Graphene modified grease and preparation method thereof

Abstract

The present application relates to the technical field of lubricating grease, and particularly relates to a graphene modified lubricating grease and a preparation method thereof; graphene / molybdenum disulfide powder is obtained as a carrier through a hydrothermal method and a freeze-drying method; then, boric acid is used as a bridging agent to form an organic-inorganic composite structure with a self-repairing function on the surface of the carrier through a dynamic reversible bond; the graphene composite additive obtained in this way not only retains the interlayer slip friction-reducing properties and high load-carrying capacity of graphene and molybdenum disulfide, but also uniformly distributes lubricating long chains, heterocyclic corrosion-inhibiting groups and extreme-pressure active boric acid esters through a covalent bond network. Due to the dynamic reversible characteristics of the boric acid ester bond and the acylhydrazone bond, when the lubricating grease is damaged due to friction loss during long-term use, the damaged area can be repaired online, the boundary lubricating film and the passivation film can be continuously recovered, so that the lubricating grease can still maintain excellent friction-reducing and wear-resisting, extreme-pressure load-carrying and wet-heat corrosion-preventing properties after long-time operation, and the service life is significantly prolonged.

Description

Technical Field

[0001] This invention relates to the field of lubricating grease technology, and in particular to a graphene-modified lubricating grease and its preparation method. Background Technology

[0002] Greases play a crucial role in reducing friction, cooling, sealing, and preventing corrosion in mechanical moving parts such as bearings and gears. However, with increasingly demanding operating conditions, traditional greases relying solely on base oils and thickeners are no longer sufficient to meet the requirements of extreme pressure, long service life, and multi-media compatibility. Therefore, various functional additives have been introduced into greases. Among them, graphene, due to its ultrathin layered structure, high mechanical strength, and inherent lubricity, is considered an ideal solid lubricant. However, the strong π-π interactions between graphene sheets easily lead to irreversible agglomeration, making direct thickening impossible and resulting in uneven dispersion, which in turn increases friction and wear. Conversely, graphene oxide, with its numerous carboxyl, hydroxyl, and epoxy groups on its surface, does improve dispersibility in base oil and thickener systems, but the presence of oxygen-containing functional groups reduces its thermal stability and hydrophobicity. In humid or wet conditions, it easily absorbs moisture and promotes electrochemical corrosion of metal surfaces. Furthermore, with prolonged use, it gradually loses its dispersing advantages due to reduction and deoxidation.

[0003] To address the aforementioned shortcomings, existing technologies have proposed several solutions: First, physically mixing graphene with two-dimensional materials such as molybdenum disulfide and boron nitride, attempting to reduce stacking through heterogeneous compounding; second, modifying the surface of graphene or graphene oxide with small organic molecules, such as alkylamine grafting or silane coupling agent treatment, to improve its affinity in oil; and third, adding passivating agents or borate ester extreme pressure agents to give the grease both corrosion resistance and wear resistance. However, most of these existing solutions have significant drawbacks: physically mixed graphene and molybdenum disulfide are prone to re-stratification and precipitation under long-term storage or high shear, resulting in poor functional maintenance; surface modifications are mostly weak physical adsorption or chemical bonding, which are easily desorbed under heat and shear, and the modified groups only improve dispersion, lacking corrosion inhibition and extreme pressure functions; simply blended borate ester extreme pressure agents are in a free state in the grease, and are easily extracted, volatilized, or hydrolyzed when exposed to water or high temperatures, not only reducing corrosion resistance but also potentially causing oil film rupture due to additive loss. Therefore, there is a need in the field for a composite additive that is stable and does not leak during use, and has multiple functions, thereby enabling greases to achieve longer-lasting overall performance. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing a graphene-modified lubricating grease and its preparation method. This invention first grows molybdenum disulfide in situ on the surface of graphene oxide using a hydrothermal method, and then obtains graphene / molybdenum disulfide powder as a carrier using a freeze-drying method. Boric acid is then used as a bridging agent to react with octyl-containing long-chain salicylaldehyde derivatives and benzotriazole derivatives containing alcohol hydroxyl groups on the carrier surface through dynamically reversible borate ester bonds and hydrazone bonds, forming an anchored organic-inorganic composite structure with self-healing function. The resulting graphene composite additive retains the interlayer slip friction-reducing properties and high load-bearing capacity of graphene and molybdenum disulfide, while uniformly distributing lubricating long chains, heterocyclic corrosion-inhibiting groups, and extreme-pressure active borate esters through a covalent bond network. Thanks to the dynamic reversible properties of borate ester bonds and hydrazone bonds, when the protective film of the grease is damaged due to frictional wear during long-term use, these active bonds can sense frictional heat and shear force, release in situ and re-bond with the metal surface, and perform online self-repair of the damaged area, continuously restoring the boundary lubrication film and passivation film. This allows the grease to maintain excellent friction reduction and anti-wear, extreme pressure bearing and humid heat corrosion protection performance even after long-term operation, and significantly extend its service life.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing graphene-modified grease, comprising the following steps: mixing PAO6 base oil and 12-hydroxystearic acid, adding lithium hydroxide solution at 80°C, heating to 200°C, saponifying / refining for 30 min, cooling to 100°C, adding graphene composite additives, continuing to stir for 1 h, homogenizing with a three-roll mill to obtain graphene-modified grease; By weight percentage: 1.8-2% 12-hydroxystearic acid, 0.35% lithium hydroxide, and 1.5-1.8% graphene-modified grease, with the balance being PAO6 base oil.

[0006] The graphene composite additive is prepared through the following steps: Step A1: Mix graphene oxide and deionized water and ultrasonically disperse for 2 hours. Then add ammonium molybdate tetrahydrate, thiourea and hexadecyltrimethylammonium bromide, and continue ultrasonic dispersion for 1 hour. Under the conditions of stirring speed of 300 rpm and temperature of 30℃, stir and add hydrochloric acid solution to adjust the pH value to 2. Transfer to a reaction vessel and heat to 200℃. React for 2 hours, centrifuge, and wash with ethanol / deionized water to obtain graphene precursor solution. Furthermore, in step A1, the ratio of graphene oxide, deionized water, ammonium molybdate tetrahydrate, thiourea, and hexadecyltrimethylammonium bromide is 0.15-0.16g: 50mL: 1.75-1.8g: 3.05g: 0.02g, and the hydrochloric acid solution has a mass fraction of 98%.

[0007] Step A2: Place the graphene precursor solution in a refrigerator at -20℃ and freeze for 10 min, then transfer it to a vacuum freeze dryer and freeze dry for 12 h to obtain freeze-dried graphene / molybdenum disulfide powder; mix the freeze-dried graphene / molybdenum disulfide powder, benzotriazole intermediate and toluene and ultrasonically disperse for 30 min, then add boric acid powder and salicylaldehyde derivative intermediate, and react for 6 h at a stirring rate of 300 rpm and a temperature of 140℃. After cooling, extract with tetrahydrofuran, rotary evaporate, wash with hexane, and vacuum dry to obtain graphene composite additive; Furthermore, in step A2, the ratio of the amount of lyophilized graphene / molybdenum disulfide powder, benzotriazole intermediate, toluene, boric acid powder, and salicylaldehyde derivative intermediate is 0.5g: 4.8-4.9g: 50mL: 2.45-2.5g: 11.6-11.7g.

[0008] The benzotriazole intermediate was prepared by the following steps: Sodium hydroxide and ethanol were mixed, and benzotriazole was added while stirring at 300 rpm and room temperature. The mixture was stirred for 10 min, heated to 35 °C and 2-chloroethanol was added. The temperature was then raised to 60 °C and the reaction was carried out for 8 h. The mixture was filtered, distilled under reduced pressure, washed with acetone / ethanol, and distilled under reduced pressure again to obtain the benzotriazole intermediate. Furthermore, in the preparation process of the benzotriazole intermediate, the ratio of sodium hydroxide, ethanol, benzotriazole and 2-chloroethanol is 4g:40mL:1.2g:0.88g.

[0009] The salicylaldehyde-derived intermediate was prepared by the following steps: Step B1: Mix 1-bromooctane and 2,4-dihydroxybenzaldehyde, stir at 300 rpm at room temperature, add potassium bicarbonate and acetonitrile, heat to 85°C, react for 24 h, cool, and recover by petroleum ether / ethyl acetate chromatography to obtain salicylaldehyde intermediate; Furthermore, in step B1, the ratio of 1-bromooctane, 2,4-dihydroxybenzaldehyde, potassium bicarbonate, and acetonitrile is 3.85 g: 2.76 g: 2.21 g: 50 mL, and the volume ratio of petroleum ether to ethyl acetate in the petroleum ether / ethyl acetate system is 20:1.

[0010] Step B2: The salicylaldehyde intermediate, 2-hydroxybenzoyl hydrazine and ethanol were mixed and reacted at a stirring rate of 300 rpm and a temperature of 80 °C for 12 h. After cooling, the mixture was filtered, washed with ethanol and dried to obtain the salicylaldehyde derivative intermediate. Furthermore, in step B2: the ratio of salicylaldehyde intermediate, 2-hydroxybenzoyl hydrazine and ethanol is 5g:3g:60mL.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention discloses a graphene-modified grease and its preparation method. First, molybdenum disulfide is grown in situ on the surface of graphene oxide by hydrothermal method, and graphene / molybdenum disulfide powder is obtained as a carrier by freeze drying. Then, boric acid is used as a bridging agent to esterify with two intermediates, salicylaldehyde derivatives containing octyloxy long chains and acylhydrazone structures and benzotriazole derivatives containing alcohol hydroxyl groups, on the surface of the carrier to form an organic-inorganic composite structure anchored by borate ester bonds. The graphene composite additive obtained in this way retains the interlayer slip friction reduction characteristics and high load-bearing capacity of graphene and molybdenum disulfide, and introduces a long-chain hydrocarbon lubricating layer, heterocyclic corrosion inhibitory groups and extreme pressure active borate esters through chemical bonds. Moreover, it will not separate in the grease due to hydrolysis or thermal diffusion. After adding the additive to the base grease, its friction reduction and anti-wear performance, extreme pressure and wet heat corrosion resistance are significantly improved, and its service life is significantly extended.

[0012] Using graphene oxide aqueous dispersion as a base, ammonium molybdate tetrahydrate and thiourea undergo a hydrothermal reaction with hexadecyltrimethylammonium bromide assisted to generate molybdenum disulfide nanosheets in situ on graphene oxide sheets. The resulting graphene / molybdenum disulfide precursor possesses a three-dimensional mutually supporting microstructure with a large specific surface area. This heterojunction effectively prevents graphene and molybdenum disulfide from stacking independently, ensuring high dispersion of both in subsequent chemical reactions and in the final lubricant. Graphene provides a high-strength framework, while molybdenum disulfide, with its hexagonal layered structure and low interlayer shear force, imparts excellent friction reduction and anti-wear effects. The synergy between the two enhances load-bearing capacity. Simultaneously, its structure serves as a reservoir of functional molecules, providing abundant sites for replenishing active substances and self-repairing functions during subsequent friction processes, ensuring continuous output of repair capabilities during long-term use. Freeze-drying the graphene precursor yields a loose and porous freeze-dried graphene / molybdenum disulfide powder, which is beneficial for the uniform adhesion of subsequent organic molecules and the boronic acid esterification reaction. When heated with benzotriazole intermediates, salicylaldehyde-derived intermediates, and boric acid, the sulfur and molybdenum atoms on the surface of molybdenum disulfide can act as Lewis acid / base sites to catalyze the esterification and dehydration reaction between boric acid and polyhydroxy molecules. The benzotriazole intermediate is chemically anchored to the support surface by reacting its alcoholic hydroxyl groups with the phenolic hydroxyl groups and acylhydrazone groups in boric acid and salicylaldehyde-derived intermediates to form boronic acid ester bonds. The heterocyclic structure of benzotriazole can form a stable complex film with metal surfaces such as copper and iron, preventing corrosion. Furthermore, it is covalently bonded to the support, making it difficult to hydrolyze and detach under long-term water storage or high-temperature conditions. Moreover, once the complex film is damaged due to corrosive media intrusion, the exposed benzotriazole groups can quickly... The process rapidly re-complexes with exposed metals, enabling active self-repair of corrosion sites and achieving long-term corrosion protection. Furthermore, the introduction of a long octyl group into 2,4-dihydroxybenzaldehyde in the salicylaldehyde derivative intermediate gives the molecule good oil solubility, followed by condensation with 2-hydroxybenzoylhydrazine to form an acylhydrazone bond. The imine and amide groups, as well as the ortho-phenolic hydroxyl groups in the acylhydrazone bond, are excellent adsorption and chelation sites on metal surfaces, forming a dense protective film on the friction pair surface. After the hydroxyl groups on this intermediate cross-link with boric acid, an organic borate ester coating with a certain network structure can be formed on the graphene / molybdenum disulfide surface. The electron-deficient centers of the borate ester and the dynamic reversibility of the acylhydrazone bond enable the formation of a boron- and nitrogen-containing friction reaction film under high temperature and high load conditions. Moreover, when the film is sheared and consumed, the protective film can be cyclically reconstructed using frictional energy, continuously repairing the scratched surface and reducing direct contact and wear. The coating itself has extreme pressure anti-wear function. It can react with the metal surface under high temperature and high load by means of the electron-deficient center of borate ester to generate a friction reaction film containing boron and nitrogen, thereby reducing direct contact and wear.

[0013] When this graphene composite additive is added to lubricating grease, inorganic sheets, organic long chains, hydrazone corrosion inhibitors, borate esters, and benzotriazole form a synergistic self-healing whole through covalent bonds. During friction, graphene and molybdenum disulfide provide a low-shear interface, and octyloxy hydrocarbon chains extend in the base oil to form an elastic fluid lubrication layer. When boundary lubrication or extreme pressure occurs, the borate ester and hydrazone structures preferentially react with the metal to generate a highly tough tribochemical film, while benzotriazole continuously passivates the nascent metal surface. More importantly, once the above protective film is damaged due to severe operating conditions, the dynamically reversible borate ester bonds and hydrazone groups can respond instantly to changes in the tribochemical environment, spontaneously releasing active components and rebonding them to the metal, performing in-situ self-repair of the damaged surface. Thus, during long-term use, the coefficient of friction and wear scar diameter are maintained at extremely low levels, and excellent rust inhibition capabilities are continuously demonstrated in humid and hot environments. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the reaction process in the preparation of the salicylaldehyde derivative intermediate and the benzotriazole intermediate of the present invention; Figure 2 This is a schematic diagram of the reaction process in the preparation of the graphene composite additive of the present invention. Detailed Implementation

[0015] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0016] In the following preparation examples, embodiments, and comparative examples, the graphene oxide used was prepared using multilayer graphene as raw material and a modified Hummer process. The multilayer graphene was NG (300 mesh) purchased from Qingdao Meilikun Graphite Preparation Plant.

[0017] Preparation Example 1: The benzotriazole intermediate was prepared by the following steps: Sodium hydroxide and ethanol were mixed, and benzotriazole was added while stirring at 300 rpm and room temperature. The mixture was stirred for 10 min, heated to 35 °C and 2-chloroethanol was added. The temperature was then raised to 60 °C and the reaction was carried out for 8 h. The mixture was filtered, distilled under reduced pressure, washed with acetone / ethanol, and distilled under reduced pressure again to obtain the benzotriazole intermediate. Furthermore, in the preparation process of the benzotriazole intermediate, the ratio of sodium hydroxide, ethanol, benzotriazole and 2-chloroethanol is 4g:40mL:1.2g:0.88g.

[0018] Preparation Example 2: The salicylaldehyde-derived intermediate was prepared by the following steps: Step B1: Mix 1-bromooctane and 2,4-dihydroxybenzaldehyde, stir at 300 rpm at room temperature, add potassium bicarbonate and acetonitrile, heat to 85°C, react for 24 h, cool, and recover by petroleum ether / ethyl acetate chromatography to obtain salicylaldehyde intermediate; Furthermore, in step B1, the ratio of 1-bromooctane, 2,4-dihydroxybenzaldehyde, potassium bicarbonate, and acetonitrile is 3.85 g: 2.76 g: 2.21 g: 50 mL, and the volume ratio of petroleum ether to ethyl acetate in the petroleum ether / ethyl acetate system is 20:1.

[0019] Step B2: The salicylaldehyde intermediate, 2-hydroxybenzoyl hydrazine and ethanol were mixed and reacted at a stirring rate of 300 rpm and a temperature of 80 °C for 12 h. After cooling, the mixture was filtered, washed with ethanol and dried to obtain the salicylaldehyde derivative intermediate. Furthermore, in step B2: the ratio of salicylaldehyde intermediate, 2-hydroxybenzoyl hydrazine and ethanol is 5g:3g:60mL.

[0020] Preparation Example 3: The graphene composite additive was prepared by the following steps: Step A1: Mix graphene oxide and deionized water and ultrasonically disperse for 2 hours. Then add ammonium molybdate tetrahydrate, thiourea and hexadecyltrimethylammonium bromide, and continue ultrasonic dispersion for 1 hour. Under the conditions of stirring speed of 300 rpm and temperature of 30℃, stir and add hydrochloric acid solution to adjust the pH value to 2. Transfer to a reaction vessel and heat to 200℃. React for 2 hours, centrifuge, and wash with ethanol / deionized water to obtain graphene precursor solution. Furthermore, in step A1, the ratio of graphene oxide, deionized water, ammonium molybdate tetrahydrate, thiourea, and hexadecyltrimethylammonium bromide is 0.16g:50mL:1.8g:3.05g:0.02g, and the hydrochloric acid solution has a mass fraction of 98%.

[0021] Step A2: Place the graphene precursor solution in a refrigerator at -20°C and freeze for 10 min. Then transfer it to a vacuum freeze dryer and freeze dry for 12 h to obtain freeze-dried graphene / molybdenum disulfide powder. Mix the freeze-dried graphene / molybdenum disulfide powder, the benzotriazole intermediate of Preparation Example 1, and toluene and ultrasonically disperse for 30 min. Then add boric acid powder and the salicylaldehyde derivative intermediate of Preparation Example 12. React at a stirring rate of 300 rpm and a temperature of 140°C for 6 h. Cool, extract with tetrahydrofuran, rotary evaporate, wash with hexane, and vacuum dry to obtain the graphene composite additive. Furthermore, in step A2, the ratio of the amount of freeze-dried graphene / molybdenum disulfide powder, benzotriazole intermediate, toluene, boric acid powder, and salicylaldehyde derivative intermediate is 0.5g:4.9g:50mL:2.5g:11.7g.

[0022] Preparation Example 4: Compared with Preparation Example 3, the ratio of graphene oxide, deionized water, ammonium molybdate tetrahydrate, thiourea and hexadecyltrimethylammonium bromide in step A1 was adjusted to 0.15g:50mL:1.75g:3.05g:0.02g, while the other steps were the same.

[0023] Preparation Example 5: Compared with Preparation Example 3, the ratio of the following in step A2 was adjusted to 0.5g:4.8g:50mL:2.45g:11.6g:lyophilized graphene / molybdenum disulfide powder, benzotriazole intermediate, toluene, boric acid powder and salicylaldehyde derivative intermediate.

[0024] Preparation Example 6: Compared with Preparation Example 3, the ratio of graphene oxide, deionized water, ammonium molybdate tetrahydrate, thiourea and hexadecyltrimethylammonium bromide in step A1 was adjusted to 0.3g:50mL:1.75g:3.05g:0.02g, while the other steps were the same.

[0025] Preparation Example 7: Compared with Preparation Example 3, the ratio of the following in step A2 was adjusted to 1g:4.8g:50mL:2.45g:11.6g:lyophilized graphene / molybdenum disulfide powder, benzotriazole intermediate, toluene, boric acid powder and salicylaldehyde derivative intermediate.

[0026] Preparation Example 8: Compared with Preparation Example 3, the ratio of graphene oxide, deionized water, ammonium molybdate tetrahydrate, thiourea and hexadecyltrimethylammonium bromide in step A1 was 0.16g:50mL:1.8g:3.05g:0.01g, and the other steps were the same.

[0027] Comparative Preparation Example 1: Compared to Preparation Example 3, the reaction at 140°C in step A2 was omitted in Comparative Preparation Example 1, and the mixture was simply mixed and ground. All other steps were the same.

[0028] Comparison ratio 2: Compared with preparation example 3, preparation example 1 did not add benzotriazole intermediate in step A2, and the other steps were the same.

[0029] Comparative Preparation Example 3: Compared to Preparation Example 3, the graphene oxide in step A1 was replaced with multilayer graphene, while the other steps remained the same.

[0030] Example 1: A method for preparing a graphene-modified grease, comprising the following steps: mixing PAO6 base oil and 12-hydroxystearic acid, adding lithium hydroxide solution at 80°C, heating to 200°C, saponifying / refining for 30 min, cooling to 100°C, adding the graphene composite additive from Example 3, continuing stirring for 1 h, homogenizing with a three-roll mill to obtain the graphene-modified grease; By weight percentage: 2% 12-hydroxystearic acid, 0.35% lithium hydroxide, and 1.8% graphene-modified grease, with the balance being PAO6 base oil.

[0031] Example 2: Compared with Example 1, Example 2, by mass percentage, contains 1.8% 12-hydroxystearic acid, 0.35% lithium hydroxide, and 1.8% graphene-modified grease, with the balance being PAO6 base oil. The other steps are the same.

[0032] Example 3: Compared with Example 1, Example 3, by mass percentage, contains 2% 12-hydroxystearic acid, 0.35% lithium hydroxide, and 1.5% graphene-modified grease, with the balance being PAO6 base oil. The other steps are the same.

[0033] Example 4: Compared with Example 1, Example 4, by mass percentage, contains 2% 12-hydroxystearic acid, 0.35% lithium hydroxide, and 0.6% graphene-modified grease, with the balance being PAO6 base oil. The other steps are the same.

[0034] Example 5: In Example 5, the graphene composite additive was replaced with that obtained in Preparation Example 4, while the other steps were the same as in Example 1.

[0035] Example 6: In Example 6, the graphene composite additive was replaced with that obtained in Preparation Example 5, while the other steps were the same as in Example 1.

[0036] Example 7: In Example 7, the graphene composite additive was replaced with that obtained in Preparation Example 6, while the other steps were the same as in Example 1.

[0037] Example 8: In Example 8, the graphene composite additive was replaced with that obtained in Preparation Example 7, while the other steps were the same as in Example 1.

[0038] Example 9: In Example 9, the graphene composite additive was replaced with that obtained in Preparation Example 8, while the other steps were the same as in Example 1.

[0039] Comparative Example 1: Compared with Example 1, the graphene composite additive in Comparative Example 1 was replaced with that obtained in Comparative Preparation Example 1, while the other steps were the same.

[0040] Comparative Example 2: Compared with Example 1, the graphene composite additive in Comparative Example 2 was replaced with that obtained in Comparative Preparation Example 2, while the other steps were the same.

[0041] Comparative Example 3: Compared with Example 1, the graphene composite additive in Comparative Example 3 was replaced with that obtained in Comparative Preparation Example 3, while the other steps were the same.

[0042] The graphene-modified greases obtained in the examples and comparative examples were subjected to performance testing: 1) Friction and wear tests were conducted using a high-temperature reciprocating friction testing machine (HT-1000). The steel balls used were made of Gcr15, with a diameter of 6mm and a hardness of HRC61. The selected loads were 5N, 8N, and 12N. The selected speed was 300r / min, the rotation radius was 5mm, and the selected temperature conditions were 30℃, 160℃, and 260℃. A white light interferometer was used to detect the wear marks, and the wear rate under different working conditions was calculated. 2) Add 2 mL of deionized water to 20 g of grease, stir at 80 °C for 3 days, and then conduct a friction and wear test to calculate the wear rate under different working conditions.

[0043] The test results are shown in the table below: Table 1. Results of Friction and Wear Tests Table 2. Results of friction and wear test after adding deionized water The test results shown in the table indicate that the examples and comparative examples are compared as follows: Comparative Example 1: The components were simply mixed and ground at room temperature, without undergoing the 140°C process in step A2. The esterification reaction at ℃ resulted in a lack of covalent bonds between the freeze-dried graphene / molybdenum disulfide powder, the benzotriazole intermediate, boric acid, and the salicylaldehyde-derived intermediate. Compared with Example 1, Comparative Example 1 lacked borate ester bonds to covalently anchor the alcohol hydroxyl groups of benzotriazole and the phenolic and hydrazone-side hydroxyl groups of the salicylaldehyde-derived intermediate to the carrier surface. Under conditions of frictional shear and the presence of water, the organic functional molecules rapidly detached from the friction interface in a free state, failing to continuously provide long-chain hydrocarbon boundary lubrication and benzotriazole passivation protection. After aging with water, the free benzotriazole was largely extracted by water, and the boric acid precipitated separately and hydrolyzed into borate ions, losing extreme pressure activity. Comparative Example 1 lacked a chemical anchoring mechanism, preventing the organic functional components from synergistically interacting with the solid lubricating carrier. The wear protection film rapidly disintegrated under hydrothermal and high-load conditions, further demonstrating the significant superiority of the borate ester covalent anchoring used in Example 1 in achieving long-lasting, hydrolysis-resistant, and multifunctional lubrication.

[0044] In Comparative Example 2, no benzotriazole intermediate was added to the composite additive in step A2; instead, the salicylaldehyde-derived intermediate was grafted onto the carrier surface via borate ester. Compared to Example 1, Comparative Example 2 lacked the chemical adsorption passivation effect of the benzotriazole heterocycle. In an aging environment with added water, due to the absence of benzotriazole inhibiting electrochemical corrosion, the corrosion micropits and oxide abrasive particles generated on the metal surface acted as three-body abrasives, exacerbating abrasive wear. Comparative Example 2 lacked the chemical passivation mechanism introduced by the benzotriazole intermediate, resulting in the composite additive possessing solid lubrication and extreme pressure functions of borate ester, but lacking long-term corrosion protection capabilities. Its tribological properties degraded sharply in an aqueous environment, further demonstrating the key contribution of benzotriazole anchored to the carrier via borate ester bonds to the overall hydrolysis and corrosion resistance of the composite material, highlighting the superiority of Example 1 in its multifunctional integrated design.

[0045] Comparative Example 3 used multilayer graphene instead of graphene oxide as the precursor for the hydrothermal reaction. Compared with Example 1, the graphene used in Comparative Example 3 had very few oxygen-containing functional groups on its surface, lacking carboxyl, hydroxyl, and epoxy groups as active sites for in-situ nucleation and growth of molybdenum disulfide. The molybdenum disulfide nanosheets generated during the hydrothermal process could not be uniformly loaded onto the graphene surface, forming a large number of free MoS2 particles. At the same time, the subsequent borate esterification reaction required the participation of hydroxyl groups on the carrier surface in the formation of borate ester bonds. Due to the extremely low hydroxyl density, the chemical modification grafting efficiency of multilayer graphene decreased significantly. At high temperatures, the unmodified areas between graphite layers adsorbed bubbles formed by the gasification of the base oil, exacerbating local oil film rupture. Comparative Example 3 lacked active sites provided by oxygen-containing functional groups on the surface of graphene oxide, preventing the precursor from effectively forming a uniform heterojunction carrier and affecting the realization of subsequent chemical modification density. It lost the protective mechanism of the combination of graphene / molybdenum disulfide synergistic friction reduction and chemical anchoring functional layers, further illustrating the key advantages of selecting graphene oxide as the starting two-dimensional carrier in Example 1 to achieve highly dispersed, highly stable, and multifunctional composite additives.

[0046] Example 2 reduced the 12-hydroxystearic acid content, slightly decreased the soap fiber network density, and changed the consistency and oil separation ability of the grease; the wear rate was very close to that of Example 1; however, at high temperature (260°C), the rigidity of the soap base skeleton weakened, the grease softening intensified, and the thickness of the calendered oil film decreased under some working conditions; this indicates that fluctuations in the thickener content within a moderate range mainly affect the high-temperature oil retention capacity, and have a limited impact on the overall excellent performance, and the ratio determined in Example 1 has a slight advantage in the high-temperature range.

[0047] Example 3 reduced the amount of graphene composite additive from 1.8% to 1.5%. The reduced additive concentration decreased the number of solid lubricating sheets that could be spread and the number of organic functional groups that could be consumed on the friction interface. After aging with water, the consumption rate of the low-concentration additive accounted for a larger proportion of the total, and the driving force for replenishing the functional layer was weak. Compared with Example 1, Example 3 reduced the supply of effective components, which reduced the boundary lubrication and corrosion inhibition film maintenance capabilities. The positive correlation between additive concentration and anti-wear performance was quantitatively verified.

[0048] Example 4 significantly reduced the graphene composite additive to 0.6%, only one-third of that in Example 1. The extremely low additive concentration could not form a complete and continuous protective film in the contact area between the steel ball and the disk, and many friction areas were in a state of boundary or even dry friction. After aging with water, the small amount of organic corrosion inhibitor was quickly consumed, and the anti-corrosion and friction-reducing capabilities of the grease collapsed. Compared with Example 1, Example 4 lacked the covering and protection mechanism of sufficient solid lubricant and chemically modified functional layer for the friction pair due to the severely insufficient addition amount, and showed a significant concentration dependence, indicating that there is a minimum effective addition level for this composite additive.

[0049] Example 5 used the graphene composite additive from Example 4; the total amount of carrier was slightly reduced, and the molybdenum disulfide loading was slightly decreased. The wear rate under normal operating conditions was slightly increased compared to Example 1; however, the difference was small; this indicates that the hydrothermal feed ratio has good process tolerance within a certain range, and small fluctuations in the carrier composition will not significantly change the main friction-reducing and wear-resistant effects; the slight difference compared to Example 1 is only due to a slight decrease in solid content, and is still far superior to the comparative examples.

[0050] Example 6 uses the graphene composite additive prepared in Example 5; the thickness of the chemically modified layer is slightly reduced, resulting in a slight shortage of the immediate supply of active groups under high load. In Example 6, due to the marginal reduction in the total amount of organic modifier, the regeneration rate of the long-chain hydrocarbon-acylhydrazone-boronate reaction membrane under extreme conditions is slightly reduced, but the overall performance is still highly acceptable.

[0051] Example 7 uses the graphene composite additive prepared in Example 6. Excess graphene oxide cannot be fully modified by molybdenum disulfide effective spacers or organic groups during subsequent freeze-drying and grafting processes. The remaining unmodified graphene oxide stacks to form hard agglomerates. These agglomerates act as stress concentration sources during friction, are crushed to form large-sized wear debris, and exacerbate furrow wear. After water aging, the agglomerates are more easily peeled off due to water penetration. Compared to Example 1, Example 7, due to excessive graphene oxide causing insufficient modification rate and particle agglomeration, lacks a lubrication mechanism for uniform dispersion and flexible sliding. The importance of matching the quality ratio of modifiers is highlighted here.

[0052] Example 8 uses the graphene composite additive prepared in Example 7; a large amount of graphene / molybdenum disulfide surface is exposed and unmodified, and the high surface energy promotes rapid aggregation and sedimentation in the grease; compared with Example 1, Example 8 has poor performance because the chemical anchoring balance is broken by the serious excess of the carrier, and the lack of passivation modification of the exposed inorganic surface leads to serious particle agglomeration and friction increase effect. This further verifies that the strict matching of the ratio of carrier to modifier is the premise for achieving good function.

[0053] Example 9 uses the graphene composite additive prepared in Example 8; hexadecyltrimethylammonium bromide is used as a morphology guiding agent to regulate the nucleation density and nanosheet size of molybdenum disulfide in hydrothermal synthesis; halving the amount of hexadecyltrimethylammonium bromide weakens its template effect on the layered growth of molybdenum disulfide, and some molybdenum disulfide is free in the graphene gaps as larger flower-shaped aggregates, resulting in a decrease in the effective contact area of ​​the heterojunction. Compared with Example 1, Example 9 has insufficient morphology regulation of molybdenum disulfide and reduced heterojunction order due to the reduction of surfactant, which weakens the synergistic lamination effect between graphene and molybdenum disulfide and the uniformity of active site distribution, thereby weakening the grafting density of the chemically modified layer. However, it still retains the basic chemical anchoring structure, so its performance is in the lower range of the example system, and it still maintains a significant advantage in physical mixing.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A graphene-modified lubricating grease and its preparation method, characterized in that: The process includes the following steps: PAO6 base oil and 12-hydroxystearic acid are mixed, lithium hydroxide solution is added at 80°C, the temperature is raised to 200°C, saponification / refining is carried out for 30 minutes, the temperature is cooled to 100°C, graphene composite additive is added, stirring is continued for 1 hour, and homogenization is carried out using a three-roll mill to obtain graphene modified grease. By weight percentage: 1.8-2% 12-hydroxystearic acid, 0.35% lithium hydroxide, and 1.5-1.8% graphene-modified grease, with the balance being PAO6 base oil.

2. The graphene-modified lubricating grease and its preparation method according to claim 1, characterized in that: The graphene composite additive is prepared through the following steps: Step A1: Mix graphene oxide and deionized water and ultrasonically disperse for 2 hours. Then add ammonium molybdate tetrahydrate, thiourea and hexadecyltrimethylammonium bromide, and continue ultrasonic dispersion for 1 hour. Under the conditions of stirring speed of 300 rpm and temperature of 30℃, stir and add hydrochloric acid solution to adjust the pH value to 2. Transfer to a reaction vessel and heat to 200℃. React for 2 hours, centrifuge, and wash with ethanol / deionized water to obtain graphene precursor solution. Step A2: Place the graphene precursor solution in a freezer at -20℃ and freeze for 10 min, then transfer it to a vacuum freeze dryer and freeze dry for 12 h to obtain freeze-dried graphene / molybdenum disulfide powder; mix the freeze-dried graphene / molybdenum disulfide powder, benzotriazole intermediate and toluene and ultrasonically disperse for 30 min, then add boric acid powder and salicylaldehyde derivative intermediate, and react for 6 h at a stirring rate of 300 rpm and a temperature of 140℃. After cooling, extract with tetrahydrofuran, rotary evaporate, wash with hexane, and vacuum dry to obtain the graphene composite additive.

3. The graphene-modified lubricating grease and its preparation method according to claim 2, characterized in that: In step A1, the ratio of graphene oxide, deionized water, ammonium molybdate tetrahydrate, thiourea, and hexadecyltrimethylammonium bromide is 0.15-0.16 g: 50 mL: 1.75-1.8 g: 3.05 g: 0.02 g, and the hydrochloric acid solution has a mass fraction of 98%.

4. The graphene-modified lubricating grease and its preparation method according to claim 2, characterized in that: In step A2, the ratio of lyophilized graphene / molybdenum disulfide powder, benzotriazole intermediate, toluene, boric acid powder, and salicylaldehyde-derived intermediate is 0.5g: 4.8-4.9g: 50mL: 2.45-2.5g: 11.6-11.7g.

5. The graphene-modified lubricating grease and its preparation method according to claim 1, characterized in that: The benzotriazole intermediate was prepared by the following steps: Sodium hydroxide and ethanol were mixed, and benzotriazole was added while stirring at 300 rpm and room temperature. The mixture was stirred for 10 min, heated to 35 °C and 2-chloroethanol was added. The temperature was then raised to 60 °C and the reaction was carried out for 8 h. The mixture was filtered, distilled under reduced pressure, washed with acetone / ethanol, and distilled under reduced pressure again to obtain the benzotriazole intermediate. In the preparation of the benzotriazole intermediate, the ratio of sodium hydroxide, ethanol, benzotriazole and 2-chloroethanol is 4g:40mL:1.2g:0.88g.

6. The graphene-modified lubricating grease and its preparation method according to claim 1, characterized in that: The salicylaldehyde-derived intermediate was prepared by the following steps: Step B1: Mix 1-bromooctane and 2,4-dihydroxybenzaldehyde, stir at 300 rpm at room temperature, add potassium bicarbonate and acetonitrile, heat to 85°C, react for 24 h, cool, and recover by petroleum ether / ethyl acetate chromatography to obtain salicylaldehyde intermediate; Step B2: The salicylaldehyde intermediate, 2-hydroxybenzoyl hydrazine and ethanol were mixed and reacted at a stirring rate of 300 rpm and a temperature of 80 °C for 12 h. After cooling, the mixture was filtered, washed with ethanol and dried to obtain the salicylaldehyde derivative intermediate.

7. The graphene-modified lubricating grease and its preparation method according to claim 6, characterized in that: In step B1, the ratio of 1-bromooctane, 2,4-dihydroxybenzaldehyde, potassium bicarbonate, and acetonitrile is 3.85 g: 2.76 g: 2.21 g: 50 mL, and the volume ratio of petroleum ether to ethyl acetate in the petroleum ether / ethyl acetate system is 20:

1.

8. The graphene-modified grease and its preparation method according to claim 6, characterized in that: In step B2: the ratio of salicylaldehyde intermediate, 2-hydroxybenzoyl hydrazine and ethanol is 5g:3g:60mL.

9. A graphene-modified lubricating grease, characterized in that: Prepared according to any one of the preparation methods described in claims 1-8.

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