Graphite / transition metal oxide composite material, preparation method thereof and application of graphite / transition metal oxide composite material in friction material

Abstract

The invention discloses a graphite / transition metal oxide composite material as well as a preparation method and application thereof in a friction material, and relates to the technical field of friction materials. The graphite / transition metal oxide composite material comprises a graphite matrix and transition metal oxide grown on the surface of the graphite matrix in situ, the transition metal oxide is selected from one of ZnO, MnO2, CuO and TiO2. Through strong interface bonding formed between the oxide and the graphite, the interface bonding strength of the graphite and a resin matrix is remarkably enhanced, crack propagation is inhibited, and the high-temperature thermal stability and friction stability of the material are improved.

Description

Technical Field

[0001] This invention relates to the field of friction materials technology, specifically to a graphite / transition metal oxide composite material, its preparation method, and its application in friction materials. Background Technology

[0002] Friction materials, as key functional materials in braking systems, are widely used in automobiles, rail transportation, and construction machinery. Their main function is to convert the kinetic energy of moving parts into heat energy through friction, thereby achieving deceleration or braking. With the continuous increase in vehicle operating speed, load levels, and braking frequency, friction materials face more stringent high-temperature, high-load, and high-energy-density conditions during service, placing higher demands on their frictional stability, wear resistance, and thermal stability.

[0003] Graphite, due to its layered crystal structure, weak interlayer bonding, and good self-lubricating properties, is widely used as a solid lubricant component in friction materials. However, under high temperature and severe frictional load conditions, graphite itself has certain limitations. On the one hand, the interfacial bonding between graphite and the resin matrix is ​​weak, making it prone to peeling and detachment during friction, hindering effective load transfer. On the other hand, graphite is prone to oxidation in high-temperature environments, significantly reducing its lubrication performance and structural stability, leading to fluctuations in the coefficient of friction, increased wear rate, and even accelerated damage to the friction material and the wear pair.

[0004] To improve the service performance of graphite in friction materials, existing technologies typically employ physical mixing to introduce metal oxides, ceramic particles, or other inorganic fillers into the friction material system, aiming to enhance the material's wear resistance and thermal stability. Existing technologies also involve coating inorganic fillers with liquid cashew phenolic resin to prepare composite friction powders, which are then compounded with various components to form friction materials. However, this method still relies on physical coating and complex formulations, failing to achieve a strong chemical interfacial bond between graphite and the filler, and still faces the risk of interfacial failure and graphite oxidation and exfoliation under high temperature and high load. Existing technologies also use micron-sized diamond to enhance mechanical and tribological properties. However, these methods still primarily rely on physical mixing, lacking a strong chemical bond between graphite and the reinforcing phase, and still suffer from interfacial failure, graphite oxidation, and performance fluctuations under high temperature and high load. Furthermore, these modification methods often suffer from uneven filler dispersion in the matrix and limited interfacial bonding effects, making it difficult to fundamentally improve the interfacial state between graphite and the matrix. Under high-temperature braking conditions, the above-mentioned composite system is still prone to problems such as graphite shedding, unstable friction film, and excessively large wear debris, which restricts the improvement of the overall performance of friction materials.

[0005] Therefore, there is an urgent need to develop a novel graphite-based composite material and its preparation method that can significantly improve the interfacial bonding ability of graphite, inhibit graphite exfoliation and oxidation, and achieve stable control of friction performance under high temperature and high friction conditions, so as to meet the application needs of high-performance friction materials, especially braking friction materials. Summary of the Invention

[0006] To address the shortcomings of the aforementioned background technologies, this invention primarily solves the problems of insufficient interfacial bonding between graphite and the matrix in existing friction materials, easy delamination and oxidation under high-temperature and high-load friction conditions, large fluctuations in the coefficient of friction, insufficient wear resistance, and accelerated damage to the wear pair. This invention provides a graphite / transition metal oxide composite material, its preparation method, and its application in friction materials. By in-situ growing transition metal oxides on the graphite surface, this invention constructs a stable composite interface structure with multi-scale characteristics, enhancing the interfacial bonding between graphite and the matrix at the material bulk level. Simultaneously, it improves the thermal stability and oxidation resistance of graphite under high-temperature friction conditions, thereby significantly improving the service stability of friction materials under harsh operating conditions.

[0007] The first objective of this invention is to provide a graphite / transition metal oxide composite material comprising a graphite matrix and transition metal oxides grown in situ on the surface of the graphite matrix. The transition metal oxide is selected from one or more of ZnO, MnO2, CuO, and TiO2.

[0008] Preferably, the transition metal oxide exhibits at least one morphology on the graphite matrix surface, including needle-like, blocky, polyhedral, and spherical shapes; the particle size of the transition metal oxide is 0.1-2 μm.

[0009] Preferably, the mass ratio of the graphite matrix to the transition metal oxide is 10~5:1.

[0010] Preferably, the transition metal oxide forms a tightly bonded composite interface on the graphite matrix surface through a chemical reaction; the graphite / transition metal oxide composite material has a residual mass of 28.1%-73.8% after ≥900°C in an air atmosphere.

[0011] Preferably, the graphite matrix has a layered crystal structure, including natural graphite or artificial graphite.

[0012] The second objective of this invention is to provide a method for preparing a graphite / transition metal oxide composite material, characterized by comprising the following steps: The graphite matrix was added to a solution containing a transition metal precursor and mixed thoroughly to obtain a dispersion system. The dispersion system was subjected to a hydrothermal reaction under closed conditions. By controlling the reaction temperature and reaction time, the transition metal oxides were nucleated and grown in situ on the graphite matrix surface to obtain a graphite / transition metal oxide composite precursor. The graphite / transition metal oxide composite precursor is heat-treated under a set temperature to obtain the graphite / transition metal oxide composite material.

[0013] Preferably, the hydrothermal reaction is carried out at a temperature of 80-150℃ for 5-10 hours.

[0014] Preferably, the ratio of transition metal precursor to graphite matrix is ​​1-3 mol / g; The transition metal precursor is selected from any one of Zn(NO3)2·6H2O, KMnO4, CuSO4·5H2O, and Ti(OC4H9)4.

[0015] Preferably, the heat treatment is performed at a temperature of 180-250℃ for 4-6 hours.

[0016] The third objective of this invention is to provide an application of graphite / transition metal oxide composite materials in friction materials.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a graphite / transition metal oxide composite material, its preparation method, and its application in friction materials. The invention utilizes transition metal oxides to construct a stable multi-scale interface structure on the graphite surface. This significantly improves the interfacial bonding strength between graphite and the resin matrix, enhancing load transfer efficiency. Furthermore, under applied loads, it acts as a crack propagation inhibitor, inducing crack deflection, bifurcation, and passivation, thereby suppressing rapid crack propagation within the graphite. This results in a graphite / transition metal oxide composite material possessing enhanced interfacial bonding strength, crack propagation inhibition capability, and high-temperature friction stability, making it particularly suitable for friction material systems operating under high-temperature, high-load, and high-frequency friction conditions.

[0018] This invention utilizes the inherent defects, oxygen-containing functional groups, or π-electron system on the surface of graphite to adsorb transition metal ions (such as Zn²⁺) through solution. + Mn 7+ (with MnO4) - (form), Cu² + Ti 4+The ions preferentially accumulate on the graphite surface; subsequently, under mild hydrothermal conditions, these ions undergo hydrolysis, redox, or precipitation reactions on the graphite surface, generating corresponding oxide nanoparticles or microparticles in situ, which are firmly anchored on the graphite substrate; finally, appropriate heat treatment further strengthens the oxide crystallization and its interfacial bonding with graphite. The resulting product is not a simple mixture, but a composite material with a multi-level "graphite core-oxide" structure.

[0019] The application of the graphite / transition metal oxide composite material of the present invention in friction materials can achieve significant enhancement of mechanical properties, substantial reduction of wear and stable improvement of friction performance through multiple mechanisms such as interface strengthening, crack propagation inhibition and friction film stabilization regulation. It is particularly suitable for the field of high-performance braking friction materials. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for preparing a graphite / transition metal oxide composite material according to the present invention; Figure 2 TEM images and EDS spectra of the graphite / transition metal oxide composites prepared in (a) Example 1, (b) Example 4, (c) Example 7 and (d) Example 10; Figure 3 (a) Infrared spectrum, (b) Raman spectrum, (c) XRD pattern and (d) thermogravimetric diagram of graphite or graphite / transition metal oxide composite materials prepared in Comparative Example 1, Example 1, Example 4, Example 7 and Example 10; Figure 4 (a) compressive strength, (b) flexural strength, (c) tensile strength and (d) thermal conductivity of the friction materials prepared in Comparative Example 1, Example 1, Example 4, Example 7 and Example 10; Figure 5 The friction coefficient curves of the friction materials prepared in Comparative Example 1, Example 1, Example 4, Example 7 and Example 10 during the thermal decay period of 100-350℃ and the thermal recovery period of 350-100℃ are shown. Figure 6 The volumetric wear rate curves of the friction materials prepared in Comparative Example 1, Example 1, Example 4, Example 7 and Example 10 are shown in (a) the volumetric wear rate curves during thermal decay at 100-350°C and (b) the volumetric wear rate at 350°C. Detailed Implementation

[0021] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0022] Graphite, as a typical layered solid lubricant, is widely used in friction materials due to its weak interlayer bonding and easy shear slip, aiming to reduce the coefficient of friction and provide a stable lubricating film. However, the interface between natural or artificial graphite and the organic resin matrix is ​​primarily a physical bond with limited strength. During the service life of friction materials, especially under extreme conditions of high temperature (>300℃), high load, and high-frequency braking, this weak interfacial bonding easily leads to the complete peeling of graphite sheets from the matrix, forming large-sized wear debris. This not only exacerbates the wear of the material itself, causing a sharp increase in the wear rate, but the unstable wear debris also disrupts the continuity of the friction interface, triggering drastic fluctuations in the coefficient of friction (usually manifested as a sudden drop followed by a sudden rise), the so-called thermal decay phenomenon. Furthermore, graphite is prone to oxidation at high temperatures, destroying its layered structure and losing its lubricating function, further accelerating the deterioration of material performance. Therefore, improving the interfacial bonding strength between graphite and the matrix and inhibiting its peeling and oxidation at high temperatures is key to developing high-performance friction materials.

[0023] Transition metal oxides, such as zinc oxide (ZnO), manganese dioxide (MnO2), copper oxide (CuO), and titanium dioxide (TiO2), typically possess high melting points, good thermal stability, and certain mechanical strength. If these oxides could be combined with graphite in a specific manner, their high stability could be utilized to protect the graphite and enhance the interface. However, traditional physical blending methods simply mix graphite powder and oxide powder, resulting in a lack of strong chemical bonds between the two. The weak interfacial bonding makes them prone to separation during friction, failing to achieve synergistic performance improvements. Furthermore, interfacial mismatch may even lead to stress concentration and accelerated degradation.

[0024] This invention addresses the issue that, while graphite possesses excellent self-lubricating properties, its contact with the resin matrix is ​​primarily physical, resulting in limited interfacial bonding. Under high temperature, high load, and high frequency friction conditions, graphite is prone to interfacial debonding and structural peeling, accompanied by rapid oxidation. This makes it difficult to maintain a stable friction film, leading to unstable friction performance, significantly increased wear rate, and even catastrophic failure of the friction material and the wear pair.

[0025] The present invention aims to provide a graphite / transition metal oxide composite material, its preparation method, and its application in friction materials. The present invention constructs a stable composite interface structure with multi-scale characteristics by in-situ growing transition metal oxides on the graphite surface, thereby enhancing the interfacial bonding ability between graphite and the matrix at the material bulk level, and improving the thermal stability and oxidation resistance of graphite under high-temperature friction conditions, thus significantly improving the service stability of friction materials under harsh working conditions.

[0026] To achieve the above objectives, the first aspect of the present invention provides a graphite / transition metal oxide composite material, the graphite / transition metal oxide composite material comprising a graphite matrix and transition metal oxides grown in situ on the surface of the graphite matrix; The transition metal oxide is selected from one of ZnO, MnO2, CuO, and TiO2.

[0027] The transition metal oxide used in this invention is an oxide phase formed in situ on the graphite surface through a process of metal ion adsorption-nucleation-growth, rather than obtained through mechanical mixing or surface coating.

[0028] This invention utilizes transition metal oxides to construct a stable multi-scale interface structure on the graphite surface. On one hand, this significantly improves the interfacial bonding strength between graphite and the resin matrix, enhancing load transfer efficiency. On the other hand, under applied loads, it acts as a crack propagation inhibitor, inducing crack deflection, bifurcation, and passivation, thereby suppressing rapid crack propagation within the graphite. Therefore, the graphite / transition metal oxide composite material simultaneously possesses enhanced interfacial bonding strength, crack propagation inhibition capability, and high-temperature friction stability, making it particularly suitable for friction material systems operating under high-temperature, high-load, and high-frequency friction conditions.

[0029] The transition metal oxide exhibits at least one morphology on the graphite matrix surface, including needle-like, blocky, polyhedral, and spherical shapes; the particle size of the transition metal oxide is 0.1-2 μm.

[0030] Transition metal oxides form a multi-scale discontinuous distribution structure on the surface of a graphite matrix, which can be used to induce crack deflection, bifurcation and passivation under frictional loads.

[0031] The particle size of transition metal oxides reaches the micrometer level. This micrometer-scale structure is used to bear frictional loads and participate in the formation of frictional films, while the submicrometer-scale structure is used to increase the specific surface area and enhance the interfacial heat conduction and energy dissipation capabilities.

[0032] Transition metal oxides increase the surface roughness and interfacial contact area of ​​graphite, thereby improving the interfacial bonding strength between graphite and the resin matrix. They also promote heat conduction along the graphite layer and interfacial direction during friction, thus inhibiting local heat accumulation and high-temperature oxidation.

[0033] In this invention, the mass ratio of the graphite matrix to the transition metal oxide is 10~5:1.

[0034] The transition metal oxide forms a tightly bonded composite interface on the graphite matrix surface through a chemical reaction, enabling the graphite / transition metal oxide composite material to simultaneously possess enhanced interfacial bonding strength, crack propagation inhibition capability, and high-temperature frictional stability.

[0035] The graphite / transition metal oxide composite material, when heated to ≥900°C in air, has a residual mass of 28.1%-73.8%.

[0036] The graphite matrix has a layered crystal structure and includes natural graphite or artificial graphite.

[0037] A second aspect of this invention provides a method for preparing a graphite / transition metal oxide composite material, comprising the following steps: The graphite matrix was added to a solution containing a transition metal precursor and mixed thoroughly to obtain a dispersion system. The dispersion system was subjected to a hydrothermal reaction under closed conditions. By controlling the reaction temperature and reaction time, the transition metal oxides were nucleated and grown in situ on the graphite matrix surface to obtain a graphite / transition metal oxide composite precursor. The graphite / transition metal oxide composite precursor is heat-treated under a set temperature to obtain the graphite / transition metal oxide composite material.

[0038] For example, see Figure 1 The method for preparing the graphite / transition metal oxide composite material shown includes: (1) Pre-growth: Graphite is added to a solution containing transition metal precursors and a uniform dispersion system is formed by stirring, ultrasonic dispersion or a combination thereof, so that transition metal ions are fully adsorbed on the graphite surface and a metal ion enrichment layer is formed on the graphite surface. (2) Hydrothermal in-situ growth: The pre-grown dispersion system is transferred to the reaction vessel and hydrothermal reaction is carried out under closed conditions. By controlling the reaction temperature, reaction time and solution environment, the transition metal oxide is nucleated and grown in situ on the graphite surface to obtain the graphite / transition metal oxide composite precursor. (3) Heat treatment: After washing and drying the composite precursor, heat treatment is carried out under a set temperature to improve the crystallinity of the transition metal oxide and enhance the interfacial bonding strength between graphite and transition metal oxide, thereby obtaining a graphite / transition metal oxide composite material.

[0039] This invention relates to a design concept and preparation technique for in-situ construction of transition metal oxide structures on the surface of graphite using chemical methods. The core of this technique lies in: firstly, utilizing the inherent defects, oxygen-containing functional groups, or π-electron systems on the graphite surface, transition metal ions (such as Zn²⁺) are adsorbed onto the graphite surface through solution adsorption. + Mn 7+ (with MnO4) - (form), Cu² + Ti 4+The ions preferentially accumulate on the graphite surface; subsequently, under mild hydrothermal conditions, these ions undergo hydrolysis, redox, or precipitation reactions on the graphite surface, generating corresponding oxide nanoparticles or microparticles in situ, which are firmly anchored on the graphite substrate; finally, appropriate heat treatment further strengthens the oxide crystallization and its interfacial bonding with graphite. The resulting product is not a simple mixture, but a composite material with a multi-level "graphite core-oxide" structure.

[0040] In this composite structure, each component has a clear function and significant synergistic effect: graphite, as the core lubricating phase, retains its basic interlayer slip capability and provides basic lubrication function; the transition metal oxides, which grow in situ and are firmly attached to the graphite surface, serve as the outer layer phase and play multiple key roles: (1) Interface anchoring and strengthening: the oxide particles are embedded in the graphite surface like "rivets". When they are wrapped by the resin matrix, they greatly increase the mechanical meshing and physical contact area between the graphite and the resin, and significantly improve the interface bonding strength through possible chemical reactions, effectively preventing the overall peeling of the graphite sheets. (2) Crack propagation inhibition and wear debris refinement: under frictional load, when the crack propagates to the interface between the graphite and oxide or to the oxide particles, it will deflect, bypass or bifurcate, consuming more energy, thereby blunting the crack tip. This makes the graphite tend to undergo more refined fragmentation, generating smaller and more uniformly distributed wear debris. These fine wear debris are more easily compacted on the surface of the friction pair, participating in the formation of a uniform, dense and stable friction film, rather than causing three-body wear as large abrasive particles. (3) Thermal management and anti-oxidation: Transition metal oxides embedded on the graphite surface can improve the overall thermal conductivity of the composite material, help the frictional heat diffuse in the in-plane direction, inhibit the formation of local hot spots, and thus delay the oxidation initiation temperature of graphite. At the same time, at high temperatures, some oxides themselves can also participate in tribochemical reactions to form a stable surface protective film mainly composed of metal oxides, which isolates oxygen and further protects the underlying graphite matrix.

[0041] The raw materials used in this invention include natural / artificial graphite, zinc nitrate, potassium permanganate, copper sulfate, tetrabutyl titanate, urea, etc., all of which are commercially available common chemical raw materials, with low cost and wide availability. The hydrothermal reaction, ultrasonic dispersion, stirring, and heat treatment processes involved all rely on conventional equipment in laboratory or industrial production. The process flow is clear, the conditions are mild and controllable, and the reproducibility is good, possessing the potential for large-scale production.

[0042] During the hydrothermal reaction, the temperature is 80-150℃ and the time is 5-10 h. During the heat treatment, the temperature is 180-250℃ and the time is 4-6 h. This is to regulate the crystallinity and interfacial bonding state of the transition metal oxides.

[0043] The ratio of transition metal precursor to graphite matrix is ​​1-3 mol / g; this ratio can be understood as 1-3 mol of transition metal precursor to 1 g of graphite matrix.

[0044] The transition metal precursor is selected from any one of Zn(NO3)2·6H2O, KMnO4, CuSO4·5H2O, and Ti(OC4H9)4.

[0045] For example, Zn(NO3)2·6H2O is used to generate ZnO in situ on the graphite surface, KMnO4 is used to generate MnO2 in situ on the graphite surface, CuSO4·5H2O is used to generate CuO in situ on the graphite surface, and Ti(OC4H9)4 generates TiO2 in situ on the graphite surface through a hydrolysis reaction, thereby realizing the controlled nucleation and growth of transition metal oxides on the graphite surface.

[0046] A third aspect of this invention provides the application of a graphite / transition metal oxide composite material in friction materials. The composite material, as a functional additive in the friction material, is used to regulate the friction film structure, inhibit graphite exfoliation, and reduce friction and wear.

[0047] The graphite / transition metal oxide composite material is introduced into the resin-based friction material system as a functional additive component, following the mixing, molding, and heat treatment methods provided in the applicant's authorized patent publication number: CN114806075B. This is used to improve the service condition of graphite in friction materials, regulate the friction film structure, and achieve synergistic improvement in friction performance and wear resistance under high temperature, high load, and high frequency friction conditions. It is particularly suitable for the field of braking friction materials.

[0048] Compared to unmodified graphite, the graphite / transition metal oxide composite material of this invention significantly enhances the interfacial bonding strength between graphite and the resin matrix by in-situ growing transition metal oxides on the graphite surface. This transforms graphite from an easily exfoliated additive phase into a functional phase capable of effectively participating in load transfer, thereby significantly improving the overall mechanical properties of the friction material. Experimental results show that, after introducing the composite material of this invention, the compressive strength, flexural strength, and tensile strength of Example 10 are increased by 38%, 35%, and 79% respectively compared to Comparative Example 1.

[0049] Therefore, compared with friction materials that do not incorporate the composite material of the present invention, its wear performance is significantly improved, and in preferred cases, the volumetric wear rate can be reduced by 55.6-75.9%, while the wear degree of the wear pair is significantly reduced.

[0050] Transition metal oxides possess high thermal stability and oxidation resistance, and under high-temperature friction conditions, they can participate in the formation of a stable friction film structure dominated by metal oxides, thereby effectively inhibiting high-temperature oxidation and catastrophic exfoliation of graphite. Experimental results show that, over a wide temperature range and under high-temperature braking conditions, the friction coefficient of the friction material incorporating the composite material of this invention remains at a high and stable level, with significantly reduced fluctuations in the friction coefficient under high-temperature conditions, exhibiting excellent frictional stability.

[0051] In summary, the application of the graphite / transition metal oxide composite material of the present invention in friction materials can achieve significant enhancement of mechanical properties, substantial reduction of wear, and stable improvement of friction performance through multiple mechanisms such as interface strengthening, crack propagation inhibition, and friction film stabilization. It is particularly suitable for the field of high-performance braking friction materials.

[0052] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0053] The graphite matrix used in the following embodiments is all natural graphite.

[0054] Example 1 A method for preparing a graphite / transition metal oxide composite material, characterized by comprising the following steps: (1) Pre-growth: Graphite is added to a solution containing transition metal precursor Zn(NO3)2·6H2O, and a uniform dispersion system is formed by stirring, ultrasonic dispersion or a combination thereof, so that the transition metal ions are fully adsorbed on the graphite surface and a metal ion enrichment layer is formed on the graphite surface, wherein the ratio of transition metal precursor to graphite is 1 mol / g. (2) Hydrothermal in-situ growth: The pre-grown dispersion system is transferred to a reaction vessel and hydrothermal reaction is carried out under closed conditions. The reaction temperature is 90℃ and the reaction time is 5h, so that the transition metal oxides are nucleated and grown in situ on the graphite surface to obtain the graphite / transition metal oxide composite precursor. (3) Heat treatment: After washing and drying the composite precursor, heat treatment is carried out at 180°C for 6 hours to improve the crystallinity of the transition metal oxide and enhance the interfacial bonding strength between graphite and transition metal oxide, thereby obtaining graphite / transition metal oxide composite material.

[0055] (4) Accurately weigh 15g of cashew nut shell oil modified phenolic resin, 20g of modified carbon fiber, 1g of carbon black, 8g of calcined alumina, 15g of fluorite, 8g of limestone, 10g of calcium sulfate, 17g of diatomaceous earth, and 6g of graphite / transition metal oxide composite material from step (3). Place the above raw materials in a high-speed mixer and mix them 5 times at 2000rpm, each time for 3s, with a 5min interval between the two mixing times to obtain a mixture; (5) Weigh 15.44g of the mixture obtained in step (4) and place it in the mold, and place it between the upper plate and the middle plate of the hot press. The pressure is set to 7.5MPa, the temperature is 160℃, and the hot pressing time is 10min. During this time, the gas is released once every 50s. After hot pressing and curing, a semi-finished product is obtained. The semi-finished product is placed in an electric heating drying oven for heat treatment. The procedure is as follows: start heating from room temperature for 15min, heat to 120℃, and hold for 60min; then continue heating for 15min, heat to 160℃, and hold for 95min; then heat for 20min, heat to 180℃; then heat for 10min, heat to 200℃, and hold for 60min. Cool to room temperature with the drying oven to obtain the modified carbon fiber reinforced resin-based friction material.

[0056] Example 2 A method for preparing a graphite / transition metal oxide composite material, the steps and parameters of which differ from those in Example 1 are as follows, while the remaining steps and parameters are the same as in Example 1.

[0057] In step (1), the ratio of transition metal precursor to graphite is 2 mol / g; in step (2), the hydrothermal time is 8 h; in step (3), the heat treatment temperature is 190℃ and the time is 5 h.

[0058] Example 3 A method for preparing a graphite / transition metal oxide composite material, the steps and parameters of which differ from those in Example 1 are as follows, while the remaining steps and parameters are the same as in Example 1.

[0059] In step (1), the ratio of transition metal precursor to graphite is 3 mol / g; in step (2), the hydrothermal temperature is 100℃ and the time is 10h; in step (3), the heat treatment temperature is 200℃ and the time is 4h.

[0060] Example 4 A method for preparing a graphite / transition metal oxide composite material, the steps and parameters of which differ from those in Example 1 are as follows, while the remaining steps and parameters are the same as in Example 1.

[0061] In step (1), the transition metal precursor is KMnO4; in step (2), the hydrothermal temperature is 150℃.

[0062] Example 5 A method for preparing a graphite / transition metal oxide composite material, the steps and parameters of which differ from those in Example 1 are as follows, while the remaining steps and parameters are the same as in Example 1.

[0063] In step (1), the transition metal precursor is KMnO4, and the ratio of the transition metal precursor to graphite is 2 mol / g; in step (2), the hydrothermal temperature is 140℃ and the time is 8h; in step (3), the heat treatment temperature is 190℃ and the time is 5h.

[0064] Example 6 A method for preparing a graphite / transition metal oxide composite material, the steps and parameters of which differ from those in Example 1 are as follows, while the remaining steps and parameters are the same as in Example 1.

[0065] In step (1), the transition metal precursor is KMnO4, and the ratio of transition metal precursor to graphite is 3 mol / g; in step (2), the hydrothermal temperature is 130℃ and the time is 10h; in step (3), the heat treatment temperature is 200℃ and the time is 4h.

[0066] Example 7 A method for preparing a graphite / transition metal oxide composite material, the steps and parameters of which differ from those in Example 1 are as follows, while the remaining steps and parameters are the same as in Example 1.

[0067] In step (1), the transition metal precursor is CuSO4·5H2O; in step (2), the hydrothermal temperature is 80℃ and the time is 8h.

[0068] Example 8 A method for preparing a graphite / transition metal oxide composite material, the steps and parameters of which differ from those in Example 1 are as follows, while the remaining steps and parameters are the same as in Example 1.

[0069] In step (1), the transition metal precursor is CuSO4·5H2O, and the ratio of the transition metal precursor to graphite is 2 mol / g; in step (2), the hydrothermal temperature is 80℃ and the time is 9h; in step (3), the heat treatment temperature is 190℃ and the time is 5h.

[0070] Example 9 A method for preparing a graphite / transition metal oxide composite material, the steps and parameters of which differ from those in Example 1 are as follows, while the remaining steps and parameters are the same as in Example 1.

[0071] In step (1), the transition metal precursor is CuSO4·5H2O, and the ratio of the transition metal precursor to graphite is 3 mol / g; in step (2), the hydrothermal time is 10 h; in step (3), the heat treatment temperature is 200℃ and the time is 4 h.

[0072] Example 10 A method for preparing a graphite / transition metal oxide composite material, the steps and parameters of which differ from those in Example 1 are as follows, while the remaining steps and parameters are the same as in Example 1.

[0073] In step (1), the transition metal precursor is Ti(OC4H9)4; in step (2), the hydrothermal temperature is 150℃ and the time is 8h.

[0074] Example 11 A method for preparing a graphite / transition metal oxide composite material, the steps and parameters of which differ from those in Example 1 are as follows, while the remaining steps and parameters are the same as in Example 1.

[0075] In step (1), the transition metal precursor is Ti(OC4H9)4, and the ratio of the transition metal precursor to graphite is 2 mol / g; in step (2), the hydrothermal temperature is 140℃ and the time is 9h; in step (3), the heat treatment temperature is 190℃ and the time is 5h.

[0076] Example 12 A method for preparing a graphite / transition metal oxide composite material, the steps and parameters of which differ from those in Example 1 are as follows, while the remaining steps and parameters are the same as in Example 1.

[0077] In step (1), the transition metal precursor is Ti(OC4H9)4, and the ratio of the transition metal precursor to graphite is 3 mol / g; in step (2), the hydrothermal temperature is 120℃ and the time is 10h; in step (3), the heat treatment temperature is 200℃ and the time is 4h.

[0078] Comparative Example 1: A method for preparing a graphite-reinforced friction material, comprising: (1) Accurately weigh 15g of cashew nut shell oil modified phenolic resin, 20g of modified carbon fiber, 1g of carbon black, 8g of calcined alumina, 15g of fluorite, 8g of limestone, 10g of calcium sulfate, 17g of diatomaceous earth, and 6g of natural graphite. Place the above raw materials in a high-speed mixer and mix them 5 times at 2000rpm, each time for 3s, with a 5min interval between the two mixing times to obtain the mixture; Weigh 15.44g of the mixture obtained in step (1) and place it in a mold between the upper and middle plates of a hot press. Set the pressure to 7.5MPa, the temperature to 160℃, and the hot pressing time to 10min. Release the gas once every 50s during the hot pressing. After hot pressing and curing, a semi-finished product is obtained. Place the semi-finished product in an electric heating drying oven for heat treatment. The procedure is as follows: start heating from room temperature for 15min, heat to 120℃, and hold for 60min; then continue heating for 15min, heat to 160℃, and hold for 95min; then heat for 20min, heat to 180℃; then heat for 10min, heat to 200℃, and hold for 60min. Cool to room temperature with the drying oven to obtain the modified carbon fiber reinforced resin-based friction material.

[0079] To illustrate the relevant properties of the graphite / transition metal oxide composite material provided by this invention, the accompanying drawings are provided.

[0080] See Figure 2 As shown, TEM images clearly show that a transition metal oxide layer was successfully coated on the graphite surface. In Example 1 (graphite / ZnO composite material), ZnO was directionally grown on the graphite surface in the form of needle-like nanostructures, with a length of approximately 60-90 μm and a diameter of 5-10 μm. Figure 2 a). In Example 4 (graphite / MnO2 composite material), MnO2 is presented as blocky particles, uniformly anchored on graphite, with a size of approximately 30-50 μm. Figure 2 b). In Example 7 (graphite / CuO composite material), the CuO consists of irregular nanoparticles with a size of approximately 0.5-2 μm, forming a continuous capping layer ( Figure 2 c). In Example 10 (graphite / TiO2 composite material), the TiO2 particles were spherical with a particle size of approximately 1-2 μm and were uniformly dispersed. Figure 2 d). The corresponding EDS energy dispersive spectroscopy analysis showed that, based on the characteristic carbon signal of graphite, there were obvious characteristic peaks of transition metal elements (Zn, Mn, Cu, Ti) and their corresponding oxygen elements, and the distribution areas of metal and oxygen elements highly overlapped. This indicates that transition metal oxides have been successfully grown in situ on the graphite surface and formed a tightly bonded composite structure, rather than a simple physical mixture.

[0081] See Figure 3 As shown, Figure 3 As shown in (a), compared to Comparative Example 1 which used pure graphite, all graphite / transition metal oxide composites (Examples 1, 4, 7, and 10) exhibited new characteristic absorption peaks in the low wavenumber region. Example 1 (graphite / ZnO) showed peaks in the 400-550 cm⁻¹ range. - A Zn-O bond vibration peak appears at position ¹, and in Example 4 (graphite / MnO2), it is at 450-550 cm⁻¹. -A Mn-O bond vibration peak appears at position ¹, and in Example 7 (graphite / CuO), it is at 430-540 cm⁻¹. - A Cu-O bond vibration peak appears at position ¹, and in Example 10 (graphite / TiO2), it is at 400-800 cm⁻¹. - The appearance of a Ti-O bond vibration peak at position ¹ directly proves the successful formation of the corresponding metal oxide phase. Raman spectroscopy ( Figure 3 b) Further evidence was provided: Example 1 at ~437 cm - The characteristic peak of ZnO appears at ¹, and in Example 4 it is at 500-700 cm⁻¹. - ¹ A characteristic broad peak of MnO2 appears within the range, with Example 7 showing a peak at ~298 cm⁻¹. - The characteristic peak of CuO appears at ¹, and in Example 10 it is at ~144 cm⁻¹. - The characteristic peak of TiO2 appears at position ¹. The appearance of these characteristic peaks confirms the presence of a well-crystallized metal oxide phase in the composite material. XRD pattern ( Figure 3 c) shows that all samples exhibited strong diffraction peaks at approximately 26.5° for the graphite (002) crystal plane, indicating that the graphite crystal structure was well preserved during the preparation process. Simultaneously, characteristic diffraction peaks of corresponding metal oxides (such as ZnO, MnO2, CuO, and TiO2) appeared in the spectra of each composite material, with no other impurity phase peaks, indicating that the transition metal oxides were successfully deposited and crystallized on the graphite surface. Combined FTIR, Raman, and XRD analyses fully demonstrate the successful preparation of a well-defined graphite / transition metal oxide composite material using the method of this invention. Thermogravimetric analysis shows ( Figure 3 d) The heat resistance of graphite / transition metal oxide composites is significantly higher than that of original graphite. In air atmosphere, after 900 degrees, the mass residual rate is 28.1%-73.8%, which is much higher than the 8.4% of original graphite.

[0082] See Figure 4 As shown, Figure 4As shown in Figure (ac), compared with the friction material prepared using pure graphite in Comparative Example 1, the mechanical properties of the various examples (Examples 1, 4, 7, and 10) incorporating graphite / transition metal oxide composites were significantly improved. Example 10 showed increases in compressive strength, flexural strength, and tensile strength of 38%, 35%, and 79%, respectively, compared to Comparative Example 1. This enhancement effect stems from the in-situ growth of the metal oxides, which increases the surface roughness and interfacial contact area of ​​the graphite, thereby significantly improving the mechanical interlocking and interfacial bonding strength between the graphite and the resin matrix. The enhancement efficiency varied depending on the oxide morphology: the needle-like structure of Example 1 (graphite / ZnO) and the blocky structure of Example 4 (graphite / MnO2) provided some enhancement; while the uniform nanoparticle structure of Examples 7 (graphite / CuO) and 10 (graphite / TiO2) more effectively promoted crack deflection and extended the propagation path, thus exhibiting superior mechanical enhancement.

[0083] Figure 4 (d) shows the thermal conductivity of the material. Compared to Comparative Example 1, the out-of-plane thermal conductivity of the embodiments containing graphite / transition metal oxides was increased by approximately 5-15%, while the in-plane thermal conductivity decreased slightly. This is because the metal oxides on the graphite surface increase its effective heat transfer area in the thickness direction, promote contact with carbon fibers, and form additional heat conduction pathways, thereby facilitating the rapid dissipation of frictional heat from the contact surface to the non-friction surface. This has a positive effect on suppressing local heat accumulation and thermal decay during high-temperature braking.

[0084] See Figure 5 As shown, during the entire thermal decay and subsequent thermal recovery process from 100-350℃, the friction coefficient curve of Comparative Example 1, using pure graphite, exhibited significant fluctuations, with a full-temperature coefficient of variation (FCV) of 0.203, indicating poor frictional stability. In contrast, the friction coefficient curves of the various embodiments (using graphite / transition metal oxide composites) were more stable, with FCV values ​​ranging from 0.140 to 0.155, demonstrating significantly improved high-temperature frictional stability. This is attributed to the in-situ growth of metal oxides on the graphite surface, which enhances the thermal stability of graphite and promotes the formation of a more stable and continuous friction film, effectively suppressing the severe frictional fluctuations caused by graphite oxidation and exfoliation at high temperatures. Especially at 350℃, the friction coefficients of the various embodiments (0.41-0.42) were significantly higher than those of Comparative Example 1 (0.38), reflecting the enhancing effect of metal oxides on interfacial shear resistance.

[0085] See Figure 6 As shown, Figure 6 As shown in Figure (a), during the temperature rise process from 100 to 350°C, the volumetric wear rate of Comparative Example 1 increased sharply with increasing temperature, from 0.14 × 10⁻⁶. -7cm³ / J increased to 0.54 × 10⁻⁶ -7 The volumetric wear rate was cm³ / J, exhibiting severe high-temperature wear. However, the volumetric wear rate of each embodiment remained at a low level (0.05 × 10⁻⁶ cm³ / J) across the entire temperature range. -7 – 0.25 × 10 -7 cm³ / J, exhibiting excellent wear resistance and stability. Specifically, at a high temperature of 350℃ ( Figure 6 (b) The volumetric wear rate of each embodiment was reduced by 55.6% to 75.9% compared to Comparative Example 1. This is mainly due to the introduction of metal oxides: on the one hand, they act as a physical barrier to delay the high-temperature oxidation of graphite; on the other hand, by enhancing interfacial bonding and regulating crack propagation, they promote the refinement and fragmentation of graphite, forming a more stable and load-bearing friction film, thereby significantly suppressing catastrophic material spalling and excessive wear. This characteristic of simultaneously achieving a high coefficient of friction and a low wear rate at high temperatures makes the graphite / transition metal oxide composite material of the present invention show great application potential in high-performance braking friction materials.

[0086] In summary, this invention provides a graphite / transition metal oxide composite material, its preparation method, and its application in friction materials. The composite material comprises a graphite matrix and a transition metal oxide phase grown in situ on the graphite matrix surface through a metal ion adsorption-nucleation-growth process. The transition metal oxide is selected from any one of ZnO, MnO2, CuO, and TiO2. The preparation method includes: dispersing graphite in a solution containing a transition metal precursor, allowing metal ions to be fully adsorbed onto the graphite surface; performing a hydrothermal reaction to allow the transition metal oxide to nucleate and grow in situ on the graphite surface, forming a composite precursor; and obtaining the graphite / transition metal oxide composite material after washing, drying, and heat treatment. This composite material, through the strong interfacial bonding formed between the oxide and graphite, significantly enhances the interfacial bonding strength between graphite and the resin matrix, inhibits crack propagation, and improves the high-temperature thermal stability and frictional stability of the material. When used as a functional additive in friction materials, it can reduce the volumetric wear rate of friction materials by 55.6-75.9% in the range of 100-350℃, while maintaining a stable and high coefficient of friction, making it suitable for high-performance braking friction materials.

[0087] This invention describes preferred embodiments and their effects. However, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments.

[0088] Although embodiments of the present invention have been shown and described above, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A graphite / transition metal oxide composite material, characterized in that, The graphite / transition metal oxide composite material includes a graphite matrix and transition metal oxides grown in situ on the surface of the graphite matrix. The transition metal oxide is selected from one of ZnO, MnO2, CuO, and TiO2.

2. The graphite / transition metal oxide composite material according to claim 1, characterized in that, The transition metal oxide exhibits at least one morphology on the graphite matrix surface, including needle-like, blocky, polyhedral, and spherical shapes; the particle size of the transition metal oxide is 0.1-2 μm.

3. The graphite / transition metal oxide composite material according to claim 1, characterized in that, The mass ratio of the graphite matrix to the transition metal oxide is 10~5:

1.

4. The graphite / transition metal oxide composite material according to claim 1, characterized in that, The transition metal oxide forms a tightly bonded composite interface on the graphite matrix surface through a chemical reaction; the graphite / transition metal oxide composite material has a residual mass of 28.1%-73.8% after ≥900°C in an air atmosphere.

5. The graphite / transition metal oxide composite material according to claim 1, characterized in that, The graphite matrix has a layered crystal structure and includes natural graphite or artificial graphite.

6. A method for preparing a graphite / transition metal oxide composite material according to any one of claims 1 to 5, characterized in that, Includes the following steps: The graphite matrix was added to a solution containing a transition metal precursor and mixed thoroughly to obtain a dispersion system. The dispersion system was subjected to a hydrothermal reaction under closed conditions. By controlling the reaction temperature and reaction time, the transition metal oxides were nucleated and grown in situ on the graphite matrix surface to obtain a graphite / transition metal oxide composite precursor. The graphite / transition metal oxide composite precursor is heat-treated under a set temperature to obtain the graphite / transition metal oxide composite material.

7. The method for preparing the graphite / transition metal oxide composite material according to claim 6, characterized in that, During the hydrothermal reaction, the temperature is 80-150℃ and the time is 5-10 h.

8. The method for preparing the graphite / transition metal oxide composite material according to claim 6, characterized in that, The ratio of transition metal precursor to graphite matrix is ​​1-3 mol / g; The transition metal precursor is selected from any one of Zn(NO3)2·6H2O, KMnO4, CuSO4·5H2O, and Ti(OC4H9)4.

9. The method for preparing the graphite / transition metal oxide composite material according to claim 6, characterized in that, During heat treatment, the temperature is 180-250℃ and the time is 4-6 hours.

10. The application of the graphite / transition metal oxide composite material according to any one of claims 1 to 5 in friction materials.

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