Modified lubricating oil additive containing graphene-silicon dioxide 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-silicon dioxide, which comprises the following steps: preparing an RGO / SiO2 nano composite material additive with SiO2 grafted on graphene by a hydrothermal method, and adding oleic acid (OA) to participate in a hydrothermal reaction to prepare an OA-RGO / SiO2 nano composite material additive with SiO2 and OA grafted on graphene; according to the preparation method, the morphology size of the lubricating oil additive is optimized, and the tribological performance and dispersion stability of the lubricating oil additive are improved; 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 / SiO2 additive is reduced by 18.42% compared with that of an RGO / SiO2 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-silica, a preparation method thereof, and an application thereof. Background Art

[0003] A lubricating oil additive refers to one or several chemical substances added to lubricating oil to improve the performance and function of the lubricating base oil. The addition of additives can improve the problem of insufficient performance of some base oils in certain aspects and enhance the performance of the 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 and ball bearings, which are common in fields such as engines, high-speed machinery, and aerospace. Their main characteristics are high speed, high pressure, and high temperature, and the contact area on the surface of the friction pair is small and the contact stress is large. Currently, 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 conducted 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, and inability to well meet the market demand for existing nanomaterials as lubricating oil additives. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems in the related art to some extent. Therefore, the main object of the present invention is to provide a modified lubricating oil additive containing graphene-silica, 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 graphene-silica.

[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-silica, comprising the following steps:

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

[0011] 2) Add absolute ethanol, tetraethyl orthosilicate, and 3-aminopropyltrimethoxysilane to the graphene oxide dispersion. After mixing evenly, perform a hydrothermal reaction to obtain mixture A;

[0012] 3) Add an absolute ethanol solution containing oleic acid to mixture A. After mixing evenly, perform a high-temperature hydrothermal reaction, and cool to room temperature to obtain mixture B;

[0013] 4) After centrifuging, washing, and drying mixture B, grind it to obtain a modified lubricating oil additive containing graphene-silica.

[0014] In some specific embodiments, the mass ratio of the graphene oxide, tetraethyl orthosilicate, 3-aminopropyltrimethoxysilane, and oleic acid is (0.1 - 0.5) g : (3 - 8) ml : (1 - 4) ml : (2 - 6) ml.

[0015] In some specific embodiments, the hydrothermal reaction in step 2) is specifically as follows: First, adjust the pH value of the reaction system to 4 - 4.5, then stir at a speed of 500 - 15000 rpm for 35 - 55 hours at 25 - 30 °C. After the stirring ends, adjust the pH value to 9.5 - 10, and then maintain stirring in a water bath at 60 - 80 °C for 1.5 - 2.5 h.

[0016] In some specific embodiments, the volume ratio of the oleic acid to the absolute ethanol in step 3) is (4 - 10) : 100.

[0017] In some specific embodiments, the conditions for the high-temperature hydrothermal reaction in step 3) are: maintain at a reaction temperature of 150 - 200 °C for 6 - 10 h.

[0018] In some specific embodiments, the specific conditions for centrifuging in step 4) are: centrifuge at a speed of 5000 rpm for 5 - 15 min.

[0019] In some specific embodiments, the drying conditions in step 5) are: maintain at a drying temperature of 60 - 100 °C for 10 - 15 h.

[0020] As the same inventive concept of the present invention, the present application also provides a modified lubricating oil additive containing graphene-silica.

[0021] As the same inventive concept of the present invention, the present application also provides the application of the modified lubricating oil additive containing graphene-silica in the field of friction and wear industry.

[0022] Compared with the prior art, the present invention has at least the following advantages:

[0023] 1) The present invention prepares an RGO / SiO2 nanocomposite additive with SiO2 grafted on graphene by a hydrothermal method, and oleic acid (OA) is added to participate in the hydrothermal reaction to prepare an OA-RGO / SiO2 nanocomposite additive with SiO2 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 micro-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 / SiO2 additive is reduced by 18.42% compared with the RGO / SiO2 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;

[0024] 2) Through tribological tests, it is confirmed 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 (Si-O) corresponding to the modified lubricating additive of the present application and the formation of iron oxide are found, proving 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;

[0025] 3) The present application conducts a bearing bench test on the prepared modified lubricating oil additive, proving that it has excellent tribological properties. Specifically, in the bearing bench test, the average amplitude, temperature, and noise of the lubricating oil containing 0.075 wt.% OA-RGO / SiO2 are reduced by 34.02%, 20.6%, and 2.78 dB respectively compared with pure oil, having good economic and social benefits. Description of the Drawings

[0026] 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.

[0027] Figure 1 It is the macroscopic morphology diagram of GO, RGO, RGO / SiO2, and OA-RGO / SiO2 in the present invention;

[0028] Figure 2 It is the Fourier transform infrared spectrum diagram of RGO in the present invention;

[0029] Figure 3 It is the Fourier transform infrared spectrum diagram of GO, RGO / SiO2, and OA-RGO / SiO2 in the present invention;

[0030] Figure 4 These are the full EDS surface scan spectra of RGO / SiO2 and OA-RGO / SiO2 in the present invention;

[0031] Figure 5 These are the element proportion diagrams of RGO / SiO2 and OA-RGO / SiO2 in the present invention;

[0032] Figure 6 These are the SEM micrographs of GO, RGO, RGO / SiO2 and OA-RGO / SiO2 in the present invention;

[0033] Figure 7 These are the average friction coefficient diagrams of pure oil, pure oil added with 0.075 wt.% of RGO / SiO2 and OA-RGO / SiO2 in the present invention;

[0034] Figure 8 These are the result diagrams of friction reduction and wear resistance of pure oil in the present invention;

[0035] Figure 9 These are the result diagrams of friction reduction and wear resistance of pure oil added with 0.075 wt.% of RGO / SiO2 in the present invention;

[0036] Figure 10 These are the result diagrams of friction reduction and wear resistance of pure oil added with 0.075 wt.% of OA-RGO / SiO2 in the present invention;

[0037] Figure 11 These are the morphology result diagrams of the wear scar regions of pure oil, pure oil added with 0.05 wt.% of RGO / SiO2 and OA-RGO / SiO2 in the present invention;

[0038] Figure 12 These are the XPS characterization analysis diagrams of the wear scar region of pure oil under friction conditions in the present invention;

[0039] Figure 13 These are the XPS characterization analysis diagrams of the wear scar region of pure oil added with 0.075 wt.% of RGO / SiO2 under friction conditions in the present invention;

[0040] Figure 14 These are the XPS characterization analysis diagrams of the wear scar region of pure oil added with 0.075 wt.% of OA-RGO / SiO2 under friction conditions in the present invention;

[0041] Figure 15 These are the stability test diagrams of pure oil, pure oil added with 0.075 wt.% of RGO / SiO2 and OA-RGO / SiO2 in the present invention;

[0042] Figure 16Vibration amplitude curves of pure oil, pure oil with 0.075 wt.% of RGO / SiO2 added, and OA-RGO / SiO2 in the present invention;

[0043] Figure 17 Temperature curves of pure oil, pure oil with 0.075 wt.% of RGO / SiO2 added, and OA-RGO / SiO2 in the present invention;

[0044] Figure 18 Noise curves of pure oil, pure oil with 0.075 wt.% of RGO / SiO2 added, and OA-RGO / SiO2 in the present invention. Detailed implementation manners

[0045] The present invention will be further described in detail below with reference to 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.

[0046] 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 numerical value, it should be understood that any range formed by combining any pair of range upper limits or preferred numerical values with any range lower limit or preferred numerical 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.

[0047] Unless otherwise specified, all percentages, parts, ratios, etc. in this article are by weight.

[0048] The materials, methods, and embodiments in this article are all exemplary and should not be construed as restrictive unless otherwise specified.

[0049] In the following embodiments, the pure oil used was Shell HELIX6 (5w-30) lubricating oil purchased from Shell (Tianjin) Petrochemical Co., Ltd.

[0050] The test methods adopted in the following embodiments include:

[0051] 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 the friction coefficient, wear scar, etc.

[0052] 1) Tribological property test;

[0053] GCr15 steel balls with a diameter of 12.7 mm and a hardness of 60-62 HRC were selected as the test pieces for the four-ball friction and wear test.

[0054] Example 1

[0055] This embodiment provides a preparation method of a modified lubricating oil additive containing graphene-silica, which comprises the following steps:

[0056] 1) Take 0.1 g of graphene oxide powder (GO powder) and add it to 60 ml of deionized water, and ultrasonically disperse for 1 h to obtain a graphene oxide dispersion;

[0057] 2) Add 8 ml of absolute ethanol, 3 ml of tetraethyl orthosilicate and 1 ml of 3-aminopropyltrimethoxysilane to the graphene oxide dispersion. After mixing evenly, first adjust the pH value of the reaction system to 4.2, and then stir at a speed of 1500 rpm / min at 25 °C for 48 hours. After the stirring is completed, adjust the pH value to 9.7, and then maintain stirring in a water bath at 60 °C for 2.5 h to obtain mixture A;

[0058] 3) Transfer mixture A to a high-temperature reaction kettle, and at the same time add a 50 ml absolute ethanol solution containing 2 ml of oleic acid, and then heat at 150 °C for 10 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;

[0059] 4) Centrifuge mixture B at a speed of 5000 rpm for 5 min, wash it 3 times with deionized water, then filter it by suction to obtain a black powder, place it in a drying oven at 60 °C for drying for 15 h, and grind it in a ball mill for 30 min to obtain a modified lubricating oil additive containing graphene-silica (abbreviated as OA-RGO / SiO2).

[0060] Example 2

[0061] This embodiment provides a preparation method of a modified lubricating oil additive containing graphene-silica, which comprises the following steps:

[0062] 1) Take 0.2 g of graphene oxide powder (GO powder) and add it to 85 ml of deionized water, and ultrasonically disperse for 1 h to obtain a graphene oxide dispersion;

[0063] 2) Add 10 ml of absolute ethanol, 5 ml of tetraethyl orthosilicate and 3 ml of 3-aminopropyltrimethoxysilane to the graphene oxide dispersion. After mixing evenly, first adjust the pH value of the reaction system to 4.2, and then stir at a speed of 1000 rpm / min at 28 °C for 48 hours. After the stirring is completed, adjust the pH value to 9.5, and then maintain stirring in a water bath at 75 °C for 2 h to obtain mixture A;

[0064] 3) Transfer mixture A to a high-temperature reaction kettle, and at the same time add a 50 ml absolute ethanol solution containing 3 ml of oleic acid, and then heat at 180 °C for 8 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;

[0065] 4) Centrifuge the mixture B at a speed of 5000 rpm for 10 min, wash it 3 times with deionized water, then perform suction filtration to obtain a black powder. Place the powder in a drying oven at 80 °C for 12 h, and grind it in a ball mill for 30 min to obtain a modified lubricating oil additive containing graphene-silica (abbreviated as OA-RGO / SiO2).

[0066] Example 3

[0067] This example provides a preparation method of a modified lubricating oil additive containing graphene-silica, which includes the following steps:

[0068] 1) Take 0.5 g of graphene oxide powder (GO powder) and add it to 100 ml of deionized water, and ultrasonically disperse it for 1 h to obtain a graphene oxide dispersion.

[0069] 2) Add 15 ml of absolute ethanol, 8 ml of tetraethyl orthosilicate, and 4 ml of 3-aminopropyltrimethoxysilane to the graphene oxide dispersion. After mixing evenly, first adjust the pH value of the reaction system to 4.5, then stir at a speed of 1000 rpm for 48 h at 30 °C. After the stirring is completed, adjust the pH value to 9.5, and then maintain stirring in a water bath at 80 °C for 1.5 h to obtain mixture A.

[0070] 3) Transfer mixture A to a high-temperature reaction kettle, and at the same time add a 50 ml absolute ethanol solution containing 6 ml of oleic acid. Then heat it at 200 °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.

[0071] 4) Centrifuge the mixture B at a speed of 5000 rpm for 10 min, wash it 3 times with deionized water, then perform suction filtration to obtain a black powder. Place the powder in a drying oven at 80 °C for 12 h, and grind it in a ball mill for 30 min to obtain a modified lubricating oil additive containing graphene-silica (abbreviated as OA-RGO / SiO2).

[0072] Comparative Example 1

[0073] This comparative example provides a lubricating oil additive, which includes the following steps:

[0074] Weigh 0.2 g of GO powder and add it to 200 ml of deionized water, then ultrasonically disperse it for 2 h. After 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. Centrifuge the reaction product at a high speed for 10 minutes at a 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).

[0075] Comparative Example 2

[0076] 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:

[0077] 1) Take 0.2 g of graphene oxide powder and add it to 85 ml of deionized water, and ultrasonically disperse it for 1 h to obtain a graphene oxide dispersion;

[0078] 2) Add 10 ml of absolute ethanol, 5 ml of tetraethyl orthosilicate, and 3 ml of 3-aminopropyltrimethoxysilane to the graphene oxide dispersion. After mixing evenly, first adjust the pH value of the reaction system to 4.2, and then stir at a speed of 1000 rpm / min at 28 °C for 48 hours. After the stirring is completed, adjust the pH value to 9.5, and then maintain stirring in a water bath at 75 °C for 2 h to obtain mixture A;

[0079] 3) Transfer mixture A into a high-temperature reaction kettle 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 reaction kettle to naturally cool to room temperature to obtain mixture B;

[0080] 4) Centrifuge mixture B at a speed of 5000 rpm / min for 10 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-silica (abbreviation: RGO / SiO2).

[0081] Performance test:

[0082] Taking Example 2 as an example, this application conducts performance tests on the modified lubricating oil additives prepared in Example 2 (OA-RGO / SiO2), Comparative Example 1 (RGO), and Comparative Example 2 (RGO / SiO2). Specifically:

[0083] 1) Morphology Test

[0084] 1.1) Macroscopic Morphology Diagram

[0085] In this application, GO, RGO, RGO / SiO2, and OA-RGO / SiO2 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. Silicon dioxide itself is white, resulting in the color of the prepared RGO / SiO2 composite being more grayish, and the color of OA-RGO / SiO2 being darker than that of RGO / SiO2.

[0086] 1.2) Infrared Characterization

[0087] The Fourier transform infrared spectra of GO, RGO, RGO / SiO2, and OA-RGO / SiO2 in this application. The Fourier transform infrared spectrum of RGO is as Figure 2 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 high-temperature reduction of GO. The C-O absorption peak in the range of 1050 - 1250 cm -1 becomes smaller. That is, the above-mentioned absorption peaks can all prove the successful reduction of GO to prepare RGO.

[0088] And the Fourier transform infrared spectra of GO, RGO / SiO2, and OA-RGO / SiO2 are as Figure 3 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 group 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 is the stretching vibration absorption peak of -OH. It can be seen from Figure 3 that in the RGO / SiO2 and OA-RGO / SiO2 curves, the broad peaks located near 465 cm -1 and near 1082 cm -1 of the Si-O-Si bond are the bending vibration peak and the asymmetric or stretching vibration peak respectively. The absorption peak near 618 cm -1 is the stretching vibration peak of the Si-O-C bond, which can prove that grafting reaction occurred between silica and RGO. The absorption peak near 1393 cm -1 is caused by the bending vibration of -OH in the carboxyl group (-COOH). The absorption peaks located near 1650 cm -1 and 1560 cm -1 are the C=C stretching vibration peaks caused by oleic acid and the C=C stretching vibration peaks caused by the reduction of graphene oxide respectively. In the OA-RGO / SiO2 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 participated in the reaction and was successfully grafted onto the composite material.

[0089] 1.3) SEM Characterization

[0090] In this test example, SEM scanning electron microscope was used to characterize the microscopic morphology of the lubricating oil additive. The shooting parameters were HV = 15 KV, Vac = 0.1 pa, SED mode, and the magnification was 8000.

[0091] Among them, the full EDS surface scanning energy spectrum diagrams of RGO / SiO2 and OA-RGO / SiO2 in this application are as shown in Figure 4 the figure. It can be seen from the figure that the red in the figure is carbon element, the blue is oxygen element, and the green is silicon element. It can be seen from the upper left position of the figure that the small spherical morphology part is mainly green, blue, and red, and the majority of green means that the silicon-containing compound generated during its preparation uniformly covered the surface of graphene oxide, resulting in the carbon and oxygen elements being blocked. However, upon careful observation, it can be found that silicon element and oxygen element overlap at the spherical particles, and it is speculated that silicon dioxide particles are generated. Combining with Figure 3 the Si-O bond in the infrared spectrum diagram, it can be determined that the spherical particles are silicon dioxide particles.

[0092] In addition, the element ratios of RGO / SiO2 and OA-RGO / SiO2 in this application are as shown in Figure 5As shown, it can be seen from the figure that the weight percentages of carbon, oxygen, and silicon in RGO / SiO2 are 57.2%, 22.9%, and 19.9% respectively. The weight percentages of carbon, oxygen, and silicon in OA-RGO / SiO2 are 44.5%, 15.5%, and 31.9% respectively. Compared with RGO / SiO2, the carbon element decreases and the silicon element increases. It is speculated that silanol hybrids may be formed or more silicon dioxide particles react with oleic acid and graft onto the surface of graphene oxide sheets.

[0093] Among them Figure 6 are the SEM micrographs of GO, RGO, RGO / SiO2, and OA-RGO / SiO2. It can be seen from the figure that graphene oxide (GO) is sheet-like; the microstructure of RGO as a whole presents a thinner and smoother sheet-like structure, and the sheets are more wrinkled, increasing the sheet spacing, which is consistent with the results of the infrared spectrum analysis of RGO. It can be seen from the figure that silicon dioxide spheres with a diameter of 760 nm in RGO / SiO2 are dispersed between the sheets. According to the structure analyzed by the infrared spectrum diagram, the spheres are grafted to the sheets. Compared with RGO / SiO2, the wrinkles of the sheets in the micrograph of OA-RGO / SiO2 are stronger and the diameter of the silicon dioxide spheres is about 460 nm. Due to the participation of oleic acid in the hydrothermal reaction, the overall morphology presents an "ovum" shape similar to OA-RGO / CuO, and the nano-silicon dioxide spheres are tightly wrapped on the surface of the sheets.

[0094] 1.4) Contact angle test

[0095] In this application, the contact angles of pure base oil, 0.075 wt% RGO / SiO2 lubricating oil, and 0.075 wt OA-RGO / SiO2 lubricating oil were measured (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 average contact angle of 0.075 wt% OA-RGO / SiO2 lubricating oil additive is 19.19°; the average contact angle of 0.075 wt% RGO / SiO2 lubricating oil is 23.96°. It shows that the OA-RGO / SiO2 lubricating oil additive has excellent compatibility and lubricity with the material surface.

[0096] 1.5) Kinematic viscosity

[0097] In this application, the kinematic viscosity of the lubricating oil additive was also measured (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 / SiO2 lubricating oil and OA-RGO / SiO2 lubricating oil are 136.5 mPa·s and 152.5 mPa·s respectively. Combining Figure 6The SEM micro-morphology shows that the particle size of OA-RGO / SiO2 is smaller and denser than that of RGO / SiO2, which results in a higher kinematic viscosity of OA-RGO / SiO2. The lubricating oil film formed by the lubricating oil additive with a high kinematic viscosity is thicker and more suitable for heavy load and high temperature working conditions.

[0098] 2) Tribological property test

[0099] In this test example, a screen-display high-temperature end-face testing machine (four-ball type) is used to test the tribological properties of the lubricating oil added with the modified lubricating oil additive. The specific test method is as follows:

[0100] 2.1) Confocal laser topography analysis

[0101] For the tribological property test, an MDW-5G screen-display high-temperature end-face device (four-ball type) is selected. The upper specimen is a ball, and the lower specimen consists of three balls, all with a diameter of 12.7 mm and a material of GCr15. The working conditions of this experiment are "392 N, 1200 rpm / min", and the test time is 1 h. Except for pure engine oil, 0.075 wt.% of the modified lubricating oil additive is added to the test lubricating oil of this application for the test. The preparation method of the lubricating oil containing the modified lubricating oil additive is ultrasonic treatment for 15 min and then stirring for 15 min. The specimens are ultrasonically treated with anhydrous ethanol for 30 min and then wiped clean with dust-free paper to ensure that there is no oil stain or dust on the specimen surface, which will not affect the test. The lubricating oil is added to the oil box of the four-ball device, and the oil should infiltrate the upper and lower specimens. Each friction test is repeated 3 times.

[0102] 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 / SiO2 is about 0.060, which is 4.76% lower than the average friction coefficient of pure oil; the average friction coefficient of OA-RGO / SiO2 is the lowest, about 0.054, which is 14.29% lower than the average friction coefficient of pure oil. In summary, it can be known that the OA-RGO / SiO2 modified lubricating oil additive can improve the friction coefficient of the lubricating oil (pure oil).;

[0103] 2.2) SEM scanning electron microscope characterization

[0104] Among them, the results of friction reduction and wear resistance in the friction and wear test are as Figures 8 - 10As shown in the figure, it can be seen that the wear scar width of the friction specimens with different lubricating oil additives is pure oil, RGO / SiO2 and OA-RGO / SiO2 from large to small. The wear scar width and maximum depth of pure oil are 463.4μm and 2.4μm respectively; the wear scar width and maximum depth of RGO / SiO2 lubricating oil additive are 435.0μm and 2.2μm respectively, which are 6.13% and 8.3% smaller than the wear scar width and depth of pure oil respectively; the wear scar width and maximum depth of OA-RGO / SiO2 lubricating oil additive are 368.7μm and 2.1μm respectively, which are 20.44% and 12.5% ​​smaller than the wear scar width and depth of pure oil respectively. Combining the three-dimensional morphology and wear scar size data in the figure, it can be seen that in the four-ball friction test under the heavy load condition of "392N, 1200rpm / min", OA-RGO / SiO2 has excellent friction reduction and anti-wear effect.

[0105] The morphology results of the wear scar area in the friction and wear test are as follows: Figure 11 As shown in the figure, there are some shallow plowing-shaped wear marks and flaking wear debris in the wear scar of pure oil, and there is a large piece of adhesive wear mark in the figure. When the pressure is too large, the oil film performance of pure oil is not enough to withstand the large test pressure, resulting in direct metal friction between the contact surfaces to form adhesive wear phenomenon, and pitting is observed on the contact surface from the local enlarged picture of the pure oil wear scar. The size of the wear scar of RGO / SiO2 is only slightly smaller than that of pure oil. Combining the wear scar of RGO / SiO2 under heavy load conditions and the friction coefficient curve, it can be seen that the reason for the large number of plowing grooves on its surface is related to the fact that the hardness of silica is large and it enters the contact surface of the specimen under a large test force, causing tearing or scratches. From the local enlarged picture of the wear scar of OA-RGO / SiO2, it can be found that its wear surface is much smoother than that of RGO / SiO2, and there is a piece of flaking wear debris on the wear scar surface. Slight pitting can be seen in the enlarged picture. This indicates that when the prepared modified lubricant additive enters the friction contact surface, the spherical nanoparticles and the RGO sheets play a synergistic role.

[0106] 2.3) XPS elemental analysis

[0107] A BRUKER Contour confocal microscope was used to carry out four-ball friction and wear tests on pure oil, 0.075wt.% RGO / SiO2, and 0.075wt.% OA-RGO / SiO2 under the working conditions of "294N, 1200rpm / min, 1h", and XPS tests were performed on the GCr15 steel balls after the tests.

[0108] Figures 12 - 14 The figure shows the XPS characterization analysis of the wear scar area of ​​the GCr15 steel ball under the working conditions of "294N, 1200rpm / min, 1h". Figures 12 - 14Pure oil, lubricating oil containing 0.075 wt.% RGO / SiO2 additive, and lubricating oil containing 0.075 wt.% OA-RGO / SiO2 additive, respectively. Figure 12 In the C1s spectrum of pure oil, the C-O (286.18 eV) is the result of the reaction with oxygen during the friction process, and the C-C (283.28 eV) can be attributed to the contaminated carbon on the surface and the carbon on the surface of the steel ball matrix during the friction process. In the O1s spectrum of pure oil, there is Fe-O (529.88 eV), which is caused by the reaction of oxygen with the metal surface during the friction process. Combining with the Fe2p spectrum of pure oil containing Fe2p 3 / 2 (711.08 eV) and Fe-O (724.88 eV), 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.

[0109] From Figure 13 the lubricating oil containing 0.075 wt.% RGO / SiO2 additive, it can be found that in the C1s spectrum, there are O=C-OH (288.58 eV), C-O (286.48 eV), and C-C (283.28 eV). The appearance of O=C-OH (288.58 eV) is attributed to the participation of RGO in the reaction during the friction process. In the O1s spectrum, there is C-O (532.88 eV), and in the Fe2p spectrum, there are Fe-O (724.28 eV), Fe2p 3 / 2 (711.08 eV), and Fe-O (707.08 eV), where Fe2p 3 / 2 indicates the formation of an iron oxide layer, and Fe-O (724.28 eV) is related to friction wear. The Si-O (103.28 eV) and Si-O (101.68 eV) chemical bonds present in the Si2p spectrum can prove that silicon dioxide or its hybrids participate in the friction process during the friction process.

[0110] From Figure 14 the lubricating oil containing 0.075 wt.% OA-RGO / SiO2, it can be found that in the C1s spectrum, there are O=C-OH (288.58 eV) and C-C (283.58 eV). The appearance of O=C-OH (288.58 eV) is attributed to the participation of RGO in the reaction during the friction process. In the O1s spectrum, there are C-O (532.18 eV) and Fe-O (529.88 eV), and in the Fe2p spectrum, there are Fe-O (724.28 eV), Fe2p 3 / 2 (711.08 eV), and Fe-O (707.08 eV), where Fe2p 3 / 2Indicates the formation of iron oxide, and Fe-O (724.28 eV) is related to friction and wear. The Si2p spectrum contains Si-O (103.18 eV), Si-O (101.58 eV), and Si 0 (99.48 eV). The presence of Si-O indicates that silicon dioxide or its hybrids are involved in the friction process during friction.

[0111] In summary, during the friction process, the modified lubricating oil additive in this application participates in the friction process. Specifically, it enters the worn surface to play a role in reducing friction and wear resistance.

[0112] 3) Stability test

[0113] This application conducts a dispersion and static experiment on pure oil, lubricating oil containing 0.075 wt.% of RGO / SiO2 additive, and lubricating oil containing 0.075 wt.% of OA-RGO / SiO2 additive. The experimental duration is 30 days.

[0114] The results are as Figure 15 described. From left to right in the figure are pure oil, RGO / SiO2, and OA-RGO / SiO2 lubricating oils. 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 of 15 days of static settlement, no precipitation or uneven dispersion occurred in RGO / SiO2 and OA-RGO / SiO2 lubricating oils on the 15th day. It should be that oleic acid played an important role in the preparation process. From the results of experiment (e) for 30 days, slight precipitation occurred in RGO / SiO2 lubricating oil, and the color of the oil changed from black to dark brown. After one month of static dispersion experiment, the color change of OA-RGO / SiO2 lubricating oil was not obvious, indicating that adding oleic acid to participate in the reaction during the hydrothermal preparation of lubricating oil additives can enhance the dispersion stability of lubricating oil additives.

[0115] 4) Friction and wear test analysis in actual application scenarios

[0116] 4.1) Bearing bench test

[0117] This application conducts a bearing bench test on pure oil, lubricating oil containing 0.075 wt.% of RGO / SiO2, and lubricating oil containing 0.075 wt.% of OA-RGO / SiO2. Specifically:[[]]

[0118] Test equipment: In the bearing testing machine in this test, the bearing model is "51306 / P5", the ball diameter is 11 mm, the number of balls is 11, the test pressure is 1.045 KN, and the rotation speed is selected as 1200 rpm / min.

[0119] The results of the vibration amplitude curve graph of the bearing bench test are as follows Figure 16 shown. It can be seen from the figure that the vibration amplitude of pure oil is the largest. The overall width of the vibration amplitude of the lubricating oil containing 0.075 wt.% of RGO / SiO2 is slightly smaller than that of pure oil, and the vibration amplitude of the lubricating oil containing 0.075 wt.% of OA-RGO / SiO2 is significantly smaller than that of pure oil. Thus, it can be known that the performance of the lubricating oil containing 0.075 wt.% of OA-RGO / SiO2 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 / SiO2 lubricating oil is 0.0891, which is 12.90% lower than the absolute average value of the amplitude curve of pure oil. The absolute average value of the amplitude curve of OA-RGO / SiO2 lubricating oil is 0.0675, which is 34.02% lower than the absolute average value of the amplitude curve of pure oil; it shows that the OA-RGO / SiO2 lubricating oil in this application can effectively reduce the vibration amplitude during the friction process;

[0120] The results of the temperature curve graph of the bearing bench test are as follows Figure 17 shown. It can be seen from the figure that the temperature of the lubricating oil containing 0.075 wt.% of OA-RGO / SiO2 is 1°C lower than that of pure oil, indicating that the OA-RGO / SiO2 lubricating oil in this application can effectively reduce the temperature rise value during the friction process;

[0121] 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. The acquisition frequency is once per minute. The results of the noise curve graph of the bearing bench test are as follows Figure 18 shown. It can be found from the figure that the average noise of pure oil is 81.68 dB, the average noise of the lubricating oil containing 0.075 wt.% of RGO / SiO2 is 80.51 dB, and the average noise of the lubricating oil containing 0.075 wt.% of OA-RGO / SiO2 is 78.90 dB; that is, the lubricating oil containing 0.075 wt.% of OA-RGO / SiO2 can effectively reduce the noise value during the friction process.

[0122] In summary, by comparing the amplitude curve, temperature curve, and noise curve in the bearing bench test of the lubricating oil, it can be known that the lubricating oil containing 0.075 wt.% of OA-RGO / SiO2 can effectively improve the lubrication effect of pure oil, has excellent tribological properties, and has good economic and social benefits.

[0123] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; 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 recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention.

Claims

1. A preparation method of a modified lubricating oil additive containing graphene-silica, 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 absolute ethanol, tetraethyl orthosilicate, and 3-aminopropyltrimethoxysilane to the graphene oxide dispersion. After mixing evenly, carry out a hydrothermal reaction to obtain mixture A; 3) Add an absolute ethanol solution containing oleic acid to mixture A. After mixing evenly, carry out a high-temperature hydrothermal reaction, and cool to room temperature to obtain mixture B; 4) After centrifuging, washing, and drying mixture B, grind it to obtain a modified lubricating oil additive containing graphene-silica.

2. The preparation method of the modified lubricating oil additive containing graphene-silica according to claim 1, characterized in that, The mass ratio of the graphene oxide, tetraethyl orthosilicate, 3-aminopropyltrimethoxysilane, and oleic acid is (0.1-0.5) g:(3-8) ml:(1-4) ml:(2-6) ml.

3. The preparation method of the modified lubricating oil additive containing graphene-silica according to claim 1, characterized in that, The hydrothermal reaction in step 2) is specifically as follows: First, adjust the pH value of the reaction system to 4-4.5, then stir at a speed of 500-15000 rpm / min at 25-30 °C for 35-55 hours. After the stirring ends, adjust the pH value to 9.5-10, and then maintain stirring in a water bath at 60-80 °C for 1.5-2.5 h.

4. The preparation method of the modified lubricating oil additive containing graphene-silica according to claim 4, characterized in that, In step 3), the volume ratio of oleic acid to absolute ethanol is (4-10):

100.

5. The preparation method of the modified lubricating oil additive containing graphene-silica according to claim 1, characterized in that, The conditions for the high-temperature hydrothermal reaction in step 3) 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-silica according to claim 1, characterized in that, The specific conditions for centrifuging in step 4) are: centrifuge at a speed of 5000 rpm / min for 5-15 min.

7. The preparation method of the modified lubricating oil additive containing graphene-silica according to claim 1, characterized in that, The drying conditions in step 4) are: maintain at a drying temperature of 60-100 °C for 10-15 h.

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

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

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