Aluminium-graphene nanocomposites with high electrical and thermal conductivity, and methods for obtaining same via microstructural control

Abstract

The present patent of invention relates to aluminium-graphene nanocomposites with high electrical and thermal conductivity, and methods for obtaining same via microstructural control, and more specifically to the incorporation of multilayer graphene nanoplatelets (mGNP or few-layer graphene), comprising up to 10 layers, into pure commercial aluminium or aluminium alloys, using electric furnaces. The nanocomposites obtained comprise an aluminium matrix with dispersed graphene as the reinforcing phase, in proportions ranging from 0.1 wt% to 3 wt%. In order to obtain the nanocomposites, gravity casting techniques were employed in resistive and induction furnaces, with adaptations to prevent oxidation through the use of an inert gas atmosphere. The methodology employed enables a significant increase in electrical conductivity, ranging from 45% to 95% relative to the as-received commercial material, depending on the amount of graphene added. The thermal diffusivity of the nanocomposites also increased by 15% to 50%, with a possible maximum of around 0.5 wt% to 1 wt% of graphene. Similarly, the general physical properties exhibited marked improvements, although the rate of improvement decreased for nanocomposites containing more than 2 wt% of graphene.

Description

High Electrical and Thermal Conductivity Aluminum-Graphene Nanocomposites and Methods for Obtaining Them via Microstructural Control

[0001] This patent application refers to a technology for the synthesis of graphene-reinforced aluminum (Al) metal matrix nanocomposites, which exhibit enhanced electrical, thermal, and mechanical properties through microstructural control of the resulting products – a solid (graphene nanoplatelets) and a liquid (aluminum or molten aluminum alloy) transforming into a solid through a peritectic reaction (involving 3 phases: 6 + LH y) where the optimization of the dispersion and quantities of dispersed phases (graphene) in the aluminum matrix were processed in more effective electric furnaces to improve physical properties. The technique stands out for the gradual and controlled addition of high-quality graphene materials in resistive furnaces and / or in an electromagnetic induction furnace, operating in an inert atmosphere.Nanocomposites can be formed from various aluminum alloys, especially alloys from the 1000 series - such as 1350 (commercially pure) - or typical casting alloys like SAE 323.

[0002] Based on the technique developed and employed here, it was possible to create nanocomposites with unprecedented properties. This was achieved thanks to the understanding and application of quantum concepts for the ideal control of the proportion and homogeneous dispersion of graphene in the metallic matrix, inducing a uniform spatial (3D) distribution of graphene in the microstructure, especially with dispersions around the alpha (α) grain boundaries – unary microstructure – or (α) and beta (β) grain boundaries, forming peritectic-type microstructures with uniform stereoscopic dispersion of graphene nanoplatelets. This distribution and dispersion engender a nanostructured network and Interconnected structure that facilitates the flow of electrons with the appearance of Cooper pairs - consequently bosons caused by electron-phonon interaction, significantly improving the electrical and / or thermal conductivity of the material, in addition to increasing other mechanical and / or physical properties, through mechanisms that increase toughness. Scientific Context and Description of the State of the Art:

[0003] The need to mitigate the effects of climate change drives the search for disruptive technological solutions in the energy transition. The demand for materials with enhanced properties for electrification, energy storage, and energy efficiency catalyzes the development of new materials. Aluminum and copper alloys, widely used in industrial applications, stand out for their lightness, electrical and thermal conductivity, and corrosion resistance. However, their intrinsic properties limit their performance in modern applications that require superior physicochemical characteristics.

[0004] Recent research in the fields of engineering and materials science—especially with the advent of nanotechnology—aims to overcome these technological barriers through the development of new materials and manufacturing routes. This scientific field has proven crucial in solving contemporary social and environmental problems, particularly in the context of climate change and environmental degradation. The creation of new materials, especially nanocomposites, offers unprecedented opportunities to improve quality of life and protect the environment.

[0005] Nanotechnology is a field of science and engineering dedicated to the study, manipulation, and control of matter at nanometric scales, generally below 100 nanometers. The origin of this technology dates back to the famous speech given by Richard Feynman in 1959, entitled "There's "Plenty of Room at the Bottom," in which he discussed the possibilities of manipulating atoms and molecules individually. This speech is widely recognized as the initial landmark that sparked scientific interest in manipulation at the nanoscale.

[0006] The evolution of nanotechnology occurred significantly in the following decades, with the development of techniques and tools that allowed the visualization and manipulation of matter at this scale. In 1981, the invention of the scanning tunneling microscope (STM) by Gerd Binnig and Heinrich Rohrer, who later received the Nobel Prize in Physics in 1986, was a crucial advance. This device allowed the direct observation of atoms on surfaces, providing a means to explore and manipulate sub-nanometric structures.

[0007] In the 1980s and 1990s, nanotechnology began to gain momentum as an interdisciplinary research field, encompassing physics, chemistry, biology, materials science, and engineering. During this period, the discovery of fullerenes (allotropic forms of carbon in closed structures, such as CeO) by Harold Kroto, Richard Smalley, and Robert Curl in 1985, which also earned them the Nobel Prize in Chemistry in 1996, and the subsequent discovery of carbon nanotubes by Sumio Lijima in 1991, opened new frontiers in materials science due to the unique properties of these structures, such as high mechanical strength, electrical and thermal conductivity.

[0008] One of the most notable advances in nanotechnology was the discovery of graphene by Andre Geim and Konstantin Novoselov in 2004. Graphene is a two-dimensional form of carbon, composed of a single layer of carbon atoms arranged in a hexagonal lattice. Its exceptional properties, such as high electron mobility, flexibility, mechanical strength, and thermal and electrical conductivity, make it a material of great interest. scientific and technological. In recognition of this discovery, Geim and Novoselov received the Nobel Prize in Physics in 2010.

[0009] Carbon atoms have a total of 6 electrons, 2 inner and 4 valence electrons, with an electronic configuration in the ground state of 1s². 2 2s 2 2p 2In graphene, each carbon atom forms bonds with three other carbon atoms in a two-dimensional planar arrangement, leaving one electron free for electrical conduction. This configuration allows electrons to move easily and rapidly along the graphene, flowing through a channel of lower electrical resistance. The presence of electrons and vacancies, known as graphinos, facilitates the linear conduction of electrical energy with minimal resistivity, due to the low density of electron-electron collisions. This minimizes losses due to the Joule effect, which normally result from these collisions or from friction between valence electrons when an electric current is established in a conductor, converting electrical energy into thermal energy. With high fermion energy levels, graphene can behave as a superconductor, even surpassing metals like gold (Au) or copper (Cu).

[0010] However, the mechanisms involved in graphene's superconductivity have not yet been fully elucidated, and achieving this characteristic is not trivial. Other effects are also relevant to controlling the physicochemical properties. For example, there are Cooper pairs, which describe a phenomenon in which two electrons, which normally repel each other due to their negative charge, pair up under certain conditions. In conventional superconducting materials, Cooper pairs are formed due to the interaction of electrons with the material's crystal lattice. When an electron moves through the material, it creates a distortion in the lattice, which can attract another electron to form a pair. These Cooper pairs have angular momentum. The total energy equals zero, which classifies them as bosons. As bosons, Cooper pairs can occupy the same quantum state, allowing the formation of a Bose-Einstein condensate that moves without energy dissipation, resulting in superconductivity.

[0011] However, pure graphene does not exhibit intrinsic superconductivity under normal conditions because the interaction required to form Cooper pairs is weak. To overcome this technical limitation, superconductivity in graphene can be induced through different methods. One is coupling graphene with a conventional superconductor. In this case, the Cooper pairs from the superconductor penetrate the graphene, inducing superconductivity at the interface. Another approach is doping the graphene with atoms or molecules that provide additional charge carriers, increasing electron density and strengthening the pairing interaction.

[0012] Furthermore, recent research has shown that superconductivity can emerge in graphene when it is twisted at specific angles, forming what is called twisted bilayer graphene. In this arrangement, interference between the two graphene layers creates planar electronic bands that significantly increase electronic interactions, favoring the formation of Cooper pairs. This phenomenon is known as "magic superconductivity" due to the specific angle required to induce this property.

[0013] We can therefore see that the fluid behavior of electrons in graphene has a significant impact on the electrical and thermal conductivity of these materials. Studies show that the electrical resistance of graphene decreases with increasing temperature when kept below 150K (or -123°C). This behavior is counterintuitive for a conductor, since, in general, higher temperatures result in greater thermal agitation of electrons and ions. Increasing the probability of electron-ion and electron-electron collisions should, in turn, increase electrical resistance. However, the literature has shown that, at low temperatures, the intensity of electron-electron collisions in graphene is such that a large portion of the electrons remains confined to the surface of the material, reducing the dissipation of the momentum of the remaining electrons. This allows these electrons to be conducted through a channel of lower resistance. Interestingly, this effect seems to intensify with increasing temperature. This phenomenon offers a new perspective on the physical mechanisms governing conductivity in nanomaterials, being particularly useful for the development of electrical devices based on graphene-containing nanocomposites.

[0014] It is therefore well-known and evident that the properties of graphene, especially those related to superconductivity, are highly dependent on its morphological characteristics and the processing routes chosen. Even so, typically, the physical and mechanical properties of graphene are exceptional. Electron mobility is extremely high, with values ​​that can exceed 200,000 cm⁻¹. 2 / Vs under ideal conditions and low temperatures, while at room temperature mobility can exceed 15,000 cm 2 / Vs. This value is significantly higher than the electron mobility in silicon, which is approximately 1,400 cm⁻¹. 2 Graphene also exhibits high thermal conductivity, with values ​​ranging from 4,800 to 5,300 W / mK, surpassing that of diamond, making it an excellent material for heat dissipation in electronic components.

[0015] Graphene's mechanical strength is another of its remarkable properties. With a tensile strength of approximately 130 GPa and a modulus of elasticity (Young's modulus) of about 1 TPa, graphene is one of the strongest materials known. Its density, however, is low. approximately 0.77 mg / m² 2 , which gives the material an extremely high strength-to-weight ratio.

[0016] Given all these properties, graphene positions itself as an excellent candidate for electrical and electronic applications in Industry 4.0. The addition of small amounts of graphene, on the order of parts per million (ppm), can result in an exponential increase in conducted electrical power. As research on graphene advances, its economic viability and industrial applications continue to grow. For example, graphene-reinforced aluminum (Al) matrix composites are already being studied, combining the advantages of aluminum, such as low weight, reduced cost, and ease of processing, with the exceptional mechanical strength and electrical and thermal conductivity properties of graphene.Research is being conducted using methods such as powder metallurgy, ball milling, compaction, extrusion, and casting, showing that aluminum nanocomposites and graphene nanoplatelets have great potential for the electrical sector, offering significant improvements in mechanical strength and electrical conductivity, while maintaining the low weight and ease of processing of aluminum.

[0017] However, the homogeneous distribution of graphene in the metallic matrix is ​​a crucial challenge to ensure that the desired properties are achieved. If the graphene is not adequately dispersed, agglomerations can occur, acting as points of weakness and discontinuity in the material. These agglomerations can decrease the mechanical strength of the composite, create heterogeneities that compromise structural integrity, and negatively affect thermal and electrical conductivity. The formation of graphene clusters can also result in weak interfaces between the phases of the composite, compromising the efficient transfer of stress and heat.

[0018] This scenario becomes even more complex when considering the casting process, in which graphene must be distributed and homogenized within a liquid metal matrix. During the aluminum casting process, for example, the high temperature can exacerbate the agglomeration of the graphene sheets to minimize the surface energy of the system. Another difficulty is related to the density difference between graphene and aluminum. Graphene is significantly lighter than aluminum, which can lead to its segregation during the metal solidification process.

[0019] Wettability between graphene and aluminum is also a challenge. Graphene tends to be hydrophobic and may not adhere easily to molten aluminum, hindering the formation of a strong and continuous interface between graphene and the metal matrix. Poor wettability can result in poor adhesion between the phases, compromising the mechanical and thermal properties of the composite. To overcome these challenges, several approaches have been explored. Functionalization of the graphene surface is a promising strategy. By chemically modifying the graphene surface, it is possible to improve its compatibility with molten aluminum, promoting better dispersion and adhesion. For example, functionalization with carboxylic or amino groups can increase wettability and the interaction between graphene and aluminum.

[0020] The use of techniques such as mechanical and ultrasonic agitation during the casting process are other approaches to improve graphene dispersion. Ultrasonic agitation, in particular, can help break up graphene agglomerates and evenly distribute graphene sheets in the molten metal. However, precise control of processing parameters, such as the intensity and duration of agitation, is crucial to avoid damage to the graphene and ensure effective dispersion. High-energy milling has also been used to pre-disperse graphene in aluminum powder before the casting process. Casting. This technique can break up graphene clusters and promote a more uniform distribution. After grinding, the aluminum powder with graphene can be compacted and cast, resulting in a more homogeneous composite.

[0021] Despite these approaches, achieving a homogeneous and stable distribution of graphene in molten aluminum, ensuring that quantum superconductivity phenomena are present in the material, still presents significant technical obstacles. New fabrication routes have succeeded in sintering aluminum-graphene composites with conductivity up to approximately 65% ​​IACS. However, our studies indicated that this value could be much higher.

[0022] The IACS, or International Annealed Copper Standard, is a reference used to measure the electrical conductivity of metallic materials. The standard was established to provide a basis for comparison, using annealed copper as a reference due to its high electrical conductivity. In the IACS system, the electrical conductivity of pure annealed copper is defined as 100%, which corresponds to an electrical conductivity of 58.0 x 10⁻⁶ ohms. 6siemens per meter (S / m). This can also be expressed as 1 / 1.7241 microohm per centimeter (pQ-cm).

[0023] Based on exhaustive searches and analyses of the state of the art, the existence of several patents and manufacturing methods for the synthesis of aluminum-graphene composites was found. However, as discussed, the products obtained so far have not achieved a conductivity greater than 65% IACS coupled with an increase in mechanical strength and the addition of graphene up to the order of 2% of the total weight. This premise is corroborated by the descriptions of the most relevant patent applications found, namely:

[0024] AU2021105915A4 discloses a methodology for producing a graphene-reinforced aluminum matrix composite material, which stands out. Due to its high electrical conductivity and significant mechanical improvements, the innovation of the process lies in the chemical treatment of graphene and the formation of the composite structure through controlled casting and forging. Initially, graphene and aluminum powder are dried, then the graphene undergoes a chemical "plating" of aluminum without electrical current, resulting in aluminized graphene powder. This structure is extruded and heated between 500-600°C. After cooling, the block is cold-formed longitudinally and annealed in an inert atmosphere at 200-300°C to relieve internal stresses and improve mechanical properties. The process results in a material with an electrical conductivity of approximately 60% IACS.

[0025] CN105112699A details a preparation method for a graphene-reinforced aluminum alloy composite material, which aims to significantly improve mechanical properties and electrical conductivity. Graphene is incorporated into the aluminum matrix in proportions ranging from 0.1% to 5.0% by weight. This method combines low-temperature milling with hot isostatic pressing and extrusion to achieve uniform graphene dispersion and excellent bonding at the graphene / aluminum interface. The document mentions that this methodology not only provides a uniform distribution of graphene in the aluminum matrix but also optimizes the electrical conductivity of the material to up to 65% IACS.

[0026] Patent CN115449672A details another method for manufacturing graphene-reinforced aluminum conductor wires, starting with mixing graphene and aluminum powder by ball milling, creating a homogeneous mixed material. This mixed material is then subjected to a rotary friction extrusion process, which integrates the graphene into the aluminum matrix, preserving its structure and properties. After extrusion, the composite is transformed into a conductor wire through drawing, which adjusts the wire diameter. and improves its mechanical and electrical properties. This process results in conductive wires that exhibit mechanical strength between 186 and 224 MPa and electrical conductivity ranging from 55% to 60% IACS.

[0027] Unlike the aforementioned patents, which utilize chemical treatments and complex processes such as rotary friction extrusion and low-temperature milling, the proposed invention employs a direct fusion technique and dispersion control during aluminum fusion to ensure the quantum superconductivity phenomena of the composite. Thus, the inventive activity is demonstrated by the unique ability to induce a uniform spatial distribution of graphene in the microstructure, especially with dispersions around the alpha (α) grain boundaries – unary microstructure – or (α) and beta (β) grain boundaries, forming peritectic-type microstructures with uniform stereoscopic dispersion of graphene nanoplatelets – in order to achieve electrical conductivity that not only significantly surpasses that of existing methods but also improves the mechanical properties of the material. It is worth noting that this is only possible thanks to the characteristics of the synthesized graphene nanoplatelets.

[0028] Furthermore, given the research conducted, no other prior art document has disclosed a synthesis methodology for these nanocomposites to establish a structure and dispersion that generate a nanostructured and interconnected network that facilitates electron flow with the appearance of Cooper pairs. In this patent, based on these concepts, the aim was to understand and apply the quantum phenomena involved to improve the physical properties (electrical, thermal, and mechanical), focusing on the performance of nanocomposites as advanced electrical and thermal conductors. In this context, the hybridizations in the electron cloud of the synthesized graphene are explored. They were crucial in explaining how Cooper pairs contributed to an unprecedented increase in electrical conductivity.

[0029] In fact, regarding the interaction of graphene with the aluminum metallic matrix, theoretical models describe that Cooper pairs in these matter condensates are primarily responsible for facilitating the transport of electrical charge in the metallic matrix, along with phonons or vibrations in the crystal lattice, forming a bound state between two electrons. From there, electrons can interact in a concatenated manner, forming a weak bound state by interacting through a network of cations and a phonon.Taking advantage of this, the casting method employed in this patent allowed the aluminum matrix with dispersed graphene to become an excellent conductor due to the formation or creation of these pairs between the valence electrons of graphene, controlling the average drift velocity of the aluminum electrons in the ground state at room temperature, as charge carriers, usually electrons, move through a conductor under the influence of an electric field.

[0030] The speed of charge carriers is influenced by factors such as the density of these carriers, the cross-sectional area of ​​the conductor, and the intensity of the electric field. The electric charge passing through the conductor in a given period is determined by the charge of the electron and the number of electrons moving within the conductor, where Cooper pairs control the drift velocity of electrons traversing a segment (I) in the time interval (t). The proposed theoretical model describes how the weak interaction between electrons mediated by virtual vibrations (phonons) neutralizes and overcomes Coulomb repulsion, forming Cooper pairs. Thus, the condensate of Cooper pairs forms an ordered structure, such that the As electrons moved, they did not encounter the irregularities in the material that generate electrical resistance.

[0031] Since electromagnetic waves can also interact with the vibrations of the metallic matrix's crystalline lattice, with graphene nanoplatelets acting as an amplifier – as in the Raman effect – it is plausible to imagine that photon pairs could interact by exchanging a virtual vibration of the medium, forming photon pairs. In fact, the formation of Cooper pairs is identical for pairs of fermions (electrons) or bosons (photons). The literature demonstrates that it is possible to detect photon pairs from a laser passing through a transparent medium, emerging simultaneously and with frequencies shifted towards the red or blue. That is, analyses of the vibrational spectrum indicate that this experimental correlation, without the need for parameter adjustments, supports the virtual vibration exchange model.Furthermore, as explained, the theory of conductivity of metals is not only a direct consequence of Cooper pairing, but evidence of this pairing in graphene has also been pointed out, and it does not imply, although it is not excluded, the possibility of other phenomena such as, for example, a state of improved conductivity of the conductor promoted by electromagnetic radiation (photons). Brief description of the objectives

[0032] From all these perspectives, the conductivity properties of the nanocomposites proposed here significantly surpass those reported in the literature. This advancement was only possible thanks to the precise understanding and control of quantum phenomena, which allowed the creation of paths of least resistance for the flow of charge carriers. It is in this context that the objectives of the present patent are outlined, which involve the careful selection of materials with synergistic structure and chemical composition, aiming to... Inducing a homogeneous dispersion of graphene in the metallic matrix. This homogeneity is achieved through a uniform spatial distribution of graphene in the microstructure, with particular emphasis on dispersions around the boundaries of alpha (α) grains – unary microstructure – or alpha (α) and beta (β) grains, resulting in peritectic microstructures with uniform stereoscopic dispersion of graphene nanoplatelets. Aligned with the objectives of this patent, the details and functionalities will be better understood in the detailed description below, in accordance with the attached figures, where: Figure 1 illustrates the processing steps for obtaining a sample of the aluminum-graphene nanocomposite in four main steps. First, two portions of aluminum are melted in separate crucibles under an inert atmosphere. Then, graphene is added to the molten aluminum, and more solid aluminum is incorporated with stirring to ensure homogeneous dispersion of the graphene. The process continues with the addition of more graphene and aluminum, always with stirring, to ensure a uniform mixture. Finally, the resulting alloy is poured into a sand mold to form the final sample. Figure 2 refers to a schematic representation of an induction furnace, also used for aluminum smelting and the synthesis of nanocomposites. In this type of furnace, the aluminum to be smelted is placed in a crucible, and the heat necessary to melt the metal is generated by currents induced in the metal through an induction coil that surrounds the crucible. These coils generate an alternating magnetic field that induces electric currents in the metal, heating it to the melting point. Figure 3 reveals the behavior of molten metal inside the crucible in induction furnaces, especially the interaction of electric currents and the agitation of the molten metal bath, illustrating how electric currents induced by the magnetic field (primary current) generate secondary currents within. from the molten metal bath. These secondary currents are responsible not only for heating the metal to melting point, but also for creating a swirling motion within the bath, which contributes to better dispersion of the graphene in the molten metal matrix. Figure 4 enhances the understanding of the electromagnetic phenomena of the induction furnace by showing how eddy currents form within the molten metal. These currents create circular patterns that generate force vectors within the molten bath, contributing to internal agitation and ensuring efficient mixing of the aluminum with the graphene. Figure 5 refers to a graph relating the electrical resistivity of different samples of the aluminum-graphene nanocomposite. The samples range from pure aluminum (Alv., as received) to mixtures containing 0.5%, 1%, and 2% graphene (G). The electrical resistivity, measured in micro-oils per centimeter (pQ-cm), initially decreases with the addition of graphene, reaching a minimum value in the sample with 1% graphene. After this concentration, the resistivity increases again in the sample with 2% graphene. The curve fitted to the data is a parabola with the equation y = 9.4x 2 - 52.2x + 109.7 and a coefficient of determination (R 2 ) of 0.9996, indicating an excellent fit to the experimental data. These results suggest that there is an optimal graphene concentration of around 0.5 to 1% to minimize the electrical resistivity of the aluminum composite. Figure 6 presents a graph relating the thermal diffusivity of different samples of the aluminum-graphene nanocomposite, corroborating what was revealed in the graph in Figure 2. Thermal diffusivity, measured in square millimeters per second (mm²). 2 / s), increases with the addition of graphene, reaching a maximum value in the sample with 1% graphene. After this concentration, the thermal diffusivity decreases slightly in the sample with 2% graphene. graphene. The curve fitted to the data is a parabola with the equation y = -lx 2 + 7x + 45.25 and a coefficient of determination (R 2 ) of 0.9505, also indicating a good fit to the experimental data. Figure 7 shows the microstructure of the nanocomposite with the addition of 0.5% graphene in the aluminum alloy (SAE 323) observed under a scanning electron microscope (SEM) at 1400x magnification, where it can be seen that the carbon precipitates in the form of graphene nanoplatelets are preferentially deposited in the intergranular regions of the aluminum matrix or even near the grain boundaries of the alloy. Figure 8 shows the microstructure of the nanocomposite with the addition of 0.5% graphene in the aluminum alloy (SAE 323) observed by SEM at 3500x magnification. Details can be observed showing how the carbon in the form of graphene nanoplatelets is preferentially deposited near the grain boundaries of the alloy. Figure 9 shows characteristic aspects of the microstructure of the Al (SAE 323) alloy nanocomposite with the addition of 1% graphene at 7000x magnification (SEM). Details of the dispersion of carbon precipitates (graphene nanoplatelets) depositing in the intergranular regions of the aluminum or even near the grain boundaries of the alloy can be observed. Figure 10 shows the microstructure observed under an optical microscope (OM) with an impression left by the indenter after Vickers microhardness testing in the region comprising the three different phases of the produced material: α, β and γ (graphene) of the nanocomposite formed by 2% graphene. Figure 11 shows a SEM image illustrating the characteristics of graphene nanoplatelets with transparency (monolayers and layered regions). folded), aspect ratio (reference bar micrograph with lpim) and morphology of these multilayer (NGM) or few-layer graphene nanoplatelets. Detailed description of the technology:

[0033] The research on high electrical and thermal conductivity aluminum-graphene nanocomposites and methods for obtaining them via microstructural control, as described above, was conceived from a better understanding and application of quantum phenomena in the casting and integration processes of graphene nanoplatelets in cast aluminum matrices. The objective was to achieve unprecedented levels of conductivity for this type of material, which was possible thanks to the rigorous control of the proportion and the homogeneous dispersion of graphene in the metallic matrix, guaranteeing a uniform three-dimensional distribution in the microstructure. In particular, the graphene nanoplatelets were dispersed in a controlled manner along the boundaries of alpha (α) grains in the unary microstructure, or of alpha (α) and beta (β) grains in peritectic microstructures, creating a uniform stereoscopic dispersion. This distribution generated a nanostructured and interconnected network that facilitates electron flow and promotes the formation of Cooper pairs.For this distribution and dispersion to occur, the use of two types of electric furnaces is relevant: resistive or electromagnetic induction.

[0034] The processing begins with the initial preparation of ceramic crucibles (for gravity melting in a resistive furnace) or graphite crucibles with a ceramic lining (for melting in an induction furnace). In both cases, the particulate materials (pure Al or Al alloys) are comminuted into granules smaller than 7 mm, and graphene is incorporated into nanoplatelets with up to 10 layers. These raw materials are weighed in mass / mass percentages. Then, for melting in resistive electric furnaces, the process begins. The gradual addition of graphene to aluminum, with intervals of manual stirring to ensure homogeneous mixing of the components. In the case of an electric furnace, the induction of bath agitation occurs through the action of the electromagnetic field, due to eddy currents and magnetic blowing (energy distribution and convection line pattern in the bath) generated by the electromagnetic flux induced by the coil current (primary) on the liquid bath (secondary). In this case, the combined action of stirring and blowing within the bath are important process parameters, as they optimize the homogenization and dispersion of the liquid (Al) and solid (graphene) phases in the bath, allowing a mechanical mixing of the added constituents that will form the nanocomposite, as shown in Figures 1, 2, 3, and 4.

[0035] Otherwise, excessive agitation without a protective atmosphere could increase gas uptake by the bath, wear on the crucible lining, and cause excessive oxidation of these alloys. After complete incorporation of the graphene, the molten material is poured into a mold for solidification, resulting in the final sample. Each step is carefully controlled to ensure uniform integration of the graphene into the aluminum matrix. Eddy currents induced by electromagnetic forces in the furnace charge and magnetic induction create intense dispersions on the molten aluminum charge and graphene. These forces run basically in a radial direction relative to the furnace axis and push the molten material inward, as predicted by Maxwell's equations, pushing the vortex away from the furnace wall. Gravity then acts against these forces, and therefore a dome (meniscus) is formed on the surface of the bath.Furthermore, a bath flow is created in the form of two parasitic toroidal loops with opposite directions of the turns. This is attributable to the fact that the radial pressure reaches its maximum around the middle of the coil due to field leakage at the coil end.

[0036] All these phenomena that occur during the casting process play a relevant role in the orientation and dispersion of graphene nanoplatelets during aluminum solidification. These processes prevent the agglomeration of nanoplatelets and induce their stabilization at grain boundaries, where the surface energy is higher. As a result, the combined effect of these phenomena not only favors the formation of Cooper pairs but also leads to a significant increase in the electrical and thermal conductivity properties of the final material.

[0037] However, we emphasize that the exceptional properties achieved in the nanocomposites were only possible thanks to the synthesis and selection of high-quality graphene, combined with the careful choice of aluminum alloys. The main alloy used here – SAE 323 – belongs to the aluminum-silicon-copper alloy family. This family is characterized by containing a high percentage of silicon, generally between 5% and 23%, which provides good casting properties and wear resistance. Copper is added to increase the mechanical strength and hardness of the alloy. The addition of magnesium, which varies from 0.2% to 0.45%, contributes to increasing the alloy's strength. In addition, the alloy contains small amounts of iron, with a maximum of 0.7%, zinc, up to 0.5%, manganese, up to 0.35%, and nickel, also up to 0.35%.

[0038] Aluminum-silicon-copper alloys also tend to exhibit better wettability with graphene compared to other alloys. The high silicon content helps reduce the surface tension of the aluminum, facilitating the propagation of the molten material over the graphene. Furthermore, the presence of copper in the range of 2% to 4% can form intermetallic compounds that improve adhesion between the graphene and the aluminum matrix. The formation of these intermetallic compounds can promote a more stable and cohesive interface. Magnesium, present in the alloy composition between 0.2% and 0.45%, can act as an agent. The bonding properties improve the interaction between graphene and the aluminum matrix. These combined characteristics make these alloys suitable for integration with graphene. However, similar results can be achieved with alloys from the 1000 series – such as the 1350 (commercially pure).

[0039] The characteristics of the high-quality graphene used for the synthesis of nanocomposites are shown in Table 1, according to the specifications: Table 1: Chemical specifications of graphene incorporated into the nanocomposite

[0040] A high carbon content of 99.420% is observed, with a minimal presence of oxygen below 0.05% and other contaminants totaling only 0.576%. Furthermore, the graphene used has a structure ranging from 1 to 10 layers, a choice that provides an ideal combination of mechanical flexibility and high electrical conductivity. This layer arrangement allows the formation of peritectic microstructures along the aluminum grain boundaries. The average surface area is 64.6 m². 2The / g concentration of graphene maximizes interfacial contact with the aluminum matrix, crucial for effective charge transfer and stress dispersion within the material. Furthermore, the pH neutrality of graphene ensures that there are no adverse reactions that could lead to corrosion or degradation of the aluminum.

[0041] In line with what is revealed in Figures 5 and 6, it is noteworthy that the addition of graphene in proportions of 0.5%, 1.0%, and 2.0% by weight to the aluminum alloy was strategically calculated, and not merely quantitative. This The approach aimed to identify the proportion that best induces the formation of conductive pathways without compromising the structural integrity of the alloy. This is because excessive additions of graphene, even if well distributed, can result in saturation and a decrease in desired properties due to agglomeration and the formation of discontinuities in the microstructure. What has been empirically demonstrated is that the ideal proportion for electrical conductivity is approximately 1% graphene addition. Both molten aluminum and graphene at high temperatures are highly oxidizable when exposed to atmospheric oxygen in an operational environment during the casting process, which can compromise relevant physical properties through the risk of contamination of the nanocomposite. This is particularly true for the microstructural function of graphene, as excessive oxidation may decrease the incorporation of this nanoreinforcement into the aluminum matrix.To mitigate this degradation effect due to graphene oxidation, the entire process of melting and feeding graphene into the crucible must occur under a protective curtain or layer of nitrogen gas (N2) over the surface of the liquid aluminum.

[0042] Following all these conditions, it was possible to achieve homogeneous dispersion of graphene within the aluminum grain boundaries, resulting in the formation of an interconnected network. This network provides a continuous system for electron conduction, overcoming the natural barriers imposed by the grain boundaries. This percolation effect occurs when the graphene concentration reaches a critical point, allowing electrons to move freely through the graphene network, drastically increasing the material's electrical conductivity. After exhaustive empirical tests, we identified the methodology and ideal graphene proportions to reach this critical performance point in nanocomposites. As demonstrated in the graphs in Figures 5 and 6, the sample with 1% graphene achieved a Resistivity lower than that of pure copper. These results were obtained after normalizing the data to standard test conditions, the values ​​of which are shown in Tables 2 and 3, and are as follows: Table 2: Normalized average electrical resistivity values ​​for the tested nanocomposites: ALV, AL0.5%G, AL1%G and AL2%G. *Source: CALLISTER; RETHWISCH, 2015. Table 3: Reference Electrical Resistivity Values. Source: CALLISTER; RETHWISCH, 2015.

[0043] The comparison of resistivity values ​​between the AL1%G nanocomposite and pure copper is particularly noteworthy and deserves special attention due to the practical implications of these results. The AL1%G nanocomposite, containing only 1% graphene, exhibits a resistivity of 0.016 pQm, which is lower than that of pure copper, whose resistivity is 0.017 pQm. In other words, the conductivity of the nanocomposite with 1% graphene exceeded 100% IACS, resulting in an unprecedented outcome.

[0044] The superior resistivity of the AL1%G nanocomposite compared to copper indicates that the addition of graphene to aluminum, by our This methodology not only improves its inherent properties but also transforms the composite into a potentially more effective material for applications demanding high electrical conductivity. Thus, the developed aluminum-graphene nanocomposite represents a significant advancement in the field of materials engineering, offering a highly effective and economical solution for applications requiring excellent electrical and mechanical properties. Examples of Implementation of the Invention

[0045] Based on what has already been revealed, the manufacturing process for the developed aluminum-graphene nanocomposites is a carefully orchestrated technique that unfolds in four main steps, designed to optimize both heat dissipation and the effective incorporation of graphene into the aluminum matrix. It begins with the preparation of two crucibles inside a resistive furnace (muffle furnace type) or induction furnace heated to 850°C – where 55 grams of aluminum are placed in each, under an inert nitrogen atmosphere. This preparatory procedure is essential to ensure that the graphene, added subsequently, disperses homogeneously throughout the alloy.

[0046] In the second step, 2 / 3 of the graphene is added to the liquid aluminum in one of the crucibles. Then, the liquid aluminum from the second crucible is poured over this mixture, to which 330 grams of solid aluminum are added. This combination is then manually stirred, facilitating the melting of the solid aluminum and allowing the graphene to incorporate uniformly into the metallic matrix.

[0047] Moving on to the third stage, the remaining third of the graphene is added, followed by the inclusion of the final 110 grams of aluminum. The second crucible, which is also melted and incorporated into the mixture through further manual stirring, is then added. This step is crucial to ensure complete homogenization of the alloy, which remains in the furnace under a controlled atmosphere for another five days to stabilize the microstructural structure of the composite.

[0048] Finally, the alloy temperature is carefully checked to ensure it is above 740°C, a prerequisite for proper molding. The alloy is then poured into a sand box containing the prepared mold for the part, ensuring dimensional accuracy and structural quality of the finished component. This method is meticulously repeated for each planned graphene proportion, with each cycle rigorously maintaining temperature parameters and inert atmosphere conditions, ensuring the uniformity and quality of the produced aluminum-graphene nanocomposite.

[0049] Subsequent processes such as ingot casting, rolling, or wire drawing of nanocomposites enable the production of semi-finished products, such as high-quality, high-conductivity profiles (cylindrical, rectangular, tubular) or electrical cables. These products exhibit superior electrical, mechanical, and thermal properties compared to commercially available lightweight metal alloys, including so-called antialloys that form intermetallic compounds. Furthermore, the aluminum-graphene nanocomposites developed here can be applied in various sectors, such as civil construction and the aerospace industry, where they contribute to the creation of lighter and stronger structures. In the automotive industry, particularly in electric vehicles, these materials can be used to increase range through lighter structures and efficient electrical conductors.Furthermore, in fields such as electronics and IoT, these alloys are essential for improving heat dissipation in compact devices. They are also useful in transmission lines and industrial automation systems, where they improve efficiency and operational stability.

[0050] Finally, it is reiterated that there are possibilities for modifications and adaptations to the methodology employed, and the descriptive account in this document should not be considered limiting, but rather illustrative, as there may be variations, for those skilled in the art, that are equivalent without, however, departing from the scope of protection of the invention.

Claims

CLAIMS 1. HIGH ELECTRICAL AND THERMAL CONDUCTIVITY ALUMINUM-GRAPHENE NANOCOMPOSITES, characterized by comprising an aluminum (Al) matrix reinforced with graphenic materials that establish - preferably - a spatial distribution with dispersions around the alpha (α) grain boundaries - in unary microstructure - or (α) and beta (β) grains when there are intermetallic phases, forming peritectic-type microstructures with uniform stereoscopic dispersion of graphene nanoplatelets forming an interconnected nanostructured network, with a graphene proportion varying between 0.1% and 3.0% by weight, the nanocomposite exhibiting an electrical conductivity greater than 70% IACS.

2. HIGH ELECTRICAL AND THERMAL CONDUCTIVITY ALUMINUM-GRAPHENE NANOCOMPOSITES, according to claim 1, characterized in that the aluminum matrix is ​​preferably derived from aluminum alloys of the 1000 series - such as 1350 (commercially pure) - or typical casting alloys such as SAE 323 or 6201 for the production of electrical cables.

3. HIGH ELECTRICAL AND THERMAL CONDUCTIVITY ALUMINUM-GRAPHENE NANOCOMPOSITES, according to claim 1, characterized by graphenic materials, in the form of multilayer graphene nanoplatelets (MGNs), used in the processing of aluminum nanocomposites, with the number of layers varying from one to ten, and having an average surface area equal to or greater than 60 m². 2 / g.

4. High electrical and thermal conductivity aluminum-graphene nanocomposites, according to the preceding claims, characterized by having an increased thermal diffusivity of 15 to 50% in In comparison to the aluminum alloy used for the synthesis of nanocomposites, this diffusivity is obtained through the formation of an interconnected nanostructured graphene network that promotes efficient heat transfer along the metallic matrix, resulting in a significant reduction in thermal resistance and improved heat dissipation.

5. METHOD FOR OBTAINING ALUMINUM-GRAPHENE NANOCOMPOSITES WITH HIGH ELECTRICAL AND THERMAL CONDUCTIVITY, characterized by encompassing the following steps: • Preparation of aluminum and graphene in crucibles heated to 850°C under an inert atmosphere; • Gradual addition of 2 / 3 of the graphene to the molten aluminum in the first crucible, followed by the incorporation of molten aluminum from the second crucible and manual stirring for homogenization; • Addition of the remaining graphene and solid aluminum to the system, followed by manual stirring and holding in an oven for microstructural stabilization; • Molding the alloy in a sand box after verifying that the temperature is above 740°C, to ensure dimensional accuracy and structural quality.

6. METHOD FOR OBTAINING ALUMINUM-GRAPHENE NANOCOMPOSITES WITH HIGH ELECTRICAL AND THERMAL CONDUCTIVITY, according to claim 5, characterized by using resistive furnaces and / or electromagnetic induction furnaces, where eddy currents and the magnetic blast generated by the induced currents assist in the agitation and homogeneous dispersion of graphene in the molten aluminum matrix.

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