A method for preparing nano-graphite powder

Abstract

The application discloses a preparation method of nano graphite powder, which comprises the following steps: uniformly mixing a carbonate and metal powder to obtain a mixed powder; compacting the mixed powder to obtain a compacted blank; and placing the compacted blank in a synthesis device to react and post-treat at a preset temperature and a preset pressure, so as to obtain the nano graphite powder. The application provides a preparation method of nano graphite powder, which uses a carbonate as an initial carbon source, and through a high-temperature and high-pressure process condition, the nano graphite powder with high purity, good particle size concentration and narrow particle size distribution range is prepared under the action of the metal powder.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, and in particular to a method for preparing nano-graphite powder. Background Technology

[0002] With its unique structure and excellent mechanical, electrical, thermal, chemical stability and adsorption properties, nanographite has shown broad application prospects in energy, electronics, composite materials, lithium-ion batteries, supercapacitors, sensors and other fields, and has become a research hotspot in the field of materials science.

[0003] Currently, nano-graphite powders are mainly prepared using three processes: mechanical grinding and air jet milling, explosive deposition, and chemical intercalation. Mechanical grinding and air jet milling can achieve large-scale production, but they suffer from problems such as wide particle size distribution, low concentration, easy introduction of grinding impurities which are difficult to remove, and difficulty in classifying nanoscale powders. Explosive deposition can produce spherical particles of 2-20 nm with a high specific surface area, but the products are mostly spherical rather than lamellar structures. Explosive-processed powders are mostly spherical, not lamellar, and nanodiamond powder is easily present. Once diamond and nano-graphite clusters are present, separation becomes relatively difficult. Chemical intercalation uses chemical reagents to etch the interlayer, resulting in nano-graphite with a layer thickness on the nanometer scale, or multilayer graphene. However, the in-plane length and width grain sizes far exceed the nanometer scale, making it difficult to prepare nano-graphite with high / low aspect ratios through chemical intercalation.

[0004] In summary, existing processes all use graphite as the initial carbon source and refine it through physical or chemical post-processing. They generally suffer from defects such as wide particle size distribution, low purity, difficulty in removing impurities, poor controllability of morphology and phase composition, and difficulty in stably preparing high-purity uniform nano-graphite powder, which seriously limits its application in high-end fields. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides a method for preparing nano-graphite powder, which uses carbonate as the initial carbon source and prepares nano-graphite powder with high purity, good particle size concentration and narrow particle size distribution under the action of metal powder through high temperature and high pressure process conditions.

[0006] To achieve the above objectives, the embodiments of the present invention adopt the following technical solutions:

[0007] A method for preparing nano-graphite powder, the method comprising the following steps:

[0008] The carbonate and metal powder are mixed evenly to obtain a mixed powder.

[0009] The mixed powder is compacted to obtain a compacted blank;

[0010] The compacted preform is placed in a synthesis device and reacted and post-treated at a preset temperature and pressure to obtain nano-graphite powder.

[0011] According to one aspect of the present invention, the mass ratio of the carbonate to the metal powder is (3-10):1.

[0012] According to one aspect of the present invention, the preset temperature is 1200-1500°C, and the preset pressure is 3-5 GPa.

[0013] According to one aspect of the present invention, the carbonate is at least one selected from sodium carbonate, calcium carbonate, and magnesium carbonate.

[0014] According to one aspect of the present invention, the carbonate is pretreated before being mixed with the metal powder, the pretreatment comprising drying the carbonate at 60-270°C and holding it at that temperature for 1-5 hours.

[0015] According to one aspect of the present invention, the metal powder is at least one selected from molybdenum powder, tantalum powder, and cobalt powder.

[0016] According to one aspect of the invention, the compaction process includes:

[0017] The mixed powder is loaded into a packaging container to obtain a packaging container containing the mixed powder;

[0018] The container containing the mixed powder is placed in a mold, and a hydraulic press is used to apply a pressure of 5-20 MPa to the container in the mold to obtain a compacted blank.

[0019] According to one aspect of the invention, the encasing container is a high-temperature resistant metal cup. Preferably, the metal cup is a molybdenum cup, a tantalum cup, or a zirconium cup.

[0020] According to one aspect of the invention, the reaction time is 5-40 min.

[0021] According to one aspect of the invention, the post-treatment includes pickling, washing, and drying.

[0022] According to one aspect of the present invention, the nano-graphite powder obtained by the above preparation method.

[0023] According to one aspect of the present invention, the nano-graphite powder can be used in lithium-ion batteries, supercapacitors, and sensors.

[0024] Advantages of this invention: A method for preparing nano-graphite powder utilizes carbonate as the initial carbon source. Under high temperature and high pressure conditions, the carbonate decomposes under the action of metal powder. Byproducts are removed by acid washing and water washing, and high-purity nano-graphite powder is rapidly prepared. The powder has good particle size concentration and a narrow particle size distribution range. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 Here is a SEM image of the nano-graphite powder obtained in Example 1;

[0027] Figure 2 Here is a SEM image of the graphite powder obtained in Comparative Example 1;

[0028] Figure 3 The image shows the SEM image of the graphite powder obtained in Comparative Example 2. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] A method for preparing nano-graphite powder, the method comprising the following steps:

[0031] The carbonate and metal powder are mixed evenly to obtain a mixed powder.

[0032] The mixed powder is compacted to obtain a compacted blank;

[0033] The compacted preform is placed in a synthesis apparatus and reacted at 3-5 GPa and 1200-1500 °C to obtain a powder mixture. The powder mixture is then post-processed to obtain nano-graphite powder.

[0034] In practical applications, the mass ratio of the carbonate to the metal powder is (3-10):1. Preferably, the carbonate has a purity greater than 99.9%, a particle size distribution of 10-90 μm, an average particle size of 50 μm, and a D90 of less than 80 μm. The metal powder has a particle size distribution of 1-10 μm, an average particle size of 5 μm, and a D90 of less than 9 μm.

[0035] In practical applications, the carbonate is at least one of sodium carbonate, calcium carbonate, and magnesium carbonate. Because carbonates are hygroscopic and prone to deterioration, they are pretreated before being mixed with the metal powder. This pretreatment includes drying at 60-270°C for 1-5 hours.

[0036] In practical applications, the metal powder is at least one of molybdenum powder, tantalum powder, and cobalt powder.

[0037] In practical applications, the compaction process includes:

[0038] The mixed powder is loaded into a packaging container to obtain a packaging container containing the mixed powder;

[0039] Place the packaged container containing the mixed powder into the mold;

[0040] A hydraulic press is used to apply a pressure of 5-20 MPa to the encapsulated container inside the mold, compressing the mixed powder to make it dense and have a certain density, thus obtaining a compacted blank. The diameter of the compacted blank is 10 mm to 30 mm, and the height is 10 mm to 25 mm; the specific dimensions of the compacted blank can be adjusted according to actual assembly requirements.

[0041] In practical applications, the density of the compacted blank is more than 80% of the theoretical relative density.

[0042] In practical applications, the encapsulating container is a high-temperature resistant metal cup. Preferably, the metal cup is a molybdenum cup, tantalum cup, zirconium cup, etc. The high-temperature resistant metal cup can isolate the mixed powder from external environmental contamination, thus acting as a shield. The hydraulic press is a four-column hydraulic press.

[0043] In practical applications, the reaction time is 5-40 minutes.

[0044] In practical applications, the synthesis apparatus is a high-temperature and high-pressure synthesis apparatus, and any existing high-temperature and high-pressure synthesis apparatus can be used without limitation. For example, the high-temperature and high-pressure synthesis apparatus includes a pyrophyllite block with a hollow cavity inside, heating components symmetrically arranged within the hollow cavity, a dolomite pressure-transmitting layer between the heating components and the pyrophyllite block, and an insulating tube disposed on the side of the heating component away from the pyrophyllite block. The internal cavity of the insulating tube is a synthesis chamber, and heating plugs are sealed at the upper and lower ends of the synthesis chamber. The heating components are carbon tubes, carbon sheets, etc., and the insulating tubes are salt tubes, magnesium oxide tubes, hexagonal boron nitride tubes, etc., and the insulating tubes can be selected according to different reaction temperatures.

[0045] In practical applications, crushing is performed before the post-processing. Conventional methods such as crushing or grinding are acceptable. The post-processing includes acid washing, water washing, and drying. Specifically, acid washing involves placing the powder mixture in a container and performing a simple wash with dilute hydrochloric acid. Water washing involves ultrasonically washing the acid-washed powder mixture with deionized water at a controlled temperature of 20-50℃, repeating the wash twice. Drying involves drying the acid-washed and water-washed powder mixture at 60-90℃ for 2-8 hours. This post-processing removes impurities such as metal oxides.

[0046] In practical applications, the nano-graphite powder can be used in lithium-ion batteries, supercapacitors, sensors, and the like.

[0047] Example 1

[0048] A method for preparing nano-graphite powder, the method comprising the following steps:

[0049] S1: Mixing:

[0050] Sodium carbonate is dried at 60-270℃ and kept at that temperature for 1-5 hours to obtain dried sodium carbonate. Molybdenum powder and dried sodium carbonate are added to a three-dimensional mixer and mixed thoroughly at a speed of 30-180 r / min for 1-3 hours to obtain a uniformly mixed powder. The mass ratio of sodium carbonate to molybdenum powder is 3:1.

[0051] S2: Cold pressing:

[0052] The mixed powder is loaded into a molybdenum cup and then placed into a mold. It is then cold-pressed using a four-column hydraulic press. The hydraulic pressure is set to 5-20 MPa, the displacement rate is 100 mm / min, and the holding time is 10-30 s. The mixed powder is compressed to a density greater than 80% of the theoretical density, resulting in a columnar compacted blank with a diameter of 10 mm and a height of 10 mm.

[0053] S3: High temperature and high pressure reaction:

[0054] The cylindrical compacted billet is placed inside a high-temperature, high-pressure synthesis apparatus. The apparatus, containing the billet, is then placed in a six-sided press. The pressure is increased to 3-5 GPa at a rate of 0.5-2 GPa / min, followed by a heating rate of 50-100℃ / min to reach the set temperature of 1200-1500℃. The mixture is held at this temperature for 5-40 minutes, during which molybdenum is converted to molybdenum oxide, and sodium carbonate decomposes into sodium oxide and graphite. After cooling and depressurization, the mixture is crushed or ground to obtain a powder mixture.

[0055] S4: Post-processing:

[0056] The powder mixture was acid-washed with dilute hydrochloric acid and then ultrasonically deionized water-washed at a controlled temperature of 20-50℃ to remove metal oxide impurities. It was then dried at 60-90℃ to obtain nano-graphite powder. The SEM image of the obtained nano-graphite powder is shown below. Figure 1 As shown.

[0057] Example 2

[0058] A method for preparing nano-graphite powder, the method comprising the following steps:

[0059] S1: Uniform mixing of powder:

[0060] Calcium carbonate is dried at 60-270℃ and kept at that temperature for 1-5 hours to obtain dried calcium carbonate. Tantalum powder and dried calcium carbonate are added to a three-dimensional mixer and mixed thoroughly at a speed of 30-180 r / min for 1-3 hours to obtain a uniformly mixed powder. The mass ratio of calcium carbonate to molybdenum powder is 10:1.

[0061] S2: Cold pressing:

[0062] The mixed powder is loaded into a molybdenum cup and then placed into a mold. It is then cold-pressed using a four-column hydraulic press. The hydraulic pressure is set to 5-20 MPa, the displacement rate is 100 mm / min, and the holding time is 10-30 s. The mixed powder is compressed to a density greater than 80% of the theoretical density to obtain a columnar compacted blank.

[0063] S3: High temperature and high pressure reaction:

[0064] The cylindrical compacted billet is placed inside a high-temperature, high-pressure synthesis apparatus. The apparatus, containing the billet, is then placed in a six-sided press. The pressure is increased to 3-5 GPa at a rate of 0.5-2 GPa / min, followed by a heating rate of 50-100℃ / min to reach the set temperature of 1200-1500℃. The mixture is held at this temperature for 5-40 minutes, during which tantalum is converted to tantalum oxide, and calcium carbonate decomposes into calcium oxide and graphite. After cooling and depressurization, the mixture is crushed or ground to obtain a powder mixture.

[0065] S4: Post-processing:

[0066] The powder mixture is acid-washed with dilute hydrochloric acid and then ultrasonically deionized water-washed at a controlled temperature of 20-50℃ to remove metal oxide impurities. Finally, it is dried at 60-90℃ to obtain nano-graphite powder.

[0067] Comparative Example 1

[0068] The only difference between Comparative Example 1 and Example 1 is the reaction temperature in the high-temperature and high-pressure reaction step of Comparative Example 1. All other aspects are the same as in Example 1. The SEM image of the obtained nano-graphite powder is shown below. Figure 2 As shown. Specifically, in Comparative Example 1:

[0069] S3: High temperature and high pressure reaction

[0070] The cylindrical compacted billet is placed inside a high-temperature, high-pressure synthesis apparatus. The apparatus, containing the billet, is then placed in a six-sided top press. The pressure is increased to 3-5 GPa at a rate of 0.5-2 GPa / min, followed by a heating rate of 50-100℃ / min to reach the set temperature of 1800℃. The mixture is then held at this temperature for 5-40 minutes, during which molybdenum is converted to molybdenum oxide, and sodium carbonate decomposes into sodium oxide and graphite. After cooling and depressurization, the mixture is crushed or ground to obtain a powder mixture.

[0071] Comparative Example 2

[0072] The only difference between Comparative Example 2 and Example 1 is the reaction temperature in the high-temperature and high-pressure reaction step of Comparative Example 2. All other aspects are the same as in Example 1. The SEM image of the obtained nano-graphite powder is shown below. Figure 3 As shown. Specifically, in Comparative Example 2:

[0073] S3: High temperature and high pressure reaction

[0074] The cylindrical compacted billet is placed inside a high-temperature, high-pressure synthesis apparatus. The apparatus, containing the billet, is then placed in a six-sided top press. The pressure is increased to 3-5 GPa at a rate of 0.5-2 GPa / min, followed by a heating rate of 50-100℃ / min to reach the set temperature of 950℃. The mixture is held at this temperature for 5-40 minutes, during which molybdenum is converted to molybdenum oxide, and sodium carbonate decomposes into sodium oxide and graphite. After cooling and depressurization, the mixture is crushed or ground to obtain a powder mixture.

[0075] Morphological characteristics:

[0076] Depend on Figures 1-3 As can be seen, the nano-graphite powder prepared in this application has a uniform particle size distribution, good particle size concentration, and a narrow particle size distribution range. In contrast, the graphite powder prepared in Comparative Example 1 exhibits abnormally large grain size, growing into 10-100 μm flakes with a high growth rate perpendicular to the C-axis, having transitioned from the nanometer scale to the scale of conventional micrometer graphite powder. In Comparative Example 2, the sodium carbonate retains its initial sodium carbonate structure, remaining white in color. While the molybdenum powder partially oxidizes and grows, it does not react with the sodium carbonate, and no graphite powder phase is formed. Therefore, this application successfully prepared nano-graphite powder with good particle size concentration and a narrow particle size distribution range by selecting appropriate carbonates and metal powders and setting specific reaction conditions.

[0077] Advantages of implementing this invention:

[0078] A method for preparing nano-graphite powder utilizes carbonate as the initial carbon source. Under high temperature and high pressure conditions, the carbonate decomposes under the action of metal powder. Byproducts are removed by acid washing and water washing, high-purity nano-graphite powder is rapidly prepared with good particle size concentration and narrow particle size distribution range.

[0079] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing nano-graphite powder, characterized in that, Includes the following steps: The carbonate and metal powder are mixed evenly to obtain a mixed powder, wherein the metal powder is at least one of molybdenum powder, tantalum powder, and cobalt powder. The mixed powder is compacted to obtain a compacted blank; The compacted preform is placed in a synthesis device and reacted and post-treated at a preset temperature and pressure to obtain nano-graphite powder. The preset temperature is 1200-1500℃ and the preset pressure is 3-5GPa.

2. The method for preparing nano-graphite powder according to claim 1, characterized in that, The mass ratio of the carbonate to the metal powder is (3-10):

1.

3. The method for preparing nano-graphite powder according to claim 1, characterized in that, The carbonate is at least one of sodium carbonate, calcium carbonate, and magnesium carbonate.

4. The method for preparing nano-graphite powder according to claim 1, characterized in that, The carbonate is pretreated before being mixed with the metal powder. The pretreatment includes drying the carbonate at 60-270°C and keeping it at that temperature for 1-5 hours.

5. The method for preparing nano-graphite powder according to claim 1, characterized in that, The compaction process includes: The mixed powder is loaded into the packaging container; Place the packaged container containing the mixed powder into the mold; A hydraulic press is used to apply pressure to the encapsulated container inside the mold to compress the mixed powder into a compacted blank.

6. The method for preparing nano-graphite powder according to claim 5, characterized in that, The encasing container is a high-temperature resistant metal cup.

7. The method for preparing nano-graphite powder according to claim 1, characterized in that, The post-processing includes crushing.

8. The method for preparing nano-graphite powder according to claim 1, characterized in that, The post-processing includes pickling, washing, and drying.

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