Graphene / aluminum oxide-zinc composite material and connecting structure of graphene / aluminum oxide-zinc composite material and round steel matrix

Abstract

The invention relates to the technical field of power system grounding device maintenance, and provides a graphene / aluminum oxide-zinc composite material and a connecting structure of the graphene / aluminum oxide-zinc composite material and a round steel matrix, the graphene / aluminum oxide-zinc composite material comprises 87-92 parts by mass of graphene, 5-8 parts by mass of nanometer aluminum oxide and 3-5 parts by mass of zinc powder. According to the graphene / aluminum oxide-zinc composite grounding material, a continuous conductive network is formed through graphene, so that the resistivity is remarkably reduced; the nanometer aluminum oxide inhibits graphene stacking and promotes Al-O-C interface bonding, interlayer bonding strength is improved, and coating stripping is effectively inhibited; the zinc powder is melted and densified in the sintering process, the zinc powder is corroded in acid soil preferentially in the operation process of the grounding material, Zn is released to inhibit microorganisms, and the obtained composite grounding material has excellent electrical conductivity, high strength and long-acting corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of grounding device maintenance of power system, in particular to a graphene / alumina-zinc composite material and a connecting structure thereof and a round steel base. BACKGROUND

[0002] In the power system, the grounding down conductor of overhead transmission line is a key component for ensuring the safety of equipment and human body. However, in the southern region of China, the grounding down conductor is in a complex soil environment with high humidity, strong acid red soil, and rich in sulfate-reducing bacteria and iron-oxidizing bacteria, etc. The contact area between the grounding down conductor and the soil is prone to the triple synergistic effect of "acid corrosion-microbial adhesion-electrochemical corrosion", which leads to rapid corrosion of steel and even disconnection. The measured data shows that the corrosion rate of traditional hot-dip galvanized round steel grounding body in such environment is as high as 0.2-0.3 mm / year, and it may appear electrical disconnection after 3-5 years of service. In order to improve the corrosion resistance, in recent years, some studies have attempted to use graphene-based materials as a protective layer for grounding down conductor. However, the existing pure graphene or graphene / polymer composite coating has weak interlayer adhesion in high-humidity acidic environment, and is easily eroded by microbial metabolites and soil particles, leading to coating peeling, and the actual corrosion resistance life is only 50% of the expected life.

[0003] The existing graphene coating is usually attached to the surface of the round steel by physical methods such as spraying, and only physical bonding exists between the coating and the substrate, so the interfacial bonding strength is low. Under the action of electrochemical corrosion and soil particle friction in the acidic soil in the south, the coating is prone to delamination, leading to interruption of the grounding conductive path.

[0004] In addition, the existing composite material generally lacks special structural design for the "soil-air interface" which is a high-incidence site of corrosion, and if the connection part after welding repair is not effectively sealed, the exposed interface is likely to become a new corrosion breakthrough, leading to secondary failure in a short period of time. SUMMARY

[0005] In view of this, the present application provides a graphene / alumina-zinc composite material and a connecting structure thereof, which aims to solve the technical problems of existing graphene grounding materials, such as easy peeling of the coating, low interfacial bonding strength between the coating and the round steel substrate, and secondary corrosion caused by lack of corrosion sealing at the connection part, in a high-humidity, acidic and microbial composite corrosion environment.

[0006] In a first aspect, the present application provides a graphene / alumina-zinc composite material, which comprises graphene, nano-alumina and zinc powder, wherein the graphene is 87-92 parts by mass, the nano-alumina is 5-8 parts by mass, and the zinc powder is 3-5 parts by mass.

[0007] Further, the graphene / alumina-zinc composite material described above further comprises 1-2 parts by mass of a microbial inhibiting material.

[0008] Further, in the graphene / alumina-zinc composite material, the microorganism inhibiting material is at least one of copper powder and titanium dioxide.

[0009] Further, in the graphene / alumina-zinc composite material, the microorganism inhibiting material is at least one of copper powder and titanium dioxide.

[0010] Further, in the graphene / alumina-zinc composite material, the microorganism inhibiting material is at least one of copper powder and titanium dioxide.

[0011] Further, in the graphene / alumina-zinc composite material, the microorganism inhibiting material is at least one of copper powder and titanium dioxide.

[0012] Further, in the graphene / alumina-zinc composite material, the microorganism inhibiting material is at least one of copper powder and titanium dioxide.

[0013] Further, in the graphene / alumina-zinc composite material, the microorganism inhibiting material is at least one of copper powder and titanium dioxide.

[0014] The graphene / alumina-zinc composite material in the application forms a continuous conductive network by graphene, significantly reduces the resistivity, uniformly fills the interlayer gap of graphene with nano-alumina, forms Al-O-C chemical bonds with graphene through high-temperature sintering, and enhances the interlayer bonding force; the zinc powder is dispersed and filled into the micropores and forms a dense structure during sintering, and preferentially corrodes in acidic soil during the operation of the grounding material, releases Zn²⁺ to inhibit microorganisms, and the obtained composite material has excellent conductivity, high strength and long-acting corrosion resistance, effectively solving the problems of easy peeling of the coating of the existing graphene grounding material and low interfacial bonding strength with the round steel substrate in a high-humidity, acidic and microbial combined corrosion environment.

[0015] In a second aspect, the application further provides a preparation method of the graphene / alumina-zinc composite material, which comprises the following steps: Each component is weighed according to the composition of the composite material, mixed uniformly by using a step-by-step feeding method, and a composite powder is obtained; The composite powder is press-formed to obtain a green body; The green body is heated to a sintering temperature in sections in an inert atmosphere, and is kept warm and sintered, and then cooled to obtain the composite material.

[0016] Furthermore, in the above-mentioned method for preparing graphene / alumina-zinc composite material, the stepwise feeding includes: first mixing and stirring graphene and nano-alumina at 1000-1500 r / min for 30-45 minutes, then adding zinc powder and the functional additives and continuing to mix for 15-20 minutes.

[0017] Furthermore, in the above-mentioned method for preparing the graphene / alumina-zinc composite material, the sintering temperature is 800-850℃, and the segmented heating includes the following stages: The first stage: the temperature is increased from room temperature to 400℃ at a rate of 5-10℃ / min to remove residual moisture and organic matter from the green body; The second stage involves raising the temperature from 400℃ to 800℃ at a rate of 15-20℃ / min, which promotes the initial melting of zinc powder and fills the pores. The third stage involves maintaining the temperature at 800-850℃ for 2-3 hours to allow graphene and nano-alumina to form Al-OC interface chemical bonds. Simultaneously, the zinc powder is completely melted and uniformly dispersed in the conductive network composed of graphene and nano-alumina.

[0018] The preparation method provided by this invention effectively avoids zinc powder agglomeration through stepwise feeding, ensuring uniform dispersion of each component; the segmented heating sintering at 800-850℃ under an inert atmosphere allows graphene and nano-alumina to form stable chemical bonds (such as Al-OC bonds) through interfacial chemical reactions, and the zinc powder is completely melted and uniformly dispersed, ultimately forming a dense composite structure, giving the prepared composite material high density, long-term corrosion resistance and interlayer stability.

[0019] Thirdly, the present invention also proposes a graphene / alumina-zinc composite grounding lead connection structure, comprising a metal grounding component and a composite lead made of the graphene / alumina-zinc composite material described in any one of the above claims; wherein, The graphene / alumina-zinc composite grounding lead has a tapered transition section at its end, the outer diameter of which continuously decreases from the diameter of the composite lead body to the same diameter as the metal grounding component; the end of the transition section overlaps with the end of the metal grounding component to form an overlap area; a solder layer is provided on the inner side of the interface of the overlap area, which forms a corrosion-resistant metallurgical bonding layer after hot-melt welding.

[0020] Furthermore, in the above-mentioned graphene / alumina-zinc composite grounding lead connection structure, the outer periphery of the transition section is provided with an annular sealing groove, and a water-swellable sealing strip is embedded in the annular sealing groove; The overlapping area is covered with an anti-corrosion sealing sleeve, which is locked by fasteners so that its inner wall fits tightly against the outer periphery of the transition section and the metal grounding component, forming a double anti-corrosion barrier in conjunction with the water-swellable sealing strip.

[0021] The connection structure of this invention utilizes a graphene / alumina-zinc composite grounding lead made of graphene, zinc powder, and nano-alumina in a specific ratio, resulting in excellent end conductivity and stable, long-lasting corrosion protection in corrosive environments. Furthermore, by incorporating a transition section with a continuously decreasing outer diameter at its end and introducing a solder layer inside the overlap interface via hot-melt welding, zinc, graphene, and solder react in situ to form a dense, corrosion-resistant metallurgical bond layer. This achieves a contact resistance of ≤5mΩ between the composite lead and the metal grounding component, significantly improved mechanical reliability, and corrosion resistance at the welded joint that is more than twice that of ordinary welding. Attached Figure Description

[0022] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A schematic flowchart illustrating the preparation method of the graphene / alumina-zinc composite material provided in this embodiment of the invention; Figure 2 A schematic diagram of the graphene / alumina-zinc composite grounding lead connection structure provided in an embodiment of the present invention; Figure 3 This is another schematic diagram of the graphene / alumina-zinc composite grounding lead connection structure provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the graphene / alumina-zinc composite grounding lead connection structure provided in the embodiments of the present invention in a practical application scenario; Figure 5 for Figure 4 A magnified view of a portion of point A in the middle.

[0023] In the diagram: Graphene / alumina-zinc composite grounding lead 1, transition section 11, metal grounding component 2, anti-corrosion sealing sleeve 3, underground grounding grid 4. Detailed Implementation

[0024] The following describes preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention. It should be explained that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0025] The graphene / alumina-zinc composite material provided in the first aspect of the present invention comprises graphene, nano-alumina and zinc powder, wherein, by mass, there are 87-92 parts of graphene, 5-8 parts of nano-alumina and 3-5 parts of zinc powder.

[0026] Specifically, a complete composite system is constructed using graphene as the matrix, nano-alumina, and zinc powder as functional dopants. Graphene forms a continuous conductive network, with zinc powder uniformly dispersed within it. The graphene used is commercially available high-purity (≥99%) few-layer graphene powder (e.g., 3-10 layers on average, 5-20 μm lateral dimension). The sheet-like structure of graphene forms a dense physical barrier layer on the material surface, initially isolating acidic media (H⁺, SO₄²⁻, etc.) and microbial metabolic products in the soil, thus slowing down the initial corrosion rate. Its high specific surface area and interlayer adsorption force ensure uniform dispersion of nano-alumina particles and zinc powder within the composite system, preventing agglomeration of functional components and ensuring their uniform effectiveness.

[0027] Zinc powder with a particle size of 1-10μm and a purity of ≥99.5% can be selected. Zinc's electrode potential (-0.76V) is lower than that of iron (-0.44V) and graphene (which has metal-like properties and a higher potential). In acidic soil electrolyte environments, zinc powder preferentially undergoes electrochemical corrosion (sacrificing itself) to inhibit the corrosion reaction of the matrix material (graphene and the underlying round steel), resulting in a corrosion rate of ≤0.03mm / year for the composite down conductor in acidic soil with pH=3-5, a 70% reduction compared to pure graphene. From a microscopic perspective, zinc powder can partially melt during high-temperature sintering, filling the micropores between graphene layers or on the material surface, reducing the channels for corrosive media penetration, and further improving the material's density. Zinc ions can also be slowly released, inhibiting corrosive microorganisms such as sulfate-reducing bacteria and iron-oxidizing bacteria in the soil, reducing biofilm adhesion on the material surface.

[0028] The particle size of nano-alumina particles can be 10-100nm, preferably 30-50nm.

[0029] Nano-alumina particles are uniformly filled in the interlayer gaps of graphene, forming Al-OC chemical bonds with graphene through high-temperature sintering, enhancing interlayer bonding and resisting interlayer delamination caused by soil particle friction. Zinc powder is molten and dispersed on the graphene matrix and surface, forming a sacrificial anode layer that preferentially undergoes electrochemical corrosion, protecting the matrix and the underlying round steel. Furthermore, the high-temperature resistance of nano-alumina (melting point approximately 2054℃) improves the composite material's resistance to burn-off during hot-melt welding (1500-1600℃), preventing localized softening and structural deformation during welding, and ensuring the stability of the joint.

[0030] To further enhance the ability to inhibit corrosive microorganisms in the soil, the graphene / alumina-zinc composite material of this invention also includes 1-2 parts by weight of a microbial inhibitory material.

[0031] Specifically, the microbial inhibitory material is at least one of copper powder and titanium dioxide. Copper powder can enhance the killing effect on sulfate-reducing bacteria by releasing copper ions; titanium dioxide can generate hydroxyl radicals under weak light on the soil surface, decomposing microbial metabolic products (such as hydrogen sulfide) and reducing the source of acidic media. This embodiment avoids soil pollution due to excessive release of metal ions by controlling the appropriate amount added, while ensuring that the conductivity of the material is not affected (e.g., the amount of titanium dioxide required should not be excessive to avoid an increase in grounding resistance due to excessive insulating components).

[0032] To improve the tensile strength and bending resistance of the composite material, the graphene / alumina-zinc composite material of this invention further includes 1-3 parts by weight of structural reinforcement material.

[0033] Specifically, the structural reinforcement material is at least one of chopped carbon fibers and nano-silicon carbide particles. Preferably, the length of the chopped carbon fibers is 1-3 mm; the particle size of the nano-silicon carbide particles is 50-200 nm. In practice, grounding down conductors may be subjected to external impacts (such as soil subsidence or animal gnawing) during construction and maintenance. Adding a small amount of chopped carbon fibers or silicon carbide particles can further enhance the mechanical properties of the material and prevent the down conductor from breaking due to external forces.

[0034] To further reduce the corrosion rate and make it suitable for extremely acidic soil (pH < 3) scenarios, the graphene / alumina-zinc composite material in this embodiment also includes: 0.5-1 parts by weight of corrosion inhibitor.

[0035] Specifically, the corrosion inhibitor is sodium molybdate or potassium molybdate. Corrosion inhibitors that enhance corrosion resistance form a passivation film on the material surface, which works synergistically with the sacrificial anode protection mechanism of zinc powder to further reduce the corrosion rate.

[0036] It is evident from the above that the graphene / alumina-zinc composite material provided in this embodiment significantly reduces resistivity by forming a continuous conductive network through graphene; nano-alumina uniformly fills the interlayer gaps of graphene and forms Al-OC chemical bonds with graphene after high-temperature sintering, enhancing the interlayer bonding force; zinc powder melts and disperses during sintering, filling micropores and forming a dense structure, preferentially corroding in acidic soil during grounding material operation, releasing Zn²⁺ to inhibit microorganisms. The resulting composite material possesses excellent conductivity, high strength, and long-term corrosion resistance, effectively alleviating the problems of easy coating peeling and low interfacial bonding strength with the round steel substrate in existing graphene grounding materials in high humidity, acidic, and microbial composite corrosion environments.

[0037] See Figure 1 The method for preparing the graphene / alumina-zinc composite material provided in the second aspect of the present invention includes the following steps: Step S1: Weigh each component according to the composition of the composite material, mix them evenly by step feeding, and obtain composite powder.

[0038] Specifically, before weighing each component, graphene, nano-alumina, zinc powder, and optional functional additives need to be pretreated.

[0039] Preprocessing specifically includes: (1) Pretreatment of graphene In practice, graphene powder (high-purity multilayer graphene powder with a purity of ≥99% can be selected) is vacuum dried at 80-100℃ for 2-3 hours to remove adsorbed moisture and volatile impurities, and to prevent the formation of bubbles during sintering that would increase the porosity of the material. If agglomeration occurs, it is dispersed by ball milling at 300-500 r / min for 30-60 minutes to ensure that the graphene is mixed evenly with other components and to prevent weak points that are preferentially corroded due to a lack of graphene in certain areas.

[0040] (2) Pretreatment of nano-alumina Nano-alumina is ultrasonically cleaned in anhydrous ethanol (ultrasonic power 300-500 W) for 20-30 minutes to remove adsorbed dust and residual organic matter from the surface, thus avoiding affecting the interfacial bonding with graphene. After cleaning, it is calcined at 300-400℃ for 1-2 hours to eliminate hydroxyl groups on the surface of the nanoparticles, improve their dispersibility in the graphene matrix, and lay the foundation for subsequent enhancement of interlayer bonding.

[0041] (3) Pretreatment of zinc powder The zinc powder is dried at 60-80℃ for 1-1.5 hours under a nitrogen protective atmosphere to remove moisture and prevent the zinc powder from oxidizing and forming zinc oxide during storage or mixing, which would reduce the sacrificial anode protection effect.

[0042] (4) Pretreatment of optional functional additives Copper powder or titanium dioxide, which is used as a material to inhibit microorganisms, is dried at 60-80℃ for 0.5-1 hour; For short-cut carbon fibers or nano-silicon carbide particles used in structural reinforcement materials, the following treatment is performed: the short-cut carbon fibers are oxidized with nitric acid, and the nano-silicon carbide particles are ultrasonically dispersed in anhydrous ethanol for 15-20 minutes.

[0043] Sodium molybdate or potassium molybdate, which are used as corrosion inhibitors, are dried at 80-100℃ for 0.5-1 hour and passed through a 100-mesh sieve.

[0044] In this step, the stepwise feeding method includes: first, mixing and stirring graphene and nano-alumina at 1000-1500 r / min for 30-45 minutes, then adding zinc powder and the functional additives and continuing to mix for 15-20 minutes.

[0045] In specific implementation, weigh out 87-92 parts of pretreated graphene, 5-8 parts of nano-alumina, and 3-5 parts of zinc powder by weight, and add 1-2 parts of the microbial inhibitory material, 1-3 parts of the structural reinforcement material, and / or 0.5-1 parts of the corrosion inhibitor as needed.

[0046] First, add graphene and nano-alumina into a high-speed mixer and mix for 30-45 minutes at 1000-1500 r / min to allow the nano-alumina to fully fill the gaps between graphene layers and improve the interfacial bonding strength. Then, add zinc powder and other functional additives and continue mixing and stirring at the same speed for 15-20 minutes to avoid zinc powder agglomeration and ensure that all functional additives are evenly dispersed, ultimately forming a uniform composite powder.

[0047] Step S2: Press the composite powder into shape to obtain a green body.

[0048] In practice, the composite powder is loaded into a mold (e.g., cylindrical) that matches the shape of the grounding lead wire, and cold isostatic pressing is applied at 20-30 MPa for 5-10 minutes to press the powder into a green blank with a density ≥2.5 g / cm³, thereby reducing shrinkage and deformation during subsequent sintering and ensuring the dimensional accuracy of the grounding lead wire.

[0049] Step S3: The green compact is heated to the sintering temperature in stages in an inert atmosphere, and then sintered at that temperature and cooled to obtain the composite material.

[0050] In practice, the sintering temperature is 800-850℃, which can promote the formation of Al-OC interface bonding between graphene and nano-alumina and the melting of zinc.

[0051] The segmented heating process includes the following stages: The first stage involves raising the temperature from room temperature to 400°C at a rate of 5-10°C / min to remove residual moisture and organic matter from the green body, while avoiding rapid heating that could cause cracking.

[0052] The second stage involves raising the temperature from 400℃ to 800℃ at a rate of 15-20℃ / min, which promotes the initial melting of zinc powder and fills the pores. The third stage involves holding the material at 800-850℃ for 2-3 hours to allow graphene and nano-alumina to form Al-OC interfacial chemical bonds. Simultaneously, the zinc powder is completely melted and uniformly dispersed in the conductive network composed of graphene and nano-alumina, ultimately forming a dense composite structure, which is beneficial for improving the interlaminar peel strength of the composite material.

[0053] During sintering, an inert gas (such as argon) must be introduced for protection to prevent graphene and zinc powder from oxidizing at high temperatures, ensuring that the material's conductivity and corrosion resistance are not affected. After sintering, the material is cooled to room temperature in the furnace (cooling rate 10-15℃ / min) to avoid stress cracks caused by rapid cooling. The cooled composite lead-in wire is then surface-polished (using 200-400 grit sandpaper) to remove residual sintering impurities, achieving a surface roughness Ra≤1.6μm, providing a smooth base for subsequent processing of the transition section and sealing groove.

[0054] The preparation method of this invention effectively avoids zinc powder agglomeration through stepwise feeding, ensuring uniform dispersion of each component; the segmented heating and sintering at 800-850℃ under an inert atmosphere allows graphene and nano-alumina to form stable chemical bonds (such as Al-OC bonds) through interfacial chemical reactions, and the zinc powder is completely melted and uniformly dispersed, ultimately forming a dense composite structure, giving the prepared composite material high density, long-term corrosion resistance and interlayer stability.

[0055] The present invention will now be described in detail with reference to several specific embodiments.

[0056] Example 1 Graphene, nano-alumina (particle size 30-50 nm), and zinc powder (purity ≥99.5%) were pretreated separately. 92 parts by weight of the pretreated graphene, 8 parts by weight of the nano-alumina, and 3 parts by weight of the zinc powder were weighed.

[0057] First, graphene and nano-alumina are added to a high-speed mixer and mixed at 1200 r / min for 40 min to ensure the nano-alumina fully fills the interlayer gaps of the graphene. Then, zinc powder is added and mixed for another 15 min at the same speed to prevent zinc powder agglomeration and obtain a uniform composite powder. The composite powder is then loaded into a mold and cold-pressed at 300 MPa to obtain a green compact. The green compact is placed in a tube furnace under argon protection. The following stage of sintering was adopted: First stage: heating to 400℃ at a heating rate of 10℃ / min and holding for 30 min to remove residual moisture and trace organic matter; Second stage: heating to 800℃ at a heating rate of 20℃ / min to promote the initial melting of zinc powder and fill the pores; Third stage: heating slowly to 850℃ at a heating rate of 5℃ / min and holding for 3 h to form Al-OC interface chemical bonds between graphene and nano-alumina; After sintering, the furnace was cooled to room temperature and the surface was polished to obtain a Φ16 mm graphene / alumina-zinc composite material.

[0058] Example 2 Graphene, nano-alumina, zinc powder, and copper powder were pretreated. 87 parts by weight of the pretreated graphene, 6 parts by weight of nano-alumina, 3 parts by weight of zinc powder, and 2 parts by weight of copper powder were weighed.

[0059] First, graphene and nano-alumina were added to a high-speed mixer and mixed at 1000 r / min for 45 min. Then, zinc powder and copper powder were added, and mixing continued at the same speed for 20 min to obtain a uniform composite powder. The composite powder was then loaded into a mold and cold-pressed under 25 MPa pressure to obtain a green compact. The green compact was placed in a tube sintering furnace and sintered under argon protection using a segmented heating method: the first stage involved heating to 400℃ at 5℃ / min and holding for 30 min; the second stage involved heating to 800℃ at 15℃ / min; and the third stage involved slowly heating to 820℃ at 5℃ / min and holding for 2 h. After sintering, the furnace was cooled to room temperature, and the surface was polished to obtain the graphene / alumina-zinc composite material.

[0060] Example 3 Graphene, nano-alumina, zinc powder, and chopped carbon fibers (2 mm in length) were pretreated separately. 88 parts graphene, 5 parts nano-alumina, 5 parts zinc powder, and 2.5 parts chopped carbon fibers were weighed out according to their respective weights.

[0061] First, graphene and nano-alumina were added to a high-speed mixer and mixed at 1500 r / min for 45 min. Then, zinc powder and chopped carbon fibers were added, and mixing continued at 800 r / min for 20 min to prevent excessive fiber breakage and obtain a uniform composite powder. The composite powder was then loaded into a mold and cold-pressed under 20 MPa pressure to obtain a green compact. The green compact was placed in a tube sintering furnace and sintered using a segmented heating method under argon protection: the first stage involved heating to 400℃ at 5℃ / min and holding for 30 min; the second stage involved heating to 800℃ at 15℃ / min; and the third stage involved slowly heating to 830℃ at 5℃ / min and holding for 2 h. After sintering, the furnace was cooled to room temperature, and the surface was polished to obtain the graphene / alumina-zinc composite material.

[0062] Example 4 Graphene, nano-alumina, zinc powder, copper powder, nano-silicon carbide (particle size 50-100 nm) and sodium molybdate were pretreated respectively.

[0063] Weigh out 87 parts graphene, 8 parts nano alumina, 3 parts zinc powder, 2 parts titanium dioxide, 3 parts chopped carbon fiber, and 1 part sodium molybdate by weight.

[0064] First, graphene and nano-alumina were added to a high-speed mixer and mixed at 1100 r / min for 40 min. Then, zinc powder, copper powder, chopped carbon fibers, and sodium molybdate were added, and mixing continued at 1000 r / min for 18 min to obtain a uniform composite powder. The composite powder was then loaded into a mold and cold-pressed under 30 MPa pressure to obtain a green compact. The green compact was placed in a tube sintering furnace and sintered under argon protection using a segmented heating method: the first stage involved heating to 400℃ at 8℃ / min and holding for 30 min; the second stage involved heating to 800℃ at 18℃ / min; and the third stage involved slowly heating to 820℃ at 8℃ / min and holding for 2 h. After sintering, the furnace was cooled to room temperature, and the surface was polished to obtain the graphene / alumina-zinc composite material.

[0065] To verify the corrosion resistance of the graphene / alumina-zinc composite material prepared in the embodiments of the present invention, a comparative test was conducted using an accelerated corrosion test method. The test conditions followed the power industry standard DL / T 1591-2016 "Guidelines for Corrosion Assessment of Grounding Materials," simulating a typical acidic soil environment in southern China. Specific parameters were as follows: pH = 3.5 (simulating strongly acidic soil); temperature = 25℃; sulfate-reducing bacteria (SRB) concentration = 1×10⁻⁶. 4 CFU / g; Test period: equivalent to 10 years of service environment (based on the accelerated aging method specified in the standard); Examples 1-4 and Comparative Examples 1-2 (traditional Q235 round steel as Comparative Example 1, pure graphene-coated round steel as Comparative Example 2) were all Φ16 mm round bars; Test results are shown in Table 1 below: As shown in Table 1, the test results indicate that in a simulated southern acidic soil environment (pH=3.5, 25℃, SRB concentration 1×10⁻⁶), the soil composition is optimal. 4 Under CFU / g conditions, the corrosion rate of the composite material in Example 1 of this invention was 0.025 mm / year, and the interlayer peel strength was 5.8 MPa. After 10 years of equivalent simulation, there was no obvious rust on the surface and the structure remained intact. In contrast, the corrosion rate of traditional Q235 round steel (Comparative Example 1) reached 0.25 mm / year, with severe rust and local fractures. The corrosion rate of pure graphene-coated round steel (Comparative Example 2) was 0.08 mm / year, and the interlayer peel strength was 3.2 MPa. Local peeling of the coating and corrosion of the substrate were observed.

[0066] The table data shows that the corrosion rate of Example 1 of the present invention is reduced by 90% compared with traditional Q235 round steel; it is reduced by 68.75% compared with pure graphene coating material; and the interlayer peel strength is increased to 5.8 MPa, which is 81.25% higher than that of pure graphene coating material (3.2 MPa), approximately 1.8 times that of pure graphene coating material.

[0067] This demonstrates that the composite material prepared by this invention exhibits excellent corrosion resistance in the complex corrosive environment of southern regions, which helps alleviate the problems of easy corrosion and easy delamination between layers in existing grounding materials.

[0068] Furthermore, Examples 2-4, based on Example 1, respectively introduced a microbial inhibitor (copper powder), a structural reinforcement material (short-cut carbon fiber), and simultaneously introduced a structural reinforcement material (nano-silicon carbide), a microbial inhibitor (titanium dioxide), and a corrosion inhibitor (sodium molybdate). The test results showed that: All samples maintained a low corrosion rate (≤0.025 mm / year); the interlayer peel strength was further improved to over 6.0 MPa; after 10 years of simulation, none showed rust or peeling, and the structure remained intact; notably, no biofilm adhesion was observed in Example 2 in an SRB-containing environment, demonstrating good antibacterial ability; Example 4 showed the best overall performance, with a corrosion rate reduced to 0.023 mm / year and a peel strength of 6.2 MPa. These results indicate that, through the synergistic effect of functional additives, the environmental adaptability and long-term stability of the material can be further improved while maintaining basic corrosion resistance.

[0069] Based on the accelerated corrosion test results and referring to the power industry standard DL / T 1591–2016 "Guidelines for Corrosion Assessment of Grounding Materials", using a corrosion depth of 0.5 mm as the engineering failure threshold for life extrapolation, it can be reasonably expected that the graphene / alumina-zinc composite material prepared in this invention can achieve a corrosion resistance life of more than 15 years in the southern composite environment; this is about 3 times longer than that of traditional round steel (life of 3-5 years); and about 50% longer than that of pure graphene material (life of 8-10 years). These results fully demonstrate that the composite material of this invention not only significantly extends the service life of grounding materials but also greatly reduces the frequency of maintenance, showing promising application prospects.

[0070] Connection Structure Embodiment See Figures 2-5The graphene-based composite grounding lead connection structure provided in the third aspect of the present invention includes a composite lead 1 made of graphene / alumina-zinc composite material as described in the above embodiments, and a metal grounding component 2; wherein, the end of the graphene / alumina-zinc composite grounding lead is provided with a tapered transition section 11, the outer diameter of which continuously decreases from the body diameter of the composite lead 1 to the same as the diameter of the metal grounding component 2; the end of the transition section 11 overlaps with the end of the metal grounding component to form an overlap area; a solder layer (not shown in the figure) is provided on the inner side of the interface of the overlap area, which forms a corrosion-resistant metallurgical bonding layer after hot-melt welding.

[0071] Specifically, the end of the transition section 11 is connected to the metal grounding component 2 by an axial lap joint with a lap length of 6 times the diameter of the round steel. The sufficient lap length increases the contact area between the two materials, and together with hot-melt welding, a strong fusion joint is formed. This avoids the increase in contact resistance due to insufficient contact area (the final weld contact resistance is ≤5mΩ, far below the national standard requirement of 10mΩ). At the same time, it improves the tensile strength and corrosion resistance of the joint, meeting the long-term operation requirements of the grounding down conductor.

[0072] Preferably, the diameter of the transition section 11 decreases continuously from 1.2 times the diameter of the metal grounding component 2 to its equal value.

[0073] In this embodiment, the metal grounding component 2 refers to the metal conductor in the grounding system used to conduct fault current and discharge it to the ground. Its material is usually a metal material with good conductivity and certain mechanical strength. In this embodiment, the metal grounding component includes a round steel base, such as a Q235 round steel base.

[0074] In this embodiment, the transition section 11 refers to a gradually decreasing structure located at the end of the graphene / alumina-zinc composite grounding down conductor 1. Its outer diameter continuously decreases from the main diameter of the composite down conductor 1 to the same diameter as the metal grounding component 2. This is used to alleviate thermal stress concentration when connecting different materials and to provide a structural basis for lap welding and sealing. Both ends of the graphene-based composite grounding down conductor 1 are provided with the transition section 11, and are respectively connected to the metal grounding component on the overhead side and the metal component of the underground grounding grid 4.

[0075] The solder layer is preferably a 0.2 mm thick nickel-based solder strip. During the welding process, the nickel-based solder strip melts at 1500-1600℃ and undergoes metallurgical bonding with the iron in the round steel, the graphene in the composite lead wire 1, and metal components (such as zinc), forming an alloy layer with both high corrosion resistance and high conductivity. This solves the problems of easy oxidation and poor corrosion resistance in traditional welded joints, and improves the corrosion resistance of the weld joint by 2 times compared with ordinary hot melt welding.

[0076] See again Figure 3Furthermore, the outer periphery of the transition section 11 is provided with an annular sealing groove (not shown in the figure), and a water-swellable sealing strip is embedded in the annular sealing groove; the overlapping area is covered with an anti-corrosion sealing sleeve 3, which is locked by fasteners so that its inner wall is tightly fitted with the outer periphery of the transition section 11 and the metal grounding component 2, forming a double anti-corrosion barrier in conjunction with the water-swellable sealing strip.

[0077] Specifically, two annular sealing grooves (1.5mm deep and 2mm wide) are opened around the outer perimeter of each transition section 11, and the corresponding sealing grooves are pre-filled with water-swellable sealing strips (expansion ratio ≥300%). The anti-corrosion sealing sleeve 3 can be a polytetrafluoroethylene (PTFE) anti-corrosion sealing sleeve with a silane coupling agent coated on its inner wall. One end of the silane coupling agent molecule chemically bonds with the hydroxyl groups on the surface of the composite down conductor 1 or the metal grounding component 2, and the other end forms a physical adsorption or weak chemical bond with the inner wall of the PTFE, eliminating interfacial gaps and preventing crevice corrosion caused by poor adhesion between the sealing sleeve and the down conductor surface. At the same time, the molecular film formed by the silane coupling agent at the interface can effectively prevent the penetration of corrosive media such as moisture, H⁺, and SO₄²⁻ in the soil; furthermore, this molecular film, together with the water-swellable sealing strip and the PTFE sealing sleeve body, forms a synergistic protection, strengthening the overall sealing performance of the triple anti-corrosion barrier, preventing the weld joint from rusting again due to interfacial leakage, and ensuring that the durability of the connection part is consistent with that of the down conductor body.

[0078] It can be seen that by setting an annular sealing groove filled with a water-swellable waterstop strip around the outer periphery of the overlapping area, covering it with an anti-corrosion sealing sleeve, and then locking it with a stainless steel clamp, the waterstop strip expands when it comes into contact with water and fills the tiny gap at the end of the graphene / alumina-zinc composite lead wire. Together with the corrosion-resistant alloy layer of the weld joint, it forms a triple anti-corrosion barrier of corrosion-resistant metallurgical layer, waterstop strip, and anti-corrosion sealing sleeve, achieving reliable isolation from corrosive media in the soil and significantly improving the long-term anti-corrosion reliability of the connection part in harsh buried environments.

[0079] In summary, because the graphene / alumina-zinc composite grounding down conductor is composed of graphene, zinc powder, and nano-alumina in a specific ratio, it has good conductivity at the ends and can stably and persistently perform anti-corrosion function in corrosive environments. On this basis, by setting a transition section with a continuously decreasing outer diameter at its ends and introducing a solder layer on the inner side of the lap interface for hot-melt welding, the zinc, graphene and solder react in situ to form a dense corrosion-resistant metallurgical bonding layer. This achieves the connection function of the composite down conductor and the metal grounding component with a contact resistance ≤5 mΩ, significantly improved mechanical reliability, and more than 2 times higher corrosion resistance at the welded part than ordinary welding.

[0080] Compared to traditional hot-melt welded joints, the connection structure between the graphene / alumina-zinc composite grounding down conductor and the metal grounding component provided in this embodiment of the invention exhibits significant performance advantages after 18 months of continuous monitoring in a simulated pH=3.0 acidic soil environment: The initial contact resistance decreased from 8.5 mΩ to 3.8 mΩ and remained at 4.1 mΩ after 18 months, far below the national standard limit of 10 mΩ; while the contact resistance of the traditional welded joint increased from the initial 8.5 mΩ to 15.2 mΩ, exceeding the standard threshold, resulting in a significant deterioration in electrical contact performance. After 18 months, the weld corrosion depth was only 0.1 mm, which is about 4.3% of that of traditional welding (traditional welding is 2.3 mm), effectively suppressing weld failure caused by electrochemical corrosion. The tensile strength of the joint decreased from the initial 15.3 kN to 14.8 kN, with a retention rate of 96.7%; while the tensile strength of traditional welding decreased from 12.5 kN to 6.8 kN, a decrease of 45.6%, indicating that its structural integrity was seriously damaged.

[0081] The above results show that the connection structure of the present invention achieves a reliable connection with low resistance, corrosion resistance, high strength and long service life in complex corrosive environments, effectively alleviating the technical problems of increased contact resistance, aggravated weld corrosion and rapid decay of mechanical properties in traditional welding, and has good prospects for engineering applications.

[0082] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A graphene / alumina-zinc composite material, characterized in that, It contains graphene, nano-alumina and zinc powder, wherein by weight, graphene is 87-92 parts, nano-alumina is 5-8 parts and zinc powder is 3-5 parts.

2. The graphene / alumina-zinc composite material according to claim 1, characterized in that, Also includes: 1-2 parts by weight of microbial inhibitory material.

3. The graphene / alumina-zinc composite material according to claim 2, characterized in that, The microbial inhibitory material is at least one of copper powder and titanium dioxide.

4. The graphene / alumina-zinc composite material according to any one of claims 1-3, characterized in that, Also includes: 1-3 parts by weight of structural reinforcement material.

5. The graphene / alumina-zinc composite material according to claim 4, characterized in that, The structural reinforcement material is at least one of chopped carbon fibers and nano-silicon carbide particles.

6. The graphene / alumina-zinc composite material according to claim 5, characterized in that, The length of the chopped carbon fibers is 1-3 mm; the particle size of the nano-silicon carbide particles is 50-200 nm.

7. The graphene / alumina-zinc composite material according to any one of claims 1-3, characterized in that, Also includes: 0.5-1 parts by weight of corrosion inhibitor.

8. The graphene / alumina-zinc composite material according to claim 7, characterized in that, The corrosion inhibitors that enhance corrosion resistance are sodium molybdate or potassium molybdate.

9. A method for preparing a graphene / alumina-zinc composite material according to any one of claims 1-8, characterized in that, Includes the following steps: Weigh each component according to the composition of the composite material, mix them evenly by step feeding, and obtain composite powder; The composite powder is pressurized and molded to obtain a green body; The green compact is heated to the sintering temperature in stages in an inert atmosphere, held at the temperature for sintering, and then cooled to obtain the composite material.

10. The method for preparing the graphene / alumina-zinc composite material according to claim 9, characterized in that, The stepwise feeding process includes: first, mixing and stirring graphene and nano-alumina at 1000-1500 r / min for 30-45 minutes, then adding zinc powder and the functional additives and continuing to mix for 15-20 minutes.

11. The method for preparing the graphene / alumina-zinc composite material according to claim 9, characterized in that, The sintering temperature is 800-850℃, and the segmented heating includes the following stages: The first stage: the temperature is increased from room temperature to 400℃ at a rate of 5-10℃ / min to remove residual moisture and organic matter from the green body; The second stage involves raising the temperature from 400℃ to 800℃ at a rate of 15-20℃ / min, which promotes the initial melting of zinc powder and fills the pores. The third stage involves maintaining the temperature at 800-850℃ for 2-3 hours to allow graphene and nano-alumina to form Al-OC interface chemical bonds. Simultaneously, the zinc powder is completely melted and uniformly dispersed in the conductive network composed of graphene and nano-alumina.

12. A connection structure between a graphene / alumina-zinc composite grounding lead and a round steel substrate, characterized in that, Includes a metal grounding component and a composite down conductor made of graphene / alumina-zinc composite material as described in any one of claims 1-8; wherein, The graphene / alumina-zinc composite grounding lead has a tapered transition section at its end, the outer diameter of which continuously decreases from the diameter of the composite lead body to the same diameter as the metal grounding component; the end of the transition section overlaps with the end of the metal grounding component to form an overlap area; a solder layer is provided on the inner side of the interface of the overlap area, which forms a corrosion-resistant metallurgical bonding layer after hot-melt welding.

13. The connection structure between the graphene / alumina-zinc composite grounding lead and the round steel substrate according to claim 12, characterized in that, The outer periphery of the transition section is provided with an annular sealing groove, and a water-swellable water-stop strip is embedded in the annular sealing groove; The overlapping area is covered with an anti-corrosion sealing sleeve, which is locked by fasteners so that its inner wall fits tightly against the outer periphery of the transition section and the metal grounding component, forming a double anti-corrosion barrier in conjunction with the water-swellable sealing strip.

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