A highly lipophilic copper nanoparticle, its preparation method and application

Abstract

The present invention discloses a highly lipophilic copper nanoparticle and its preparation method and application. The highly lipophilic copper nanoparticle has uniform particle size, controllable size, highly lipophilic surface, good corrosion resistance, excellent suspension stability in base oil, and can be made into a highly stable nano-copper fluid. The prepared nano-copper fluid belongs to the high-tech field of lubrication such as anti-extreme pressure and heavy load. The nano-copper fluid involved in this patent has the advantages of simple preparation process, clear composition, uniform and controllable particle size, and stable quality. At the same time, the preparation process is a continuous flow reaction, with good safety performance, high automation, and low production cost, providing broad application prospects for later application in the lubrication field.

Description

Technical Field

[0001] The present invention belongs to the fields of nanomaterials and lubrication technology, and particularly relates to a highly lipophilic copper nanoparticle, a preparation method thereof, and an application thereof. Background Art

[0002] Friction of moving parts and the resulting component wear are inevitable during the operation of mechanical equipment and are one of the sources of energy consumption. The energy consumed by friction worldwide each year accounts for about 1 / 3 of the total energy; wear can lead to serious problems such as increased energy consumption, rising temperature, and mechanical equipment failures. In order to reduce the energy consumption, equipment loss, resource waste, and safety hazards caused by friction and wear, solid or liquid lubricants are often used on the rolling, rotating, and sliding surfaces of mechanical equipment to reduce the direct contact of the friction interface, greatly reduce the friction coefficient and wear, and lower the temperature of the friction part. With the use of heavy-duty mechanical equipment, ordinary lubricants often cannot meet the stringent requirements of heavy loads, high temperatures, high speeds, etc. It is necessary to add nano-solid particles to the lubricating oil to enhance the performance of the lubricant, make the moving parts wear-resistant, anti-extreme pressure, reduce friction, and improve the operating conditions of the equipment.

[0003] High-performance lubricating additives are the core components of lubricating oil. Although the addition amount is small, they endow the lubricating oil with new characteristics and make up for the performance defects of the lubricating base oil.

[0004] Nanomaterials have the advantages of small size, large specific surface area, and special small-size effect. Nano-copper has electrical conductivity, thermal conductivity, and excellent physical and chemical properties, and is widely used in fields such as heat conduction materials, conductive materials, highly efficient catalysts, lubricating oil additives, biomedicine, metallurgy, and petrochemical industry; in the mechanical field, especially in the automotive industry, nano-copper is an excellent solid lubricant. However, nano-copper particles are generally extremely fine (scale in the 1-100 nanometer level) elemental powders, which are difficult to prepare and are easily oxidized and corroded. The performance and application of nano-copper also depend on its preparation method, and the characteristics of nano-copper prepared by different methods vary greatly.

[0005] At present, the most commonly used methods for preparing nanocopper mainly include three categories: physical methods, chemical methods, and biological methods. Biological methods are generally difficult to carry out large-scale and continuous production, so they will not be discussed here. Physical methods mainly include melt spraying method, high-temperature evaporation method, vapor deposition method, etc. The nanocopper prepared by these physical methods may have relatively pure components, but its surface is easily oxidized. Moreover, the physically prepared nanocopper generally has a relatively large particle size, its surface is not functionalized, and it does not have dispersion stability in oily media. In contrast, the liquid-phase reduction method generally uses very cheap copper salts in its process technology. The production process is simple and easy to implement, and it can be produced in large quantities. After adopting continuous and automated production, the cost is relatively low and the quality is easy to stabilize. Moreover, by appropriately adjusting the process parameters, nanocopper powder with controllable shape, uniform particle size, and meeting application requirements can be efficiently produced. It is currently the most important way to produce nanocopper powder in the laboratory and industrial fields.

[0006] Copper material itself is relatively soft and has good ductility, so it can be used as a solid lubricant; metallic copper is cheaper than gold, silver, and indium, less toxic than lead, has a higher melting point and better corrosion resistance than zinc and tin, and is also easy to form alloys with other materials; although copper does not have as strong a load-carrying capacity as molybdenum disulfide, it has the lubrication behavior of a high-viscosity fluid and has self-repairing performance at low friction speeds; and nanocopper shows unique advantages in the field of tribology because of its special nano effect and high surface activity.

[0007] Nanocopper has excellent anti-friction, anti-wear, and self-repairing functions. It is a new type of high-performance nano lubricant and an additive for self-repairing lubricating oil. It is a wear-resistant material that can significantly improve the anti-wear and friction-reducing performance of lubricating oil, can automatically repair the worn parts of the friction pairs of mechanical equipment, and has remarkable wear resistance and energy-saving effects.

[0008] However, the high surface activity, poor oxidation stability, easy agglomeration, and incompatibility with lubricating oil of nanocopper materials limit the application of nanocopper materials in the field of tribology. Using emerging nano surface modification technologies to prepare nanocopper materials with good chemical stability and good dispersion stability in oily media such as lubricating oil provides broad prospects for the application of nanocopper lubricants.

[0009] As early as the 19th century, scientists began to study particle systems at the nanoscale. In 1963, Uyeda first obtained metal nanoparticles by gas evaporation condensation method and carried out electron microscopy and electron diffraction studies. In 1990, nanomaterial science was officially established as a new branch of materials science and has gradually been applied in various fields.

[0010] The research on nanomaterials in China emerged at the end of the last century. Nanocopper has become a research hotspot in this field due to its good wear and friction reduction performance.

[0011] Dong Chunfa (Research on the Preparation of Monodisperse Nano-Silver and Nano-Copper by Chemical Reduction Method, Doctoral Dissertation of Huazhong University of Science and Technology, 2014) used the microemulsion method and hydrazine hydrate and gum arabic (GA) to obtain monodisperse nanocopper sol. The nanocopper sol prepared by this method is not easily oxidized, has better dispersion stability, and is not prone to agglomeration or precipitation. However, the production capacity of this method is small, and a large amount of wastewater is generated during the preparation process.

[0012] Hu Zeshan et al. (Preparation of Nano-Copper Borate Particles and Their Tribological Properties as Lubricating Oil Additives, Tribology, 2000, 20(4): 292-295) used copper nitrate and borax as raw materials and prepared nano-particles of copper borate by supercritical carbon dioxide drying technology. This nano-copper borate can improve the anti-wear and load-carrying capacity as a lubricating oil additive. However, nano-copper borate will increase the friction coefficient, and the cost of the product is relatively high.

[0013] Chen et al. (Preparation of Nano-Copper Powder by Gel Casting Method and Its Application in Lubrication, The Chinese Journal of Nonferrous Metals, 2018, 28(6): 1186-1191) used the gel casting method to prepare nanocopper materials with copper nitrate, acrylamide, and N,N-methylenebisacrylamide. The nanocopper powder prepared by the gel casting method has higher purity, better dispersion stability, and more uniform particle size. It also has the disadvantages of small production capacity and high cost.

[0014] Liu Yifei (Preparation and Tribological Properties of Hexagonal Boron Nitride Supported Nano-Copper Lubricating Additive, Lubrication Engineering, 2022, 47(2): 122-128) used hexagonal boron nitride to support nanocopper as a lubricating oil additive. The preparation method is to grind the suspension of hexagonal boron nitride powder, separate to obtain the aqueous solution of boron nitride nanosheets, then mix with oleic acid and carry out a hydrothermal reaction to obtain modified boron nitride nanosheets. Then, copper nitrate solution is added to the boron nitride nanosheets for a coating reaction. After washing and drying, copper-hexagonal boron nitride nanocomposite powder is obtained by thermal reduction method. Compared with the nanocopper prepared by traditional methods, the copper-hexagonal boron nitride nanocomposite has better tribological properties, more stable friction and wear reduction performance, and better lubrication effect. However, it requires a long time of grinding, separation, as well as complex chemical reactions and post-treatment during the production process. Therefore, it is difficult to carry out large-scale continuous and automated production, and the production cost is relatively high.

[0015] In addition to loading nano - copper on hexagonal boron nitride, Deng Jiaqi et al. (A modified nano - copper and nano - copper - epoxy resin composite material and its preparation method, Chinese invention patent, CN201711192030.7) modified the surface of nano - copper with methyl orthosilicate to prepare a nano - copper - epoxy resin composite material. Since the nano - copper - epoxy resin composite material is coated with silica on the surface, its antioxidant performance is better than that of the nano - copper material prepared by the traditional method, and its service life is extended. However, it is difficult for this material to be stably dispersed in lubricating oil.

[0016] Many years ago, continuous - flow technology had been studied in the field of organic synthesis and had been applied in a certain range. In recent years, continuous - flow chemical engineering technology has developed from niche professional application research into a widespread chemical industry production technology. Many fields are exploring the possibility of using this new technology to expand production capacity, improve product quality, and at the same time reduce the risks and costs in the production process.

[0017] The continuous - flow process technology has many advantages such as high production efficiency, good stability, high product selectivity, good product quality, low pollution, high intelligence level, and good flexibility. Therefore, this technology has now gradually risen from the use in a few chemical products in the past to the entire scope of chemical synthesis. At the same time, continuous - flow technology has also stood out in the production of fine chemicals and pharmaceutical intermediates and has begun to play a crucial role in the mass production of high - performance nanomaterials.

[0018] This invention elucidates a preparation method for continuously preparing copper nanoparticles with uniform size, controllable particle size, strong oil solubility, and excellent suspension stability, as well as their nanofluids, to solve the problems of poor dispersion stability and suspension of nano - copper in oily media such as lubricating oil, and to overcome the phenomena of agglomeration or precipitation. This patent uses emerging nanomaterial synthesis and modification technologies to in - situ modify the surface of nano - copper, turning ordinary nano - copper into oil - soluble nanoparticles, which can be more stably suspended in lubricating oil, without precipitation and without being captured by the filter in the lubrication system, and can play a lubricating role for a long time. Moreover, it has the characteristics of low preparation cost, simple process, and continuous preparation. Summary of the Invention

[0019] The purpose of this invention is: aiming at the disadvantages of poor stability, uneven particle size distribution, easy oxidation and corrosion, easy precipitation, and high cost exposed when existing copper nanoparticles are applied, especially in the lubrication application field, to adopt a simple - operation and continuous - flow production method to obtain copper nanoparticles with uniform particle size and controllable size, and then conduct in - situ surface modification of the nanoparticles, and use the oil - phase extraction method to obtain highly stable nano - copper fluids, which have the characteristics of low preparation cost and simple process, thus showing broad application prospects.

[0020] To achieve the above object, the present invention adopts the following technical solutions:

[0021] A method for preparing highly lipophilic copper nanoparticles includes the following steps:

[0022] (1) Using a molecule or polymer containing a hydrophilic group (MAA, PEG or PVA) as a dispersant during the reduction reaction, mixing it with a copper salt, with a molar ratio of the two being 1:0.5 to 1:2, using water as the medium for the reduction reaction, and stirring evenly at room temperature to obtain raw material I; the dispersant can prevent the aggregation of copper nanoparticles during the preparation process and reduce the particle size of copper nanoparticles;

[0023] (2) An aqueous solution of a metal copper salt reducing agent with a certain concentration is used as raw material II. Raw material I and raw material II are mixed in a certain proportion, such as a molar ratio of 40:1 to 60:1, passed through a first mixer, and continuously added to a first tubular reactor at a constant speed. Using water as the reaction solution, a continuous flow reduction reaction is carried out under microwave irradiation at a power of 900 W and a frequency of 2450 MHz and at 50 - 90 °C for 0.01 - 1 h, preferably 0.1 - 0.3 h, to obtain a copper nanoparticle suspension; the wall of the first tubular reactor can transmit microwaves; under the radiation of microwaves, a continuous flow reduction reaction is carried out, and the non-thermal effect of microwaves is used to improve the conversion rate of copper salts; continuous flow reduces the backmixing in traditional batch reactors, so it can reduce the size of copper nanoparticles, control the size of copper nanoparticles, and improve the uniformity of nanoparticles;

[0024] (3) Mixing the copper nanoparticle suspension in step (2) and raw material III (a solution of a molecule or polymer containing a mercapto or amino group, one end of which can chelate with the surface of copper nanoparticles and the other end is a lipophilic long chain) in a second mixer, and then entering a second tubular reactor. Under microwave irradiation at a power of 900 W and a frequency of 2450 MHz, a continuous flow modification reaction is carried out at 50 - 90 °C, preferably 0.2 - 0.3 h, to overcome the backmixing effect in the surface modification of copper nanoparticles in the traditional process and complete the surface modification of copper nanoparticles to obtain modified copper nanoparticles;

[0025] (4) In the modified copper nanoparticles in step (3), by adding a low-boiling-point oily solvent (one or a mixture of petroleum ether, heptane, cyclohexane), stirring evenly (slowly stirring at a temperature of 50 - 90 °C for 0.01 - 1 h, preferably 0.1 - 0.2 h), and standing, in-situ phase transfer occurs, and the copper nanoparticles enter the oil phase from the water phase to obtain an oily suspension of copper nanoparticles;

[0026] (5) The oily suspension of copper nanoparticles in step (4) is ultra-high speed centrifuged to obtain a sludge-like precipitate, which is washed and purified to obtain highly lipophilic copper nanoparticles.

[0027] In the above preparation method, in the reduction stage of the first stage, a continuous-flow microwave irradiation reduction method is adopted, which greatly reduces the reduction reaction temperature, improves the raw material conversion rate at the same time, and also reduces the average particle size of the nano copper. In the modification stage of the second stage, a continuous-flow microwave irradiation modification method is adopted, which greatly reduces the reaction temperature of the surface modification, improves the surface modification effect at the same time, reduces the agglomeration of the nano copper, increases the lipophilicity of the nano copper surface, and also improves the suspension stability in the organic medium. And after reduction and in-situ modification, a phase transfer method is used instead of the drying method in the traditional preparation to overcome the agglomeration of the nano copper during the drying process and directly obtain a highly stable nano copper fluid.

[0028] The inner layer of the highly lipophilic copper nanoparticles prepared by the above preparation method is spherical copper nanoparticles, and the outer layer is coated with lipophilic molecules or polymers; they can be evenly dispersed in the base oil; their application in lubricating oil: The highly lipophilic copper nanoparticles are evacuated and heated to remove volatile organic substances to obtain pure nano copper particles, which are stirred evenly with the base oil and treated by ultrasonic waves to obtain a copper nanofluid for use as a lubricating oil.

[0029] Beneficial effects:

[0030] The present invention adopts advanced production technologies and solutions. With the help of a hydrophilic molecule or polymer as a dispersant, it is dissolved in the copper precursor solution, and then a liquid-phase method is used to carry out a reduction reaction on the copper salt to form copper nanoparticles; and in the presence of a lipophilic polymer, an in-situ coordination coating reaction is carried out; with the help of an advanced continuous-flow reaction device, the nanoparticles are continuously and rapidly prepared and modified, and finally a copper nanofluid with a uniform particle distribution is obtained through phase transfer and phase separation. This production technology has the following characteristics: 1) Realize continuous-flow reaction and break the defect of small output of nanofluids; 2) Use highly hydrophilic raw material (I) to prevent the agglomeration of nano copper during the formation process and make the copper nanoparticles larger; 3) Use a hydrophilic polymer containing an amino group or a mercapto group to carry out coordination coating of nano copper to prepare modified nano copper particles with good oil solubility, and the finally formed nanofluid is more stable and not easy to precipitate; 4) Adopt a phase transfer method to transfer nano copper from the aqueous phase to the oil phase through lipophilic modification, overcoming the shortcoming of easy agglomeration of ordinary methods; 5) Adopt an advanced continuous-flow reaction device, with lower cost, simpler operation and higher repeatability; 6) Adopt reduction and in-situ modification under microwave enhancement, which greatly reduces the reaction temperature, prevents the boiling of the aqueous system, and overcomes the decomposition of raw materials at higher temperatures; it also greatly reduces the time required for chemical reactions, strengthens the production process, thereby reducing energy consumption and cost.

[0031] The products produced using the present invention have the following advantages: 1) The particle size is controllable and uniform; 2) Continuous reaction and production are achieved, overcoming the defect of small output of products in traditional technologies; 3) The natural advantage of the tubular reactor is that backmixing is small, and it can be easily combined with microwave irradiation technology to continuously and rapidly prepare nanoparticles with controllable and uniform particle size; 4) In-situ modification and phase transfer, the surface is coated with molecules or polymer ligands rich in lipophilic groups, which can overcome the agglomeration problem of native copper nanoparticles. The modified copper nanoparticles are not easily agglomerated and have a smaller hydrodynamic diameter; 5) The self-designed continuous flow reaction device has a simple preparation process and high yield, reducing errors or mistakes caused by manual operation, with lower production costs, which is conducive to larger-scale industrial production in the future. Therefore, this invention patent overcomes the defects of small output, poor particle size uniformity, easy corrosion, and easy agglomeration and precipitation in the production of copper nanoparticles by traditional technologies. Description of the Drawings

[0032] Figure 1 Schematic diagram of the microwave-enhanced device for preparing copper nanofluid according to the implementation of the present invention;

[0033] Figure 2 Copper nanoparticles prepared by the microwave-enhanced device of the present invention;

[0034] Figure 3 Schematic diagram of the traditional hot water heating device for copper nanofluid;

[0035] Figure 4 Copper nanoparticles prepared by the traditional hot water heating device;

[0036] Figure 5 Long-term stability detection chart of the nanofluidic copper prepared according to the implementation of the present invention;

[0037] Figure 6 Conductivity detection chart of the nanofluidic copper prepared according to the implementation of the present invention;

[0038] Figure 7 Relationship between wear scar diameter and mass fraction of copper nanoparticles;

[0039] Figure 8 Schematic diagram of the structure of the highly lipophilic copper nanoparticles of the present invention. Detailed Description of the Invention

[0040] The following will describe the implementation of the present invention in detail in combination with examples. Those skilled in the art will understand that the following examples are only the preferred examples of the present invention for better understanding the present invention, but the protection scope of the present invention is not limited to the following examples.

[0041] Example 1

[0042] (1) Accurately weigh 3.6 g of PVA, dissolve it in water to 60 mL, stir until completely dissolved, and add 16 g of CuSO4·5H2O and stir well to obtain Raw Material I;

[0043] (2) Take 20 g of hydrazine hydrate, add 10 mL of water, and stir evenly. This 30 mL solution is used as Raw Material II;

[0044] (3) Take 5 g of oleylamine, add 10 mL of ethanol, and stir evenly. This solution is used as Raw Material III;

[0045] (4) Use the device as Figure 1 shown, and use a peristaltic pump of the same model for constant-rate sample injection (the flow rate ratio is the volume ratio of Raw Material I and Raw Material II, and the flow rates are controlled at 0.5 ml / min and 0.1875 ml / min respectively), and mix in a three-way mixer;

[0046] (5) The tubular reactor flows at a constant rate and reacts under microwave irradiation at 70 °C, a power of 900 W, and a frequency of 2450 MHz. An appropriate tube length is used to make the reduction reaction time of the mixed fluid 10 min;

[0047] (6) In the next three-way mixer, introduce Raw Material III using a third constant flow pump. The tubular reactor flows at a constant rate and reacts under microwave irradiation at 80 °C, a power of 900 W, and a frequency of 2450 MHz. An appropriate tube length is used to make the residence time of the mixed fluid 10 min;

[0048] (7) Flow the reaction product in (6) into a reaction kettle, add 100 mL of heptane, stir for 3 h, then let it stand for a whole day and night. After oil-water separation, a heptane fluid of nanocopper can be obtained; In order to achieve continuous flow and automated operation, two or more reaction kettles can be used alternately;

[0049] (8) Add 200 mL of acetone to the crude product (the heptane fluid containing nanocopper), stir, wash, and centrifuge, and then repeat 2 times to complete purification. Then add base oil (such as PAO), disperse it at high speed and stir evenly, then perform ultrasonic dispersion, and then distill and recover heptane to finally obtain a pure nanocopper fluid with PAO as the base fluid.

[0050] In (5), the method of microwave irradiation is used to reduce copper ions. Utilizing the non-thermal effect of microwaves, at a relatively low temperature, boiling of water is prevented, and premature and rapid decomposition of the reducing agent at a higher temperature is also prevented. Even at a relatively low temperature, the non-thermal effect of microwaves can greatly shorten the reduction reaction time. Meanwhile, the relatively low temperature can also prevent the aggregation of nano-copper particles. In (6), the method of microwave irradiation is also used for surface modification of nano-copper. Utilizing the non-thermal effect of microwaves, at a relatively low temperature, boiling of water is prevented, and decomposition or hydrolysis of the modifier at a higher temperature is also prevented. The non-thermal effect of microwaves can also greatly shorten the reaction time of surface modification, obtaining copper nanoparticles with good surface modification, no aggregation, and a stably suspended nano-copper fluid. The phase transfer method can obtain a nano-copper fluid with high concentration, high stability, and PAO as the base fluid.

[0051] In this example, microwave irradiation is used for reduction and surface modification, and the average particle size is 30.2 ± 3.2 nm, as Figure 2 shown in the scanning electron microscope photo.

[0052] Example 2

[0053] In Example 1, the method of microwave irradiation was used to accelerate the reaction in both the stage of reducing copper ions and the surface modification of nano-copper.

[0054] In this example, the device shown in Figure 3 is used. Instead of using the method of microwave irradiation, the method of conventional heating is used for reduction and modification reactions, so as to make a comparison and check the influence of microwaves on chemical reactions.

[0055]

[0056] In this example, the method of microwave irradiation is not used to reduce copper ions, nor is the method of microwave irradiation used to modify nano-copper particles. The prepared nano-copper has an average particle size of 40.2 ± 3.5 nm, as Figure 4 shown in the scanning electron microscope photo.

[0057] Comparing Example 1 and Example 2, the nano-copper prepared and modified using microwave irradiation has smaller and more uniform particles, while the nano-copper particles prepared using the conventional heating method are larger and more severely aggregated.

[0058] Example 3

[0059] In Example 1, in both the stage of reducing copper ions and the surface modification of copper nanoparticles, the method of microwave irradiation was used for the reaction process, obtaining better results.

[0060] In Example 2, it was found that when both reduction and modification were carried out using the method of conventional heating, the reaction effect was not good at 80 °C.

[0061] In this implementation, instead of using the method of microwave irradiation, the method of increasing the temperature of conventional heating is adopted for the in-situ modification reaction of copper nanoparticles. A comparison is made to see the influence of microwave on the modification reaction.

[0062]

[0063] It can be seen from this that: under the condition of conventional heating, increasing the modification temperature can significantly improve the effect of surface modification, while the non-thermal effect of microwave irradiation is significant, which can greatly improve the surface modification reaction, and the concentration of the prepared copper nanofluid is relatively high. Using microwave irradiation at a lower temperature can also reduce the aggregation of nano-copper and increase the suspension stability of nano-copper.

[0064] Example 4

[0065] In this example, nanofluids are prepared by different preparation methods, and are respectively prepared and modified under microwave irradiation, as well as prepared and modified by the ordinary heating method, and the suspension stabilities of the obtained nanofluids are compared.

[0066] The static stability of the nanofluid is represented by the stability index, and the densities of the fresh and the nanofluid placed for a certain time are measured. The nano-copper fluid obtained by the ordinary heating method completely settled after being placed for 3 days, while the relationship between the stability index of the nanofluid prepared by the microwave method and the placement time is as Figure 5 shown. It can be seen from the figure that for the nano-copper fluid prepared by the microwave reduction and modification method, the stability index will not change within 90 days, indicating that the prepared nano-magnetic fluid has good stability.

[0067] Example 5

[0068] Copper ion solutions I with certain concentrations are prepared, and their concentrations are: 0.2, 0.4, 0.8, and 1.6 M, and then the nano-copper powder is prepared respectively using the Figure 1 device shown. The detailed steps are shown in Example 1.

[0069] Nano-copper powders are prepared from solutions with different copper ion concentrations respectively, and the resistivity of the products is measured using a powder conductivity meter (ST-2722 type powder conductivity meter, Suzhou Jingge Electronics Co., Ltd.). Figure 6 The resistivity of the nano-copper powders prepared from raw materials with different concentrations is shown. When the copper particle concentration reaches 0.4 M, the resistivity is the highest, about 3000 Ω·cm. From Figure 6 it can also be seen that generally, for the nano-copper powder prepared from a high-concentration copper solution, its resistivity gradually decreases and its conductivity increases. Moreover, for the copper powder prepared using a higher-concentration solution, the production capacity can be improved. However, as the particle size of the nano-copper powder increases, its suspension stability gradually decreases.

[0070] Example 6

[0071] Using base oil N60, the particle size of the prepared nano copper is 30 nanometers. Nanofluids with nano copper concentrations of 0, 0.05%, 0.1%, 0.15%, 0.25%, 0.5% and 1% are respectively prepared. Using a four-ball wear testing machine, the load size is 300 N, at a rotational speed of 1450 RPM and room temperature of 25 degrees. Standard steel balls of GGr15 with a diameter of 12.7 mm and a hardness of HRC59 - 61 are used for a 30-minute wear test, and then the wear scar diameter is observed with a microscope.

[0072] Figure 7 For the relationship between the wear scar diameter and the mass fraction of nano copper, it can be seen that as long as the base oil contains 0.05% nano copper particles, its wear can be greatly reduced.

[0073] The above are only relatively significant embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A method for preparing highly lipophilic copper nanoparticles, characterized in that, It includes the following steps: (1) Add a molecule or polymer containing a hydrophilic group and a copper salt into water, mix evenly to prepare a copper salt precursor solution as Raw Material I; use a metal copper salt reducing agent as Raw Material II; use a solution of a molecule or polymer containing a mercapto or amino group as Raw Material III; (2) Mix Raw Material I and Raw Material II through a first mixer, and then flow into a first tubular reactor at a constant speed. Under the radiation of microwave, carry out a continuous flow reduction reaction to obtain a nano-copper suspension; (3) Flow Raw Material III and the nano-copper suspension obtained in step (2) into a second mixer for mixing, and then pass through a second tubular reactor. Under microwave radiation, carry out a continuous flow modification reaction to obtain modified nano-copper particles; (4) In the modified nano-copper particles obtained in step (3), by adding a low-boiling-point oily solvent, stirring evenly and standing still, in-situ phase transfer occurs, and the nano-copper particles enter the oil phase from the water phase to obtain an oily suspension of nano-copper; (5) For the oily suspension of nano-copper in step (4), ultra-high-speed centrifugation is carried out to obtain a sludge-like precipitate, which is washed and purified to obtain highly lipophilic copper nanoparticles; The conditions for the continuous flow reduction reaction in step (2) are: under microwave irradiation with a power of 900 W and a frequency of 2450 MHz, stay at a temperature of 50 - 90 °C for 0.01 - 1 h; The conditions for the continuous flow modification reaction in step (3) are: under microwave irradiation with a power of 900 W and a frequency of 2450 MHz, stay at a temperature of 50 - 90 °C for 0.01 - 1 h.

2. The preparation method of the highly lipophilic copper nanoparticles according to claim 1, wherein, The molecule or polymer containing a hydrophilic group in step (1) is MAA, PEG or PVA.

3. The preparation method of the highly lipophilic copper nanoparticles according to claim 1, characterized in that, The molar ratio of the molecule or polymer containing a hydrophilic group to the copper salt in step (1) is 1 : 0.5 - 1 :

2.

4. The preparation method of the highly lipophilic copper nanoparticles according to claim 1, characterized in that, The copper salt in step (1) is CuSO4·5H2O.

5. The preparation method of the highly lipophilic copper nanoparticles according to claim 1, characterized in that, The low-boiling-point oily solvent in step (4) includes one or a mixture of petroleum ether, heptane, and cyclohexane.

6. A highly lipophilic copper nanoparticle prepared by the preparation method according to any one of claims 1 - 5.

7. An application of the highly lipophilic copper nanoparticle according to claim 6 in lubricating oil.

8. The application according to claim 7, wherein Vacuumize and heat the highly lipophilic copper nanoparticles to remove volatile organic substances, obtain pure nano-copper particles, stir evenly with base oil, and perform ultrasonic treatment to obtain a copper nanofluid for use as a lubricating oil.

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