Nanodiamond micropowder and method for preparing the same

Abstract

This invention discloses a nanodiamond powder and its preparation method. Using surplus, idle 1μm-sized diamond powder from the industry as raw material, a complete process is employed: planetary wet inert atmosphere ball milling, fine grinding with multi-specification steel balls, multi-stage composite purification, centrifugal classification combined with freeze-drying. This process precisely prepares nanodiamond powder with a particle size less than 100nm, narrow particle size distribution, complete crystallization, high purity, and excellent dispersibility. This invention achieves high-value recycling of ultrafine surplus diamond powder, solving the industry problem of surplus and low added value of 1μm-sized diamond powder. The process is simple, environmentally friendly, has low production costs, and good batch-to-batch consistency, enabling large-scale industrial production. The prepared nanodiamond powder can be widely used in high-end fields such as semiconductor polishing, biofluorescent labeling, quantum sensing, and nanocomposite materials.

Description

Technical Field

[0001] This invention belongs to the field of superhard material preparation technology, specifically relating to a nanodiamond powder and its preparation method. Background Technology

[0002] Nanodiamond powder is a core category of ultrahard nanomaterials. Nanodiamonds with a particle size of less than 100 nm possess irreplaceable application value in cutting-edge high-end fields such as precision polishing of semiconductor wafers, grinding of precision optical devices, biofluorescent labeling, targeted drug delivery, quantum sensing detection, and the preparation of high-performance nanocomposite materials, due to their ultra-high hardness, excellent thermal conductivity, excellent chemical inertness, good biocompatibility, and unique quantum size effect. With the rapid development of high-end manufacturing, the semiconductor industry, and the biopharmaceutical industry in China, the market's performance requirements for nanodiamond powder continue to increase, urgently demanding high-quality nanodiamond products with precisely controllable particle size, narrow particle size distribution, complete crystal structure, clean and impurity-free surface, and excellent dispersion stability.

[0003] Currently, mainstream nanodiamond preparation processes suffer from numerous unavoidable technical defects, failing to simultaneously meet the demands for high-quality, low-cost, large-scale, and green production. Traditional mechanical crushing methods readily introduce metallic impurities, severely damaging the diamond crystal structure during the crushing process. Furthermore, the powder agglomerates significantly due to van der Waals forces, resulting in a wide particle size distribution and making it impossible to stably prepare monodisperse 100-nanometer-scale diamond micropowder. While detonation synthesis can prepare ultrafine nanodiamond primary particles, the product contains a large amount of non-diamond impurities such as graphite and amorphous carbon, requiring rigorous purification processes involving strong acids and alkalis. This not only significantly increases surface defects and reduces product consistency but also poses serious safety hazards and environmental risks. High-temperature high-pressure (HPHT) and chemical vapor deposition (CVD) methods can prepare high-purity diamond, but the products are mostly thin films or micron-sized aggregates. Subsequent crushing completely destroys crystal integrity, and these methods involve large equipment investments, high production costs, and low product yields, hindering industrial-scale mass production.

[0004] Meanwhile, the diamond industry suffers from a significant imbalance in its production capacity structure: market demand is highly concentrated on 5-7μm mainstream diamond micron powder, while ultrafine diamond micron powder around 1μm lacks large-scale, high-value-added applications. Industry companies, influenced by production inertia, continue to produce this particle size, resulting in a large backlog of 1μm diamond micron powder inventory, idle resources, and extremely low added value, causing serious resource waste and reduced production capacity. Currently, the industry lacks high-value-added deep processing technologies for this type of backlog of ultrafine diamond powder. How to achieve resource-based regeneration and high-value utilization of backlogged materials, while simultaneously overcoming the technological bottlenecks in nanodiamond preparation, has become a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the multiple pain points of existing technologies in the preparation of nanodiamonds, such as low purity, severe agglomeration, large lattice damage, high cost, inability to achieve large-scale production, and the industry's stockpiling and resource waste of ultrafine diamond powder with a particle size of about 1μm. This invention provides a method for preparing nanodiamond powder. Using idle and stockpiled 1μm diamond powder from the industry as raw material, this invention optimizes wet inert ball milling, steel ball gradation, composite purification, and freeze-drying processes to achieve high-value recycling of waste materials. It precisely prepares nanodiamond powder with a particle size <100nm, high purity, high dispersion, and complete crystallization. The process is simple, environmentally friendly, and suitable for industrial-scale production.

[0006] A method for preparing nanodiamond powder includes the following steps:

[0007] S1. Raw material preparation: Select stockpiled diamond micro powder with a particle size of about 1μm as the raw material to realize the resource utilization of industrial waste.

[0008] S2. Pre-treatment of the ball mill jar: The inner wall of the ball mill jar for the planetary ball mill is cleaned with water and ethanol in turn to remove residual impurities and oil stains from the jar wall, and then dried until completely dry to avoid impurities contaminating the raw materials.

[0009] S3. Material preparation: Add the diamond micro powder raw material prepared in step S1 to the sealed ball mill jar, and add pure water and dispersant in sequence. The mass ratio of the raw material, pure water and dispersant is 1:(3-5):(0.02-0.05).

[0010] S4. Adding grinding media: Add steel balls to the ball mill jar. The mass ratio of the steel balls to the diamond micro powder raw material is (5-10):1. The steel balls include three types of steel balls with different particle sizes: small, medium and large. The diameter range of the steel balls is 1-10mm. The multi-level steel ball ratio can realize all-round and multi-angle grinding, improve grinding uniformity and grinding efficiency.

[0011] S5. Planetary ball mill: Inert gas is introduced into the ball mill jar to keep the ball mill jar in a sealed state. The ball mill jar is installed into the planetary ball mill, and the inert gas atmosphere is maintained throughout the process.

[0012] S6. Purification: After ball milling, the slurry is taken out and dehydrated and dried. Then, it is processed through a multi-stage process of heating oxidation, cold acid soaking, molten salt purification, pure water washing and ultrasonic cleaning to completely remove harmful substances such as graphite, amorphous carbon and metal impurities, and obtain high-purity nano diamond slurry.

[0013] S7. Centrifugal classification: The purified slurry is classified by gradient speed using centrifugal equipment to accurately screen and obtain nano-diamond micro powder slurry with different particle size ranges, so as to achieve precise particle size control.

[0014] S8. Freeze-drying: The graded slurry is placed in a freeze dryer for drying, replacing the traditional high-temperature drying and hot air drying processes. This avoids the problem of particle hard agglomeration caused by liquid phase surface tension and high temperature, and retains the nanoscale characteristics and dispersion performance of the powder to the greatest extent, ultimately obtaining highly dispersible nanodiamond powder. The steps S1-S8 are performed in sequence.

[0015] Preferably, in step S3, the dispersant is a mixture of at least one or more of ethanol, polyethylene glycol, and sodium silicate. The mass ratio of raw materials, pure water, and dispersant is any value within the range of 1:(3-5):(0.02-0.05), such as 1:3:0.02, 1:4:0.02-0.05, 1:5:0.05, etc.

[0016] In any of the above embodiments, it is preferred that, in step S4, the steel balls are high-carbon chromium bearing steel balls with a diameter of 1-10 mm, and the mass ratio of the small, medium, and large steel balls is (1-3):(1-3):(1-2). The high-carbon chromium bearing steel balls are selected from three specifications: 3 mm, 5 mm, and 8 mm and graded accordingly. Specifically, the mass ratio of the small, medium, and large steel balls can be any value within the range of (1-3):(1-3):(1-2), such as 1:1:1, 1:2:3, 1:3:3, or 3:2:1.

[0017] In any of the above schemes, it is preferred that the inert gas in step S5 is argon or nitrogen.

[0018] In any of the above schemes, it is preferred that, in step S5, the planetary ball mill is set with a transverse rotation speed of 100-200 r / min and a longitudinal rotation speed of 10 r / min, and continuous ball milling is performed for 24-72 hours. The transverse rotation speed can be any value within the range of 100-200 r / min, such as 100 r / min, 100 r / min, or 200 r / min.

[0019] In any of the above schemes, the preferred method for purification in step S6 includes: (1) heating oxidation: heating the diamond micro powder prepared by mechanical crushing to 400℃ and holding for 2 hours to oxidize it, so that the metal components in the impurities are converted into metal oxides, and then cooling; (2) cold acid soaking: soaking the diamond micro powder cooled in step (1) in cold acid to convert the metal oxides into soluble metal salts, and then washing with water to separate the preliminarily purified diamond micro powder; (3) molten salt purification: placing the preliminarily purified diamond micro powder in a molten mixed inorganic salt at 270-320℃ and holding for 1-2 hours; then cooling, rinsing with pure water, ultrasonic cleaning for 15-30 minutes, and drying to obtain high-purity diamond micro powder.

[0020] Preferably, in any of the above embodiments, the mixed inorganic salt is a mixture of inorganic chloride and inorganic nitrate; the mass ratio of the pre-purified diamond powder to the mixed inorganic salt is 1:2; the weight of the inorganic chloride in the mixed inorganic salt accounts for 50-75% of the total weight of the mixed inorganic salt; the inorganic chloride is one or more of NaCl, KCl, and LiCl; and the inorganic nitrate is one or more of NaNO3 and KNO3.

[0021] In any of the above schemes, a preferred embodiment is that in step S8, the graded slurry is placed in a freeze dryer for drying. The first stage is a pre-freezing stage, with the temperature set at -60℃; the second stage is a sublimation drying stage, with the temperature slowly increased from -20℃ to 0℃ over 35 hours; and the third stage is a desorption drying stage, with the temperature set at 50℃ over 4 hours, to obtain the final product. The graded nanodiamond solid-liquid mixture slurry is treated using freezer drying technology to eliminate the liquid phase surface tension generated by traditional high-temperature drying and natural drying, thus preventing the nanodiamond particles from forming hard agglomerates.

[0022] A nanodiamond powder is obtained by any of the preparation methods described above. The prepared nanodiamond powder has a median particle size D50 < 100 nm, a product purity ≥ 99.7%, and uniform particle size distribution without hard agglomerates.

[0023] Beneficial effects:

[0024] This invention discloses a nanodiamond powder and its preparation method, belonging to the field of superhard material preparation technology. Through a complete process including planetary wet inert atmosphere ball milling, multi-specification steel ball gradation for fine grinding, multi-stage composite purification, centrifugal classification combined with freeze drying, nanodiamond powder with a particle size less than 100nm, narrow particle size distribution, complete crystallization, high purity, and excellent dispersibility is precisely prepared. This invention achieves high-value recycling of ultrafine compacted diamond powder, solving the industry problem of stockpiled and low-value-added 1μm particle size diamond powder. The wet inert ball milling process effectively avoids high-temperature graphitization of diamond, lattice damage, and material adhesion loss, while freeze drying completely eliminates the problem of hard powder agglomeration. This invention features a simple, environmentally friendly process, low production cost, and good batch consistency, enabling large-scale industrial production. The prepared nanodiamond powder can be widely used in high-end fields such as semiconductor polishing, biofluorescent labeling, quantum sensing, and nanocomposite materials. Specifically:

[0025] (1) Raw material innovation to realize the high-value utilization of industrial resources: This invention abandons the traditional high-purity diamond raw materials and uses ultrafine diamond powder with a particle size of about 1μm, which has been stockpiled, has low added value, and is idle and wasted in the industry for a long time, as raw material. It breaks through the technical pain points of traditional nano diamond preparation process, such as high cost, serious product agglomeration, low purity, large lattice damage and resource waste. Through precise process modification and deep processing, industrial waste is transformed into high-end 100-nanometer diamond powder, solving the problems of industry capacity backlog and resource waste, greatly reducing raw material costs and realizing green circular production.

[0026] (2) Wet inert planetary ball milling process, which takes into account both high-efficiency grinding and crystal integrity: Compared with the traditional dry ball milling, the present invention adopts a pure water wet grinding system. Relying on the high-intensity multi-angle impact force generated by the combined motion of the planetary ball mill's revolution and rotation, combined with the lubrication, heat dissipation and suspension effect of the liquid medium, it completely solves the problems of material sticking to the wall, uneven grinding, material loss and dust pollution in dry grinding. At the same time, the inert gas sealed atmosphere can effectively suppress the high-temperature graphitization of diamond caused by frictional heat generation during the grinding process, protect the integrity of the diamond crystal lattice structure in all aspects, and improve the product yield and purity.

[0027] (3) Multi-stage composite purification process to ensure ultra-high product purity: The composite purification method combining heating oxidation, cold acid soaking and molten salt purification can completely remove metal impurities, surface graphitized carbon, amorphous carbon and other impurities generated during the grinding process. Compared with the single purification process, the purification effect is more thorough, the consistency of product batches is significantly improved, and the final product purity can reach more than 99.7%.

[0028] (4) Freeze-drying molding completely solves the problem of hard agglomeration of nanoparticles: The freeze-drying technology replaces the traditional drying process, avoiding problems such as particle agglomeration and particle size increase caused by high temperature and liquid phase surface tension. The dried nanodiamond micro powder has no hard agglomeration, excellent dispersibility, and narrow particle size distribution, which perfectly meets the needs of high-end precision application scenarios. Attached Figure Description

[0029] Figure 1 Particle size distribution of diamond micron powder prepared using the preparation method of Example 1;

[0030] Figure 2 Particle size distribution of diamond micron powder prepared using the preparation method of Example 2;

[0031] Figure 3 Particle size distribution of diamond micron powder prepared using the preparation method of Example 3. Detailed Implementation

[0032] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0033] Example 1

[0034] A method for preparing nanodiamond powder includes the following steps in sequence:

[0035] (1) Raw material preparation: Select 2 kg of stockpiled diamond micro powder with a particle size of 1 μm;

[0036] (2) Pretreatment of ball mill jar: A 20L stainless steel ball mill jar is selected. The inner wall is cleaned with water and ethanol in turn to remove residual impurities and oil stains. Then, it is dried in an oven at 120℃ for 2 hours until completely dry to avoid contamination of raw materials by impurities.

[0037] (3) Material preparation: Add 2kg of diamond powder, 8kg of pure water and 60g of polyethylene glycol (PEG-4000) as a dispersant to the ball mill jar, stir and mix thoroughly. The mass ratio of raw materials, pure water and dispersant (polyethylene glycol) is 1:4:0.03.

[0038] (4) Adding steel balls: Add a total of 15kg of high carbon chromium bearing steel balls of three specifications: 3mm, 5mm and 8mm, with a ball-to-material ratio of 7.5:1; of which 5kg are 3mm steel balls, 7.5kg are 5mm steel balls and 2.5kg are 8mm steel balls;

[0039] (5) Planetary ball milling: Argon gas is introduced into the ball milling jar to replace the air and the jar is sealed. It is then installed into the planetary ball mill, and the transverse speed is set to 150 r / min and the longitudinal speed is set to 10 r / min. The ball milling is carried out continuously in a closed manner for 48 hours.

[0040] (6) Purification: After ball milling, the slurry is removed, dehydrated and dried, and then subjected to (1) heating oxidation: the diamond micro powder prepared by the above mechanical crushing method is heated to 400℃ and kept at the temperature for 2 hours to oxidize (to convert the metal components in the impurities into metal oxides). A dilute sulfuric acid aqueous solution with a concentration of 8% is added at a molar ratio of 1.2:1 to the iron in the diamond micro powder. The mixture is soaked and reacted at room temperature for 2 hours. The acid solution after soaking is left in an acid-resistant tank. The diamond micro powder is taken out of the acid-resistant tank and rinsed repeatedly with clean water until the pH of the rinsed aqueous solution is 7. Heating, drying and water washing are then performed. After obtaining the diamond micro powder, the diamond micro powder and a mixed inorganic salt (NaCl:LiCl:NaNO3 = 3:3:4 (weight ratio)) were placed in an alumina crucible at a weight ratio of 1:2. The mixture was heated to 320°C in a muffle furnace under an air atmosphere and held for 1.5 hours. After cooling, the mixture was removed from the crucible and placed in an aluminum alloy trough. Three times the weight of water was added to completely dissolve the mixed inorganic salt in the water. The diamond micro powder was then separated and extracted and repeatedly soaked and rinsed with clean water. Finally, the diamond micro powder was ultrasonically cleaned in pure water for 15 minutes.

[0041] (7) Centrifugal classification: Gradient classification is carried out using high-speed centrifugation equipment (the centrifugal speed used here is determined according to the particle size of the target product, so the centrifugal speed parameter is common in the industry). After centrifugation, nano-diamond micro powder slurry is obtained.

[0042] (8) Freeze-drying: The graded slurry is placed in a freeze dryer for drying: the first stage is the pre-freezing stage, with the temperature set at -60℃; the second stage is the sublimation drying stage, with the temperature slowly increased from -20℃ to 0℃ and kept at that temperature for 35 hours; the third stage is the desorption drying stage, with the temperature set at 50℃ and kept at that temperature for 4 hours to obtain the final product.

[0043] The nanodiamond powder prepared in this embodiment was tested and found to have a median particle size (D50) of 0.076 μm, a product purity of 99.7%, no hard agglomerates, and a uniform particle size distribution, as shown below. Figure 1 As shown.

[0044] Example 2

[0045] A method for preparing nanodiamond powder, similar to Example 1, except that the following steps are included in the order of their steps:

[0046] (1) Raw material preparation: Select 2 kg of stockpiled diamond micro powder with a particle size of 1 μm;

[0047] (2) Pretreatment of the ball mill jar: Select a 20L stainless steel lined ball mill jar, clean and dry it for later use;

[0048] (3) Material preparation: Add 2kg diamond micro powder, 6kg pure water and 40g polyethylene glycol, stir evenly, the mass ratio of raw materials, pure water and dispersant is 1:3:0.02;

[0049] (4) Adding steel balls: Add a total of 10 kg of 3mm, 5mm and 8mm high carbon chromium bearing steel balls, with a ball-to-material ratio of 5:1; of which 3 kg are 3mm steel balls, 5.5 kg are 5mm steel balls and 1.5 kg are 8mm steel balls;

[0050] (5) Planetary ball milling: under an argon atmosphere, the sealed tank is set with a transverse rotation speed of 200 r / min and a longitudinal rotation speed of 10 r / min, and the ball milling is carried out continuously for 24 hours;

[0051] (6) Purification: After ball milling, the slurry is removed, dehydrated and dried, and then subjected to (1) heating oxidation: the diamond micro powder prepared by the above mechanical crushing method is heated to 400℃ and kept at the temperature for 2 hours for oxidation. A dilute sulfuric acid aqueous solution with a concentration of 8% is added according to the molar ratio of iron in the diamond micro powder of 1.2:1. The mixture is soaked and reacted at room temperature for 2 hours. The acid solution after soaking is left in an acid-resistant tank. The diamond micro powder is taken out of the acid-resistant tank and repeatedly rinsed with clean water until the pH of the rinsed aqueous solution is 7. The washed diamond micro powder is heated and dried, and then... Then, diamond micro powder and mixed inorganic salt (NaCl:LiCl:NaNO3 = 3:3:4 (weight ratio)) were placed in an alumina crucible at a weight ratio of 1:2. The mixture was heated to 320°C in a muffle furnace under an air atmosphere and held for 1.5 hours. After cooling, the mixture was removed from the crucible and placed in an aluminum alloy trough. Water with a weight of 3 times that of the mixed inorganic salt was added to completely dissolve the mixed inorganic salt in the water. Then, the diamond micro powder was separated and extracted and repeatedly soaked and rinsed with clean water. Finally, the diamond micro powder was ultrasonically cleaned in pure water for 15 minutes.

[0052] (7) Centrifugal classification: Gradient classification is carried out using high-speed centrifugation equipment (the centrifugal speed used here is determined according to the particle size of the target product, so the centrifugal speed parameter is common in the industry). After centrifugation, nano-diamond micro powder slurry is obtained.

[0053] (8) Freeze-drying: The graded slurry is placed in a freeze dryer for drying: the first stage is the pre-freezing stage, with the temperature set at -60℃; the second stage is the sublimation drying stage, with the temperature slowly increased from -20℃ to 0℃ and kept at that temperature for 35 hours; the third stage is the desorption drying stage, with the temperature set at 50℃ and kept at that temperature for 4 hours to obtain the final product.

[0054] The nanodiamond powder prepared in this embodiment was tested and found to have a median particle size (D50) of 0.09 μm, a product purity of 99.7%, and excellent powder dispersibility. The particle size distribution is as follows: Figure 2 As shown.

[0055] Example 3

[0056] A method for preparing nanodiamond powder includes the following steps in sequence:

[0057] (1) Raw material preparation: Select 2 kg of stockpiled diamond micro powder with a particle size of 1 μm;

[0058] (2) Pretreatment of the ball mill jar: Clean and dry the 20L stainless steel lined ball mill jar for later use.

[0059] (3) Material preparation: Add 2kg diamond powder, 10kg pure water and 100g polyethylene glycol, stir evenly, and the mass ratio of raw materials, pure water and dispersant is 1:5:0.05;

[0060] (4) Adding steel balls: Add a total of 20kg of 3mm, 5mm and 8mm high carbon chromium bearing steel balls, with a ball-to-material ratio of 10:1; of which 6kg are 3mm steel balls, 11kg are 5mm steel balls and 3kg are 8mm steel balls;

[0061] (5) Planetary ball milling: Argon gas sealed atmosphere, transverse rotation speed 100 r / min, longitudinal rotation speed 10 r / min, continuous ball milling for 72 h;

[0062] (6) Purification: After ball milling, the slurry is removed, dehydrated and dried, and then subjected to (1) heating oxidation: the diamond micro powder prepared by the above mechanical crushing method is heated to 400℃ and kept at the temperature for 2 hours for oxidation. A dilute sulfuric acid aqueous solution with a concentration of 8% is added according to the molar ratio of iron in the diamond micro powder of 1.2:1. The mixture is soaked and reacted at room temperature for 2 hours. The acid solution after soaking is left in an acid-resistant tank. The diamond micro powder is taken out of the acid-resistant tank and repeatedly rinsed with clean water until the pH of the rinsed aqueous solution is 7. The washed diamond micro powder is heated and dried, and then... Then, diamond micro powder and mixed inorganic salt (NaCl:LiCl:NaNO3 = 3:3:4 (weight ratio)) were placed in an alumina crucible at a weight ratio of 1:2. The mixture was heated to 320°C in a muffle furnace under an air atmosphere and held for 1.5 hours. After cooling, the mixture was removed from the crucible and placed in an aluminum alloy trough. Water with a weight of 3 times that of the mixed inorganic salt was added to completely dissolve the mixed inorganic salt in the water. Then, the diamond micro powder was separated and extracted and repeatedly soaked and rinsed with clean water. Finally, the diamond micro powder was ultrasonically cleaned in pure water for 15 minutes.

[0063] (7) Centrifugal classification: Gradient classification is carried out using high-speed centrifugation equipment (the centrifugal speed used here is determined according to the particle size of the target product, so the centrifugal speed parameter is common in the industry). After centrifugation, nano-diamond micro powder slurry is obtained.

[0064] (8) Freeze-drying: The graded slurry is placed in a freeze dryer for drying: the first stage is the pre-freezing stage, with the temperature set at -60℃; the second stage is the sublimation drying stage, with the temperature slowly increased from -20℃ to 0℃ and kept at that temperature for 35 hours; the third stage is the desorption drying stage, with the temperature set at 50℃ and kept at that temperature for 4 hours to obtain the final product.

[0065] The nanodiamond powder prepared in this embodiment was tested and found to have a median particle size (D50) of 0.096 μm, a product purity of 99.7%, a narrow particle size distribution, and no agglomeration. The particle size distribution is as follows: Figure 3 As shown.

[0066] Compared to existing technologies, the preparation method of nanodiamond powder in this invention has high resource utilization and low production cost: This invention uses 1μm ultrafine diamond powder, which is often left unused in the industry, as raw material, turning waste into treasure and realizing the high-value recycling of industrial waste. This significantly reduces the raw material cost for preparing nanodiamond powder, solving the industry's pain points of overcapacity and resource waste, and aligns with the concepts of green manufacturing and circular economy development. The product has excellent performance and is suitable for high-end applications: This invention protects the diamond crystal structure through wet inert ball milling, removes various impurities through multi-stage composite purification, and completely solves the powder agglomeration problem with freeze-drying. The prepared nanodiamond powder has a purity of ≥99.7% and a stable particle size control. With a particle size distribution within 100nm, uniform crystallization, and excellent dispersibility, it can meet the stringent requirements of high-end fields such as semiconductors, biomedicine, and quantum sensing. The process is stable and reliable, enabling large-scale mass production: the entire process of this invention is simple to operate and highly controllable in terms of parameters, avoiding the shortcomings of traditional detonation, CVD, and HPHT methods, which are complex, have poor safety, and low yield. The equipment has wide adaptability and good batch product consistency, enabling large-scale continuous industrial production. It is green, safe, and environmentally friendly: the entire process is carried out in a wet and closed manner, with no dust emission. The inert atmosphere production eliminates safety hazards. The purification process is controllable and has low emissions of waste. Compared with traditional strong acid and strong alkali purification processes, the environmental friendliness and safety are greatly improved.

[0067] Although embodiments of the invention have been shown and described, those skilled in the art will understand 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 claims and their equivalents.

Claims

1. A method for preparing nanodiamond powder, characterized in that, Includes the following steps: S1. Raw material preparation: Select stockpiled diamond micro powder with a particle size of about 1μm as the raw material for preparation. S2. Pre-treatment of the grinding jar: Clean the inner wall of the grinding jar of the planetary ball mill, and dry it for later use. S3. Material preparation: Add the diamond micro powder raw material prepared in step S1 to the sealed ball mill jar, and add pure water and dispersant in sequence. The mass ratio of the raw material, pure water and dispersant is 1:(3-5):(0.02-0.05). S4. Adding grinding media: Add steel balls to the ball mill jar, wherein the mass ratio of the steel balls to the diamond micro powder raw material is (5-10):1; the steel balls include three types of steel balls with different particle sizes: small, medium and large. S5. Planetary ball mill: Inert gas is introduced into the ball mill jar to keep the ball mill jar in a sealed state. The ball mill jar is installed into the planetary ball mill, and the inert gas atmosphere is maintained throughout the process. S6. Purification: After ball milling, the slurry is taken out, dehydrated and dried, and then processed through a multi-stage process of heating oxidation, cold acid soaking, molten salt purification, pure water washing and ultrasonic cleaning to obtain high-purity diamond micro powder. S7. Centrifugal classification: Nano-diamond powder slurry is obtained by gradient classification using high-speed centrifugation equipment; S8. Freeze-drying: The graded slurry is placed in a freeze dryer and dried to obtain the final product; Steps S1-S8 are performed sequentially.

2. The method for preparing nanodiamond powder according to claim 1, characterized in that, In step S2, the inner wall of the planetary ball mill's grinding jar is cleaned with water and ethanol in sequence to remove residual impurities and oil stains from the jar wall, and then dried until completely dry to avoid impurities contaminating the raw materials.

3. The method for preparing nanodiamond powder according to claim 1, characterized in that, In step S3, the dispersant is at least one or a mixture of ethanol, polyethylene glycol, and sodium silicate.

4. The method for preparing nanodiamond powder according to claim 1, characterized in that, In step S4, the steel balls are high carbon chromium bearing steel balls with a diameter of 1-10mm. The mass ratio of the three different particle sizes of small, medium and large steel balls is (1-3):(1-3):(1-2). The high carbon chromium bearing steel balls are selected from three specifications of 3mm, 5mm and 8mm for gradation.

5. The method for preparing nanodiamond powder according to claim 1, characterized in that, In step S5, the inert gas is argon or nitrogen, and the planetary ball mill is set with a transverse rotation speed of 100-200 r / min and a longitudinal rotation speed of 10 r / min, and continuous ball milling for 24-72 h.

6. The method for preparing nanodiamond powder according to claim 1, characterized in that, In step S6, the specific purification methods include: (1) heating oxidation: heating the diamond micro powder prepared by mechanical crushing to 400℃ and holding for 2 hours for oxidation, and then cooling; (2) cold acid soaking: soaking the diamond micro powder cooled in step (1) in cold acid, and then washing with water to separate the diamond micro powder after preliminary purification; (3) molten salt purification: placing the diamond micro powder after preliminary purification in step (2) in a molten mixed inorganic salt at 270-320℃ and holding for 1-2 hours; cooling, rinsing with pure water, ultrasonic cleaning for 15-30 minutes, and drying to obtain high-purity diamond micro powder.

7. The method for preparing nanodiamond powder according to claim 6, characterized in that, The mixed inorganic salt is a mixture of inorganic chloride and inorganic nitrate, and the mass ratio of the pre-purified diamond powder to the mixed inorganic salt is 1:2; the weight of the inorganic chloride in the mixed inorganic salt accounts for 50-75% of the total weight of the mixed inorganic salt; the inorganic chloride is one or more of NaCl, KCl, and LiCl; the inorganic nitrate is one or more of NaNO3 and KNO3.

8. The method for preparing nanodiamond powder according to claim 1, characterized in that, In step S8, the graded slurry is placed in a freeze dryer for drying. The first stage is the pre-freezing stage, with the temperature set at -60℃; the second stage is the sublimation drying stage, with the temperature slowly increased from -20℃ to 0℃ over 35 hours; the third stage is the desorption drying stage, with the temperature set at 50℃ over 4 hours, to obtain the final product.

9. A nanodiamond powder, obtained by the preparation method according to any one of claims 1-8.

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