Nano graphite powder as well as preparation method and application thereof

Abstract

The invention relates to the technical field of graphite materials, in particular to nano graphite powder as well as a preparation method and application thereof. The method comprises the following steps: heating natural crystalline flake graphite with Dv50 of 30-50 microns to 500-650 DEG C in an air atmosphere, preserving heat for 0.5-2 hours, and cooling to room temperature to obtain oxidized natural crystalline flake graphite powder A; dispersing the oxidized natural crystalline flake graphite powder A in water to obtain a suspension B; putting the suspension liquid B into a high-pressure homogenizing crusher, and performing homogenizing treatment to obtain suspension liquid C; centrifuging the suspension C to obtain a precipitate D; and washing the precipitate D with deionized water, and drying to obtain the nano graphite powder. According to the method disclosed by the invention, defects are introduced into natural crystalline flake graphite in a graphite oxide manner, so that the homogenizing pressure or cycle index required by a high-pressure homogenizer is reduced; through an oxidation process and parameter adjustment of a high-pressure homogenizer, the particle size can be controlled; the process is safe and reliable and has no safety risk.

Description

Technical Field

[0001] The present invention relates to the technical field of graphite materials, and in particular to a nano graphite powder, a preparation method thereof and an application thereof. Background Art

[0002] Nano graphite powder is a nano material with a size less than 100 nm obtained by physically or chemically exfoliating and processing graphite. Its nano size endows unique physical and chemical properties, such as high specific surface area, excellent electrical / thermal conductivity, mechanical strength and chemical stability. Nano graphite powder is widely used in high-temperature lubrication, solid coatings and lubricating oil additives. Its high-temperature resistance (up to more than 400 °C in a non-oxidizing environment) and environmentally friendly characteristics make it an important candidate material to replace sulfur-containing and metal-containing lubricants.

[0003] The patent application with the patent publication number CN1508066A describes a method for preparing nano graphite powder by a detonation method. This patent uses the detonation method to prepare nano graphite powder. The explosion process is completed in an extremely short time, and key parameters such as temperature and pressure fluctuate greatly, which easily causes large differences between batches and affects the consistency of material properties at the same time; at the same time, it involves flammable and explosive chemicals, and has strict requirements for the safety protection of operators and the production environment, and there are great safety risks.

[0004] The patent application with the patent publication number CN101270313A describes a method for preparing a flaky nano graphite lubricating oil additive. This patent needs to use concentrated sulfuric acid and strong oxidants during the intercalation process. The discharge of acidic wastewater and waste gas is not friendly to the environment. At the same time, it has high safety risks, complex processes, harsh reaction conditions and low efficiency.

[0005] However, the existing nano graphite powder preparation technologies (such as intercalation redox method, chemical vapor deposition, etc.) still face challenges in large-scale production, structural homogeneity and cost control. How to balance the preparation efficiency, performance optimization and environmental friendliness of nano graphite powder has become the key technical bottleneck for promoting its industrial application. Summary of the Invention

[0006] The main purpose of the present invention is to provide a nano graphite powder, a preparation method thereof and an application thereof to solve the above technical problems.

[0007] To achieve the above object, a preparation method of a nano graphite powder provided by the present invention includes the steps: S1, heating natural flake graphite with a Dv50 of 30 - 50 μm in an air atmosphere to 500 - 650 °C, holding for 0.5 - 2 h, and after the temperature in the treatment furnace is cooled to room temperature, obtaining oxidized natural flake graphite powder A; S2, dispersing the oxidized natural flake graphite powder A in water to obtain a suspension B; S3. Place suspension B into a high-pressure homogenizing crusher, and after homogenization treatment, obtain the treated suspension C; S4. Centrifuge suspension C to obtain precipitate D; S5. After washing precipitate D with deionized water, dry it to obtain nano-graphite powder.

[0008] Preferably, in step S1, in a continuous high-temperature furnace, heat at a heating rate of 8 - 12 °C / min to 500 °C, and then heat at a heating rate of 4 - 6 °C / min to 500 - 650 °C.

[0009] Preferably, in step S1, heat at a heating rate of 10 °C / min to 500 °C, and then heat at a heating rate of 5 °C / min to 530 - 580 °C.

[0010] Preferably, in step S1, heat at a heating rate of 10 °C / min to 500 °C, and then heat at a heating rate of 5 °C / min to 550 °C.

[0011] Preferably, in step S2, in the oxidized natural flake graphite powder A, mix it with water at a ratio of 1:15 - 20 of the oxidized natural flake graphite powder A to water, and then add 0.4 - 0.6 wt% of sodium dodecyl sulfate. After mechanical stirring of the prepared mixture, obtain suspension B.

[0012] Preferably, in step S3, place suspension B into a high-pressure homogenizer, set the pressure of the high-pressure homogenizer to 100 - 200 MPa, treat for 10 - 20 min, and circulate the treatment for 10 - 20 times to obtain the treated suspension C.

[0013] Preferably, in step S4, place the above suspension C into a centrifuge, treat at 5000 rpm for more than 30 min to obtain precipitate D.

[0014] Preferably, add 5 times the weight of deionized water to precipitate D, stir with a mechanical stirrer for 30 min, then centrifuge at 5000 rpm for 30 min to obtain a precipitate. Repeat adding deionized water more than 3 times. Put the powder containing a small amount of deionized water into a dryer, dry at 110 - 130 °C for more than 5 h, and finally obtain nano-graphite powder.

[0015] The present invention also provides a nano-graphite powder prepared by using the preparation method of the nano-graphite powder described in any one of the above.

[0016] The present invention also provides an application of the described nano-graphite powder in lubricants.

[0017] The nano-graphite powder in the present invention, its preparation method and its application in lubricants. The nano-graphite powder is prepared by oxidizing natural flake graphite at 500 - 650 °C in an air atmosphere, which causes cracks to form on the basal plane of the flake graphite. The oxidation introduces defects into the graphite lattice. After the oxidized graphite is cooled to room temperature, it is put into a high-pressure homogenizer, with the pressure set at 100 - 200 MPa, the homogenization treatment time at 10 - 20 min, and the number of cycles at 10 - 20 times. After homogenization treatment, centrifugal separation and water washing are carried out, and after drying, nano-graphite powder with a particle size of 10 - 100 nm is obtained. The method in the present invention has at least the following beneficial effects: (1) After natural flake graphite is oxidized in an air environment, its essence is an exothermic reaction between carbon and oxygen, and the oxidation preferentially starts from the edges and defects, introducing defects such as vacancies and cracks. The increase in crystal defects destroys the SP 2 conjugated network, mainly showing the following states: Structure destruction: The original layered crystal structure of natural flake graphite is disintegrated due to the oxidation reaction. The edges and defects of the flake graphite are preferentially oxidized, resulting in interlayer peeling and surface etching, presenting pores and cracks microscopically; Particle size reduction: The escape of carbon atoms during the oxidation process reduces the size of graphite particles; Decrease in crystal order: The layered ordered structure is destroyed and the crystal size decreases; Generation of surface functional groups: The oxidation reaction introduces oxygen-containing functional groups on the graphite surface, and these groups enhance the hydrophilicity and chemical reactivity of the material; (2) After natural flake graphite is oxidized in an air environment, defects such as vacancies and cracks are introduced. The increase in crystal defects destroys the SP2 conjugated network, thereby reducing the crystallinity of the material and weakening the interlayer van der Waals force at the same time, making the graphite more easily broken by the shear force of the high-pressure homogenizer, obtaining nano-graphite powder with finer particle size, reducing the homogenization pressure or the number of cycles required by the high-pressure homogenizer, and saving energy consumption; (3) By adjusting the oxidation conditions to control the degree of oxidation and affecting the degree of defects introduced into the material, as the degree of oxidation increases, the number of defects increases, the shear force of the high-pressure homogenizer has a higher degree of fragmentation on the graphite, the Dv50 is smaller, and at the same time the graphite structure uniformity decreases, the degree of fragmentation is more controllable, and the particle size distribution (K value) tends to be smaller; through the adjustment of the oxidation process and the parameters of the high-pressure homogenizer, the particle size can be controlled and a sample with a narrower particle size distribution can be obtained at the same time, which is more efficient; (4) The hydrophobic chain of SDS (sodium dodecyl sulfate) adsorbs on the surface of graphite particles, with the hydrophilic sulfate group facing the aqueous phase. It prevents particle agglomeration through charge repulsion. The particles are more easily and uniformly broken by the shear force of the high-pressure homogenizer, and it also reduces the liquid surface tension, enhances the cavitation effect during the high-pressure homogenization process, and improves the utilization rate. Moreover, the nano-graphite powder with a small amount of surface functional groups does not affect subsequent applications in fields such as lubricants. Since the amount is small and does not affect the application, there is no need for an acid washing process. (5) Compared with the existing detonation method and intercalation method, the method of combining oxidation and high-pressure homogenizer for crushing is safe and reliable during the process, without safety risks, and does not produce waste acid, which is environmentally friendly. Description of the Drawings

[0018] The drawings, as part of the present invention, are used to provide a further understanding of the present invention. The schematic embodiments and descriptions of the present invention are used to explain the present invention, but do not constitute an improper limitation to the present invention. Obviously, the drawings in the following description are only some embodiments. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. In the drawings: Figure 1 It is the SEM image of the nano-graphite powder in Example 1. Detailed Embodiments

[0019] The following clearly and completely describes the technical problems to be solved, the technical solutions adopted, and the technical effects achieved by the embodiments of the present invention in combination with the drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other equivalent or significantly modified embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention. The embodiments of the present invention can be embodied in various different ways defined and covered in the claims.

[0020] It should be noted that in the following description, many specific details are given for the convenience of understanding. However, it is obvious that the implementation of the present invention can be without these specific details.

[0021] It should be noted that without clear limitation or conflict, the various embodiments and technical features in the present invention can be combined with each other to form technical solutions.

[0022] Example 1: Load natural flake graphite with a Dv50 of 30 μm into a continuous high-temperature furnace, introduce an air atmosphere, heat it to 500 °C at a rate of 10 °C / min and then to 550 °C at a rate of 5 °C / min, hold for 1 h, and take out the powder after the temperature in the furnace to be treated cools to room temperature to obtain oxidized natural flake graphite powder A. In the above-mentioned oxidized natural flake graphite powder A, it is mixed according to the ratio of graphite powder to water of 1:19, and then 0.5 wt% of SDS (sodium dodecyl sulfate) is added. The prepared mixture is stirred with a mechanical stirrer for 1 h to obtain suspension B; The suspension B is put into a high-pressure homogenizer. The pressure of the high-pressure homogenizer is set to 160 MPa and processed for 12 min. It is cycled and processed 15 times according to this parameter to obtain the processed suspension C; The above suspension C is put into a centrifuge and processed at 5000 rpm for 30 min to obtain precipitate D; 5 times the weight of deionized water is added to precipitate D. After stirring with a mechanical stirrer for 30 min, it is centrifuged at 5000 rpm for 30 min. After the powder precipitates, adding deionized water and precipitation are repeated 3 times. The powder containing a small amount of deionized water is put into a dryer and dried at 120 °C for 5 h to finally obtain nano-graphite powder.

[0023] Example 2 (minimum oxidation time): Natural flake graphite with Dv50 of 30 μm is loaded into a continuous high-temperature furnace, and an air atmosphere is introduced. It is heated to 500 °C at 10 °C / min and then to 550 °C at 5 °C / min, and held for 30 min. After the temperature in the processing furnace is cooled to room temperature, the powder is taken out to obtain oxidized natural flake graphite powder A; In the above-mentioned oxidized natural flake graphite powder A, it is mixed according to the ratio of graphite powder to water of 1:19, and then 0.5 wt% of SDS (sodium dodecyl sulfate) is added. The prepared mixture is stirred with a mechanical stirrer for 1 h to obtain suspension B; The suspension B is put into a high-pressure homogenizer. The pressure of the high-pressure homogenizer is set to 170 MPa and processed for 20 min. It is cycled and processed 20 times according to this parameter to obtain the processed suspension C; The above suspension C is put into a centrifuge and processed at 5000 rpm for 30 min to obtain precipitate D; 5 times the weight of deionized water is added to precipitate D. After stirring with a mechanical stirrer for 30 min, it is centrifuged at 5000 rpm for 30 min. After the powder precipitates, adding deionized water and precipitation are repeated 3 times. The powder containing a small amount of deionized water is put into a dryer and dried at 120 °C for 5 h to finally obtain nano-graphite powder.

[0024] Example 3 (maximum oxidation temperature): Natural flake graphite with Dv50 of 50 μm is loaded into a continuous high-temperature furnace, and an air atmosphere is introduced. It is heated to 500 °C at 10 °C / min and then to 650 °C at 5 °C / min, and held for 1 h. After the temperature in the processing furnace is cooled to room temperature, the powder is taken out to obtain oxidized natural flake graphite powder A; In the above-mentioned oxidized natural flake graphite powder A, it is mixed according to the ratio of graphite powder to water of 1:19, and then 0.5 wt% of SDS (sodium dodecyl sulfate) is added. The prepared mixture is stirred with a mechanical stirring rod for 1 h to obtain suspension B; The suspension B is put into a high-pressure homogenizer, the pressure of the high-pressure homogenizer is set to 150 MPa, and it is processed for 15 min. It is cycled and processed 16 times according to this parameter to obtain the processed suspension C; The above suspension C is put into a centrifuge and processed at 5000 rpm for 30 min to obtain precipitate D; 5 times the weight of deionized water is added to precipitate D, and it is stirred with a mechanical stirring rod for 30 min and then centrifuged at 5000 rpm for 30 min. After the powder precipitates, the process of adding deionized water and precipitation is repeated 4 times. The powder containing a small amount of deionized water is put into a dryer and dried at 100 °C for 6 h to finally obtain nano-graphite powder.

[0025] Example 4 (lowest homogenizer pressure): The natural flake graphite with Dv50 of 30 μm is loaded into a continuous high-temperature furnace, and an air atmosphere is introduced. It is heated to 500 °C at a rate of 10 °C / min, and then to 550 °C at a rate of 5 °C / min, and held for 1 h. After the temperature in the processing furnace cools to room temperature, the powder is taken out to obtain the oxidized natural flake graphite powder A; In the above-mentioned oxidized natural flake graphite powder A, it is mixed according to the ratio of graphite powder to water of 1:19, and then 0.5 wt% of SDS (sodium dodecyl sulfate) is added. The prepared mixture is stirred with a mechanical stirring rod for 1 h to obtain suspension B; The suspension B is put into a high-pressure homogenizer, the pressure of the high-pressure homogenizer is set to 100 MPa, and it is processed for 18 min. It is cycled and processed 20 times according to this parameter to obtain the processed suspension C; The above suspension C is put into a centrifuge and processed at 5000 rpm for 30 min to obtain precipitate D; 5 times the weight of deionized water is added to precipitate D, and it is stirred with a mechanical stirring rod for 30 min and then centrifuged at 5000 rpm for 30 min. After the powder precipitates, the process of adding deionized water and precipitation is repeated 4 times. The powder containing a small amount of deionized water is put into a dryer and dried at 120 °C for 5 h to finally obtain nano-graphite powder.

[0026] Example 5 (highest homogenizer pressure): The natural flake graphite with Dv50 of 40 μm is loaded into a continuous high-temperature furnace, and an air atmosphere is introduced. It is heated to 500 °C at a rate of 10 °C / min, and then to 550 °C at a rate of 5 °C / min, and held for 1 h. After the temperature in the processing furnace cools to room temperature, the powder is taken out to obtain the oxidized natural flake graphite powder A; In the above-mentioned oxidized natural flake graphite powder A, it is mixed according to the ratio of graphite powder to water of 1:19, and then 0.5 wt% of SDS (sodium dodecyl sulfate) is added. The prepared mixture is stirred with a mechanical stirrer for 1 h to obtain suspension B; The suspension B is put into a high-pressure homogenizer, the pressure of the high-pressure homogenizer is set to 200 MPa, and it is processed for 20 min. It is cycled and processed 12 times according to this parameter to obtain the processed suspension C; The above suspension C is put into a centrifuge and processed at 5000 rpm for 30 min to obtain precipitate D; 5 times the weight of deionized water is added to precipitate D, and it is stirred with a mechanical stirrer for 30 min and then centrifuged at 5000 rpm for 30 min. After the powder precipitates, the powder containing a small amount of deionized water is put into a dryer and dried at 110 °C for 5 h to finally obtain nano graphite powder.

[0027] Comparative Example 1 (without oxidation process) The difference from Example 1 is that there is no step 1, and the natural flake graphite with Dv50 of 30 μm is processed starting from step 2.

[0028] Comparative Example 2 (crushed by a jet mill) The difference from Example 1 is that there are no steps 2, 4, and 5. In step 3, the oxidized natural flake graphite powder A is put into a jet mill, and the air compressor pressure of the jet mill is set to 0.8 MPa, and it is continuously crushed for 2 h to obtain the crushed graphite powder.

[0029] Comparative Example 3 (low-temperature oxidation) The difference from Example 1 is that in step 1, the heating program is changed to 10 °C / min to 300 °C, 5 °C / min to 400 °C, and keep warm for 1 h.

[0030] Table 1

[0031] The data in Table 1 are the test results of Examples 1-5 and Comparative Examples 1-3.

[0032] Testing method: (1) Dv50 and K value are tested using Malvern Zetasizer (DLS) to obtain the values of Dv50, Dv90, and Dv10. The K value = ((Dv90 - Dv10) / Dv50); (2)Value of A: For each sample, 10 points are selected for sampling, and 10 SEM photos are taken for each sample. The linear measurement function in the SEM is used for measurement. 10 particles are selected from each photo, and the 10 particles should include the largest and smallest particles in the SEM image. The maximum diameter of the 10 particles is measured, and the average diameter of the 10 particles is calculated. Then, the average of the average maximum diameters of the 10 SEM photos is calculated to obtain the value of A (nm).

[0033] From the data of Example 1 and Examples 2 and 3, it can be seen that by adjusting the oxidation conditions (time, temperature), the particle size and particle size distribution of the final nano-graphite powder can be adjusted. During the oxidation process, defects such as vacancies and cracks will be introduced into the flake graphite. The increase in crystal defects destroys the SP 2 conjugated network, thereby reducing the crystallinity of the material and weakening the intermolecular van der Waals force at the same time, making the graphite more easily broken by the shear force of the high-pressure homogenizer to obtain graphite powder with finer particle size. By adjusting the oxidation conditions to control the degree of oxidation, the degree of defects introduced into the material is affected. As the degree of oxidation increases, the number of defects increases, the shear force of the high-pressure homogenizer has a higher degree of fragmentation on the graphite, the Dv50 is smaller, and at the same time, the uniformity of the graphite structure decreases, the degree of fragmentation is more controllable, and the particle size distribution (K value) tends to be smaller.

[0034] From the data of Example 1 and Examples 4 and 5, it can be seen that by adjusting the pressure of the homogenizer, the particle size and particle size distribution of the nano-graphite powder can be controlled. When the pressure of the high-pressure homogenizer is controlled at 100 - 200 MPa, the graphite particles are mainly crushed by the synergistic action of shear force and cavitation effect. The micro-jet generated by the cavitation effect impacts the edge defects of the oxidized graphite, accelerating the fracture of the lamellae, and the shear force further peels off. The greater the pressure of the high-pressure homogenizer, the "lateral fracture" and "longitudinal peeling" of the lamellae occur, and the particle size of the crushed particles is smaller. At the same time, through multiple cycles, the particles are destructively crushed, the lamellar structure collapses, forming nano-scale particles, and the K value decreases. At the same time, the hydrophobic chain of SDS adsorbs on the surface of the graphite particles, and the hydrophilic sulfate group faces the aqueous phase. The charge repulsion effect prevents the particles from agglomerating. The particles are more easily and uniformly broken by the shear force of the high-pressure homogenizer, and the liquid surface tension is also reduced, enhancing the cavitation effect during the high-pressure homogenization process and improving the utilization rate.

[0035] From the data of Example 1 and Comparative Example 1, it can be seen that without oxidizing the natural flake graphite, no additional defects are introduced into the material, and the shear force of the high-pressure homogenizer has a low degree of fragmentation on the graphite. Under the same parameters of the high-pressure homogenizer, the degree of fragmentation in Comparative Example 1 is lower than that in Example 1. The Dv50 of the unoxidized graphite powder is large, and because of the high uniformity of the graphite structure, the degree of fragmentation is uncontrollable. At the same time, the oxidation treatment changes the surface of the graphite from hydrophobic to hydrophilic, making it more easily dispersed in water or polar solvents, reducing the agglomeration phenomenon during the high-pressure homogenization process, and the K value of the oxidized nano-graphite powder is smaller.

[0036] From the data of Example 1 and Comparative Example 2, it can be seen that for the graphite powder pulverized by the jet mill, the Dv50 still did not reach the nanoscale after 2 hours of treatment, and the K value was large. The jet mill mainly realizes crushing by accelerating the mutual collision of particles through high-speed air flow. The stripping efficiency of the layered structure (weakened van der Waals force) of graphite oxide is low, and large particle residues (D50>5 μm) are easily generated. To obtain graphite powder with a smaller particle size, long-term cyclic crushing is adopted, which is difficult to achieve precise control. Therefore, the particle size distribution is wide. The jet mill uses dry pulverization. After oxidation, graphite is prone to agglomeration due to van der Waals force in the dry state. The high-pressure homogenizer uses a liquid medium, and has better dispersion stability. At the same time, SDS is added to further optimize the dispersion effect. Therefore, the particle size distribution of the graphite powder treated by the high-pressure homogenizer is narrower.

[0037] From the data of Example 1 and Comparative Example 3, it can be seen that at a lower temperature, oxygen preferentially attaches to the active sites at the edges or defects of the particles, resulting in local oxidation. Compared with oxidation at a higher temperature, the degree of oxidation is lower, fewer defects are introduced, the Dv50 of the graphite powder is larger, and the K value is larger.

[0038] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for preparing nano graphite powder, characterized in that: Includes steps: S1, heating natural flake graphite with a Dv50 of 30-50 μm to 500-650° C. in an air atmosphere, keeping the temperature for 0.5-2 h, and cooling the temperature in the treatment furnace to room temperature to obtain oxidized natural flake graphite powder A; S2, dispersing the oxidized natural flake graphite powder A in water to obtain a suspension B; S3, placing the suspension B into a high-pressure homogenizer and performing homogenization to obtain a treated suspension C; S4, centrifuging the suspension C to obtain a precipitate D; S5, the precipitate D is washed with deionized water and then dried to obtain nano-graphite powder.

2. The method for preparing nano graphite powder according to claim 1, characterized in that: In step S1, the temperature is heated to 500°C at a heating rate of 8-12°C / min, and then heated to 500-650°C at a heating rate of 4-6°C / min.

3. The method for preparing nano graphite powder according to claim 2, characterized in that, In step S1, the temperature is heated to 500°C at a heating rate of 10°C / min, and then heated to 530-580°C at a heating rate of 5°C / min.

4. The method for preparing nano graphite powder according to claim 3, characterized in that: In step S1, the temperature is raised to 500°C at a rate of 10°C / min, and then further raised to 550°C at a rate of 5°C / min.

5. The method for preparing nano graphite powder according to claim 1, characterized in that: In the step S2, the oxidized natural flake graphite powder A is mixed with water in a ratio of 1:15-20, and then 0.4-0.6wt% of sodium dodecyl sulfate is added, and the prepared mixture is mechanically stirred to obtain a suspension B.

6. The method for preparing nano graphite powder according to claim 1, characterized in that: In the step S3, the suspension B is placed in a high-pressure homogenizer, the pressure of the high-pressure homogenizer is set to 100-200 MPa, the treatment is carried out for 10-20 minutes, and the treatment is circulated for 10-20 times to obtain a treated suspension C.

7. The method for preparing nano graphite powder according to claim 1, characterized in that: In the step S4, the suspension C is placed in a centrifuge and processed at 5000 rpm for more than 30 minutes to obtain a precipitate D.

8. The method for preparing nano graphite powder according to claim 1, characterized in that: In the step S5, 5 times the weight of deionized water is added to the precipitate D, and the mixture is stirred for 30 minutes using a mechanical stirring rod and then centrifuged at 5000 rpm for 30 minutes to obtain a precipitate. The deionized water is added repeatedly for more than 3 times, and the powder containing a small amount of deionized water is placed in a dryer and dried at 110-130° C. for more than 5 hours to obtain nano graphite powder.

9. A nano graphite powder, characterized in that: The nano graphite powder is prepared by the method for preparing the nano graphite powder according to any one of claims 1 to 8.

10. Use of the nano-graphite powder according to claim 9 in lubricants.

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