Nanographite powder and its preparation method and application

Abstract

The present invention relates to the technical field of graphite materials, and in particular to a kind of nano graphite powder and its preparation method and application. The method comprises the steps of: heating natural flake graphite with a Dv50 of 30-50 μm to 500-650°C in an air atmosphere, keeping warm for 0.5-2h, cooling to room temperature, and obtaining oxidized natural flake graphite powder A; dispersing the oxidized natural flake graphite powder A in water to obtain a suspension B; placing the suspension B in a high-pressure homogenizing crusher, and homogenizing the suspension to obtain a suspension C; centrifuging the suspension C to obtain a precipitate D; and washing the precipitate D with deionized water, and drying to obtain nano graphite powder. The method in the present invention introduces defects in natural flake graphite by graphite oxidation, thereby reducing the homogenization pressure or number of cycles required for the high-pressure homogenizer; adjusting the parameters of the oxidation process and the high-pressure homogenizer to adjust the particle size; and the process is safe and reliable without safety risks.

Description

Technical Field

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

[0002] Nanographite powder is a nanomaterial with a size of less than 100 nm, produced by physically or chemically exfoliating and processing graphite. Its nanometer size imparts unique physical and chemical properties, such as high surface area, excellent electrical and thermal conductivity, mechanical strength, and chemical stability. Nanographite powder is widely used in high-temperature lubrication, solid coatings, and lubricant additives. Its high-temperature resistance (up to 400°C in non-oxidizing environments) and environmental friendliness make it a promising candidate to replace sulfur- and metal-containing lubricants.

[0003] The patent application with patent publication number CN1508066A describes a method for preparing nanographite powder by detonation. This patent uses the detonation method to prepare nanographite powder. The explosion process is completed in an extremely short time. Key parameters such as temperature and pressure fluctuate greatly, which easily leads to large differences between batches and affects the consistency of material properties. At the same time, it involves flammable and explosive chemicals, which places strict requirements on the safety protection of operators and the production environment, and poses a great safety risk.

[0004] Patent application CN101270313A describes a method for preparing flaky nanographite lubricant additives. This patent requires the use of concentrated sulfuric acid and a strong oxidant during the intercalation process, resulting in environmentally unfriendly acidic wastewater and exhaust gas emissions. Furthermore, the patent presents high safety risks, a complex process, harsh reaction conditions, and low efficiency.

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

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

[0007] To achieve the above object, the present invention provides a method for preparing nano graphite powder, comprising the steps of:

[0008] 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;

[0009] S2, dispersing the oxidized natural flake graphite powder A in water to obtain a suspension B;

[0010] S3, placing the suspension B into a high-pressure homogenizer for homogenization to obtain a treated suspension C;

[0011] S4, centrifuging the suspension C to obtain a precipitate D;

[0012] S5, the precipitate D is washed with deionized water and then dried to obtain nano-graphite powder.

[0013] Preferably, in step S1, in a continuous high-temperature furnace, heating is performed to 500°C at a heating rate of 8-12°C / min, and then heating is performed to 500-650°C at a heating rate of 4-6°C / min.

[0014] Preferably, in step S1, heating is performed to 500°C at a heating rate of 10°C / min, and then heating is performed to 530-580°C at a heating rate of 5°C / min.

[0015] Preferably, in step S1, heating is performed to 500°C at a heating rate of 10°C / min, and then heating is performed to 550°C at a heating rate of 5°C / min.

[0016] Preferably, in 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 lauryl sulfate is added, and the prepared mixture is mechanically stirred to obtain suspension B.

[0017] Preferably, in 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 10-20 times to obtain a treated suspension C.

[0018] Preferably, in 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.

[0019] Preferably, 5 times the weight of deionized water is added to the precipitate D, stirred for 30 minutes using a mechanical stirring rod, and then centrifuged at 5000 rpm for 30 minutes to obtain a precipitate. 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.

[0020] The present invention also provides a nano-graphite powder, which is prepared by the method for preparing the nano-graphite powder as described in any one of the above items.

[0021] The invention also provides an application of the nano graphite powder in lubricants.

[0022] The nanographite powder, preparation method, and application in lubricants disclosed herein are characterized by oxidation treatment of natural flake graphite at 500-650°C in air, which cracks the basal surface of the flake graphite. The oxidation introduces defects into the graphite lattice. The oxidized graphite is cooled to room temperature, and then placed in a high-pressure homogenizer at a pressure of 100-200 MPa, homogenizing for 10-20 minutes, and 10-20 cycles. After homogenization, the mixture is centrifuged and washed with water, and dried to obtain nanographite powder of 10-100 nm. The method disclosed herein has at least the following beneficial effects:

[0023] (1) After natural flake graphite is oxidized in air, its essence is an exothermic reaction between carbon and oxygen, and oxidation starts first from the edges and defects, which will introduce defects such as vacancies and cracks. The increase in crystal defects destroys the SP 2 The conjugate network mainly reflects the following states:

[0024] Structural destruction: The original layered crystal structure of natural flake graphite collapses due to oxidation reaction. The edges and defects of flake graphite are preferentially oxidized, resulting in interlayer peeling and surface etching, and microscopically showing pores and cracks.

[0025] Particle size reduction: The escape of carbon atoms during oxidation reduces the size of graphite particles;

[0026] The crystal order is reduced: the layered ordered structure is destroyed and the crystal size is reduced;

[0027] Surface functional group formation: Oxidation reaction introduces oxygen-containing functional groups on the graphite surface. These groups enhance the hydrophilicity and chemical reactivity of the material.

[0028] (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, making the graphite easier to be broken by the shear force of the high-pressure homogenizer, obtaining nano-graphite powder with finer particle size, reducing the homogenization pressure or number of cycles required by the high-pressure homogenizer, and saving energy consumption;

[0029] (3) 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 graphite fragmentation, 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. By adjusting 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, which is more efficient.

[0030] (4) The hydrophobic chains of SDS (sodium dodecyl sulfate) adsorb on the surface of graphite particles, and the hydrophilic sulfate groups face the water phase, preventing the particles from agglomerating through charge repulsion. The particles are more easily broken evenly by the shear force of the high-pressure homogenizer, which also reduces the surface tension of the liquid, enhances the cavitation effect during the high-pressure homogenization process, and improves the utilization rate. In addition, the nanographite powder with a small amount of functional groups on the surface does not affect the subsequent application in lubricants and other fields. Since the amount is small and does not affect the application, there is no need for a pickling process.

[0031] (5) Compared with the existing detonation method and intercalation method, the crushing process is safe and reliable, without safety risks, and does not produce waste acid, which is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an undue limitation of the present invention. Obviously, the drawings described below are only some embodiments. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without inventive effort. In the accompanying drawings:

[0033] Figure 1 This is the SEM image of the nanographite powder in Example 1. DETAILED DESCRIPTION

[0034] The following is a clear and complete description of the technical problems solved by the embodiments of the present invention, the technical solutions adopted, and the technical effects achieved, in conjunction with the accompanying drawings and specific embodiments. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other equivalent or obviously modified embodiments obtained by ordinary technicians in this field without paying creative work fall within the scope of protection of the present invention. The embodiments of the present invention can be concretized in a variety of different ways as defined and covered in the claims.

[0035] It should be noted that in the following description, many specific details are given for ease of understanding, but it is obvious that the present invention can be implemented without these specific details.

[0036] It should be noted that, in the absence of clear limitations or conflicts, the various embodiments of the present invention and the technical features therein can be combined with each other to form a technical solution.

[0037] Example 1:

[0038] Natural flake graphite with a Dv50 of 30 μm was placed in a continuous high-temperature furnace, and air atmosphere was introduced. The temperature was increased to 500°C at 10°C / min and then to 550°C at 5°C / min, and the temperature was kept at that temperature for 1 hour. After the temperature in the furnace was cooled to room temperature, the powder was taken out to obtain oxidized natural flake graphite powder A.

[0039] The oxidized natural flake graphite powder A was mixed with water in a ratio of 1:19, and 0.5 wt% of SDS (sodium dodecyl sulfate) was added. The prepared mixture was stirred with a mechanical stirring rod for 1 hour to obtain a suspension B.

[0040] Suspension B was placed in a high-pressure homogenizer with the pressure set to 160 MPa for 12 min. This parameter was cycled 15 times to obtain a treated suspension C.

[0041] The suspension C was placed in a centrifuge at 5000 rpm for 30 min to obtain a precipitate D;

[0042] Add 5 times the weight of deionized water to precipitate D, stir with a mechanical stirring rod for 30 minutes, and then centrifuge at 5000 rpm for 30 minutes. After the powder is precipitated, repeat the addition of deionized water and precipitation three times. Put the powder containing a small amount of deionized water into a dryer and dry it at 120°C for 5 hours to obtain nanographite powder.

[0043] Example 2 (minimum oxidation time):

[0044] Natural flake graphite with a Dv50 value of 30 μm was placed in a continuous high-temperature furnace, and air atmosphere was introduced. The temperature was increased to 500°C at 10°C / min and then to 550°C at 5°C / min, and the temperature was kept at that temperature for 30 minutes. After the temperature in the furnace was cooled to room temperature, the powder was taken out to obtain oxidized natural flake graphite powder A.

[0045] The oxidized natural flake graphite powder A was mixed with water in a ratio of 1:19, and 0.5 wt% of SDS (sodium dodecyl sulfate) was added. The prepared mixture was stirred with a mechanical stirring rod for 1 hour to obtain a suspension B.

[0046] Suspension B was placed in a high-pressure homogenizer with a pressure of 170 MPa for 20 min. The homogenizer was cycled 20 times according to this parameter to obtain a treated suspension C.

[0047] The suspension C was placed in a centrifuge at 5000 rpm for 30 min to obtain a precipitate D;

[0048] Add 5 times the weight of deionized water to precipitate D, stir with a mechanical stirring rod for 30 minutes, and then centrifuge at 5000 rpm for 30 minutes. After the powder is precipitated, repeat the addition of deionized water and precipitation three times. Put the powder containing a small amount of deionized water into a dryer and dry it at 120°C for 5 hours to obtain nanographite powder.

[0049] Example 3 (maximum oxidation temperature):

[0050] Natural flake graphite with a Dv50 of 50 μm was placed in a continuous high-temperature furnace, and air atmosphere was introduced. The temperature was increased to 500°C at 10°C / min and then to 650°C at 5°C / min, and the temperature was kept at that temperature for 1 hour. After the temperature in the furnace was cooled to room temperature, the powder was taken out to obtain oxidized natural flake graphite powder A.

[0051] The oxidized natural flake graphite powder A was mixed with water in a ratio of 1:19, and 0.5 wt% of SDS (sodium dodecyl sulfate) was added. The prepared mixture was stirred with a mechanical stirring rod for 1 hour to obtain a suspension B.

[0052] Suspension B was placed in a high-pressure homogenizer with the pressure set to 150 MPa for 15 min. This parameter was cycled 16 times to obtain a treated suspension C.

[0053] The suspension C was placed in a centrifuge at 5000 rpm for 30 min to obtain a precipitate D;

[0054] Add 5 times the weight of deionized water to precipitate D, stir with a mechanical stirring rod for 30 minutes, and then centrifuge at 5000 rpm for 30 minutes. After the powder is precipitated, repeat the addition of deionized water and precipitation 4 times. Put the powder containing a small amount of deionized water into a dryer and dry it at 100°C for 6 hours to obtain nanographite powder.

[0055] Example 4 (lowest homogenizer pressure):

[0056] Natural flake graphite with a Dv50 of 30 μm was placed in a continuous high-temperature furnace, and air atmosphere was introduced. The temperature was increased to 500°C at 10°C / min and then to 550°C at 5°C / min, and the temperature was kept at that temperature for 1 hour. After the temperature in the furnace was cooled to room temperature, the powder was taken out to obtain oxidized natural flake graphite powder A.

[0057] The oxidized natural flake graphite powder A was mixed with water in a ratio of 1:19, and 0.5 wt% of SDS (sodium dodecyl sulfate) was added. The prepared mixture was stirred with a mechanical stirring rod for 1 hour to obtain a suspension B.

[0058] Suspension B was placed in a high-pressure homogenizer with a pressure of 100 MPa for 18 min. The homogenizer was cycled 20 times according to this parameter to obtain a treated suspension C.

[0059] The suspension C was placed in a centrifuge at 5000 rpm for 30 min to obtain a precipitate D;

[0060] Add 5 times the weight of deionized water to precipitate D, stir with a mechanical stirring rod for 30 minutes, and then centrifuge at 5000 rpm for 30 minutes. After the powder is precipitated, repeat the addition of deionized water and precipitation 4 times. Put the powder containing a small amount of deionized water into a dryer and dry it at 120°C for 5 hours to obtain nanographite powder.

[0061] Example 5 (highest homogenizer pressure):

[0062] Natural flake graphite with a Dv50 value of 40 μm was placed in a continuous high-temperature furnace, and air atmosphere was introduced. The temperature was increased to 500°C at 10°C / min and then to 550°C at 5°C / min, and the temperature was kept at that temperature for 1 hour. After the temperature in the furnace was cooled to room temperature, the powder was taken out to obtain oxidized natural flake graphite powder A.

[0063] The oxidized natural flake graphite powder A was mixed with water in a ratio of 1:19, and 0.5 wt% of SDS (sodium dodecyl sulfate) was added. The prepared mixture was stirred with a mechanical stirring rod for 1 hour to obtain a suspension B.

[0064] Suspension B was placed in a high-pressure homogenizer with the pressure set to 200 MPa for 20 min. This parameter was cycled 12 times to obtain a treated suspension C.

[0065] The suspension C was placed in a centrifuge at 5000 rpm for 30 min to obtain a precipitate D;

[0066] Add 5 times the weight of deionized water to precipitate D, stir with a mechanical stirring rod for 30 minutes, and then centrifuge at 5000 rpm for 30 minutes. After the powder is precipitated, repeat the addition of deionized water and precipitation 4 times. Put the powder containing a small amount of deionized water into a dryer and dry it at 110°C for 5 hours to obtain nanographite powder.

[0067] Comparative Example 1 (no oxidation process)

[0068] The difference from Example 1 is that step 1 is omitted, and the natural flake graphite with a Dv50 of 30 μm is processed starting from step 2.

[0069] Comparative Example 2 (crushing using a jet mill)

[0070] The difference from Example 1 is that there are no steps 2, 4, and 5. Step 3 is to put the oxidized natural flake graphite powder A into a jet mill, set the air compressor pressure of the jet mill to 0.8 MPa, and circulate and continuously grind for 2 hours to obtain the crushed graphite powder.

[0071] Comparative Example 3 (Low-temperature Oxidation)

[0072] 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 keeping warm for 1 hour.

[0073] Table 1

[0074]

[0075] The data in Table 1 are the test results of Examples 1-5 and Comparative Examples 1-3.

[0076] Test method:

[0077] (1) Dv50 and K values ​​were measured using a Malvern Zetasizer (DLS) to obtain the values ​​of Dv50, Dv90, and Dv10. K value = ((Dv90-Dv10) / Dv50);

[0078] (2) A value: 10 points were selected for sampling of each sample, and 10 SEM photos were taken for each sample. The linear measurement function in the SEM was used for measurement. 10 particles were selected from each photo. The 10 particles should include the largest and smallest particles in the SEM image. The maximum diameter of the 10 particles was measured, and the average diameter of the 10 particles was calculated. The average maximum diameter of the 10 SEM photos was then averaged to obtain the A value (nm).

[0079] From the data of Examples 1, 2 and 3, it can be seen that the particle size and particle size distribution of the final nanographite powder can be adjusted by adjusting the oxidation conditions (time, temperature). During the oxidation process, defects such as vacancies and cracks are introduced into the flake graphite. The increase in crystal defects destroys the SP 2 The conjugated network reduces the crystallinity of the material and weakens the interlayer van der Waals forces, making the graphite more easily broken by the shear force of the high-pressure homogenizer, resulting in finer graphite powder. 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 graphite fragmentation, the Dv50 decreases, and the graphite structural uniformity decreases, the degree of fragmentation is more controllable, and the particle size distribution (K value) tends to be smaller.

[0080] From the data of Example 1 and Example 4, 5, by adjusting the particle diameter and the particle size distribution of homogenizer pressure control nano graphite powder, when high pressure homogenizer pressure is controlled at 100-200MPa, mainly with shearing force and cavitation effect synergistic effect, graphite particles are pulverized, the micro-jet impact oxidized graphite edge defect produced by cavitation effect, accelerates lamella fracture, shearing force is further peeled off, and the high pressure homogenizer pressure is larger, and lamella occurs " transverse fracture " and " longitudinal peeling ", and the particle size of pulverization is smaller, and by multiple circulations simultaneously, particle is crushed, and lamellar structure disintegrates, forms nano-scale particles, and K value reduces. Simultaneously, the hydrophobic chain of SDS adsorbs graphite particle surface, and hydrophilic sulfate radical, towards water phase, stops particle agglomeration by charge repulsion, and particle is more easily evenly broken by the shearing force of high pressure homogenizer, also reduces liquid surface tension, strengthens the cavitation effect in high pressure homogenization process, improves utilization rate.

[0081] From the data of Example 1 and Comparative Example 1, it can be seen that when the natural flake graphite is not subjected to oxidation treatment, no additional defects are introduced into the material, the shear force of the high-pressure homogenizer does not have a high degree of graphite fragmentation, and 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 the graphite structure has high uniformity, the degree of fragmentation is uncontrollable. At the same time, the oxidation treatment changes the graphite surface from hydrophobic to hydrophilic, making it easier to disperse 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.

[0082] The data from Example 1 and Comparative Example 2 show that the Dv50 of graphite powder pulverized using a jet mill does not reach the nanometer level even after 2 hours of treatment, and the K value is large. Jet mills primarily achieve crushing by accelerating particles into collisions through high-speed airflow. This has low efficiency in stripping the layered structure of graphite oxide (weakened van der Waals forces), and is prone to producing large residual particles (D50 > 5 μm). To achieve a smaller graphite powder size, long-term cyclic crushing is used, making precise control difficult, resulting in a wide particle size distribution. Jet mills use dry pulverization, and oxidized graphite is prone to agglomeration due to van der Waals forces in a dry state. High-pressure homogenizers, on the other hand, use a liquid medium, resulting in better dispersion stability. The addition of SDS further optimizes the dispersion effect, resulting in a narrower particle size distribution for graphite powder treated with a high-pressure homogenizer.

[0083] From the data of Example 1 and Comparative Example 3, it can be seen that at lower temperatures, oxygen preferentially attaches to active sites at the edges or defects of the particles, resulting in local oxidation. Compared with oxidation at higher temperatures, the degree of oxidation is lower, fewer defects are introduced, the graphite powder Dv50 is larger, and the K value is larger.

[0084] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. A method for preparing nano graphite powder, characterized in that, Including 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; specifically comprising: mixing the oxidized natural flake graphite powder A with water in a ratio of 1:15-20, adding 0.4-0.6 wt % of sodium lauryl sulfate, and mechanically stirring the prepared mixture to obtain a suspension B; S3, placing suspension B into a high-pressure homogenizer with a pressure of 100-200 MPa, treating for 10-20 minutes, and circulating the treatment 10-20 times 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, wherein In step S1, the temperature is raised to 500°C at a heating rate of 8-12°C / min, and then 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, wherein In step S1, the temperature is increased to 500°C at a rate of 10°C / min, and then heated to 530-580°C at a rate of 5°C / min.

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

5. The method for preparing nano graphite powder according to claim 1, wherein In 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.

6. The method for preparing nano graphite powder according to claim 1, wherein In 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 three 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.

7. A nano graphite powder, characterized in that: The nano-graphite powder is prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the nano-graphite powder according to claim 7 in a lubricant.

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