Modified lubricating oil additive containing graphene-copper oxide as well as preparation method and application of modified lubricating oil additive

Abstract

The invention discloses a preparation method of a modified lubricating oil additive containing graphene-copper oxide, which comprises the following steps: preparing an RGO / CuO nano composite material additive with CuO grafted on graphene through a hydrothermal method, and adding oleic acid (OA) to participate in a hydrothermal reaction to prepare an OA-RGO / CuO nano composite material additive with CuO and OA grafted on graphene; the preparation method not only optimizes the morphology size of the lubricating oil additive, but also improves the tribological performance and dispersion stability of the lubricating oil additive. The microstructure of the composite material is observed through an SEM scanning electron microscope, it is found that a sheet layer on the surface of the composite material added with oleic acid is thinner and wrinkled, the particle size of nano particles is smaller, the nano particles are wrapped by the sheet layer more tightly, and the nano particle diameter of the OA-RGO / CuO additive is reduced by 48.89% compared with that of the RGO / CuO additive; in a contact angle test, the nano additive in which oleic acid participates in a hydrothermal reaction can further reduce the surface energy of the nano additive, and the contact angle is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials, and particularly relates to a modified lubricating oil additive containing graphene - copper oxide, and a preparation method and application thereof. Background Art

[0002] With the continuous development of the times, the level of industrialization occupies an extremely important position in the national economic development. An important indicator to measure a country's industrialization level is the production and manufacturing level of industrial machinery, and friction and wear are crucial to the quality of mechanical equipment. Reducing friction and wear of mechanical equipment has become an important direction affecting industrial development. Using the lubricating effect of lubricating oil to reduce friction and wear of machines is the most widespread practice at present.

[0003] Lubricating oil additives refer to one or several chemical substances added to lubricating oil to improve the performance and functions of lubricating base oil. The addition of additives can improve the problems of insufficient performance of some base oils in certain aspects and enhance the performance of lubricating base oil. The addition amount of additives is small but the effect is obvious. Generally, industrial lubricating oil additives account for less than 10% of the total weight of the oil, and internal combustion engine lubricating oil additives account for about 20% of the total weight of the oil. The application of lubricating oil additives can improve the quality and performance of lubricating oil, meet the requirements of some special working conditions, reduce equipment wear, improve efficiency, extend the oil change cycle of equipment, and increase its service life.

[0004] High - pair friction pairs mainly refer to friction components mainly in line and point contact, such as gears, ball bearings, etc., which are commonly found in fields such as engines, high - speed machinery, aerospace, etc. Their main characteristics are high speed, high pressure, high temperature, small contact area on the friction pair surface, large contact stress, etc. At present, the research on high - pair friction pairs mainly includes surface modification of materials, lubricant research, tribology theory research, etc. Developing new lubricating oil additives using nanomaterials is one of the main directions to solve the current friction and wear of high - pair friction pairs.

[0005] At present, many domestic and foreign scholars have carried out modification research on a large number of nanomaterials as lubricating oil additives, but there is little research on the synergistic effect of different properties of different materials or the complex compounding method, resulting in problems such as high cost, poor comprehensive performance of existing nanomaterials as lubricating oil additives, and inability to well meet market demands. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems in the related technologies to some extent. For this reason, the main object of the present invention is to provide a modified lubricating oil additive containing graphene - copper oxide, aiming to solve the problems of high cost and poor comprehensive performance of existing lubricating oil additives.

[0007] The present invention also provides a preparation method and an application of the modified lubricating oil additive containing oil graphene - copper oxide.

[0008] The object of the present invention is achieved by the following technical solutions:

[0009] A preparation method of a modified lubricating oil additive containing graphene - copper oxide, comprising the following steps:

[0010] 1) Take graphene oxide powder and add it to deionized water. After dispersing evenly, a graphene oxide dispersion is obtained;

[0011] 2) Add copper sulfate particles to deionized water. After dispersing evenly, a copper sulfate solution is obtained;

[0012] 3) Mix the graphene oxide dispersion and the copper sulfate solution evenly, then drop in ammonia water for hydrothermal reaction to obtain mixture A;

[0013] 4) Add an anhydrous ethanol solution containing oleic acid to mixture A, carry out high - temperature hydrothermal reaction, and cool to room temperature to obtain mixture B;

[0014] 5) Centrifuge, wash and dry mixture B, and then grind to obtain a modified lubricating oil additive containing graphene - copper oxide.

[0015] In some specific embodiments, the mass ratio of the graphene oxide, copper sulfate and oleic acid is (0.1 - 0.5) g : (0.8 - 2.0) g : (2 - 8) ml.

[0016] In some specific embodiments, the conditions of the hydrothermal reaction in step 3) are: the pH value of the reaction system is 9.5 - 10, the reaction temperature is 60 - 100 °C, and the reaction time is 1 - 2 h.

[0017] In some specific embodiments, the volume ratio of the oleic acid to the anhydrous ethanol in step 4) is (5 - 15) : 100.

[0018] In some specific embodiments, the conditions of the high - temperature hydrothermal reaction in step 4) are: maintaining at a reaction temperature of 150 - 200 °C for 6 - 10 h.

[0019] In some specific embodiments, the specific conditions of the centrifugation in step 5) are: centrifuging at a rotation speed of 4000 - 6000 rpm / min for 10 - 20 min.

[0020] In some specific embodiments, the drying conditions in step 5) are: maintaining at a drying temperature of 60 - 100 °C for 10 - 15 h.

[0021] As the same inventive concept of the present invention, the present application also provides a modified lubricating oil additive containing graphene - copper oxide.

[0022] As the same inventive concept of the present invention, the present application also provides the application of the modified lubricating oil additive containing graphene - copper oxide in the field of friction and wear industry.

[0023] Compared with the prior art, the present invention has at least the following advantages:

[0024] 1) The present invention prepares an RGO / CuO nanocomposite additive with CuO grafted on graphene by a hydrothermal method, and oleic acid (OA) is added to participate in the hydrothermal reaction to prepare an OA - RGO / CuO nanocomposite additive with CuO and OA grafted on graphene; this preparation method not only optimizes the morphology and size of the lubricating oil additive, but also improves the tribological properties and dispersion stability of the lubricating oil additive. By observing its microscopic morphology through SEM scanning electron microscopy, it is found that the lamellae on the surface of the composite material with oleic acid added are thinner and become wrinkled, the particle size of the nanoparticles is smaller, and they are more tightly wrapped by the lamellae. The nanoparticle diameter of the OA - RGO / CuO additive is reduced by 48.89% compared with the RGO / CuO additive; in the contact angle test, the nano - additive with oleic acid participating in the hydrothermal reaction can further reduce its surface energy, and the contact angle is greatly reduced;

[0025] 2) Through tribological tests, the present application proves that the modified lubricating additive of the present application has excellent tribological properties; and in the XPS elemental analysis of the wear scars of the specimens, the elements corresponding to the modified lubricating additive of the present application and the formation of iron oxide are found, which proves that the modified lubricating oil additive has undergone a tribochemical reaction and new oxides are generated during the friction process to reduce the friction and wear of the specimens;

[0026] 3) The present application conducts a bearing bench test on the prepared modified lubricating oil additive and proves that it has excellent tribological properties. Specifically, in the bearing bench test, the average amplitude, temperature, and noise of the lubricating oil containing 0.05 wt.% OA - RGO / CuO are reduced by 45.65%, 42.11%, and 3.42 dB respectively compared with pure oil, having good economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention, the drawings required for use in the specific embodiments or the description of the prior art will be briefly introduced below.

[0028] Figure 1 It is the macroscopic morphology diagram of GO, RGO, RGO / CuO, and OA - RGO / CuO in the present invention;

[0029] Figure 2Fourier transform infrared spectroscopy diagram of RGO in the present invention;

[0030] Figure 3 Fourier transform infrared spectroscopy diagrams of GO, RGO / CuO, and OA-RGO / CuO in the present invention;

[0031] Figure 4 EDS surface scanning energy spectrum panoramic diagrams of RGO / CuO and OA-RGO / CuO in the present invention;

[0032] Figure 5 Element proportion diagrams of RGO / CuO and OA-RGO / CuO in the present invention;

[0033] Figure 6 SEM micrographs of GO, RGO, RGO / CuO, and OA-RGO / CuO in the present invention;

[0034] Figure 7 Average friction coefficient diagrams of pure oil, pure oil added with 0.05 wt.% of RGO / CuO, and OA-RGO / CuO in the present invention;

[0035] Figure 8 Anti-friction and anti-wear result diagrams of pure oil in the present invention;

[0036] Figure 9 Anti-friction and anti-wear result diagrams of pure oil added with 0.05 wt.% of RGO / CuO in the present invention;

[0037] Figure 10 Anti-friction and anti-wear result diagrams of pure oil added with 0.05 wt.% of OA-RGO / CuO in the present invention;

[0038] Figure 11 Morphology result diagrams of the wear scar regions of pure oil, pure oil added with 0.05 wt.% of RGO / CuO, and OA-RGO / CuO in the present invention;

[0039] Figure 12 XPS characterization and analysis diagrams of the wear scar region of pure oil under friction conditions in the present invention;

[0040] Figure 13 XPS characterization and analysis diagrams of the wear scar region of pure oil added with 0.05 wt.% of RGO / CuO under friction conditions in the present invention;

[0041] Figure 14 XPS characterization and analysis diagrams of the wear scar region of pure oil added with 0.05 wt.% of OA-RGO / CuO under friction conditions in the present invention;

[0042] Figure 15Stability test diagrams of pure oil, pure oil with 0.05 wt.% of RGO / CuO added, and OA-RGO / CuO in the present invention;

[0043] Figure 16 Vibration amplitude curve diagrams of pure oil, pure oil with 0.05 wt.% of RGO / CuO added, and OA-RGO / CuO in the present invention;

[0044] Figure 17 Temperature curve diagrams of pure oil, pure oil with 0.05 wt.% of RGO / CuO added, and OA-RGO / CuO in the present invention;

[0045] Figure 18 Noise curve diagrams of pure oil, pure oil with 0.05 wt.% of RGO / CuO added, and OA-RGO / CuO in the present invention. Detailed implementation manners

[0046] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The following embodiments are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0047] When expressing a certain quantity, concentration, or other value or parameter in the form of a range, a preferred range, or a preferred upper limit and lower limit of a value, it should be understood that any range formed by combining any upper limit of the range or a preferred value with any lower limit of the range or a preferred value is specifically disclosed, regardless of whether the range is specifically disclosed. Unless otherwise indicated, the numerical range values listed herein include the endpoints of the range and all integers and fractions within the range.

[0048] Unless otherwise stated, all percentages, parts, ratios, etc. in this article are by weight.

[0049] The materials, methods, and embodiments in this article are all exemplary and should not be construed as restrictive unless otherwise specified.

[0050] In the following embodiments, the pure oil used was Shell HELIX6 (5w-30) lubricating oil purchased from Shell (Tianjin) Petrochemical Co., Ltd.

[0051] The test methods used in the following embodiments include:

[0052] By separately testing the main properties of each test sample, the tribological properties of the lubricant additive are reflected; the main properties tested in this application are friction coefficient, wear scar, etc.

[0053] 1) Tribological test;

[0054] Select a GCr15 steel ball with a diameter of 12.7 mm and a hardness of 60 - 62 HRC as the test piece for the four-ball friction and wear test.

[0055] Example 1

[0056] This example provides a preparation method of a modified lubricating oil additive containing graphene - copper oxide, which includes the following steps:

[0057] 1) Take 0.1 g of graphene oxide powder (GO powder) and add it to 75 ml of deionized water, and ultrasonically disperse for 2 h to obtain a graphene oxide dispersion;

[0058] 2) Add 0.8 g of copper sulfate particles to 100 ml of deionized water, and ultrasonically disperse for 15 min to obtain a copper sulfate solution;

[0059] 3) After mixing the graphene oxide dispersion in step 1) and the copper sulfate solution in step 2) evenly, dropwise add ammonia water to adjust the pH value to 9.5, and stir for 2 h at a reaction temperature of 60 °C to carry out a hydrothermal reaction to obtain mixture A;

[0060] 4) Transfer mixture A into a high-temperature reaction kettle, and at the same time add 50 ml of absolute ethanol solution containing 2 ml of oleic acid, then transfer it to an oven and heat at 150 °C for 6 h to carry out a high-temperature hydrothermal reaction. After the reaction is completed, wait for the high-temperature reaction kettle to cool naturally to room temperature to obtain mixture B;

[0061] 5) Centrifuge mixture B at a speed of 5000 rpm for 10 min, wash it 3 times with deionized water, then filter it by suction to obtain a black powder, put it into an oven at 60 °C and dry for 15 h, and grind it in a ball mill for 20 min to obtain a modified lubricating oil additive containing graphene - copper oxide (abbreviation: OA - RGO / CuO).

[0062] Example 2

[0063] This example provides a preparation method of a modified lubricating oil additive containing graphene - copper oxide, which includes the following steps:

[0064] 1) Take 0.3 g of graphene oxide powder and add it to 100 ml of deionized water, and ultrasonically disperse for 2 h to obtain a graphene oxide dispersion;

[0065] 2) Add 1.0 g of copper sulfate particles to 100 ml of deionized water, and ultrasonically disperse for 15 min to obtain a copper sulfate solution;

[0066] 3) After mixing the graphene oxide dispersion in step 1) and the copper sulfate solution in step 2) evenly, dropwise add ammonia water to adjust the pH value to 9.8, and stir for 1.5 h at a reaction temperature of 80 °C to carry out a hydrothermal reaction to obtain mixture A;

[0067] 4) Transfer mixture A into a high-temperature reactor, and simultaneously add 50 ml of anhydrous ethanol solution containing 4.5 ml of oleic acid. Then transfer it into an oven and heat it at 180 °C for 8 h to carry out a high-temperature hydrothermal reaction. After the reaction is completed, wait for the high-temperature reactor to cool naturally to room temperature to obtain mixture B;

[0068] 5) Centrifuge mixture B at a speed of 5000 rpm for 15 min, wash it 3 times with deionized water, then filter it by suction to obtain a black powder. Put it into an oven at 80 °C and dry it for 12 h, and grind it in a ball mill for 30 min to obtain a modified lubricating oil additive containing graphene - copper oxide (abbreviated as OA - RGO / CuO).

[0069] Example 3

[0070] This example provides a preparation method of a modified lubricating oil additive containing graphene - copper oxide, which includes the following steps:

[0071] 1) Take 0.5 g of graphene oxide powder and add it to 120 ml of deionized water, and ultrasonically disperse it for 2 h to obtain a graphene oxide dispersion;

[0072] 2) Add 2.0 g of copper sulfate particles to 100 ml of deionized water, and ultrasonically disperse it for 15 min to obtain a copper sulfate solution;

[0073] 3) After mixing the graphene oxide dispersion in step 1) and the copper sulfate solution in step 2) evenly, dropwise add ammonia water to adjust the pH value to 9.7, and stir at a reaction temperature of 100 °C for 1 h to carry out a hydrothermal reaction to obtain mixture A;

[0074] 4) Transfer mixture A into a high-temperature reactor, and simultaneously add 50 ml of anhydrous ethanol solution containing 8 ml of oleic acid. Then transfer it into an oven and heat it at 200 °C for 10 h to carry out a high-temperature hydrothermal reaction. After the reaction is completed, wait for the high-temperature reactor to cool naturally to room temperature to obtain mixture B;

[0075] 5) Centrifuge mixture B at a speed of 5000 rpm for 20 min, wash it 3 times with deionized water, then filter it by suction to obtain a black powder. Put it into an oven at 100 °C and dry it for 10 h, and grind it in a ball mill for 40 min to obtain a modified lubricating oil additive containing graphene - copper oxide (abbreviated as OA - RGO / CuO).

[0076] Comparative Example 1

[0077] This comparative example provides a lubricating oil additive, which includes the following steps:

[0078] Weigh 0.2 g of GO powder and add it to 200 ml of deionized water, and ultrasonically disperse it for 2 h. After the GO is completely dissolved in deionized water, add ammonia water to the GO aqueous solution to adjust the pH value to 9.5 - 10. Then add 0.33 g of vitamin C, stir evenly, and transfer it to a magnetic stirring device with a heating mantle for stirring in a water bath at 90 °C for 1.5 - 2 h. After that, transfer the mixture into a high-temperature reaction kettle and react at 180 °C for 4 hours. After the reaction is completed, naturally cool it to room temperature. Perform high-speed centrifugation on the reaction product for 10 minutes at a rotation speed of 5000 rpm / min. Wash it twice with deionized water and then perform suction filtration. Put the obtained black powder into a drying oven and dry it at 80 °C for 12 h. Finally, grind it with a ball mill for 30 min to finally obtain black and fluffy RGO powder (abbreviation: RGO).

[0079] Comparative Example 2

[0080] This comparative example provides a lubricating oil additive, which is basically the same as Example 2, except that oleic acid is not added during the high-temperature hydrothermal reaction. The specific steps are as follows:

[0081] 1) Take 0.3 g of graphene oxide powder and add it to 100 ml of deionized water, and ultrasonically disperse it for 2 h to obtain a graphene oxide dispersion;

[0082] 2) Add 1.0 g of copper sulfate particles to 100 ml of deionized water, and ultrasonically disperse it for 15 min to obtain a copper sulfate solution;

[0083] 3) After mixing the graphene oxide dispersion in step 1) and the copper sulfate solution in step 2) evenly, drop in ammonia water to adjust the pH value to 9.8, and stir for 1.5 h at a reaction temperature of 80 °C for hydrothermal reaction to obtain mixture A;

[0084] 4) Transfer mixture A into a high-temperature reaction kettle and heat it at 180 °C for 8 h for high-temperature hydrothermal reaction. After the reaction is completed, wait for the high-temperature reaction kettle to naturally cool to room temperature to obtain mixture B;

[0085] 5) Centrifuge mixture B at a rotation speed of 5000 rpm / min for 15 min, wash it 3 times with deionized water, then perform suction filtration to obtain black powder, put it into a drying oven at 80 °C and dry it for 12 h, and grind it with a ball mill for 30 min to obtain a modified lubricating oil additive containing graphene - copper oxide (abbreviation: RGO / CuO).

[0086] Performance test:

[0087] Taking Example 2 as an example, performance tests were carried out on the modified lubricating oil additives prepared in Example 2 (OA - RGO / CuO), Comparative Example 1 (RGO), and Comparative Example 2 (RGO / CuO). Specifically:

[0088] 1) Morphology test

[0089] 1.1) Macroscopic morphology diagram

[0090] In this application, GO, RGO, RGO / CuO, and OA-RGO / CuO were observed with the naked eye, and the results are as Figure 1 shown. The graphene oxide (GO) in this application is brownish-black. After being prepared by the reducing agent VC and hydrothermal method, the oxygen-containing functional groups on its surface are destroyed, forming pure black and lipophilic RGO. The color of RGO / CuO is pure black, and the color of OA-RGO / CuO is also black, but it looks more fluffy as a whole.

[0091] 1.2) Infrared characterization

[0092] The Fourier transform infrared spectra of GO, RGO, RGO / CuO, and OA-RGO / CuO in this application. The Fourier transform infrared spectrum of RGO is as Figure 3 shown. It can be seen from the figure that the hydroxyl (-OH) absorption peak of graphene oxide near 3410 cm -1 becomes much smaller than that of graphene oxide. There are two C=C stretching absorption peaks in the range of 1550 - 1950 cm -1 , and the C=O absorption peak in this section of the GO curve disappears. And the C=C near 1950 cm -1 is one of the manifestations of the high-temperature reduction of GO. The C-O absorption peak in the range of 1050 - 1250 cm -1 becomes smaller, that is, the above absorption peaks can all prove the successful reduction of GO to prepare RGO.

[0093] And the Fourier transform infrared spectra of GO, RGO / CuO, and OA-RGO / CuO are as Figure 2 shown. It can be seen from the figure that the functional groups of the GO material and the functional groups of the additives after preparation, etc. In the GO curve, the peak near 3410 cm -1 is the -OH stretching vibration peak of the hydroxyl (-OH) and carboxyl (-COOH) in graphene oxide. The two absorption peaks in the range of 2850 cm -1 -2920 cm -1 are the C-H stretching vibration absorption peaks of saturated carbon-hydrogen bonds (-CH2, CH3). The absorption peaks at 1730 cm -1 and 1624 cm -1 are the C=O and C=C stretching vibration peaks of GO. The characteristic peak at 1250 cm -1 is the C-O stretching vibration caused by the hydroxyl in the oxygen-containing functional groups (such as epoxy groups) on graphene oxide. The characteristic peak at 1043 cm -1The nearby absorption peak is the stretching vibration absorption peak of C-O-C, 860 cm -1 The absorption peak near it is the stretching vibration absorption peak of -OH. As can be seen from Figure 2 the RGO / CuO and OA-RGO / CuO curves both have Cu-O stretching vibration peaks at 465 cm -1 , 518 cm -1 and 590 cm -1 , which proves that copper oxide (CuO) is formed on the surface of RGO. The C-O stretching vibration peak is near 1220 cm -1 , which is caused by the oxygen-containing functional groups remaining during the reduction of GO to RGO. The absorption peak near 1391 cm -1 is due to the -OH in the carboxyl group (-COOH), and the absorption peak near 1560 cm -1 is the C═C stretching vibration peak caused by the reduction of graphene oxide, and the absorption peak at 1736 cm -1 is the C═O vibration absorption peak. In the OA-RGO / CuO curve, the double peaks at 2850 cm -1 -2950 cm -1 are the C-H stretching vibration peaks, which are also the significant characteristic peaks of oleic acid; it proves that oleic acid participates in the reaction and is successfully grafted onto the composite material.

[0094] 1.3) SEM Characterization

[0095] In this test example, SEM scanning electron microscopy was used to characterize the microscopic morphology of the lubricating oil additive, and the shooting parameters were HV = 15 KV, Vac = 0.1 pa, SED mode, and magnification of 8000.

[0096] Among them, the full EDS surface scanning energy spectrum diagrams of RGO / CuO and OA-RGO / CuO in this application

[0097] The results are as Figure 4 shown. As can be seen from the figure, the red in the figure is carbon element, the blue is oxygen element, and the green is copper element. It can be seen at the position slightly to the right of the center of the figure that the small spherical morphology part is mainly green and blue. Combining with the Cu-O bond in the aforementioned infrared spectrum, it can be determined that the spherical particles are copper oxide particles.

[0098] In addition, the element ratios of RGO / CuO and OA-RGO / CuO in this application are as Figure 5 shown. It can be known from the figure that the weight ratios of carbon, oxygen, and copper elements in RGO / CuO are 64.8%, 15.5%, and 19.7% respectively; while the weight ratios of carbon, oxygen, and copper elements in OA-RGO / CuO are 72%, 15.2%, and 12.8% respectively. Compared with RGO / CuO, the carbon element increases and the copper element decreases. The reason may be related to the introduction of oleic acid.

[0099] Among them Figure 6 are the SEM micrographs of GO, RGO, RGO / CuO, and OA-RGO / CuO. It can be seen from the figures that graphene oxide (GO) is in a sheet-like shape; the overall microstructure of RGO presents a thinner and smoother sheet-like structure, and the sheets are more wrinkled, increasing the interlayer spacing, which is consistent with the results of the infrared spectroscopy analysis of RGO. It can be seen from the figure that RGO / CuO presents a thin and wrinkled sheet shape, and spherical copper oxide particles with a diameter of about 900 nm are dispersed among the wrinkled sheets. Compared with RGO / CuO, in addition to the same wrinkled sheets, the spherical copper oxide particles of OA-RGO / CuO are about 460 nm, which is about half of the former, and the small balls are no longer simply located or grafted on the surface of the sheets. Due to the addition of oleic acid, the copper oxide small balls are wrapped on the sheets, presenting an overall "ovum" shape.

[0100] 1.4) Contact angle measurement

[0101] This application measured the contact angles of pure base oil, 0.05 wt.% RGO / CuO lubricating oil, and 0.05 wt.% OA-RGO / CuO lubricating oil (using an HKCA-15 contact angle measuring instrument). The contact angle of pure base oil is the largest, with an average angle of 30.66°; the contact angle of 0.05 wt.% OA-RGO / CuO lubricating oil is the smallest, with an average angle of 13.30°, which is 56.62% smaller than that of pure oil; the average contact angle of 0.05 wt.% RGO / CuO lubricating oil is 21.61°. This shows that the OA-RGO / CuO lubricating oil additive has excellent compatibility and lubricity with the material surface.

[0102] 1.5) Kinematic viscosity

[0103] This application also measured the kinematic viscosity of the lubricating oil additive (using an NDJ-5S rotational viscometer). Among them, the kinematic viscosity of pure base oil (pure oil) is 104.5 mPa·s, and the kinematic viscosity of RGO lubricating oil is 111.0 mPa·s, which is slightly higher than that of pure oil. The kinematic viscosities of RGO / CuO lubricating oil and OA-RGO / CuO lubricating oil are 121.0 mPa·s and 123.0 mPa·s respectively. Analyzing the reasons, the addition of CuO and RGO leads to an increase in kinematic viscosity. The lubricating oil formed by a lubricating oil additive with a high kinematic viscosity forms a thicker oil film, which is more suitable for heavy-load and high-temperature working conditions.

[0104] 2) Tribological performance test

[0105] This test example selected a screen-display high-temperature end-face testing machine (four-ball type) to conduct tribological performance tests on the lubricating oil added with modified lubricating oil additives. The specific test method is as follows:

[0106] 2.1) Confocal Laser Topography Analysis

[0107] For the tribological performance test, an MDW-5G digital display high-temperature end-face device (four-ball type) was selected. The upper specimen was a single ball, and the lower specimen consisted of three balls, all with a diameter of 12.7 mm and made of GCr15. The experimental conditions for this experiment were "392 N, 1200 rpm / min", and the test time was 1 h. In addition to pure engine oil, 0.05 wt.% of the modified lubricating oil additive was added to the test lubricating oil of this application for the experiment. The lubricating oil containing the modified lubricating oil additive was prepared by ultrasonic treatment for 15 min and then stirred for 15 min. The specimens were ultrasonically treated with absolute ethanol for 30 min and then wiped clean with dust-free paper to ensure that there was no oil stain or dust on the specimen surface, which would not affect the experiment. The lubricating oil was added to the oil box of the four-ball device, and the oil should infiltrate the upper and lower specimens. Each friction test was repeated 3 times.

[0108] The results of its friction coefficient are as Figure 7 shown. It can be seen from the figure that among them, the friction coefficient of pure oil is the highest, which is 0.063; the average friction coefficient of RGO / CuO is about 0.057, which is 9.52% lower than the average friction coefficient of pure oil; the average friction coefficient of OA-RGO / CuO is the lowest, about 0.052, which is 17.46% lower than the average friction coefficient of pure oil. In summary, it can be known that the OA-RGO / CuO modified lubricating oil additive can improve the friction coefficient of lubricating oil (pure oil).

[0109] 2.2) SEM Scanning Electron Microscope Characterization

[0110] Among them, the results of friction reduction and wear resistance in the friction and wear test are as Figures 8 - 10 shown. It can be seen from the figure that the wear scar width sizes of the friction specimens with different lubricating oil additives from large to small are pure oil, RGO / CuO, and OA-RGO / CuO. The wear scar width and maximum depth of pure oil are 463.4 μm and 2.4 μm respectively; the wear scar width and maximum depth of the RGO / CuO lubricating oil additive are 395.7 μm and 2.3 μm respectively, which are 14.61% and 4.2% smaller than those of pure oil in terms of wear scar width and depth respectively; the wear scar width and maximum depth of the OA-RGO / CuO lubricating oil additive are 340.1 μm and 2.2 μm respectively, which are 36.61% and 8.3% smaller than those of pure oil in terms of wear scar width and depth respectively; combined with the three-dimensional topography and wear scar size data in the figure, it can be known that OA-RGO / CuO has excellent friction reduction and wear resistance effects in the four-ball friction test under the heavy load condition of "392 N, 1200 rpm / min".

[0111] Among them, the topography results of the wear scar area in the friction and wear test are as Figure 11As shown, it can be seen from the figure that there are some shallow plough-shaped wear marks and spalled wear debris in the wear scar of pure oil. There is a large area of adhesive wear in the figure. When the pressure is too high, the performance of the pure oil film is insufficient to withstand the large test pressure, resulting in direct metal friction between the contact surfaces and forming an adhesive wear phenomenon. And pitting can be observed in the local enlarged view of the pure oil wear scar. The plough-shaped wear scar of RGO / CuO shows that the wear scar size is smaller than that of pure oil. Copper oxide in the composite additive enters the friction surface during the test operation, resulting in slightly more wear marks on the surface than the plough-shaped wear marks of pure oil. There are pitting and wear debris in the local enlarged view of the wear scar, but some small copper oxide particles can also be found on the plough groove. At the same time, the adhesive wear mark is much less than that of pure oil. The wear scar of OA-RGO / CuO shows that the plough-shaped wear scar is less than that of RGO / CuO. Combining with its three-dimensional topography and local enlarged view in Figures 8 - 10 it is found that it is not adhesive wear but a chemical reaction or physical deposition of the lubricant additive on the contact surface after observation, and there is some slight pitting in the local enlarged view. It shows that when the prepared modified lubricant additive enters the friction contact surface, the spherical nanoparticles and the sheets of RGO play a synergistic role.

[0112] 2.3) XPS elemental analysis

[0113] Use a BRUKER Contour confocal microscope to conduct a four-ball test friction and wear test on pure oil, 0.05 wt.% RGO, 0.05 wt.% RGO / CuO, and 0.05 wt.% OA-RGO / CuO under the working conditions of "294 N, 1200 rpm / min, 1 h", and conduct XPS tests on the GCr15 steel balls after the test.

[0114] Figures 12 - 14 The XPS characterization analysis of the wear scar area of GCr15 steel balls under the working conditions of "294 N, 1200 rpm / min, 1 h" is shown as follows, Figures 12 - 14 They are pure oil, lubricating oil containing 0.05 wt.% RGO / CuO additive, and lubricating oil containing 0.05 wt.% OA-RGO / CuO additive respectively. Figure 12 In the C1s spectrum of pure oil, the C-O (286.18 eV) contained is the result of the reaction with oxygen during the friction process, and C-C (283.28 eV) can be attributed to the carbon contaminated on the surface during the friction process and the carbon on the surface of the steel ball matrix. In the O1s spectrum of pure oil, there is Fe-O (529.88 eV), and the Fe-O is caused by the reaction of oxygen with the metal surface during the friction process. Combining with the Fe2p contained in the Fe2p 3 / 2 (711.08 eV) and Fe-O (724.88 eV) in the spectrum of pure oil, it can be seen that iron oxide is formed on the friction surface of pure oil. Fe2p 3 / 2(711.08 eV) is the satellite peak of Fe2O3.

[0115] From Figure 13 The C1s spectrum of the lubricating oil containing 0.05 wt.% RGO / CuO additive contains O═C-OH (288.08 eV), C-O (286.08 eV), and C-C (283.48 eV). Among them, O═C-OH is a peak that does not exist in the C1s of pure oil. The appearance of this sub-peak is attributed to the sp 2 Hybrid carbon structure from the RGO / CuO component because the CuO / RGO additive is the only possible carbon source. This indicates that the RGO / CuO additive is deposited on the surface of the wear track during the friction process. The O1s spectrum contains C-O (533.5 eV) and Fe-O (529.88 eV). Since Cu-O is also located near the 529.88 eV position, whether there is Cu-O specifically needs to be analyzed in combination with the Cu2p spectrum. From the Cu2p spectrum, it is found to contain Cu-O (952.68 eV), Cu-O (932.68 eV), and Cu-O (932.18 eV). Among them, Cu-O (932.68 eV) corresponds to Cu2p 3 / 2 Indicates the presence of copper oxide. Cu-O (952.68 eV) is a satellite peak corresponding to a higher binding energy, indicating a stronger electron interaction in the copper oxide. In the Fe2p spectrum, there are Fe-O (724.08 eV), Fe 3+ (719.88 eV), Fe2p 3 / 2 (711.88 eV), Fe-O (707.08 eV). Among them, Fe2p 3 / 2 Indicates the formation of an iron oxide layer.

[0116] From Figure 14 In the case of 0.05 wt.% OA-RGO / CuO, it can be found that the C1s spectrum contains O═C-OH (288.08 eV), C-O (286.08 eV), and C-C (283.48 eV). The appearance of O═C-OH (288.08 eV) is attributed to the participation of RGO in the reaction. The O1s spectrum contains C-O (531.58 eV) and Fe-O (530.08 eV). Since Cu-O is also located near the 530.08 eV position, whether there is Cu-O specifically needs to be analyzed in combination with the Cu2P spectrum. From the Cu2p spectrum, Cu-O (952.88 eV), Cu-O (932.68 eV), and Cu-O (950.08 eV) are found. Among them, Cu-O (932.68 eV) and Cu-O (950.08 eV) correspond to Cu2p 3 / 2 and Cu2p 1 / 2The presence of copper oxide is indicated. Cu - O (952.88 eV) is the satellite peak corresponding to a higher binding energy, indicating a stronger electron interaction in copper oxide. The Fe2p spectrum contains Fe - O (724.08 eV), Fe2p 3 / 2 (711.88 eV), Fe - O (707.08 eV), where Fe2p 3 / 2 indicates the formation of an iron oxide layer, and Fe - O (724.08 eV) is related to friction and wear.

[0117] In summary, during the friction process, the modified lubricating oil additive in this application participates in the friction process, specifically entering the worn - scar contact surface to play a role in reducing friction and wear resistance.

[0118] 3) Stability test

[0119] This application conducts a dispersion and static - state experiment on pure oil, lubricating oil containing 0.05 wt.% of RGO / CuO additive, and lubricating oil containing 0.05 wt.% of OA - RGO / CuO additive. The experimental duration is 30 days.

[0120] The results are as Figure 15 described. From left to right in the figure are pure oil, RGO / CuO - containing lubricating oil, and OA - RGO / CuO - containing lubricating oil. It can be found from the figure that in the first day of static dispersion, no uneven dispersion or precipitation was found in all lubricating oils containing additives, indicating good compatibility between the lubricating oil additive and the base oil. From the experimental results on the 15th day of static dispersion, the color of the RGO / CuO lubricating oil changed from the initial black to dark brown, and the lubricating oil additive slightly precipitated in the pure oil. The reason may be that the copper oxide particles in the RGO / CuO lubricating oil precipitated first as time went by. The fact that there was no precipitation or uneven dispersion in the OA - RGO / CuO lubricating oil on the 15th day should be due to the important role of oleic acid in the preparation process. From the results of the 30 - day experiment in (e), the precipitation of the RGO / CuO lubricating oil was the most obvious, and the color of the oil changed from dark brown to brown - black. After a one - month static dispersion experiment, the color change of the OA - RGO / CuO lubricating oil was not obvious, indicating that adding oleic acid to participate in the reaction during the hydrothermal preparation of the lubricating oil additive can enhance the dispersion stability of the lubricating oil additive.

[0121] 4) Friction and wear test analysis in actual application scenarios

[0122] 4.1) Bearing bench test

[0123] This application conducts a bearing bench test on pure oil, lubricating oil containing 0.05 wt.% of RGO / CuO, and lubricating oil containing 0.05 wt.% of OA - RGO / CuO. Specifically:

[0124] Testing equipment: In the bearing testing machine for this test, the bearing selected is of the model "51306 / P5", with a ball diameter of 11 mm, 11 balls, a test pressure of 1.045 KN, and a rotational speed of 1200 rpm / min.

[0125] The results of the vibration amplitude curve graph of the bearing bench test are as Figure 16 shown. It can be seen from the graph that the vibration amplitude of pure oil is the largest. The overall width of the vibration amplitude of the lubricating oil containing 0.05 wt.% of RGO / CuO is slightly smaller than that of pure oil, and the vibration amplitude of the lubricating oil containing 0.05 wt.% of OA-RGO / CuO is significantly smaller than that of pure oil. It can also be found from the vibration amplitude curve graph that except for the amplitude curve graph of the lubricating oil containing 0.05 wt.% of OA-RGO / CuO, the "jump points" of the amplitude curves of other lubricating oils are more numerous and the amplitude values of the "jump points" are also relatively large. Thus, it can be known that the performance of the lubricating oil containing 0.05 wt.% of OA-RGO / CuO is better. After taking the absolute average value of the amplitude curve data of the three lubricating oils, the absolute average value of the amplitude curve of pure oil is 0.1023, the absolute average value of the amplitude curve of RGO / CuO lubricating oil is 0.0772, which is 24.54% lower than the absolute average value of the amplitude curve of pure oil. The absolute average value of the amplitude curve of OA-RGO / CuO lubricating oil is 0.0556, which is 45.65% lower than the absolute average value of the amplitude curve of pure oil; indicating that the OA-RGO / CuO lubricating oil in this application can effectively reduce the vibration amplitude during the friction process;

[0126] The results of the temperature curve graph of the bearing bench test are as Figure 17 shown. It can be seen from the graph that the temperature of the lubricating oil containing 0.05 wt.% of OA-RGO / CuO is 2°C lower than that of pure oil, indicating that the OA-RGO / CuO lubricating oil in this application can effectively reduce the temperature rise amplitude during the friction process;

[0127] Place the noise meter at a fixed position near the bearing specimen, and use a portable noise tester to measure the noise during the bearing bench test, with a sampling frequency of once per minute. The results of the noise curve graph of the bearing bench test are as Figure 18 shown. It can be found from the graph that the average noise of pure oil is 81.68 dB, the average noise of the lubricating oil containing 0.05 wt.% of RGO / CuO is 79.55 dB, and the average noise of the lubricating oil containing 0.05 wt.% of OA-RGO / CuO is 78.26 dB; that is, the lubricating oil containing 0.05 wt.% of OA-RGO / CuO can effectively reduce the noise value during the friction process.

[0128] In summary, by comparing the amplitude curve, temperature curve, and noise curve in the bearing bench test of lubricating oil, it can be seen that the lubricating oil containing 0.05 wt.% OA-RGO / CuO can effectively improve the lubrication effect of pure oil, has excellent tribological properties, and has good economic and social benefits.

[0129] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention, and they should all be covered by the scope of the claims and the specification of the present invention.

Claims

1. A preparation method of a modified lubricating oil additive containing graphene - copper oxide, characterized in that, It includes the following steps: 1) Take graphene oxide powder and add it to deionized water. After dispersing evenly, a graphene oxide dispersion is obtained; 2) Add copper sulfate particles to deionized water. After dispersing evenly, a copper sulfate solution is obtained; 3) Mix the graphene oxide dispersion and the copper sulfate solution evenly, then drop in ammonia water for hydrothermal reaction to obtain mixture A; 4) Add an anhydrous ethanol solution containing oleic acid to mixture A, carry out high-temperature hydrothermal reaction, and cool to room temperature to obtain mixture B; 5) Centrifuge, wash and dry mixture B, and then grind it to obtain a modified lubricating oil additive containing graphene - copper oxide.

2. The preparation method of the modified lubricating oil additive containing graphene - copper oxide according to claim 1, characterized in that, The mass ratio of the graphene oxide, copper sulfate and oleic acid is (0.1 - 0.5) g : (0.8 - 2.0) g : (2 - 8) ml.

3. The preparation method of the modified lubricating oil additive containing graphene - copper oxide according to claim 1, characterized in that, The conditions of the hydrothermal reaction in step 3) are: the pH value of the reaction system is 9.5 - 10, the reaction temperature is 60 - 100 °C, and the reaction time is 1 - 2 h.

4. The preparation method of the modified lubricating oil additive containing graphene - copper oxide according to claim 4, characterized in that, The volume ratio of oleic acid to anhydrous ethanol in step 4) is (5 - 15) :

100.

5. The preparation method of the modified lubricating oil additive containing graphene - copper oxide according to claim 1, characterized in that, The conditions of the high-temperature hydrothermal reaction in step 4) are: maintain at a reaction temperature of 150 - 200 °C for 6 - 10 h.

6. The preparation method of the modified lubricating oil additive containing graphene - copper oxide according to claim 1, characterized in that, The specific conditions of centrifugation in step 5) are: centrifuge at a rotation speed of 4000 - 6000 rpm / min for 10 - 20 min.

7. The preparation method of the modified lubricating oil additive containing graphene - copper oxide according to claim 1, characterized in that, The drying conditions in step 5) are: maintain at a drying temperature of 60 - 100 °C for 10 - 15 h.

8. A modified lubricating oil additive containing graphene - copper oxide prepared by the preparation method according to any one of claims 1 - 7.

9. An application of the modified lubricating oil additive containing graphene - copper oxide according to claim 8 in the field of friction and wear industry.

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