bath at 78°C to obtain a brownish-black viscous substance. The product was transferred to a tube furnace and heated to 345°C at 5°C / min under an argon atmosphere. The temperature was held for 1 hour, and then heated to 795°C at 10°C / min. A mixture of ammonia (flow rate 50 mL / min) and methane (flow rate 20 mL / min) was introduced and the mixture was held for 2 hours. The methane and ammonia were then turned off, and the mixture was allowed to cool naturally to room temperature under a pure argon atmosphere to obtain the crude product.

[0031] B2. The crude product was dispersed in 80g of anhydrous ethanol, and 0.3g of polyvinylpyrrolidone was added. The mixture was ultrasonically dispersed at 40kHz and 300W for 30min, followed by centrifugation at 8000r / min for 15min. The precipitate was collected. The precipitate was washed three times with 20g of anhydrous ethanol and vacuum dried at 58℃ for 12h to obtain quaternary transition metal boron carbonitride nanoclusters. Example

[0032] The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts, the steps of which include: S1. Place the core-shell structured nano-metal powder in a vacuum drying oven and dry it at 80℃ for 4 hours to obtain the dried core-shell structured nano-metal powder; dissolve 6g of γ-aminopropyltriethoxysilane in 30g of polyethylene glycol, add 1.0g of deionized water, and stir at 32℃ for 30min under nitrogen protection to obtain the coupling agent treatment solution.

[0033] S2. Add 55g of dried core-shell structured nano-metal powder to the coupling agent treatment solution and stir at 1800r / min for 2.5h under nitrogen protection. Add 4g of quaternary transition metal boron carbonitride nanoclusters, 3g of polyvinylpyrrolidone and 0.5g of acetic acid, and ultrasonically disperse at 20kHz and 500W for 60min to obtain a slurry. Filter the slurry through a 1μm filter membrane to obtain the product.

[0034] Preparation of core-shell structure modified nano-metal powder: A1. Under argon protection, 250g of deionized water was added to a reaction vessel, along with 7g of copper nitrate and 0.12g of chromium nitrate, and 0.8g of polyvinylpyrrolidone. The mixture was stirred at room temperature for 30 minutes and then heated to 82°C to obtain a metal salt solution. 1.2g of hydrazine hydrate was dissolved in 25g of deionized water, and the pH was adjusted to 12.0 with 3g of ammonia to obtain a reducing agent solution. The reducing agent solution was added dropwise to the metal salt solution at 0.5mL / min. After the addition was complete, the mixture was stirred at 82°C for 2 hours to obtain a Cu-Cr alloy nanoparticle suspension.

[0035] A2. Add the 1.7g Cu-Cr alloy nanoparticle suspension prepared in step A1 to a solution of 2.0g silver nitrate dissolved in 12g deionized water, and continue stirring for 10min. Then, add a reducing solution containing 1.0g hydrazine hydrate and 12g deionized water dropwise, and continue stirring at 82℃ for 30min to obtain a suspension. Cool the suspension naturally to room temperature, centrifuge at 8000r / min for 15min, and collect the precipitate. Wash the precipitate three times alternately with 30g deionized water and 30g anhydrous ethanol, and vacuum dry at 62℃ for 4h to obtain core-shell structure modified nano-metal powder.

[0036] Preparation of quaternary transition metal boron carbonitride nanoclusters: B1. Under strictly anhydrous and oxygen-free conditions (high-purity argon), dissolve 3.5g hafnium tetrachloride and 2.5g zirconium tetrachloride in 60g anhydrous ethanol and react at room temperature for 30min with stirring to obtain a hafnium-zirconium mixed chloride solution. Dissolve 1.3g sodium borohydride in 35g ethylene glycol and stir for 15min under ice-water bath cooling to obtain a sodium borohydride ethylene glycol solution. Under vigorous stirring, add the hafnium-zirconium mixed chloride solution dropwise to the sodium borohydride ethylene glycol solution at 1mL / min, keeping the temperature ≤5℃ during the addition. After the addition is complete, continue stirring in the ice-water bath. The reaction mixture was stirred for 2 hours to obtain a reaction mixture. The reaction mixture was allowed to stand at room temperature for 4 hours, and then most of the solvent was evaporated in an 82°C water bath to obtain a brownish-black viscous substance. The product was transferred to a tube furnace and heated to 355°C at 5°C / min under an argon atmosphere. The temperature was held for 1 hour, and then heated to 805°C at 10°C / min. A mixed gas of ammonia (flow rate 50 mL / min) and methane (flow rate 20 mL / min) was introduced and the mixture was held for 4 hours. The methane and ammonia were then turned off, and the mixture was allowed to cool naturally to room temperature under a pure argon atmosphere to obtain the crude product.

[0037] B2. The crude product was dispersed in 120g of anhydrous ethanol, and 0.8g of polyvinylpyrrolidone was added. The mixture was ultrasonically dispersed at 40kHz and 300W for 30min, and then centrifuged at 8000r / min for 15min. The precipitate was collected. The precipitate was washed three times with 30g of anhydrous ethanol and dried under vacuum at 62℃ for 12h to obtain quaternary transition metal boron carbonitride nanoclusters.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that no quaternary transition metal boron carbonitride nanoclusters are added; the remaining steps are exactly the same as in Example 1.

[0039] Comparative Example 2 The difference between this comparative example and Example 1 is that the core-shell structure modified nano-metal powder is replaced with an equal mass of ordinary nano-copper powder. The remaining steps are exactly the same as in Example 1.

[0040] Comparative Example 3 The difference between this comparative example and Example 1 is that γ-aminopropyltriethoxysilane is not added in S1, while the remaining steps are exactly the same as in Example 1.

[0041] According to relevant national and industry standards, the performance of the nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts provided in the above embodiments and comparative examples was tested. The test methods are as follows: Take 10kV vacuum circuit breaker contacts (copper-chromium alloy, 40mm diameter, 5mm thickness) from the same batch of production. Simulate arc erosion defects (micropore diameter 50-100μm, depth 20-30μm, crack width 10-20μm, length 100-300μm) are uniformly prepared on the contact surface using electrical discharge machining. The contact surface to be repaired is wiped clean with anhydrous ethanol and allowed to air dry at room temperature for 10 minutes. Each protective agent sample is thoroughly shaken in a brown bottle for 30 seconds. Using a high-pressure micro-mist spray gun (0.5mm nozzle diameter), under spraying pressure of 0.25MPa and spraying distance of 90mm, the sample is applied along the contact surface. The contact was sprayed twice evenly in a zigzag pattern, with a 4-minute interval between each spray. The amount of each spray was controlled at 0.5 mL / cm². After spraying, the contact was placed in a fume hood and left to stand for 25 minutes at 25°C and 50% relative humidity to allow the polyethylene glycol 400 dispersion medium to completely evaporate (residual rate <0.1%). Then, the contact was installed in a vacuum circuit breaker test fixture, and the circuit breaker was subjected to a low-current aging treatment with 20% of the rated current (i.e., 2 kA) of 50 Hz AC current for 22.5 minutes. During the aging process, the micro-arc energy density on the contact surface was approximately 0.5 J / mm². After aging, the contact was allowed to cool naturally to room temperature.

[0042] The contact resistance of each contact before and after treatment was measured using a micro-ohmmeter (measurement accuracy ±0.1μΩ, four-terminal method, test current 10A). Each contact was measured 5 times and the average value was taken. The contact resistance reduction rate was calculated according to the formula: Reduction rate (%) = (resistance before treatment - resistance after treatment) / resistance before treatment × 100%.

[0043] The aged contacts were subjected to 50 standard breaking tests. The breaking current was the rated short-circuit breaking current of 20kA (AC RMS value). The interval between each breaking test was 3 minutes. After each breaking test, the contacts were allowed to cool to room temperature (about 10 minutes). The contact resistance was measured using the same micro-ohmmeter. The contact resistance value after the 50th breaking test was recorded. The contact resistance retention rate was calculated using the formula: Retention rate (%) = Resistance after the 50th breaking test / Resistance after initial treatment × 100%.

[0044] A microhardness tester (Vickers indenter, applied force 0.98N (i.e., 100gf), holding time 15s) was used to measure the Vickers hardness at 5 different locations randomly selected on the surface of the repair layer (avoiding obvious defects). The average value was taken and compared with the Vickers hardness (HV120) of the untreated contact substrate (contacts from the same batch that underwent the same arc ablation pretreatment but were not coated with protective agent). The surface hardness improvement rate was calculated according to the formula: Improvement rate (%) = (Repair layer hardness - Substrate hardness) / Substrate hardness × 100%.

[0045] Linear scratch tests were performed on the surface of the repair layer using a scratch tester (Rockwell C indenter, cone angle 120°, tip radius 200μm, loading rate 100N / min, scratch length 5mm, maximum load 100N). The critical load (Lc, unit N) at which the repair layer begins to peel off from the substrate was determined by acoustic emission signal and frictional force abrupt change. Each sample was tested once in three different directions and the average value was taken.

[0046] The surface morphology of the repair layer was observed using field emission scanning electron microscopy (accelerating voltage 15kV, working distance 10mm, magnification 5000x). Five fields of view (approximately 50μm × 50μm each) were randomly selected to evaluate the filling of micropores and cracks: Excellent: All micropores and cracks were completely filled and the surface was smooth; Good: More than 90% of micropores and cracks were filled, and the surface was basically smooth; Medium: 60%-90% of micropores and cracks were filled, with a small number of unfilled areas on the surface; Poor: Less than 60% of micropores and cracks were filled, and a large number of unfilled defects were visible on the surface. All tests were conducted under standard environmental conditions of 25±1℃ and 50±5% relative humidity, with each sample tested three times and the average value taken.

[0047] The performance test data above are shown in Table 1.

[0048] Table 1 Performance Test Results Contact resistance reduction rate (%) 35.2 28.6 40.1 18.3 12.5 22.7 Contact resistance retention rate after 50 interruptions (%) 88.5 84.2 91.3 65.8 52.3 71.6 Surface hardness improvement rate (%) 26.8 21.5 30.2 8.6 4.2 15.3 Critical peel load (N) 58.3 49.7 63.5 32.1 18.6 41.2 Surface morphology of the repair layer (filling status) excellent good excellent middle Difference good As can be seen from the above, Examples 1-3 successfully solved the following prior art problems compared to Comparative Examples 1-3: First, Comparative Example 1, lacking the addition of quaternary transition metal boron carbonitride nanoclusters, exhibited a contact resistance reduction rate of only 18.3% (far lower than the 28.6-40.1% of Examples 1-3), a contact resistance retention rate of only 65.8% after 50 cycles of switching (far lower than the 84.2-91.3% of Examples 1-3), a surface hardness improvement rate of only 8.6% (far lower than the 21.5-30.2% of Examples 1-3), a critical peel load of only 32.1 N (far lower than the 49.7-63.5 N of Examples 1-3), and a surface filling rate of only moderate. This indicates that the lack of this inorganic modified compound prevented the formation of ceramic phase pinning and chemical anchoring in the repair layer, resulting in significantly insufficient resistance to secondary ablation and interfacial bonding strength. Examples 1-3, by introducing the "core-shell-claw" three-layer structure of TMB-CN-NC, achieved ceramic phase pinning, multiple hydrogen bond coordination anchoring, and nanoscale uniform composite, thereby significantly improving the arc ablation resistance and interfacial bonding strength of the repair layer. Secondly, in Comparative Example 2, ordinary nano-copper powder was used to replace the core-shell structure nano-metal powder. Its contact resistance reduction rate was only 12.5%, the retention rate after 50 breaks was only 52.3%, the hardness improvement rate was only 4.2%, the critical peel load was only 18.6N, and the surface filling was poor. All indicators were the worst, indicating that it lacked the preferential melting and spreading effect of the low melting point silver shell and the metallurgical bonding ability of the high melting point copper-chromium alloy core. It could not effectively fill the micropore cracks and the repair layer had extremely poor density. Examples 1-3, through the core-shell structure design, enabled the outer shell silver to melt and fill the defects during low current aging, and the core copper-chromium to form a metallurgical bond with the substrate after exposure, thereby achieving efficient contact resistance reduction and long-term ablation resistance stability. Furthermore, Comparative Example 3, which did not use a coupling agent, showed a contact resistance reduction rate of 22.7%, a retention rate of 71.6%, a hardness improvement rate of 15.3%, a critical peel load of 41.2 N, and good surface filling. Although these were better than Comparative Examples 1 and 2, they were still significantly worse than Examples 1-3. This indicates that the lack of a coupling agent led to the agglomeration of nano-metal powder and weak interfacial bonding, making it impossible to form a uniform and dense repair layer. Examples 1-3 formed an organic coating layer on the surface of nanoparticles through the hydrolysis and condensation reaction of γ-aminopropyltriethoxysilane. Combined with the steric hindrance of polyvinylpyrrolidone and the slight etching effect of acetic acid, long-term stable dispersion of nanoparticles and strong chemical bonding with the substrate were achieved. In summary, Examples 1-3 synergistically solve the technical problems in the prior art, such as poor resistance to secondary ablation of the repair layer, low interfacial bonding strength, easy agglomeration of nanoparticles, insufficient filling of micropores and cracks, and inability to achieve long-term repair without disassembly on site.

Claims

1. A method for preparing a nanocomposite protective agent for arc erosion repair of contacts in a 10kV vacuum circuit breaker, characterized in that the steps include... include: S1. By weight, place the core-shell structured nano-metal powder in a vacuum drying oven and dry it at 60-80℃ to obtain the dried core-shell structured nano-metal powder; dissolve 2-6 parts of γ-aminopropyltriethoxysilane in 21-30 parts of polyethylene glycol, add 0.5-1.0 parts of deionized water, and stir at 28-32℃ under nitrogen protection to obtain the coupling agent treatment solution; S2. Add 35-55 parts of dried core-shell structured nano-metal powder to the coupling agent treatment solution and stir under nitrogen protection; add 1-4 parts of quaternary transition metal boron carbonitride nanoclusters, 0.5-3 parts of polyvinylpyrrolidone and 0.1-0.5 parts of acetic acid, and disperse by ultrasonication to obtain a slurry; filter the slurry.

2. The preparation method of the nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts according to claim 1, characterized in that, In step S1, the drying time at 60-80℃ is 2-4 hours.

3. The preparation method of the nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts according to claim 1, characterized in that, In step S2, the ultrasonic dispersion time is 45-60 min.

4. The preparation method of the nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts according to claim 1, characterized in that, The preparation method of the modified nano-metal powder with the core-shell structure includes: A1. Under argon protection, 150-250 parts of deionized water are added to a reaction vessel, along with 5-7 parts of copper nitrate and 0.08-0.12 parts of chromium nitrate, and 0.3-0.8 parts of polyvinylpyrrolidone. The mixture is stirred and heated at room temperature to obtain a metal salt solution; 0.8-1.2 parts of hydrazine hydrate are dissolved in 15-25 parts of deionized water, and the pH is adjusted to 10.0-12.0 with 1-3 parts of ammonia to obtain a reducing agent solution; the reducing agent solution is added dropwise to the metal salt solution until the addition is complete. Then, the mixture was stirred at 78-82℃ to obtain a Cu-Cr alloy nanoparticle suspension; A2, 1.5-1.7 parts of the Cu-Cr alloy nanoparticle suspension prepared in step A1 were added to a solution of 1.5-2.0 parts of silver nitrate dissolved in 8-12 parts of deionized water, and stirring was continued. Then, a reducing solution containing 0.6-1.0 parts of hydrazine hydrate and 8-12 parts of deionized water was added dropwise, and the mixture was stirred at 78-82℃ to obtain a suspension; the suspension was naturally cooled to room temperature, centrifuged, and the precipitate was collected; the precipitate was washed with deionized water and anhydrous ethanol, and then dried under vacuum.

5. The preparation method of the nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts according to claim 4, characterized in that, In step A1, the reaction is stirred at 78-82℃ for 1-2 hours.

6. The preparation method of the nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts according to claim 4, characterized in that, In step A2, the vacuum drying temperature is 58-62℃.

7. The preparation method of the nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts according to claim 1, characterized in that, The preparation method of the quaternary transition metal boron carbonitride nanoclusters includes: B1. Under anhydrous and oxygen-free conditions, dissolving 3.0-3.5 parts of hafnium tetrachloride and 2.2-2.5 parts of zirconium tetrachloride in 40-60 parts of anhydrous ethanol, and reacting at room temperature with stirring to obtain a hafnium-zirconium mixed chloride solution; dissolving 1.0-1.3 parts of sodium borohydride in 25-35 parts of ethylene glycol, and stirring under ice-water bath cooling to obtain a sodium borohydride ethylene glycol solution; adding the hafnium-zirconium mixed chloride solution to the sodium borohydride ethylene glycol solution with stirring, and continuing to stir the reaction in an ice-water bath after the addition is complete to obtain a reaction mixture; The reaction mixture was allowed to stand and age at room temperature, then evaporated in a water bath at 78-82℃ to obtain the product. The product was transferred to a tube furnace and heated to 345-355℃ under an argon atmosphere. A mixture of ammonia and methane was introduced, and the temperature was raised to 795-805℃ and held. The methane and ammonia were then turned off, and the mixture was allowed to cool naturally to room temperature under a pure argon atmosphere to obtain the crude product. B2. The crude product was dispersed in 80-120 parts of anhydrous ethanol, and 0.3-0.8 parts of polyvinylpyrrolidone were added. The mixture was ultrasonically dispersed, centrifuged, and the precipitate was collected. The precipitate was washed with anhydrous ethanol and dried under vacuum at 58-62℃.

8. The preparation method of the nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts according to claim 7, characterized in that, The temperature is raised to 795-805℃ and held for 2-4 hours.

9. A nanocomposite protective agent for arc erosion repair of contacts in a 10kV vacuum circuit breaker, characterized in that, The nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts is prepared according to any one of claims 1-8.

10. The application of the nanocomposite protective agent according to claim 9 for arc erosion repair of 10kV vacuum circuit breaker contacts, characterized in that, The application of the nanocomposite protective agent for arc erosion repair of 10kV vacuum circuit breaker contacts in the arc erosion repair of 10kV vacuum circuit breaker contacts.