A method for producing a single-walled carbon nanotube composite material for powder metallurgy and a product

Abstract

This invention discloses a method for preparing single-walled carbon nanotube composite materials for powder metallurgy and the resulting product, relating to the interdisciplinary fields of resource recycling, powder metallurgy, and composite materials. The method includes S1, adding tail gas-derived single-walled carbon nanotube composite powder with an iron content of 60%–95% by mass to an organic solvent for ultrasonic dispersion for 0.5–4 hours, while simultaneously adding a complexing activator to selectively dissolve the oxide layer on the surface of the iron nanoparticles and enhance their activity. The powder is then dried to obtain an interface-activated composite powder. By utilizing the high-iron-content single-walled carbon nanotube composite powder derived from tail gas, the direct high-value utilization of industrial byproducts is achieved, reducing raw material costs and mitigating environmental burden. During the preparation process, powder ball milling activation, flexible interface film formation, and micro-rearrangement are employed to achieve uniform distribution of carbon nanotubes among iron nanoparticles and form a stable interfacial interlocking, improving load transfer efficiency and the mechanical properties of the composite material.

Description

Technical Field

[0001] This invention relates to the interdisciplinary fields of resource recycling, powder metallurgy, and composite materials, specifically to a method for preparing single-walled carbon nanotube composite materials for powder metallurgy and the resulting product. Background Technology

[0002] Single-walled carbon nanotubes (SWNTs) possess excellent mechanical and functional properties. Their large-scale production, especially through chemical vapor deposition (CVD), can efficiently generate the target product. However, this process typically generates a large amount of exhaust gas. This exhaust gas is rich in composite particles with iron nanoparticles as the core and SWNTs and amorphous carbon grown or attached to the surface. After dust removal, condensation, and collection, low-purity SWNT composite powder with extremely high iron content (typically 60%-95% by mass) can be obtained. Current technologies usually treat this type of powder as an intermediate product, requiring expensive purification processes, or even treating it directly as solid waste, which not only wastes resources but also increases environmental disposal pressure.

[0003] Traditional iron-based powder metallurgy materials (such as iron-graphite materials) are widely used in industry due to their good formability and low cost. However, they still face bottlenecks in terms of strength, hardness, wear resistance, and electrical and thermal conductivity, making it difficult to meet the demands of high-end equipment for lightweight, long lifespan, and multifunctionality. Existing research attempts to introduce high-purity single-walled carbon nanotubes as a reinforcing phase into the iron matrix, but three core problems remain in iron-based systems: nanoscale single-walled carbon nanotubes are difficult to disperse uniformly in micron-sized iron powder and tend to agglomerate; the interfacial bonding between single-walled carbon nanotubes and the iron matrix is ​​weak, resulting in low load transfer efficiency; and the high cost of high-purity single-walled carbon nanotube raw materials severely restricts their industrial application.

[0004] Therefore, how to directly convert high-iron-content single-walled carbon nanotube composite powder derived from exhaust gas into a high-value product, bypassing expensive purification steps, while simultaneously solving the problems of dispersion and interfacial bonding in the iron matrix, and developing a new low-cost, high-performance composite material, has become a research topic with economic, environmental, and technological challenges. This invention addresses these technical problems by proposing an innovative powder metallurgy preparation method and its corresponding composite material product. This method enables the direct high-value utilization, uniform dispersion, and interfacial strengthening of exhaust gas-derived single-walled carbon nanotube composite powder, significantly improving the multi-scale synergistic strengthening performance of iron-based composite materials. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing single-walled carbon nanotube composite materials for powder metallurgy and a product thereof, so as to overcome the above-mentioned shortcomings in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing single-walled carbon nanotube composite materials for powder metallurgy, the method comprising the following steps: S1, adding tail gas-derived single-walled carbon nanotube composite powder with an iron mass content of 60% to 95% to an organic solvent for ultrasonic dispersion for 0.5 to 4 hours, while adding a complexing activator to selectively dissolve the oxide layer on the surface of the iron nanoparticles and improve its activity, and drying to obtain an interface-activated composite powder; S2. The composite powder is mechanically ball-milled under an inert atmosphere, and a binder is added at a content of 0.1 to 3 wt% of the total composite powder mass. By controlling the ball milling energy and ball-to-powder ratio, the bundled single-walled carbon nanotubes are decoupled and embedded on the surface and gaps of the iron nanoparticles, while a three-dimensional carbon nanotube network is formed inside the composite powder. S3. The ball-milled composite powder is subjected to heat treatment in an inert or reducing atmosphere for 2 to 60 minutes at a temperature of 300 to 650°C to cause diffusion and structural reconstruction on the surface of the iron nanoparticles in the composite powder, and to form anchoring nodes on the outer wall of the single-walled carbon nanotubes, thus forming a core-shell composite structure of carbon nanotubes covering iron nanoparticles and stabilizing the three-dimensional network. S4. Load the heat-treated composite powder into the mold and perform gradient cold pressing. The pre-pressing pressure is 200-400MPa, the main pressing pressure is 400-800MPa, and the pressure is held for 30-180 seconds to obtain the compact. S5. The compact is subjected to staged sintering under a reducing or inert atmosphere. Under the condition that the temperature is gradually increased to 900-1350℃ and the total sintering time is controlled to be 40-240min, the iron nanoparticles form initial diffusion connections and interparticle diffusion necks, thereby achieving material densification and matrix reconstruction. At the same time, some carbon elements in the single-walled carbon nanotubes diffuse into the iron matrix in a limited manner to form an iron-carbon solid solution and retain the carbon nanotube reinforcement structure. The sintering gas dew point is controlled below -40℃ to obtain an iron-based composite material with an internal continuous iron matrix, a three-dimensional carbon nanotube reinforcement network, and a multi-scale synergistic reinforcement structure of carbon nanotube-coated iron nanoparticles.

[0007] A product of single-walled carbon nanotube composite material for powder metallurgy includes: a metal matrix: a continuous metal matrix structure formed by pressing and sintering iron nanoparticles together; Single-walled carbon nanotubes: distributed in the interparticle gaps between adjacent iron nanoparticles and extending along the interparticle gaps, forming a three-dimensional interconnection network structure that runs through multiple iron nanoparticles within the volume space of the composite material defined by the continuous metal matrix structure formed by sintering iron nanoparticles, so that the network is connected between adjacent iron nanoparticles through at least one single-walled carbon nanotube connection path. Interface bonding layer: formed by binder or its heat treatment conversion product, and continuously distributed on the particle surface and particle contact area of ​​iron nanoparticles, with a thickness of 10nm to 500nm.

[0008] Beneficial effects In the above technical solution, the present invention provides a method and product for preparing single-walled carbon nanotube composite materials for powder metallurgy. By utilizing high-iron-content single-walled carbon nanotube composite powder derived from exhaust gas, the invention achieves direct high-value utilization of industrial by-products, reducing raw material costs and alleviating environmental burden. During the preparation process, through powder ball milling activation, flexible interface film formation, and micro-rearrangement, carbon nanotubes are uniformly distributed among iron nanoparticles and form a stable interlocking interface, improving load transfer efficiency and the mechanical properties of the composite material. Combined with gradient cold pressing and graded sintering, a multi-scale synergistic strengthening structure is constructed within the iron matrix, consisting of a continuous metal matrix, a three-dimensional carbon nanotube reinforcing network, and carbon nanotube-coated iron nanoparticles. This achieves interface stability and three-dimensional network connectivity, significantly improving the material's strength, hardness, wear resistance, and electrical and thermal conductivity.

[0009] It should be understood that the foregoing general description and the following detailed description are exemplary and illustrative only, and are not intended to limit this disclosure.

[0010] This application provides an overview of various implementations or examples of the technology described in this disclosure, and is not a full disclosure of the entire scope or all features of the disclosed technology. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0012] Figure 1 A schematic diagram of the preparation method of single-walled carbon nanotube composite material for powder metallurgy provided in the embodiments of the present invention; Figure 2 This is a schematic diagram illustrating the performance testing methods, standards, and parameters provided in the embodiments of the present invention; Figure 3 A performance comparison table of the embodiments and comparative sample is provided for the embodiments of the present invention. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0014] Reference Figure 1-3 As shown, the present invention provides a method for preparing single-walled carbon nanotube composite materials for powder metallurgy. The method includes the following steps: S1, adding tail gas-derived single-walled carbon nanotube composite powder with an iron mass content of 60% to 95% to an organic solvent for ultrasonic dispersion for 0.5 to 4 hours, while adding a complexing activator to selectively dissolve the oxide layer on the surface of the iron nanoparticles and improve its activity, and drying to obtain an interface-activated composite powder.

[0015] S1 includes the following steps: S11, adding tail gas-derived single-walled carbon nanotube composite powder with an iron content of 60% to 95% to an organic solvent for uniform dispersion, and stirring to initially disperse the composite powder in the solvent to form a suspension. S12. The obtained suspension is subjected to ultrasonic treatment for 0.5 to 4 hours to induce micro-cavitation and shearing in the bundled single-walled carbon nanotubes in the liquid, gradually separating them from the aggregated state, increasing the surface area of ​​the carbon nanotubes, and improving their uniform distribution on the surface of iron nanoparticles. S13. During the ultrasonic dispersion process, a complexing activator is added to selectively dissolve the oxide layer on the surface of iron nanoparticles and form active sites, thereby improving the surface reactivity of iron nanoparticles and their interfacial bonding ability with carbon nanotubes. The complexing activator includes citric acid, oxalic acid, acetic acid, tartaric acid, ethylenediaminetetraacetic acid, ethylenediamine, triethanolamine, or aniline. S14. After ultrasonic treatment and activation, the composite powder particles can be further dispersed in the suspension by stirring or static sedimentation to reduce local agglomeration and make single-walled carbon nanotubes uniformly embedded on the surface of iron nanoparticles and between particles. S15. Remove moisture and solvent from the uniformly dispersed suspension by vacuum drying, spray drying or oven drying, and control the drying temperature within 60-120℃ to obtain interface-activated composite powder, thereby enhancing the surface activity of the composite powder.

[0016] Specifically, step S1 provided by this invention involves interfacial activation treatment of exhaust gas-derived high-iron-content single-walled carbon nanotube composite powder to achieve high powder dispersibility and enhanced interfacial bonding ability, laying the foundation for subsequent pressing, sintering and multi-scale synergistic strengthening of composite materials.

[0017] Specifically, S1 includes the following steps: Adding exhaust gas-derived single-walled carbon nanotube composite powder with an iron content of 60%–95% to an organic solvent, including acetone, ethanol, isopropanol, or N-methylpyrrolidone, to form a preliminary suspension. Continuously stirring the composite powder using magnetic stirring, mechanical stirring, or a rotary shearing device ensures a uniform suspension in the solvent and inhibits local agglomeration. Simultaneously, a propeller impeller or blade mixer generates shear force and rotational flow, promoting thorough powder dispersion. The stirring speed and duration can be adjusted to obtain a stable suspension system. To further improve the dispersion effect, the suspension temperature can be controlled to enhance the surface wettability of the composite powder. A suitable solvent or mixed solvent system is selected based on the powder characteristics to balance the surface activity of the iron nanoparticles and the dispersibility of the carbon nanotubes. A dispersing agent or surfactant, including polyvinylpyrrolidone or sodium dodecyl sulfate, can be added at 0.01 wt%–1 wt% of the total powder mass to prevent the powder from re-agglomerating during settling by forming a microscopically stable structure in the suspension. Composite powders can form a stable and uniform initial suspension system in liquids, providing a reliable basis for uniform contact between carbon nanotubes and iron nanoparticles, subsequent interface activation, and the formation of three-dimensional networks. At the same time, it reduces the problems of weak interfacial bonding and material performance degradation caused by early agglomeration.

[0018] In S12, the suspension is subjected to continuous ultrasonic treatment for 0.5–4 hours, forming microscopic cavitation bubbles and localized shear flow. This causes the bundled single-walled carbon nanotubes to gradually deagglomerate into single tubes or small bundles under shear stress and cavitation impact. Deagglomeration into single tubes or small bundles means that the original bundles or aggregates of multiple entangled carbon nanotubes are gradually separated in the liquid medium, with some bundles breaking down into single carbon nanotubes or forming fine bundle structures containing a small number of carbon nanotubes. This significantly increases the specific surface area of ​​the carbon nanotubes and improves their contact and adhesion uniformity on the surface of iron nanoparticles. In practice, probe-type ultrasonic devices or ultrasonic bath devices can be used to treat the suspension. Probe-type ultrasound generates strong shear stress and cavitation impact through high-energy local vibration, suitable for the fine dispersion of small-volume, high-concentration powders; ultrasonic baths, on the other hand, use overall vibration to uniformly stress large-volume suspensions, suitable for continuous industrial processing. During the processing, the depolymerization efficiency of carbon nanotubes and the surface protection of iron nanoparticles can be balanced by adjusting the ultrasonic power, frequency, treatment time, and liquid temperature, avoiding excessive vibration that could lead to particle agglomeration or carbon nanotube structural breakage. Furthermore, adding an appropriate amount of solvent and controlling the temperature or gently stirring during ultrasonic treatment can ensure uniform liquid flow and shearing, improving the depolymerization effect and maintaining suspension stability. The single-walled carbon nanotubes in the composite powder can achieve a controllable transformation from an initial aggregated state to a single or small bundle state, allowing carbon nanotubes to form a uniform coating on the surface of iron nanoparticles and between particle gaps. This provides a reliable foundation for subsequent ball milling, interface activation, and three-dimensional network formation, while simultaneously improving the interfacial bonding strength and mechanical properties of the composite material.

[0019] In S13, a complexing activator is added during the ultrasonic dispersion process to selectively dissolve the oxide layer on the surface of iron nanoparticles and form active sites, thereby improving the surface reactivity of iron nanoparticles and their interfacial bonding ability with carbon nanotubes. The complexing activator can be selected from citric acid, oxalic acid, acetic acid, tartaric acid, ethylenediaminetetraacetic acid, ethylenediamine, triethanolamine, or aniline, etc.

[0020] The specific implementation method includes adding a complexing activator at 0.1–5 wt% of the total powder mass to the composite powder that has formed a suspension, and then subjecting it to full contact with the powder in an ultrasonic treatment device. Through ultrasonic cavitation and liquid microflow, the complexing activator molecules rapidly contact the surface of the iron nanoparticles. Under the coordination or acidic action of the oxide layer on the particle surface and the complexing agent, the local oxide film is selectively dissolved, exposing the metal active sites, while avoiding damage to the carbon nanotube structure. The oxide layer dissolution rate and active site formation efficiency can be optimized by controlling the liquid temperature (20–60°C), ultrasonic power, and treatment time. If necessary, stepwise or slow dropwise addition can be used to ensure uniform activation of the iron nanoparticle surface and controllable active site density. After activation, the surface activity of the iron nanoparticles is significantly enhanced, allowing for a tighter interfacial bond with the carbon nanotubes during subsequent drying, ball milling, and sintering processes. Through the synergistic effect of physical interlocking and chemical bonding, a stable interfacial structure is formed, enhancing the load transfer capacity and mechanical properties of the composite material.

[0021] In step S14, after ultrasonic treatment and complexation activation, to further improve the uniform distribution of composite powder particles in the suspension, the suspension system can be redispersed to allow the composite powder particles to redistribute uniformly in the liquid medium and reduce local agglomeration. Specifically, the suspension can be continuously stirred by mechanical stirring, magnetic stirring, or a low-speed rotary mixing device to ensure that the particles form a stable flow state in the liquid and avoid particle accumulation due to local sedimentation.

[0022] In some embodiments, particle rearrangement can also be achieved through static sedimentation. This involves allowing the suspension to stand for a certain period after ultrasonic treatment is stopped, allowing the suspension to settle slowly under gravity. During sedimentation, microscopic rearrangement and re-contact occur between particles, gradually loosening and redistributing previously locally aggregated particle clusters, thereby reducing the degree of powder agglomeration.

[0023] Through stirring dispersion or static sedimentation, single-walled carbon nanotubes can redistribute with particle flow in a liquid medium and gradually embed themselves on the surface of iron nanoparticles and in the interstitial regions between particles. This allows carbon nanotubes to form bridging connections between multiple iron nanoparticles, resulting in an interface-activated composite powder. During subsequent drying, pressing, and sintering processes, the uniform distribution of carbon nanotubes is maintained, and stable reinforcing pathways are formed between iron nanoparticles, thus providing a foundation for constructing a continuous carbon nanotube reinforcement network within the composite material.

[0024] The present invention provides another preferred method, S2, mechanically ball-milling the composite powder under an inert atmosphere, while adding a binder with a content of 0.1 to 3 wt% of the total composite powder mass. By controlling the ball milling energy and the ball-to-powder ratio, the bundled single-walled carbon nanotubes are decoupled and embedded on the surface and gaps of the iron nanoparticles, while forming a through-hole three-dimensional carbon nanotube network inside the composite powder. S2 includes the following sub-steps: S21, placing the interface-activated composite powder in a ball mill container and injecting inert gas or reducing gas to form a protective environment, ensuring that the composite powder does not come into contact with air during the ball milling process, and ensuring the chemical stability of the binder; S22. By adjusting the ball milling speed to 200-400 rpm, the ball-to-material ratio to 5-20:1, and the ball milling time to 10-60 minutes, the composite powder is subjected to mechanical shearing and impact, and the bundled single-walled carbon nanotubes are gradually disintegrated to form a single or few-root bundle state, realizing the transformation of carbon nanotubes from an aggregated state to a dispersed state, providing a basis for the construction of three-dimensional networks. S23. During the ball milling process, a binder is added, the content of which is controlled at 0.1 to 3 wt% of the total composite powder mass. Under the mechanical shearing and impact of the ball milling, the binder is evenly distributed and forms a continuous flexible interface film on the surface of the iron nanoparticles and between the particles. The flexible interface film covers the particle surface and wets the carbon nanotubes, realizing the initial mechanical interlocking and interface bonding between the carbon nanotubes and the iron nanoparticles. At the same time, it provides support and guidance for the carbon nanotubes to form a three-dimensional network inside the composite powder. S24. Under the action of the flexible interface film, the single-walled carbon nanotubes extend along the gap between particles and gradually form a three-dimensional network that runs through the composite powder. By controlling the filling density of the composite powder, the particle size distribution and the pressing or vibration-assisted measures, a reasonable gap between particles is maintained, providing space for the carbon nanotube network to extend, cross-link and distribute evenly. At the same time, the flexible interface film further stabilizes the combination of carbon nanotubes and particles, realizing the continuity and stability of the three-dimensional network structure. S25. After ball milling, the particle size and dispersibility of the composite powder are tested. Laser diffraction particle size analysis and high-resolution scanning electron microscopy are used for joint characterization. At the same time, the composite powder optical scattering or in-situ conductivity monitoring technology is combined to obtain the particle distribution, carbon nanotube network integrity and local agglomeration of the composite powder in real time. Then, by adjusting the ball milling speed, ball-to-material ratio, ball milling time or by using static homogenization treatment, the internal microstructure of the composite powder is precisely controlled so that the carbon nanotubes form a continuous three-dimensional network along the particle gaps and are evenly distributed, while enhancing the interfacial interlocking between carbon nanotubes and iron nanoparticles.

[0025] Specifically, in step S2, the interface-activated composite powder obtained in step S1 can be placed into a ball mill jar and ball-milled under an inert gas protective environment such as argon, nitrogen, or helium to prevent oxidation of iron nanoparticles during the ball milling process. The ball milling equipment can be a planetary ball mill, a drum ball mill, or a vibratory ball mill. By adjusting the ball milling speed, ball-to-powder ratio, and milling time, the composite powder is subjected to continuous impact, friction, and shear forces in the ball mill jar, thereby promoting thorough mixing and structural rearrangement of the powder particles. This includes the following implementation methods; In step S21, the obtained interface-activated composite powder is placed in a ball mill container. A protective atmosphere is established inside the ball mill container before ball milling to prevent the composite powder from reacting with oxygen or moisture in the air during the milling process. Specifically, after adding the composite powder to the ball mill jar, a vacuum device is used to evacuate the inside of the container, removing the air. Then, an inert gas or reducing gas is introduced into the ball mill container to create a protective atmosphere. The inert gas can be argon or nitrogen, and the reducing gas can be hydrogen or a mixture of hydrogen and an inert gas.

[0026] In some embodiments, the ball milling container can be repeatedly purged using a "vacuum-gas-filling" cycle to further reduce the residual oxygen content inside the container, thereby improving the stability of the protective environment. After gas purging, the internal atmosphere is kept stable by sealing the ball milling jar structure, and an inert or reducing environment is maintained continuously during ball milling to prevent re-oxidation of the iron nanoparticle surface. Alternatively, a gas interface or sealed valve can be installed in the ball milling equipment to allow protective gas to be injected into the ball milling container before ball milling and to maintain a stable atmosphere during the process. Simultaneously, pressure monitoring or flow control devices can be used to regulate the gas state inside the ball milling jar, keeping the protective atmosphere stable and ensuring that the composite powder does not come into contact with air during ball milling. This prevents oxidation of the iron nanoparticles during mechanical ball milling and avoids chemical degradation or structural damage of the binder in an oxidizing environment, thus maintaining the chemical stability of the binder and providing a stable reaction environment for subsequent carbon nanotube embedding on the iron nanoparticle surface and the formation of a three-dimensional network structure.

[0027] In S22, by adjusting the ball milling speed to 200–400 rpm, the ball-to-material ratio to 5–20:1, and the ball milling time to 10–60 minutes, the composite powder undergoes interparticle collisions and structural rearrangement under the combined action of mechanical shearing force, impact force, and friction force. This causes the bundled single-walled carbon nanotubes to gradually unravel and form single or few-root bundles, realizing the transformation of carbon nanotubes from an aggregated state to a dispersed state, thus providing a foundation for the subsequent construction of a three-dimensional carbon nanotube network.

[0028] In practice, planetary ball mills, vibratory ball mills, or drum ball mills can be used to process the composite powder. Stainless steel balls, zirconia balls, or tungsten carbide balls with a diameter of 3–10 mm can be used as the milling media, which are added to the milling container according to a preset ball-to-material ratio. By adjusting the rotation speed of the milling equipment, the milling media are lifted by the frictional force of the inner wall of the milling container, resulting in periodic falling and rolling motions. When the milling media are lifted to a certain height, they detach from the inner wall of the container and fall into the powder layer, thereby generating impact and shear forces on the composite powder. By matching and controlling the milling speed with the size of the milling container, the vertical falling height of the milling media in the milling container is maintained within the range of 20–80 mm to ensure that the milling media has sufficient impact kinetic energy without causing damage to the carbon nanotube structure or excessive cold welding of the powder.

[0029] In some embodiments, the vertical drop height of the ball milling media is preferably controlled within the range of 30 to 60 mm to improve the decoupling efficiency of carbon nanotubes while ensuring the strength of mechanical shearing action; more preferably, it is 35 to 50 mm to promote the intercalation and distribution of carbon nanotubes on the surface of iron nanoparticles and in the interparticle gaps while maintaining the structural integrity of carbon nanotubes.

[0030] During ball milling, the collisions and rolling between iron nanoparticles mechanically decouple the bundled single-walled carbon nanotubes. Decoupling refers to the gradual loosening and separation of the originally entangled bundle structure of multiple carbon nanotubes under mechanical shearing and friction. Some carbon nanotubes are completely separated into single structures, while others form small bundles composed of a small number of carbon nanotubes, significantly reducing the aggregation of carbon nanotubes. Simultaneously, driven by mechanical force, the carbon nanotubes gradually embed into the micropores or interparticle regions on the surface of the iron nanoparticles, forming a dispersed and interconnected structure among multiple iron nanoparticles.

[0031] In practical operation, the ball milling energy can be adjusted through staged ball milling. For example, a lower rotation speed can be used for premixing in the initial stage of ball milling to ensure thorough mixing of the powder and avoid damage to the carbon nanotube structure. Subsequently, the ball milling speed can be gradually increased to enhance the mechanical shearing effect, thereby promoting the decoupling and uniform dispersion of carbon nanotubes. At the same time, intermittent ball milling can be used to control the temperature rise during ball milling, for example, pausing for several minutes every 10-20 minutes to prevent excessively high temperatures from affecting the stability of the carbon nanotube structure. This allows for effective decoupling and dispersion of carbon nanotubes while ensuring the integrity of the carbon nanotube structure, enabling the carbon nanotubes to gradually transform from a locally aggregated state to a uniformly distributed state in the composite powder, and forming interconnected structures between the iron nanoparticles.

[0032] In S23, a binder is added during the ball milling process, with its content controlled at 0.1–3 wt% of the total composite powder mass. Under the mechanical shearing and impact of the ball milling, the binder is gradually dispersed and uniformly distributed in the composite powder, forming a continuous flexible interface film on the surface of the iron nanoparticles and in the interparticle regions. This flexible interface film covers the particle surface and wets the carbon nanotubes, thereby achieving preliminary mechanical interlocking and interfacial bonding between the carbon nanotubes and the iron nanoparticles. At the same time, it provides support and guidance for the carbon nanotubes to form a penetrating three-dimensional network structure inside the composite powder.

[0033] In practice, organic binders such as polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, stearic acid, or paraffin can be selected as binders. The binder can be added directly to the ball milling system in powder form, or it can be first dissolved in a small amount of organic solvent (such as ethanol or isopropanol) to form a binder solution, and then mixed with the composite powder before being added to the ball milling container, thereby improving the uniformity of the binder dispersion in the powder system.

[0034] During ball milling, the binder is gradually stretched and spread onto the surface of iron nanoparticles due to the impact, friction, and shear forces generated by the milling media, forming a continuous or semi-continuous flexible interfacial film structure. This flexible interfacial film can, on the one hand, form a flexible connecting layer between iron nanoparticles, thereby reducing the tendency for direct cold welding between particles; on the other hand, it can wet and coat carbon nanotubes, making it easier for carbon nanotubes to adhere to the surface of iron nanoparticles and the interparticle regions.

[0035] As the ball milling process continues, carbon nanotubes gradually enter the interstitial region between particles under mechanical force and are fixed between multiple iron nanoparticles with the assistance of a flexible interface film. This allows carbon nanotubes to form connection paths between different particles, thereby gradually building an interconnected carbon nanotube connection structure inside the composite powder.

[0036] In S24, a stable interparticle structure can be formed by controlling the particle size distribution of the composite powder. For example, iron nanoparticles or micron-sized iron nanoparticles of different particle sizes can be introduced into the composite powder, allowing smaller particles to fill the spaces between larger particles, thereby forming a continuous and controllable interparticle structure. This interparticle structure can provide channels for the extension and distribution of carbon nanotubes. The particle size distribution can be achieved by sieving, classifying, or mixing powders of different particle sizes, enabling the composite powder to form a relatively stable packing structure.

[0037] In the powder processing, the structure of composite powders can also be adjusted by vibration-assisted or light compaction. For example, the composite powder can be placed on a vibrating platform or vibrating screen for a short time to cause the powder particles to rearrange under the action of vibration and form a uniform packing state; or a low-pressure pre-compression method can be used to keep the powder particles in stable contact but still retain a certain gap structure to avoid complete densification between particles, which would affect the formation of carbon nanotube networks.

[0038] During ball milling and particle movement, carbon nanotubes gradually extend along the interparticle gaps and form connecting structures between different particles. The flexible interface film provides fixation and guidance for the carbon nanotubes during this process, enabling them to stably adhere to the surface of iron nanoparticles and form bridging structures between multiple particles, thereby gradually constructing a three-dimensional carbon nanotube network that permeates the interior of the composite powder.

[0039] As carbon nanotubes extend and cross-link between particles, an interconnected spatial network structure gradually forms within the composite powder. The flexible interface film plays a stabilizing role in the network structure, ensuring that the carbon nanotubes remain stably distributed on the particle surface and in the interstitial regions, and preventing re-aggregation or detachment during subsequent powder processing or pressing, thus guaranteeing the continuity and stability of the three-dimensional carbon nanotube network structure.

[0040] In step S25, after ball milling, the composite powder is characterized for particle size, dispersibility, and the continuity of the three-dimensional carbon nanotube network to ensure uniform distribution of carbon nanotubes and iron nanoparticles and the formation of a stable three-dimensional network structure. Specifically, a laser diffraction particle size analyzer is first used to determine the particle size distribution of the powder, obtaining the volume distribution and average particle size information of particles of different sizes. Simultaneously, a high-resolution scanning electron microscope is used to observe the spatial distribution of single-walled carbon nanotubes and iron nanoparticles in the composite powder, confirming the intercalation of carbon nanotubes along particle gaps and the network continuity. Furthermore, optical scattering technology or in-situ conductivity monitoring methods can be used to analyze the conductivity and local aggregation of the carbon nanotube network in the powder in real time, providing a basis for subsequent microstructure control.

[0041] During the testing process, if localized carbon nanotube agglomeration or network discontinuity is found, optimization can be achieved by adjusting the ball milling process parameters. This includes appropriately adjusting the ball milling speed, ball-to-powder ratio, and milling time to enhance the mechanical shearing, impact, and friction between the powders, promoting further deagglomeration of the carbon nanotubes and their embedding on the surface and between the iron nanoparticles. Simultaneously, a static homogenization treatment can be employed to allow the composite powder to rearrange under its own gravity or micro-vibration, eliminating localized agglomeration areas and further stabilizing the interfacial interlocking between the carbon nanotubes and iron nanoparticles.

[0042] To ensure the continuity and uniformity of the three-dimensional network, an iterative closed-loop optimization strategy can be established: first, characterization is performed to obtain the powder particle distribution and carbon nanotube network state; then, based on the detection results, the ball milling parameters or homogenization treatment conditions are adjusted, and the characterization and control are repeated until the carbon nanotube network inside the powder is uniformly penetrated and forms a stable mechanically interlocked structure with the iron nanoparticles. This method guarantees the network structure and interfacial bonding strength of the composite powder, providing a reliable foundation for subsequent pressing and sintering, thereby improving the mechanical properties, electrical conductivity, and overall uniformity of the final composite material.

[0043] In the preferred embodiment provided by the present invention, S3, the ball-milled composite powder is subjected to heat treatment in an inert or reducing atmosphere for 2 to 60 minutes at a temperature of 300 to 650°C, so that the iron nanoparticles of the composite powder undergo diffusion and structural reconstruction, and anchoring nodes are formed on the outer wall of the single-walled carbon nanotubes, forming a core-shell composite structure of carbon nanotubes covering iron nanoparticles and stabilizing the three-dimensional network.

[0044] S3 includes the following sub-steps: S31, placing the ball-milled composite powder in a heat treatment furnace, and introducing an inert gas or reducing gas before heating to form a protective environment, so that the active surface of the iron nanoparticles exposed during the ball milling process remains in a reduced or inert state during the heating process, so as to inhibit surface oxidation and maintain interfacial activity. S32. A phased heating method is adopted to achieve structural control. First, a preheating treatment of 5 to 30 minutes is carried out in the range of 300 to 450℃ to gradually release the internal stress generated during ball milling, while promoting the softening or partial decomposition of the binder, so that the interface between single-walled carbon nanotubes and iron nanoparticles can be further bonded. Then, the temperature is raised to 450 to 650℃ for 2 to 30 minutes of diffusion heat treatment, so that the surface atoms of iron nanoparticles diffuse and migrate and trigger surface structure reconstruction. S33. The composite powder is thermally activated by gradient heating, and the migration of iron nanoparticles on the surface is regulated in an inert or reducing atmosphere to enrich the iron nanoparticles at the active sites and form nanoscale anchoring nodes, so that a stable interface bonding structure is constructed between carbon nanotubes and iron nanoparticles. At the same time, the migration activity of iron nanoparticles is improved by periodically adjusting the concentration of reducing gas or by using a pulsed gas input method to promote the formation of interface anchoring nodes. S34. By gradient heating and controlling the atomic diffusion on the surface of iron nanoparticles under inert or reducing gas, while applying a magnetic field of 0.05 to 0.5T to induce the orientation of iron nanoparticles, the iron nanoparticles migrate to the outer wall of carbon nanotubes and accumulate at defects and active sites to form anchoring nodes, which promotes the partial coating or partial coating of iron nanoparticles by carbon nanotubes, forming a three-dimensional network structure of carbon nanotubes and achieving stable interface bonding. S35. The three-dimensional carbon nanotube network is fixed by anchoring nodes with iron nanoparticles. At the same time, nano-carbon bridges are generated in situ at the intersection of carbon nanotubes by pyrolysis of the binder or trace carbon source gas, so that adjacent carbon nanotubes are connected. The wetting of the iron nanoparticle interface is regulated by vibration assistance or local diffusion, so that a continuous and stable spatial skeleton structure is formed inside the three-dimensional carbon nanotube network.

[0045] Specifically, the ball-milled composite powder is heat-treated in an inert atmosphere such as argon or nitrogen, or a reducing atmosphere such as hydrogen or a 5% hydrogen-nitrogen mixture. The treatment time is controlled to be 2–60 minutes and the temperature to be 300–650℃, in order to achieve the following effects: atomic diffusion and surface structure reconstruction occur on the surface of iron nanoparticles, and single-walled carbon nanotubes are partially coated or anchored along the interparticle gaps, forming a core-shell composite structure of carbon nanotubes coating iron nanoparticles, while stabilizing the three-dimensional network of carbon nanotubes. This includes the following sub-steps: In S31, the ball-milled composite powder is placed in a heat treatment furnace. Before heating, an inert gas such as argon or nitrogen, or a reducing gas such as hydrogen or a 5% hydrogen-nitrogen mixture, is introduced to form a stable protective environment. This allows the active surface of the iron nanoparticles exposed during ball milling to remain in a reduced or inert state during the heating process, thereby inhibiting surface oxidation and maintaining interfacial activity. This provides a foundation for the subsequent formation of single-walled carbon nanotube anchoring nodes and the stability of the three-dimensional network structure.

[0046] In practice, the composite powder can be evenly spread on a high thermal conductivity metal tray or quartz boat, with the powder layer thickness controlled at 3–10 mm to ensure that the gas can fully penetrate the powder and replace the air in the furnace. By controlling the gas flow rate and pressure, a protective atmosphere can be evenly covered to each powder particle. Simultaneously, slight vibration or stirring can be used to ensure that the inert or reducing gas fully contacts the surface of the iron nanoparticles. A slow heating method can be adopted during the heating process, with the temperature rise rate controlled at 2–5 °C / min to avoid oxidation of the iron nanoparticle surface or reduction of interfacial activity. Throughout the process, the furnace status can be monitored in real time using temperature sensors and oxygen concentration detectors to ensure that the powder surface is always in a reducing or inert environment, thus maintaining interfacial activity and protecting the powder. This not only effectively inhibits the oxidation of iron nanoparticles and maintains a highly active surface, but also improves the surface chemical reactivity of the powder, enabling the iron nanoparticles to migrate and accumulate at the active sites of carbon nanotubes in subsequent heat treatment stages, forming nanoscale anchoring nodes. This provides a reliable guarantee for the stable coating, bridging connection, and formation of the overall spatial framework structure of the carbon nanotube three-dimensional network, thereby significantly enhancing the multi-scale synergistic strengthening effect of the composite material.

[0047] In S32, a staged heating method is used to regulate the structure of the ball-milled composite powder. First, a preheating treatment of 5–30 minutes within the range of 300–450℃ is performed to gradually release the internal stress generated during ball milling, preventing powder particles from cracking or interfacial damage due to thermal stress. Simultaneously, within this temperature range, the binder in the powder softens or partially decomposes, forming a continuous flexible film on the particle surface, thereby enhancing the interfacial adhesion between single-walled carbon nanotubes and iron nanoparticles. In practice, the composite powder can be uniformly spread on a high thermal conductivity metal tray or quartz boat, and the heating rate can be controlled at 2–5℃ / min to ensure uniform heat transfer to each particle. This stage can be combined with slight airflow vibration or tray rotation to maintain good dispersion of the powder during heating and prevent localized agglomeration.

[0048] Subsequently, the temperature is gradually increased to 450–650℃, and diffusion heat treatment is performed within this range for 2–30 minutes. This allows the surface atoms of the iron nanoparticles to acquire sufficient migration energy, resulting in diffusion and rearrangement, and triggering surface structure reconstruction. During this process, the surface atoms of the iron nanoparticles migrate along the active sites and bending regions of the carbon nanotubes, gradually accumulating to form nanoscale anchoring nodes, thereby achieving a stable interfacial bond between the carbon nanotubes and the particles. A controlled atmosphere can be used during implementation, such as continuously introducing inert or reducing gases, to prevent oxidation of the iron nanoparticles. Simultaneously, by adjusting the gas flow rate and pressure, it is ensured that the atmosphere uniformly covers the powder surface during the heat treatment process. This diffusion heat treatment not only strengthens the interfacial bond between carbon nanotubes and iron nanoparticles but also provides a structural basis for the stability of the three-dimensional carbon nanotube network, the formation of cross-particle bridging, and the subsequent multi-scale synergistic strengthening of composite materials. It also effectively improves the compressibility and sintering density of the composite powder.

[0049] In S33, a precisely controlled gradient heating program is used during the heating process to gradually increase the powder temperature from the end temperature of the previous stage to 450–650°C, with the heating rate controlled at 1–5°C / min. This is to avoid excessive thermal stress that could lead to particle breakage or interface damage. During the heat treatment process, an inert gas (such as argon or nitrogen) or a reducing gas (such as hydrogen or a 5% hydrogen-nitrogen mixture) is continuously introduced. By adjusting the gas flow rate, pressure, and concentration, a uniform atmosphere is achieved to cover the powder surface, inhibiting the oxidation of iron nanoparticles while maintaining surface active sites. The structural defects, bending regions, and surface active sites of the carbon nanotubes formed during ball milling decoupling serve as preferential binding sites for iron nanoparticles, causing them to migrate along the outer wall of the carbon nanotubes and accumulate at the active sites, gradually forming nanoparticles. Meter-scale anchoring nodes are used to construct a stable interfacial bonding structure between carbon nanotubes and iron nanoparticles. To improve the migration activity of iron nanoparticles, the local chemical potential gradient can be altered by periodically adjusting the reducing gas concentration or using a pulsed gas input method, thereby enhancing atomic diffusion efficiency and promoting the formation and uniform distribution of interfacial anchoring nodes. During implementation, tray rotation, gas micro-vibration, or slight powder flow can be used to ensure uniform heating and exposure of powder particles, guaranteeing controlled coverage of the carbon nanotube outer wall and stability of the three-dimensional network structure between particles. This achieves stable bonding between the carbon nanotube outer wall and iron nanoparticles, while simultaneously forming nanoscale anchoring nodes, enhancing interfacial load transfer capacity, and providing a solid structural foundation for subsequent three-dimensional network stabilization, bridging formation, and multi-scale synergistic reinforcement of composite materials.

[0050] In S34, during the heat treatment process, the temperature of the composite powder is gradually increased by gradient heating. At the same time, under the protection of inert gas or reducing gas, the diffusion of atoms on the surface of iron nanoparticles is regulated, so that the iron nanoparticles migrate along the particle surface to the outer wall of the single-walled carbon nanotube. They preferentially accumulate at the structural defects, bending regions and surface active sites of the carbon nanotubes to form nanoscale anchoring nodes, thereby achieving a stable interfacial bond between carbon nanotubes and iron nanoparticles.

[0051] To further enhance the directionality of iron nanoparticle migration and the coating effect of carbon nanotubes, a constant or pulsed magnetic field can be applied during heat treatment, with the magnetic field strength controlled in the range of 0.05–0.5T. The magnetism of the iron nanoparticles causes them to align in an orientation, promoting their migration along the particle-carbon nanotube interface. At the same time, it induces some particles to form coating or semi-coating structures on the outer wall of the carbon nanotubes, thereby achieving spatial connectivity and stability of the three-dimensional carbon nanotube network between particles.

[0052] In practical implementation, a tubular or box-type heat treatment furnace with magnetic control function can be used. The composite powder is evenly spread in a tray or rotating hopper. By controlling the heating rate, holding time, and magnetic field strength, the iron nanoparticles achieve directional diffusion and anchoring under the combined action of temperature and magnetic force. Slight vibration or gas disturbance can be used to ensure uniform heating of the powder particles and avoid local agglomeration, thereby allowing the carbon nanotubes to extend along the interparticle gaps and form a tight bond with the particle surface, achieving the continuity and stability of the three-dimensional network.

[0053] Through the synergistic effect of magnetic field induction and atomic migration, iron nanoparticles and carbon nanotubes form a core-shell coating structure, while stabilizing the three-dimensional network of carbon nanotubes, thereby enhancing the interfacial bonding and improving the multi-scale synergistic strengthening performance of the composite material. This provides a solid structural foundation for subsequent pressing, sintering and final material properties.

[0054] In S35, after heat treatment, the three-dimensional carbon nanotube network is fixed through the nanoscale anchoring nodes formed by the aforementioned iron nanoparticles, stabilizing the distribution and spatial position of carbon nanotubes among the particles. Simultaneously, the binder remaining during ball milling undergoes pyrolysis at the heat treatment temperature, or trace amounts of carbon source gas (such as acetylene, carbon monoxide, or methane) are introduced during heat treatment to generate nano-carbon bridges in situ at the intersections of carbon nanotubes, enabling adjacent carbon nanotubes to be connected at these intersections, thereby further enhancing the overall connectivity and stability of the three-dimensional network. To ensure that the carbon nanotube network forms a continuous and stable spatial framework structure within the composite powder, vibration assistance or slight stirring can be applied to the composite powder during heat treatment. This optimizes the microscopic contact between particles, preventing local agglomeration and improving interfacial wettability. This promotes a more uniform and compact contact between iron nanoparticles and carbon nanotubes, thereby enhancing the mechanical interlocking effect and interfacial bonding strength between the carbon nanotubes and iron nanoparticles.

[0055] Specific implementation methods can employ tubular or box-type heat treatment furnaces with vibration or rotation functions. The composite powder is uniformly distributed in the hopper. By controlling the heating rate, holding time, and atmosphere flow rate, the binder is pyrolyzed and trace amounts of carbon source gas are deposited at the intersections of carbon nanotubes to form nano-carbon bridges. Simultaneously, vibration or local airflow disturbance is used to ensure uniform micro-gap between particles, balanced carbon nanotube extension and bridging effects, and to achieve the continuity and stability of the three-dimensional network structure. Through the combined effects of anchor node fixation, nano-carbon bridge bridging, and vibration-assisted wetting, the three-dimensional carbon nanotube network forms a stable, continuous, and load-bearing spatial skeleton structure within the composite powder, providing a solid structural foundation for subsequent powder pressing, sintering, and the final mechanical properties and multi-scale synergistic strengthening of the composite material.

[0056] In the preferred embodiment provided by the present invention, S4, the heat-treated composite powder is loaded into a mold for gradient cold pressing, the pre-pressing pressure is 200-400 MPa, the main pressing pressure is 400-800 MPa, and the pressure is held for 30-180 seconds to obtain a compact. S4 includes the following sub-steps: S41, the composite powder after ball milling is loaded into the mold cavity, and unidirectional cold pressing or bidirectional pressing is performed under inert atmosphere or dry environment conditions. The pressing pressure is 400-800MPa, and the pressure is held for 30-120 seconds, so that the iron nanoparticles make initial contact and arrangement and form a compact structure. At the same time, the carbon nanotubes distributed in the interparticle gaps are gradually oriented and extended to build an initial three-dimensional connection skeleton. S42. During the pressing process, iron nanoparticles undergo local slippage and rearrangement under external pressure, and the gaps between particles gradually shrink. Carbon nanotubes are pressed into the gaps between particles and extend along the particle contact path. At the same time, the binder forms a continuous flexible interface film under pressure and covers the particle surface and contact area, so that a multi-point contact structure is formed between carbon nanotubes, iron nanoparticles and interface film, thereby gradually building a stable three-dimensional skeleton connection relationship in the gaps between particles. S43. After pressing, the density, porosity and integrity of the carbon nanotube network of the compact are tested. When local pores or uneven network distribution are detected, supplementary pressing can be applied while the compact is still in the mold. The supplementary pressing pressure is 10% to 40% of the main pressing pressure and is maintained for 1 to 10 seconds to fill the local gaps and promote the redistribution of the carbon nanotube network. If necessary, vibration-assisted adjustment is combined to make the carbon nanotubes extend evenly along the interparticle gaps and form a stable three-dimensional reinforced network structure that penetrates the interparticle gaps.

[0057] Specifically, in step S41, to achieve stable pressing and molding of the composite powder, the ball-milled composite powder can first be molded under an inert atmosphere or a low-humidity drying environment. Specifically, a cylindrical or irregularly shaped mold made of stainless steel or hard alloy can be used. Before filling the mold, a thin layer of graphite lubricant or boron nitride release agent is sprayed onto the inner wall of the mold to reduce frictional resistance during pressing and prevent powder adhesion. Then, a vibrating feeding device or a leveling mechanism is used to uniformly fill the mold cavity with the composite powder, forming a uniformly deposited layer within the mold. After filling, a hydraulic press or a servo-electric press is used for unidirectional cold pressing or bidirectional pressing, gradually loading and maintaining a pressure range of 400–800 MPa for 30–120 seconds, causing the iron nanoparticles to contact and align under pressure, forming a continuous pressed structure. Simultaneously, during the pressing process, the single-walled carbon nanotubes distributed in the interparticle gaps gradually extend and orient themselves along the interparticle gaps under external force, thereby constructing an initial three-dimensional connecting framework between the particles.

[0058] In step S42, during the continuous loading of pressure, local sliding, rotation, and micro-rearrangement occur between the iron nanoparticles, gradually increasing the contact area between the particles and forming a more stable particle contact network. Simultaneously, carbon nanotubes distributed in the interparticle gaps are pressed into the gaps under pressure and extend along the particle contact path or pore channels, thus forming a continuous conductive path between multiple particles. If the composite powder contains a binder or its precursor component, this component will spread on the particle surface and contact area under pressure, gradually forming a continuous flexible interface film. This interface film can coat the iron nanoparticles and fill local microporous areas, creating a multi-point contact and interlocking structure between the carbon nanotubes, iron nanoparticles, and the interface film. Through this structural action, the carbon nanotubes can form a stable spatial support framework in the interparticle gaps, while simultaneously enhancing the interfacial bonding strength between the carbon nanotubes and metal particles, thereby gradually constructing a stable three-dimensional framework connection relationship within the compact.

[0059] In step S43, after the pressing process is completed, the quality of the compact structure can be evaluated through online or offline detection. Specifically, density measuring devices, porosity analysis equipment, or microscopic imaging equipment can be used to detect the overall density and internal pore distribution of the compact. Simultaneously, scanning electron microscopy or conductivity testing can be used to evaluate the uniformity and continuity of the carbon nanotube network distribution. When the detection results show localized pore concentration or uneven carbon nanotube network distribution, supplementary pressing can be applied while the compact is still in the mold. This involves reapplying pressure within the range of 10% to 40% of the original pressing pressure and holding it for 1 to 10 seconds to further compact the localized pore areas and promote particle rearrangement. If necessary, low-amplitude vibration or micro-impact can be superimposed during the supplementary pressing process to induce micro-flow of the composite powder within the mold, thereby promoting the redistribution of carbon nanotubes along the particle gaps and forming a more uniform and continuous network structure. Through the above-mentioned detection and pressure adjustment process, it can be ensured that the three-dimensional carbon nanotube reinforcement network is uniformly distributed inside the compact and stably penetrates the interparticle gaps, providing a stable structural basis for the formation of high-strength iron-based composite materials in the subsequent sintering process.

[0060] The process of dense arrangement of iron nanoparticles and construction of carbon nanotube network can be achieved in the compaction stage, so that carbon nanotubes form a three-dimensional connecting skeleton that runs through multiple particles in the interparticle gaps, while ensuring the continuous distribution of the interface bonding layer, thereby providing good initial microstructure conditions for interface diffusion and structural solidification in the subsequent sintering stage.

[0061] During the pressing process, the three-dimensional framework of carbon nanotubes and the interface of iron nanoparticles form an interlocking and fixed structure through a flexible film and micro-rearrangement. After the compact is completed, the density, porosity, and integrity of the carbon nanotube network can be tested. Based on the test results, the short-term repressing pressure, duration, or vibration parameters can be further adjusted to achieve a uniform and stable distribution of the three-dimensional network inside the compact.

[0062] In the preferred embodiment of the present invention, S5, the compact is subjected to staged sintering under a reducing atmosphere or an inert atmosphere. Under the condition that the temperature is gradually raised to 900-1350℃ and the total sintering time is controlled to be 40-240 min, the iron nanoparticles form initial diffusion connections and interparticle diffusion necks, thereby achieving material densification and matrix reconstruction. At the same time, some carbon elements in the single-walled carbon nanotubes diffuse into the iron matrix in a limited manner to form an iron-carbon solid solution and retain the carbon nanotube reinforcement structure. The sintering gas dew point is controlled below -40℃, resulting in an iron-based composite material with an internal continuous iron matrix, a three-dimensional carbon nanotube reinforcement network, and a multi-scale synergistic reinforcement structure of carbon nanotube-coated iron nanoparticles.

[0063] S5 includes the following sub-steps: S51, Place the compact in the sintering furnace and introduce inert gas or reducing gas to form a stable protective environment so that the surface of the iron nanoparticles remains in a reduced or inert state during the heating process. The dew point of the sintering gas is controlled below -40℃. Pulsed reducing gas input or gas flow rate fluctuation can be used in the gas to achieve local interface activity regulation. S52. Using a gradient heating method, the temperature is first slowly increased to 900-1100℃ and held for 10-60 minutes to allow the iron nanoparticles to form preliminary diffusion connections and diffusion necks between particles, thus achieving preliminary densification of the material. During this process, the residual flexible binder film provides wetting and microflow on the particle surface, assisting the iron nanoparticles to migrate along the carbon nanotube surface, providing an active interface for the formation of nanoscale anchoring nodes, while maintaining the integrity of the three-dimensional network of carbon nanotubes and the interlocking structure of the interface. S53. Continue heating to 1100-1350℃ and control the total sintering time to 40-240 minutes to further densify and reconstruct the iron matrix, reduce the interparticle voids to form a continuous matrix structure, and allow the carbon elements in some single-walled carbon nanotubes to diffuse in a limited manner under the catalysis of iron nanoparticles to form an iron-carbon solid solution. At the same time, the three-dimensional carbon nanotube reinforcement network is retained, and the residual flexible binder film assists the three-dimensional carbon nanotube network to extend, interlock and fix in the matrix. S54. During the high-temperature densification stage, carbon nanotubes and iron nanoparticles form a stable interface bond through nanoscale anchoring nodes. The three-dimensional carbon nanotube network is fixed inside the iron matrix, forming a reinforcing network that penetrates the interparticle gaps. The residual flexible binder film works synergistically with the nanoscale anchoring nodes to achieve microscopic interlocking of the interface and structural stability, forming a multi-scale synergistic strengthening structure of a continuous iron matrix, a three-dimensional carbon nanotube reinforcing network, and carbon nanotube-coated iron nanoparticles.

[0064] S54 includes the following steps: In the high-temperature densification stage, through a graded heating and heat preservation strategy, and by continuously supplying an inert or reducing atmosphere, a dynamic core-shell structure is formed on the surface of iron nanoparticles. The core-shell layer undergoes microscopic atomic rearrangement with temperature control. At the same time, the three-dimensional network of carbon nanotubes extends uniformly in the interparticle gaps and gradually solidifies. The iron nanoparticles migrate directionally along the surface of carbon nanotubes by precisely controlling the temperature gradient, preferentially forming nanoscale anchoring nodes at structural defects and active sites. Local self-assembly is driven by the difference in interfacial energy, further stabilizing the coupling between the core-shell structure and the three-dimensional network. S542. The residual flexible binder film is synergistically integrated with the nanoscale anchoring nodes under the action of interfacial wetting to achieve microscopic interlocking between carbon nanotubes and iron nanoparticles. During the sintering process, the network microstructure and interfacial wetting are adjusted synchronously through periodic pulse atmosphere or micro-vibration, which promotes the adaptive rearrangement and uniform distribution of carbon nanotubes. Reversible microflow is formed at the interface through the wetting film, realizing local self-repair of the interface.

[0065] S543. By controlling the heating rate gradient, holding time, and atmosphere composition, iron nanoparticles migrate along the surface of carbon nanotubes to the active sites, forming a continuous enrichment layer. At the same time, the residual flexible film forms microflow at the interface, promoting the microscopic synergy of the core-shell structure, nano-anchoring nodes, and carbon nanotube three-dimensional network. By utilizing the interfacial energy difference and atomic migration dynamics, the dual optimization of macroscopic framework continuity and microscopic interlocking is achieved, ensuring the stable existence of the three-dimensional reinforcement network at high temperatures. S544. The iron matrix is ​​continuously densified, and the three-dimensional carbon nanotube network is fixed in the interparticle gaps. The core-shell structure and the interface anchoring nodes work together to ensure that the nanostructure of the carbon nanotube-coated iron nanoparticles is complete. Through the synergistic effect of atomic directional migration, interface self-assembly and flexible film wetting, a multi-scale synergistic reinforcement structure of iron-based continuous matrix, three-dimensional carbon nanotube reinforcement network and carbon nanotube-coated iron nanoparticles is achieved.

[0066] S5. The compact is subjected to staged sintering under a reducing or inert atmosphere. The temperature is gradually increased to 900–1350℃, and the total sintering time is controlled to be 40–240 min. This allows the iron nanoparticles to form initial diffusion connections and interparticle diffusion necks, achieving material densification and matrix reconstruction. Simultaneously, carbon elements from some single-walled carbon nanotubes diffuse into the iron matrix in a limited manner, forming an iron-carbon solid solution while retaining the carbon nanotube reinforcement structure. The sintering gas dew point is controlled below -40℃, resulting in an iron-based composite material with an internal continuous iron matrix, a three-dimensional carbon nanotube reinforcement network, and a multi-scale synergistic reinforcement structure of carbon nanotube-coated iron nanoparticles. S51. Place the pressed compact in a sintering furnace and introduce inert or reducing gas to create a stable protective environment. This ensures that the surface of the iron nanoparticles remains in a reduced or inert state during the heating process, and the dew point of the sintering gas is controlled below -40°C. For atmosphere control, pulsed reducing gas input or gas flow rate fluctuation regulation can be used to precisely adjust the local interfacial activity while preventing oxide formation. Technical methods include using tubular, box-type, or high-temperature vacuum furnaces equipped with high-precision gas flow controllers and dew point monitoring systems to achieve real-time atmosphere feedback and adjustment. These measures ensure that the surface of the iron nanoparticles remains active, providing conditions for the formation of stable anchoring nodes for carbon nanotubes. S52. Using a gradient heating method, the temperature is slowly increased to 900–1100℃ and maintained for 10–60 minutes to allow preliminary diffusion connections and diffusion necks to form between iron nanoparticles, achieving initial densification of the material. During this process, the residual flexible binder film provides wetting and microflow on the particle surface, assisting the migration of iron nanoparticles along the carbon nanotube surface, providing an active interface for the formation of nanoscale anchoring nodes, while maintaining the integrity of the three-dimensional carbon nanotube network and the interlocking structure of the interface.

[0067] The technical means to achieve this can be through high-precision tubular or box-type vacuum / protective atmosphere heat treatment furnaces with zoned heating capabilities, allowing for controllable temperature gradients at different locations within the furnace. This ensures the uniformity and controllability of atomic migration and diffusion processes on the surface of iron nanoparticles. The furnace can be equipped with high-precision thermocouples or infrared temperature sensors for real-time monitoring, and these sensors are linked in a closed-loop control system to achieve precise regulation of the heating rate, temperature gradient, and holding time.

[0068] In terms of atmosphere control, inert gases (such as argon and nitrogen) or reducing gases (such as hydrogen or a 5% hydrogen-nitrogen mixture) are introduced into the furnace. The gas flow rate can be controlled by a precision flow meter and can be combined with pulse input or fluctuation adjustment to maintain local interfacial activity, avoid oxidation of the iron nanoparticle surface, and promote preferential bonding between carbon nanotubes and iron nanoparticles through interfacial energy difference.

[0069] In terms of material micro-control, the residual flexible binder softens or partially decomposes during heating to form an interfacial film, achieving wetting and microflow. This allows iron nanoparticles to migrate along the outer wall of carbon nanotubes, preferentially accumulating in the bending regions, defects, and active sites of the carbon nanotubes, forming nanoscale anchoring nodes. To ensure the integrity of the three-dimensional carbon nanotube network, intermittent vibration, rotation, or slight agitation can be used to help rearrange and interlock the carbon nanotubes along the interparticle gaps, while preventing local aggregation or breakage.

[0070] Under the synergistic effect of macroscopic temperature gradient and microscopic interface wetting, preliminary diffusion connections and interparticle diffusion necks can be formed between iron nanoparticles, achieving preliminary densification of the material. At the same time, the formation of nanoscale anchoring nodes and the integrity of the three-dimensional carbon nanotube network and the interfacial interlocking structure are ensured, providing a foundation for subsequent high-temperature sintering and final strengthening of the material.

[0071] S53. Continue heating to 1100–1350℃ and control the total sintering time to 40–240 minutes to further densify and reconstruct the iron matrix, reducing interparticle porosity and forming a continuous matrix structure. This allows carbon elements in some single-walled carbon nanotubes to diffuse in a limited manner under the catalysis of iron nanoparticles, forming an iron-carbon solid solution, while retaining the three-dimensional carbon nanotube reinforcing network. The residual flexible binder film assists in the extension, interlocking, and fixation of the three-dimensional carbon nanotube network within the matrix. Specific technical means include using a high-precision box-type or tubular vacuum / protective atmosphere sintering furnace. The furnace body should have zoned heating function and controllable temperature gradient capability. The furnace temperature should be monitored in a closed loop using high-precision thermocouples or infrared sensors to achieve precise control of the heating rate, holding time, and total sintering time, thereby ensuring the densification of iron nanoparticles and the stability of the three-dimensional carbon nanotube network.

[0072] In terms of temperature gradient and micro-control, iron nanoparticles can migrate along the outer wall of carbon nanotubes to active sites through a step-by-step heating and gradient heat preservation strategy, forming nanoscale anchoring nodes. At the same time, carbon in some single-walled carbon nanotubes diffuses in a limited manner under the catalysis of iron nanoparticles to form an iron-carbon solid solution, ensuring that the carbon nanotube reinforcement network extends, interlocks and is fixed inside the matrix.

[0073] In terms of interface wetting and microflow, the residual flexible binder film softens at high temperature or generates a flexible interface film in situ with trace carbon source gas, which allows carbon nanotubes to rearrange and interlock along the surface of iron nanoparticles, while filling the micropores between particles, thus achieving the continuity and stability of the network.

[0074] In addition, a vibration table or acoustic excitation-assisted sintering can be used to fine-tune the particle position at high temperature, so that the micro-displacement of iron nanoparticles and the three-dimensional network of carbon nanotubes can be coordinated to further enhance the interfacial interlocking and structural uniformity, thereby forming a multi-scale synergistic strengthening structure of iron-based continuous dense matrix, three-dimensional carbon nanotube reinforcing network and carbon nanotube-coated iron nanoparticles.

[0075] S54. During the high-temperature densification stage, carbon nanotubes and iron nanoparticles form a stable interface bond through nanoscale anchoring nodes. The three-dimensional carbon nanotube network is fixed inside the iron matrix, forming a reinforcing network that penetrates the interparticle gaps. The residual flexible binder film works synergistically with the nanoscale anchoring nodes to achieve microscopic interlocking of the interface and structural stability, forming a multi-scale synergistic strengthening structure of a continuous iron matrix, a three-dimensional carbon nanotube reinforcing network, and carbon nanotube-coated iron nanoparticles.

[0076] S541. During the high-temperature densification stage, a dynamic core-shell structure is formed on the surface of iron nanoparticles through a graded heating and holding strategy, with a continuous supply of inert or reducing atmosphere. The core-shell layer undergoes microscopic atomic rearrangement with temperature control, while the three-dimensional carbon nanotube network extends uniformly and gradually solidifies between particles. The directional migration of iron nanoparticles along the carbon nanotube surface is precisely controlled by the temperature gradient, preferentially forming nanoscale anchoring nodes at structural defects and active sites. The technical means to achieve this is that, during the high-temperature densification stage, a graded heating and holding strategy can be implemented using a precision tubular or box-type heat treatment furnace. This allows the composite powder to gradually release residual stress from ball milling during the heating process, while simultaneously controlling the temperature gradient to regulate the migration behavior of atoms on the surface of the iron nanoparticles. Before heat treatment, an inert gas (such as argon or nitrogen) or a reducing gas (such as hydrogen or a 5% hydrogen-nitrogen mixture) is introduced to create a protective environment, inhibiting oxidation of the iron nanoparticle surface and maintaining interfacial activity, providing active sites for the stable bonding between carbon nanotubes and iron nanoparticles. The furnace body can be heated in zones and is equipped with high-precision thermocouples and a closed-loop temperature control system to achieve precise monitoring and adjustment of local temperature. This ensures that iron nanoparticles migrate directionally along the surface of carbon nanotubes to defect or curved areas and preferentially accumulate at structurally active sites to form nanoscale anchoring nodes.

[0077] During heat treatment, interfacial self-assembly and activity regulation can be achieved through pulsed atmosphere control. The atmosphere control system includes a high-precision flow meter, a fast-switching valve, and a controller. It can periodically adjust the flow rate and pulse width of inert gas or reducing gas according to a preset program, thereby forming local reduction or activation regions on the surface of iron nanoparticles. This promotes the migration of iron nanoparticles and the extension of carbon nanotubes along the interparticle gaps, achieving stable three-dimensional network interlocking. The micro-vibration auxiliary device can apply vibrations with adjustable frequency and amplitude outside the furnace or under the powder tray. Through micro-displacement and shearing action, it reduces local agglomeration, allowing the carbon nanotube network to extend and cross-link uniformly between particles, while enhancing the mechanical interlocking of the carbon nanotube and iron nanoparticle interfaces.

[0078] Furthermore, the softening and in-situ decomposition of residual binder or trace carbon source gas at high temperatures can form a flexible interfacial wetting film that covers the surface of iron nanoparticles and carbon nanotubes, generating local microflow and adaptive rearrangement effects. This allows the three-dimensional carbon nanotube network to gradually solidify and form continuous connections between the core and shell structures. Combining staged heating, gradient temperature control, pulsed atmosphere, micro-vibration, and the wetting effect of the flexible film, the carbon nanotubes in the composite powder can extend and be fixed along the interparticle gaps to form a stable three-dimensional reinforcing network. At the same time, the core-shell structure and nano-anchoring nodes work together to achieve a multi-scale synergistic strengthening structure, providing a solid microscopic foundation for subsequent pressing, sintering, and the final material properties.

[0079] S542. The residual flexible binder film, under interfacial wetting, synergizes with nanoscale anchoring nodes to achieve microscopic interlocking between carbon nanotubes and iron nanoparticles. During sintering, periodic pulsed atmosphere or micro-vibration adjustment optimizes the network microstructure and interfacial wetting, promoting adaptive rearrangement and uniform distribution of carbon nanotubes. Technical means include using tubular or box-type heat treatment systems to perform gradient heating and staged thermal activation on the ball-milled composite powder. Before heat treatment, an inert or reducing gas is introduced to create a protective environment, ensuring that the active sites on the iron nanoparticle surface remain in a reduced or inert state during heating, inhibiting surface oxidation, and providing an active interface for subsequent bonding between carbon nanotubes and iron nanoparticles. The heat treatment furnace can employ zoned heating control, combined with high-precision thermocouples and local temperature sensors, to achieve gradient heating and closed-loop regulation, ensuring that iron nanoparticles migrate directionally along the carbon nanotube surface towards defects and active sites, thereby forming stable nanoscale anchoring nodes.

[0080] During heat treatment, the surface activity, redox state, and wettability of carbon nanotubes can be dynamically controlled by periodically pulsed atmosphere. The atmosphere control unit includes an inert gas or reducing gas storage device, an electronic mass flow meter, and a fast-switching valve. The gas on / off cycle, flow rate, and pulse width can be set to achieve precise adjustment of local interfacial activity and atomic migration rate. Through pulsed atmosphere input, iron nanoparticles preferentially migrate along the carbon nanotube surface towards defects and active sites, while simultaneously inducing the formation of preferential bonding sites along the interparticle gaps, achieving interfacial self-assembly.

[0081] The micro-vibration auxiliary device can install a vibration table or piezoelectric vibrator on the furnace shell. By adjusting the frequency and amplitude, the powder is subjected to micro-displacement and shearing at high temperatures. This promotes the rearrangement, extension, cross-linking, and formation of a three-dimensional network of carbon nanotubes along the interparticle gaps, while reducing local agglomeration and stress concentration. During this process, residual binder or trace amounts of carbon source gas form a flexible wetting film in situ at the carbon nanotube intersections, enabling interfacial micro-flow and adaptive rearrangement. This stabilizes the interfacial interlocking between the three-dimensional carbon nanotube framework and the iron nanoparticles, and provides support for the formation of the core-shell anchoring structure.

[0082] By monitoring the microscopic dispersion state of the composite powder using optical or electrical sensors, and combining pulsed atmosphere, gradient temperature control, and micro-vibration assistance, closed-loop control of the heat treatment process is achieved. This ensures that the three-dimensional carbon nanotube network extends uniformly and is stably interlocked within the iron matrix, forming a core-shell structure of carbon nanotubes coating iron nanoparticles. Simultaneously, it achieves multi-scale interface interlocking and a continuous three-dimensional reinforcing framework, providing a stable microstructural foundation for subsequent pressing and sintering.

[0083] S543. By controlling the heating rate gradient, holding time, and atmosphere composition, iron nanoparticles migrate along the surface of carbon nanotubes to active sites, forming a continuous enrichment layer. Simultaneously, the residual flexible film creates microflow at the interface, promoting microscopic synergy between the core-shell structure, nano-anchoring nodes, and the three-dimensional network of carbon nanotubes. The technical means include precisely controlling the heating rate gradient, holding time, and protective atmosphere composition during the high-temperature densification stage to induce the migration of iron nanoparticle surface atoms along the outer wall of the carbon nanotubes to structural defects and active sites. In this process, graded heating and temperature gradient control ensure that the migration rate of iron nanoparticles is controllable, preferentially enriching them in the bending regions of the carbon nanotubes, tube wall defects, or active sites formed during ball milling, gradually forming a continuous enrichment layer. This constructs nanoscale anchoring nodes at the interface between the carbon nanotubes and iron nanoparticles, achieving a stable bond between the particle surface and the carbon nanotubes.

[0084] Simultaneously, under high-temperature conditions, residual binders or trace amounts of carbon source gas soften, pyrolyze, or generate flexible films in situ, leading to localized microflows at the interface. These microflows promote microscopic synergy between the core-shell structure, nano-anchored nodes, and the three-dimensional carbon nanotube network, enabling carbon nanotubes to rearrange, cross-link, and interlock along particle gaps, further enhancing network continuity and stability. Precise control of the atmosphere flow rate, pulsed gas input, and adjustable vibration assistance ensure uniform distribution of interfacial activity and achieve uniformity and integrity of the carbon nanotube network at the microscale.

[0085] It can achieve dual optimization between macroscopic framework continuity and microscopic interface interlocking. The nano-anchoring nodes formed by the directional migration of iron nanoparticles, the wetting effect of flexible films, and the interface self-assembly effect work together to ensure the stable existence of the three-dimensional carbon nanotube reinforcement network during high-temperature sintering, while maintaining the strong interfacial bonding between carbon nanotubes and iron nanoparticles, providing a reliable guarantee for the formation of multi-scale synergistic reinforcement structure.

[0086] S544. The iron matrix achieves continuous densification, and the three-dimensional carbon nanotube network is fixed in the interparticle gaps. The core-shell structure and interface anchoring nodes work together to ensure the integrity of the nanostructure of carbon nanotube-coated iron nanoparticles. Through the synergistic effects of atomic directional migration, interface self-assembly, and flexible film wetting, a multi-scale synergistic reinforcement structure is achieved, consisting of a continuous iron matrix, a three-dimensional carbon nanotube reinforcing network, and carbon nanotube-coated iron nanoparticles. Specific technical means include: achieving nanoscale anchoring nodes through atomic directional migration, which can be achieved by using graded heating and gradient temperature control to allow iron nanoparticles to migrate along the surface of carbon nanotubes towards structural defects and active sites. At the same time, the temperature accuracy is monitored in a closed loop by a local temperature sensor to ensure the controllability of the migration path of iron nanoparticles; interface self-assembly can be achieved by precisely controlling the flow rate and pulse input of inert or reducing atmosphere during sintering, so that the atoms on the surface of carbon nanotubes and iron nanoparticles spontaneously arrange themselves to form preferential binding sites driven by the micro-interfacial energy difference. At the same time, adjustable gas flow rate or micro-vibration is used to help maintain interfacial activity and network uniformity; flexible film wetting effect can be achieved by softening residual binder at high temperature or generating a flexible film in situ with trace amounts of carbon source gas, realizing local micro-flow at the interface, allowing carbon nanotubes to rearrange and interlock along the particle surface, while ensuring network continuity and the stability of the three-dimensional skeleton.

[0087] In specific operations, high-precision tubular or box-type heat treatment furnaces can be used to achieve zoned heating and temperature gradient control. Combined with a high-precision gas flow control system and pulsed atmosphere conditioning, along with a vibration table or acoustic exciter, the uniform distribution and stable interlocking of micro-interface activity and carbon nanotube three-dimensional network can be ensured. At the same time, the atomic migration rate can be finely adjusted by using heat treatment temperature, atmosphere composition and heating rate to achieve synergistic optimization of nanoscale anchoring nodes, interface self-assembly and flexible film wetting effect.

[0088] The present invention provides a single-walled carbon nanotube composite material for powder metallurgy, comprising: a metal matrix: a continuous metal matrix structure formed by pressing and sintering iron nanoparticles together; Single-walled carbon nanotubes: distributed in the interparticle spaces between adjacent iron nanoparticles and extending along the interparticle spaces, forming a three-dimensional interconnection network structure that runs through multiple iron nanoparticles within the volume space of the composite material defined by the continuous metal matrix structure formed by the sintering of iron nanoparticles, so that the network is connected between adjacent iron nanoparticles through at least one single-walled carbon nanotube connection path. Interface bonding layer: formed by binder or its heat treatment conversion product, and continuously distributed on the particle surface and particle contact area of ​​iron nanoparticles, with a thickness of 10nm to 500nm.

[0089] A stable interface bond is formed between single-walled carbon nanotubes and iron nanoparticles through nanoscale anchoring nodes. These nanoscale anchoring nodes are distributed along the particle contact area and the structural defects of the carbon nanotubes, enabling the carbon nanotubes to form a uniformly extended three-dimensional interconnection network within the interparticle gaps. At the same time, a flexible film in the interface bonding layer covers the surface of the iron nanoparticles and the interparticle gaps, forming carbon bridges or micro-interlocking structures at the network intersections. This enhances the interfacial bonding strength between the carbon nanotubes and the metal matrix and maintains the stability of the three-dimensional network.

[0090] Specifically, the composite material consists of a metal matrix, single-walled carbon nanotubes distributed within the metal matrix, and an interfacial bonding layer. The metal matrix is ​​formed by pressing and high-temperature sintering iron nanoparticles to create a continuous and dense metal structure. During sintering, the iron nanoparticles bond with each other through diffusion necks and atomic migration, forming a stable three-dimensional continuous matrix that provides the composite material with mechanical load-bearing capacity and thermal and electrical conductivity channels.

[0091] Single-walled carbon nanotubes are distributed within the interparticle spaces between adjacent iron nanoparticles and extend along these spaces, forming a three-dimensional interconnected network structure that runs through multiple iron nanoparticles. During fabrication, the mechanical shearing and impaction effects of ball milling decouple the carbon nanotubes from an aggregated state to a single or bundled state, ensuring their uniform distribution on the surface and between the iron nanoparticles, thus providing the structural basis for the three-dimensional network formation. Subsequently, heat treatment induces atomic diffusion and structural reconstruction on the surface of the iron nanoparticles, forming nanoscale anchoring nodes on the outer wall of the carbon nanotubes. This establishes a stable interfacial bonding structure between the carbon nanotubes and the iron nanoparticles, further solidifying the three-dimensional network.

[0092] The interfacial bonding layer, formed by a binder or its heat-treated conversion product, is continuously distributed on the surface and contact area of ​​the iron nanoparticles, with its thickness controlled within the range of 10 nm to 500 nm. At high temperatures, the interfacial bonding layer softens through the binder and generates a flexible film in situ using a trace amount of carbon source gas. This achieves surface wetting and microflow of the iron nanoparticles, causing carbon nanotubes to rearrange, interlock, and fill the interparticle gaps along the particle surface. Carbon bridges or micro-interlocking structures are formed at network intersections, enhancing the interfacial bonding strength and maintaining the stability of the three-dimensional network.

[0093] Nanoscale anchoring nodes are distributed along the particle contact area and structural defects of carbon nanotubes. They are formed through the directional migration of iron nanoparticles and the interface self-assembly effect during heat treatment. This effectively fixes carbon nanotubes to the particle surface and interparticle gaps, allowing the three-dimensional network to extend uniformly and interlock within the metal matrix. This fully realizes the reinforcing effect of carbon nanotubes while ensuring the structural stability of the composite material during high-temperature pressing and use.

[0094] In practical implementation, a high-precision vacuum or protective atmosphere sintering furnace can be used. Through zoned heating and temperature gradient control, the densification of iron nanoparticles, the formation of carbon nanotube anchoring nodes, and the stabilization of the interfacial bonding layer can be achieved. An inert gas or reducing gas can be used, and interfacial activity can be maintained through pulsed gas input or flow rate regulation. If necessary, vibration-assisted or acoustic excitation can be combined to synchronize powder micro-rearrangement with network adaptive rearrangement, thereby obtaining powder metallurgy composite materials with uniform three-dimensional network distribution, stable interfacial interlocking, and excellent mechanical properties.

[0095] The exhaust gas-derived single-walled carbon nanotube composite powder used in the following examples all comes from the exhaust gas bag collection system of the carbon nanotube production line, and its main components are nano-iron and single-walled carbon nanotubes.

[0096] Example 1 20 g of tail gas-derived single-walled carbon nanotube composite powder with an iron content of approximately 80 wt% (the remainder being single-walled carbon nanotubes and a small amount of amorphous carbon) was placed in 200 mL of acetone and ultrasonically dispersed for 2 hours. Subsequently, it was dried in a vacuum drying oven at 80 °C for 12 hours to obtain a pretreated powder. The pretreated powder was placed in the grinding jar of a dual-drive planetary ball mill, protected with high-purity argon gas, and stainless steel grinding balls were added at a ball-to-material ratio of 10:1. The milling was performed at 350 rpm for 25 minutes. After milling, the powder was loaded into a cylindrical mold with a diameter of 20 mm and unidirectionally cold-pressed under a pressure of 600 MPa for 60 seconds to obtain a compact. The compact was then placed in a tubular sintering furnace, and flowing hydrogen gas with a dew point <-50 °C was introduced. The temperature was increased to 1250 °C at a rate of 5 °C / min and held for 2 hours, then cooled to room temperature with the furnace.

[0097] Example 2 Same as Example 1, but the ball milling time is extended to 40 minutes, and the remaining steps and parameters are completely identical.

[0098] Example 3 Same as Example 1, but the sintering temperature was adjusted to 1150°C, while the remaining steps and parameters remained unchanged.

[0099] Example 4 In the pretreated powder obtained in step S1 of Example 1, ordinary reduced iron powder with a particle size of about 5 μm was added to increase the total iron content of the mixed powder to about 90 wt% (single-walled carbon nanotubes and carbon phase about 10 wt%). Then, the powder was ball-milled, pressed and sintered according to steps S2-S4 of Example 1.

[0100] Comparative Example 1 (Conventional Iron-Based Materials) Instead of using exhaust gas-derived powder, pure iron powder with an iron content equivalent to that of Example 1 was used directly, with a small amount of pure graphite powder added to simulate carbon content. Traditional iron-graphite materials were prepared using the same ball milling, pressing, and sintering processes as in Example 1.

[0101] Comparative Example 2 (High-purity single-walled carbon nanotubes added as a control) High-purity single-walled carbon nanotubes (iron content <5wt%) were mechanically mixed with pure iron powder to achieve a final composite powder with a single-walled carbon nanotube mass fraction comparable to that of Example 1. After processing according to steps S2-S4 of Example 1, severe powder agglomeration was observed, making pressing difficult. The sintered sample exhibited extremely low strength, rendering effective mechanical testing impossible.

[0102] Comparative Example 3 (No pretreatment / ball milling control) The same exhaust gas-derived powder as in Example 1 was used, but pretreatment and ball milling were skipped, and the powder was directly pressed and sintered (parameters same as in Example 1). The resulting sample was porous and had extremely poor mechanical properties.

[0103] Performance Testing and Analysis All samples are tested for performance according to recognized international standards (ASTM, ISO), including indicators such as hardness, strength and abrasion resistance, to ensure that the results are comparable and repeatable.

[0104] The test results and analysis are as follows: Method effectiveness: The materials prepared in Examples 1-4 are significantly better than those in Comparative Example 1 in terms of hardness, strength and wear resistance, which fully demonstrates that the method of the present invention can convert exhaust gas-derived powder into high-performance iron-based composite materials.

[0105] Key aspects of the process: Comparing Example 1 with Comparative Examples 2 and 3, it is evident that "pretreatment + ball milling" is the core step in ensuring the dispersion of single-walled carbon nanotubes, establishing a stable interface, and forming a three-dimensional network. Without this step (Comparative Example 3) or by simply mixing high-purity single-walled carbon nanotubes (Comparative Example 2), effective materials cannot be obtained, thus verifying the originality of the process design in this invention.

[0106] Performance controllability: By adjusting the total iron content (Example 4) or ball milling / sintering parameters (Examples 2 and 3), the mechanical, electrical conductivity, and wear resistance properties of the material can be controlled within a certain range to meet different application requirements.

[0107] Testing Standardization and Repeatability: All performance tests are performed in accordance with standards to ensure accurate and reliable data, providing support for the feasibility and industrial application of patented technologies.

[0108] Economic and environmental value: This invention uses exhaust gas recovery powder as raw material, avoiding the high cost and high energy consumption purification process of high-purity single-walled carbon nanotubes, and realizes the transformation of "waste" into high-performance materials, which has significant economic benefits and environmental value.

[0109] In summary, this invention provides an innovative route for efficiently converting exhaust gas-derived high-iron-content single-walled carbon nanotube powder into high-performance iron-based composite materials. The process is feasible, the material properties are excellent, and it has broad prospects for industrial application.

[0110] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a single-walled carbon nanotube composite material for powder metallurgy, characterized in that, The method includes the following steps: S1, adding tail gas-derived single-walled carbon nanotube composite powder with an iron mass content of 60% to 95% to an organic solvent for ultrasonic dispersion for 0.5 to 4 hours, while adding a complexing activator to selectively dissolve the oxide layer on the surface of the iron nanoparticles and improve its activity, and drying to obtain interface-activated composite powder. S2. The composite powder is mechanically ball-milled under an inert atmosphere, and a binder is added at a content of 0.1 to 3 wt% of the total composite powder mass. By controlling the ball milling energy and ball-to-powder ratio, the bundled single-walled carbon nanotubes are decoupled and embedded on the surface and gaps of the iron nanoparticles, while a three-dimensional carbon nanotube network is formed inside the composite powder. S3. The ball-milled composite powder is subjected to heat treatment in an inert or reducing atmosphere for 2 to 60 minutes at a temperature of 300 to 650°C to cause diffusion and structural reconstruction on the surface of the iron nanoparticles in the composite powder, and to form anchoring nodes on the outer wall of the single-walled carbon nanotubes, thus forming a core-shell composite structure of carbon nanotubes covering iron nanoparticles and stabilizing the three-dimensional network. S4. Load the heat-treated composite powder into the mold and perform gradient cold pressing. The pre-pressing pressure is 200-400MPa, the main pressing pressure is 400-800MPa, and the pressure is held for 30-180 seconds to obtain the compact. S5. The compact is subjected to staged sintering under a reducing or inert atmosphere. Under the condition that the temperature is gradually increased to 900-1350℃ and the total sintering time is controlled to be 40-240min, the iron nanoparticles form initial diffusion connections and interparticle diffusion necks, thereby achieving material densification and matrix reconstruction. At the same time, some carbon elements in the single-walled carbon nanotubes diffuse into the iron matrix in a limited manner to form an iron-carbon solid solution and retain the carbon nanotube reinforcement structure. The sintering gas dew point is controlled below -40℃ to obtain an iron-based composite material with an internal continuous iron matrix, a three-dimensional carbon nanotube reinforcement network, and a multi-scale synergistic reinforcement structure of carbon nanotube-coated iron nanoparticles.

2. The method for preparing a single-walled carbon nanotube composite material for powder metallurgy according to claim 1, characterized in that, S1 includes the following steps: S11, adding tail gas-derived single-walled carbon nanotube composite powder with an iron mass content of 60% to 95% to an organic solvent for uniform dispersion, and stirring to initially disperse the composite powder in the solvent to form a suspension. S12. The obtained suspension is subjected to ultrasonic treatment for 0.5 to 4 hours to induce micro-cavitation and shearing in the bundled single-walled carbon nanotubes in the liquid, gradually separating them from the aggregated state, increasing the surface area of ​​the carbon nanotubes, and improving their uniform distribution on the surface of iron nanoparticles. S13. During the ultrasonic dispersion process, a complexing activator is added to selectively dissolve the oxide layer on the surface of iron nanoparticles and form active sites, thereby improving the surface reactivity of iron nanoparticles and their interfacial bonding ability with carbon nanotubes. S14. After ultrasonic treatment and activation, the composite powder particles can be further dispersed in the suspension by stirring or static sedimentation to reduce local agglomeration and make single-walled carbon nanotubes uniformly embedded on the surface of iron nanoparticles and between particles. S15. Remove moisture and solvent from the uniformly dispersed suspension by vacuum drying, spray drying or oven drying, and control the drying temperature within 60-120℃ to obtain interface-activated composite powder, thereby enhancing the surface activity of the composite powder.

3. A method for preparing a single-walled carbon nanotube composite material for powder metallurgy according to claim 1 or 2, characterized in that, The complexing activator includes citric acid, oxalic acid, acetic acid, tartaric acid, ethylenediaminetetraacetic acid, ethylenediamine, triethanolamine, or aniline.

4. The method for preparing a single-walled carbon nanotube composite material for powder metallurgy according to claim 1, characterized in that, S2 includes the following sub-steps: S21, placing the interface-activated composite powder in a ball mill container, injecting inert gas or reducing gas to form a protective environment, ensuring that the composite powder does not come into contact with air during the ball milling process, and ensuring the chemical stability of the binder; S22. By adjusting the ball milling speed to 200-400 rpm, the ball-to-material ratio to 5-20:1, and the ball milling time to 10-60 minutes, the composite powder is subjected to mechanical shearing and impact, causing the bundled single-walled carbon nanotubes to gradually disintegrate and form single or few bundles, thus realizing the transformation of carbon nanotubes from an aggregated state to a dispersed state, providing a basis for the construction of three-dimensional networks. S23. During the ball milling process, a binder is added, the content of which is controlled at 0.1 to 3 wt% of the total composite powder mass. Under the mechanical shearing and impact of the ball milling, the binder is evenly distributed and forms a continuous flexible interface film on the surface of the iron nanoparticles and between the particles. The flexible interface film covers the particle surface and wets the carbon nanotubes, realizing the initial mechanical interlocking and interface bonding between the carbon nanotubes and the iron nanoparticles. At the same time, it provides support and guidance for the carbon nanotubes to form a three-dimensional network inside the composite powder. S24. Under the action of the flexible interface film, the single-walled carbon nanotubes extend along the gap between particles and gradually form a three-dimensional network that runs through the composite powder. By controlling the filling density of the composite powder, the particle size distribution and the pressing or vibration-assisted measures, a reasonable gap between particles is maintained, providing space for the carbon nanotube network to extend, cross-link and distribute evenly. At the same time, the flexible interface film further stabilizes the combination of carbon nanotubes and particles, realizing the continuity and stability of the three-dimensional network structure. S25. After ball milling, the particle size and dispersibility of the composite powder are tested. Laser diffraction particle size analysis and high-resolution scanning electron microscopy are used for joint characterization. At the same time, the composite powder optical scattering or in-situ conductivity monitoring technology is combined to obtain the particle distribution, carbon nanotube network integrity and local agglomeration of the composite powder in real time. Then, by adjusting the ball milling speed, ball-to-material ratio, ball milling time or by using static homogenization treatment, the internal microstructure of the composite powder is precisely controlled so that the carbon nanotubes form a continuous three-dimensional network along the particle gaps and are evenly distributed, while enhancing the interfacial interlocking between carbon nanotubes and iron nanoparticles.

5. The method for preparing a single-walled carbon nanotube composite material for powder metallurgy according to claim 1, characterized in that, S3 includes the following sub-steps: S31, placing the ball-milled composite powder in a heat treatment furnace, and introducing an inert gas or reducing gas before heating to form a protective environment, so that the active surface of the iron nanoparticles exposed during the ball milling process remains in a reduced or inert state during the heating process, thereby inhibiting surface oxidation and maintaining interfacial activity. S32. A phased heating method is adopted to achieve structural control. First, a preheating treatment of 5 to 30 minutes is carried out in the range of 300 to 450℃ to gradually release the internal stress generated during ball milling, while promoting the softening or partial decomposition of the binder, so that the interface between single-walled carbon nanotubes and iron nanoparticles can be further bonded. Then, the temperature is raised to 450 to 650℃ for 2 to 30 minutes of diffusion heat treatment, so that the surface atoms of iron nanoparticles diffuse and migrate and trigger surface structure reconstruction. S33. The composite powder is thermally activated by gradient heating, and the migration of iron nanoparticles on the surface is regulated in an inert or reducing atmosphere to enrich the iron nanoparticles at the active sites and form nanoscale anchoring nodes, so that a stable interface bonding structure is constructed between carbon nanotubes and iron nanoparticles. At the same time, the migration activity of iron nanoparticles is improved by periodically adjusting the concentration of reducing gas or by using a pulsed gas input method to promote the formation of interface anchoring nodes. S34. By gradient heating and controlling the atomic diffusion on the surface of iron nanoparticles under inert or reducing gas, while applying a magnetic field of 0.05 to 0.5T to induce the orientation of iron nanoparticles, the iron nanoparticles migrate to the outer wall of carbon nanotubes and accumulate at defects and active sites to form anchoring nodes, which promotes the partial coating or partial coating of iron nanoparticles by carbon nanotubes, forming a three-dimensional network structure of carbon nanotubes and achieving stable interface bonding. S35. The three-dimensional carbon nanotube network is fixed by anchoring nodes with iron nanoparticles. At the same time, nano-carbon bridges are generated in situ at the intersection of carbon nanotubes by pyrolysis of the binder or trace carbon source gas, so that adjacent carbon nanotubes are connected. The wetting of the iron nanoparticle interface is regulated by vibration assistance or local diffusion, so that a continuous and stable spatial skeleton structure is formed inside the three-dimensional carbon nanotube network.

6. The method for preparing a single-walled carbon nanotube composite material for powder metallurgy according to claim 1, characterized in that, S4 includes the following sub-steps: S41, the composite powder after ball milling is loaded into the mold cavity, and unidirectional cold pressing or bidirectional pressing is performed under inert atmosphere or dry environment conditions. The pressing pressure is 400-800MPa, and the pressure is held for 30-120 seconds, so that the iron nanoparticles make initial contact and arrangement and form a compact structure. At the same time, the carbon nanotubes distributed in the interparticle gaps are gradually oriented and extended to build an initial three-dimensional connection skeleton. S42. During the pressing process, iron nanoparticles undergo local slippage and rearrangement under external pressure, and the gaps between particles gradually shrink. Carbon nanotubes are pressed into the gaps between particles and extend along the particle contact path. At the same time, the binder forms a continuous flexible interface film under pressure and covers the particle surface and contact area, so that a multi-point contact structure is formed between carbon nanotubes, iron nanoparticles and interface film, thereby gradually building a stable three-dimensional skeleton connection relationship in the gaps between particles. S43. After pressing, the density, porosity and integrity of the carbon nanotube network of the compact are tested. When local pores or uneven network distribution are detected, supplementary pressing can be applied while the compact is still in the mold. The supplementary pressing pressure is 10% to 40% of the main pressing pressure and is maintained for 1 to 10 seconds to fill the local gaps and promote the redistribution of the carbon nanotube network. If necessary, vibration-assisted adjustment is combined to make the carbon nanotubes extend evenly along the interparticle gaps and form a stable three-dimensional reinforced network structure that penetrates the interparticle gaps.

7. The method for preparing a single-walled carbon nanotube composite material for powder metallurgy according to claim 1, characterized in that, S5 includes the following sub-steps: S51, placing the compact in a sintering furnace and introducing inert gas or reducing gas to form a stable protective environment, so that the surface of the iron nanoparticles remains in a reduced or inert state during the heating process. The dew point of the sintering gas is controlled below -40℃. Pulsed reducing gas input or gas flow rate fluctuation can be used in the gas to achieve local interface activity adjustment. S52. Using a gradient heating method, the temperature is first slowly increased to 900-1100℃ and held for 10-60 minutes to allow the iron nanoparticles to form preliminary diffusion connections and diffusion necks between particles, thus achieving preliminary densification of the material. During this process, the residual flexible binder film provides wetting and microflow on the particle surface, assisting the iron nanoparticles to migrate along the carbon nanotube surface, providing an active interface for the formation of nanoscale anchoring nodes, while maintaining the integrity of the three-dimensional network of carbon nanotubes and the interlocking structure of the interface. S53. Continue heating to 1100-1350℃ and control the total sintering time to 40-240 minutes to further densify and reconstruct the iron matrix, reduce the interparticle voids to form a continuous matrix structure, and allow the carbon elements in some single-walled carbon nanotubes to diffuse in a limited manner under the catalysis of iron nanoparticles to form an iron-carbon solid solution. At the same time, the three-dimensional carbon nanotube reinforcement network is retained, and the residual flexible binder film assists the three-dimensional carbon nanotube network to extend, interlock and fix in the matrix. S54. During the high-temperature densification stage, carbon nanotubes and iron nanoparticles form a stable interface bond through nanoscale anchoring nodes. The three-dimensional carbon nanotube network is fixed inside the iron matrix, forming a reinforcing network that penetrates the interparticle gaps. The residual flexible binder film works synergistically with the nanoscale anchoring nodes to achieve microscopic interlocking of the interface and structural stability, forming a multi-scale synergistic strengthening structure of a continuous iron matrix, a three-dimensional carbon nanotube reinforcing network, and carbon nanotube-coated iron nanoparticles.

8. The method for preparing a single-walled carbon nanotube composite material for powder metallurgy according to claim 7, characterized in that, S54 includes the following steps: S541 In the high-temperature densification stage, through a graded heating and heat preservation strategy, and by continuously supplying an inert or reducing atmosphere, a dynamic core-shell structure is formed on the surface of iron nanoparticles. The core-shell layer undergoes microscopic atomic rearrangement with temperature control. At the same time, the three-dimensional network of carbon nanotubes extends uniformly in the interparticle gaps and gradually solidifies. The iron nanoparticles migrate directionally along the surface of carbon nanotubes by precisely controlling the temperature gradient, preferentially forming nanoscale anchoring nodes at structural defects and active sites. Local self-assembly is driven by the difference in interfacial energy, further stabilizing the coupling between the core-shell structure and the three-dimensional network. S542. The residual flexible binder film is synergistically integrated with the nanoscale anchoring nodes under the action of interfacial wetting to achieve microscopic interlocking between carbon nanotubes and iron nanoparticles. During the sintering process, the network microstructure and interfacial wetting are synchronously adjusted through periodic pulse atmosphere or micro-vibration, which promotes the adaptive rearrangement and uniform distribution of carbon nanotubes. Reversible microflow is formed at the interface through the wetting film to achieve local self-repair of the interface. S543. By controlling the heating rate gradient, holding time, and atmosphere composition, iron nanoparticles migrate along the surface of carbon nanotubes to the active sites, forming a continuous enrichment layer. At the same time, the residual flexible film forms microflow at the interface, promoting the microscopic synergy of the core-shell structure, nano-anchoring nodes, and carbon nanotube three-dimensional network. By utilizing the interfacial energy difference and atomic migration dynamics, the dual optimization of macroscopic framework continuity and microscopic interlocking is achieved, ensuring the stable existence of the three-dimensional reinforcement network at high temperatures. S544. The iron matrix is ​​continuously densified, and the three-dimensional carbon nanotube network is fixed in the interparticle gaps. The core-shell structure and the interface anchoring nodes work together to ensure that the nanostructure of the carbon nanotube-coated iron nanoparticles is complete. Through the synergistic effect of atomic directional migration, interface self-assembly and flexible film wetting, a multi-scale synergistic reinforcement structure of iron-based continuous matrix, three-dimensional carbon nanotube reinforcement network and carbon nanotube-coated iron nanoparticles is achieved.

9. A product of a single-walled carbon nanotube composite material for powder metallurgy, used in the production of the single-walled carbon nanotube composite material for powder metallurgy as described in any one of claims 1-8, characterized in that, Includes: Metal matrix: a continuous metal matrix structure formed by pressing and sintering iron nanoparticles together; Single-walled carbon nanotubes: distributed in the interparticle gaps between adjacent iron nanoparticles and extending along the interparticle gaps, forming a three-dimensional interconnection network structure that runs through multiple iron nanoparticles within the volume space of the composite material defined by the continuous metal matrix structure formed by sintering iron nanoparticles, so that the network is connected between adjacent iron nanoparticles through at least one single-walled carbon nanotube connection path. Interface bonding layer: formed by binder or its heat treatment conversion product, and continuously distributed on the particle surface and particle contact area of ​​iron nanoparticles, with a thickness of 10nm to 500nm.

10. The product of a single-walled carbon nanotube composite material for powder metallurgy according to claim 9, characterized in that, The single-walled carbon nanotubes and iron nanoparticles form a stable interface bond through nanoscale anchoring nodes. These nanoscale anchoring nodes are distributed along the particle contact area and the structural defects of the carbon nanotubes, enabling the carbon nanotubes to form a uniformly extending three-dimensional interconnection network within the particle gaps. Simultaneously, the flexible film in the interface bonding layer covers the surface of the iron nanoparticles and the particle gaps, forming carbon bridges or micro-interlocking structures at the network intersections. This enhances the interfacial bonding strength between the carbon nanotubes and the metal matrix and maintains the stability of the three-dimensional network.

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