Application of dodecyl phosphoric acid modified MXenes, MXenes nanofluid, preparation method and application of MXenes nanofluid, high-bearing lubricating grease and preparation method and application of high-bearing lubricating grease

Abstract

The invention provides application of dodecyl phosphoric acid modified MXenes, an MXenes nanofluid, a preparation method and application of the MXenes nanofluid, high-bearing lubricating grease and a preparation method and application of the high-bearing lubricating grease, and relates to the technical field of lubricating materials. The dodecyl phosphoric acid modified MXenes have lipophilicity, can be stably and uniformly dispersed in lubricating oil, and can be used as an additive in urea-based lubricating grease, so that the lubricating grease is uniformly stressed and has higher bearing capacity. Meanwhile, the dodecyl phosphoric acid modified MXenes carry surface hydroxyl groups and can interact with soap fibers and / or polar base oil, so that the structural stability of the lubricating grease is improved. The lubricating grease added with the MXenes nanofluid has excellent bearing resistance and has a wide application prospect in the field of machinery with long service life and high load.

Description

Technical Field

[0001] The present invention relates to the technical field of greases, and specifically relates to the application of dodecyl phosphate modified MXenes, MXenes nanofluids and their preparation methods and applications, high load-bearing greases and their preparation methods and applications. Background Art

[0002] During the production process of major equipment, it is inevitable to encounter frictional losses and severe wear failures under extreme conditions. In the entire system, there are a large number of mechanical equipment with high energy consumption, high safety risks and low utilization efficiency, which have caused great obstacles to the progress of manufacturing technology and enterprise cost management. Therefore, it is essential to incorporate greases, which are commonly used lubricants for large mechanical equipment, into the scope of implementing friction reduction and wear resistance of mechanical equipment to improve the smooth operation of equipment components.

[0003] With the increasingly strict technical standards, bearings also face some extreme working conditions, such as alternating heavy loads and high speeds, which can cause irreversible damage to the bearings. Therefore, the grease for the transmission system of metal processing equipment needs to meet the normal operation under extreme pressure conditions while satisfying the daily operation, and the grease for ensuring a long maintenance cycle of the equipment and maintenance-free bearings needs to have excellent anti-friction performance and extreme pressure anti-wear performance at the same time. However, the load-bearing capacity of traditional polyurea grease under fretting friction and wear conditions is at most no more than 300 N, and the load-bearing capacity is limited. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide the application of dodecyl phosphate modified MXenes, a kind of MXenes nanofluid and its preparation method and application, high load-bearing grease and its preparation method and application. The MXenes nanofluid provided by the present invention can significantly improve the load-bearing capacity of polyurea grease when used in polyurea grease.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides the application of dodecyl phosphate modified MXenes as an additive in grease.

[0007] The present invention also provides a kind of MXenes nanofluid, which comprises dodecyl phosphate modified MXenes and base oil.

[0008] Preferably, the mass content of MXenes in the MXenes nanofluid is 0.2-5%.

[0009] The present invention also provides the preparation method of the MXenes nanofluid according to the above technical solution, which comprises the following steps:

[0010] Mix the aqueous dispersion of MXenes, the first base oil and dodecyl phosphoric acid, adjust the pH value to 2-2.5, modify MXenes, and perform solid-liquid separation. The obtained solid component is MXenes modified with dodecyl phosphoric acid;

[0011] Mix the MXenes modified with dodecyl phosphoric acid with the second base oil to obtain MXenes nanofluid.

[0012] Preferably, the mass ratio of MXenes to the amount of substance of dodecyl phosphoric acid is 1 g: 2.4-4.2 mmol;

[0013] The first base oil and the second base oil include one or more of mineral oil, hydrocarbon oil, ester oil and polyether lubricating oil;

[0014] The mass ratio of MXenes to the first base oil is 8-20: 1000.

[0015] The present invention also provides the application of the MXenes nanofluid described in the above technical solution or the MXenes nanofluid prepared by the preparation method described in the above technical solution in grease.

[0016] The present invention also provides a high-load grease, which is characterized in that, by mass percentage, the preparation raw materials include 84-94% of MXenes nanofluid and 6-16% of thickener;

[0017] The base oil and / or thickener in the MXenes nanofluid contains carbonyl;

[0018] The MXenes nanofluid is the MXenes nanofluid described in the above technical solution or the MXenes nanofluid prepared by the preparation method described in the above technical solution;

[0019] The thickener includes organic thickener and / or inorganic thickener; the organic thickener includes polyurea thickener and / or metal soap.

[0020] Preferably, the polyurea thickener includes a polyurea thickener obtained by the reaction of monoamine, diamine and diisocyanate;

[0021] The metal soap includes one or more of lithium soap, calcium soap, aluminum soap and barium soap;

[0022] The inorganic thickener includes one or more of bentonite, silica, attapulgite, aluminum silicate and boron nitride.

[0023] The present invention also provides a preparation method of the high-load grease described in the above technical solution, which includes the following steps: mix the preparation raw materials, and perform heating and dispersion, refining and cooling in sequence to obtain the high-load grease.

[0024] The present invention also provides the application of the high-load grease described in the above technical solution or the high-load grease prepared by the preparation method described in the above technical solution as a lubricating grease for mechanical equipment.

[0025] The MXenes modified with dodecyl phosphate adopted by the present invention have lipophilicity and can be stably and uniformly dispersed in the base oil. As an additive used in the grease, the grease is uniformly stressed and has a higher load-bearing capacity.

[0026] In the MXenes nanofluid provided by the present invention, the MXenes modified with dodecyl phosphate have lipophilicity and can be stably dispersed in the base oil, improving the distribution uniformity of the additive MXenes modified with dodecyl phosphate. Further, the prepared grease is uniformly stressed and has a higher load-bearing capacity. At the same time, the MXenes modified with dodecyl phosphate carry surface hydroxyl groups and can interact with soap fibers and / or the base oil to improve the structural stability of the lubricating oil composition; the MXenes nanofluid and the thickener act synergistically to form a surface friction film, making the grease have excellent anti-load-bearing performance.

[0027] The preparation process of the high-MXenes nanofluid provided by the present invention is simple, the raw materials are green and environmentally friendly, the production cost is low, and it is suitable for industrial production.

[0028] In the high-load grease provided by the present invention, the MXenes modified with dodecyl phosphate can interact with the carbonyl groups in the base oil and / or the thickener. The formation of the complex can provide additional cross-linking points and intermolecular interactions, enhance the soap fiber structure of the grease, keep the soap fiber molecules from being damaged, enhance the viscosity of the grease, improve its mechanical strength and structural stability, and effectively improve the structural stability of the grease. At the same time, the MXenes nanofluid improves the tribological performance and extreme pressure performance of the grease. Moreover, the MXenes nanofluid functionalized with dodecyl phosphate surface groups has lipophilicity, has good dispersion uniformity in the lubricating oil composition, is uniformly stressed during the friction process, greatly improves its load-bearing performance, and avoids the non-uniformity of the grease caused by directly adding MXenes solids, thereby affecting the anti-load-bearing performance of the grease. The high-load grease provided by the present invention has excellent anti-load-bearing performance and lubricating performance, has broad application prospects in the fields of long-life and high-load machinery, and achieves the purpose of green environmental protection, safety and health.

[0029] The preparation process of the high-load grease provided by the present invention is simple, the raw materials are green and environmentally friendly, the production cost is low, and it is suitable for industrial production. Description of the Drawings

[0030] Figure 1Flow chart for the preparation of MXenes nanofluid in Example 1;

[0031] Figure 2 Macrographs of the greases in Comparative Example 1 and Examples 2 - 5;

[0032] Figure 3 Rheological properties of the greases in Comparative Example 1 and Examples 2 - 5 - thixotropy and comparison chart of thixotropic loop areas;

[0033] Figure 4 SEM micrographs and EDS element distribution maps of the grease in Example 4;

[0034] Figure 5 Curves of friction coefficient changes (extreme pressure performance) of the greases in Comparative Example 1 and Example 4 under variable load conditions;

[0035] Figure 6 Friction coefficient curves of the greases in Comparative Example 1 and Example 4 after 30 min of long - term grinding at 50 °C, frequency 25 Hz, and different loads;

[0036] Figure 7 Three - dimensional topography maps of the worn surfaces of the greases in Comparative Example 1 and Example 4 after 30 min of long - term grinding at 50 °C, frequency 25 Hz, and different loads;

[0037] Figure 8 Comparison bar charts of the wear amounts of the worn surfaces of the greases in Comparative Example 1 and Example 4 after 30 min of long - term grinding at 50 °C, frequency 25 Hz, and different loads;

[0038] Figure 9 For Comparative Example 1 (a) and Example 4 (b 1 and b 2 ) SEM micrographs of the wear scar surfaces of the greases at 50 °C, frequency 25 Hz, and load 200 N (a and b 1 ) and EDS element distribution maps (b 2 ). Detailed implementation mode

[0039] The present invention provides the application of dodecyl phosphate - modified MXenes as additives in greases.

[0040] Adding grease additives is the most direct and effective method to improve the tribological properties and anti-load-carrying properties of greases. Due to their ultrathin longitudinal dimensions and weak interlayer interactions, two-dimensional MXenes nanomaterials can not only significantly reduce the shear resistance between friction contact surfaces but also form a friction protection film on the metal surface, exhibiting excellent anti-friction and anti-wear properties. As grease additives, they have great application potential. However, when directly adding few-layer MXene solids, the MXene particle sizes span a large range and do not reach the nanoscale after homogenization processes such as traditional mixing and grinding. At the same time, the dispersion uniformity of MXenes in the grease soap fiber structure is poor, which greatly limits the further improvement and optimization of the tribological properties of greases by MXenes. In this invention, MXenes are modified with dodecyl phosphoric acid, making MXenes change from hydrophilic to lipophilic, with good dispersibility in base oils. As an additive for greases, it can be evenly dispersed and can carry higher loads, improving the dispersion uniformity and force uniformity of MXene additives in greases, and thus significantly enhancing the load-carrying capacity and anti-friction and anti-wear properties of urea-based greases.

[0041] This invention also provides an MXene nanofluid, which includes dodecyl phosphoric acid-modified MXenes and a base oil. In this invention, the mass content of MXenes in the MXene nanofluid is preferably 0.2 - 5%, and in specific embodiments, it can be 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0042] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in this field.

[0043] In this invention, the base oil preferably includes one or more of mineral oils, hydrocarbon oils, ester oils and polyether lubricating oils. In this invention, the mineral oil preferably includes one or more of 150N, 150SN and 300N. In this invention, the hydrocarbon oil preferably includes one or more of polyalphaolefins, paraffin oils, naphthenic oils and aromatic oils. In this invention, the ester oil preferably includes one or more of trimethylolpropane oleate, ditrimethylolpropane ester and diol fatty acid ester. In this invention, the polyether lubricating oil preferably includes one or more of OSP46, OSP68 and OSP150. In this invention, the kinematic viscosity of the base oil at 40 °C is preferably 28 - 62 mm 2 / s, and in specific embodiments, it can be 28 mm 2 / s, 30 mm 2 / s, 35 mm 2 / s, 40 mm 2 / s, 45 mm 2 / s, 50 mm2 / s, 55 mm 2 / s, 60 mm 2 / s or 62 mm 2 / s.

[0044] The present invention also provides a method for preparing the MXenes nanofluid according to the above technical solution, comprising the following steps:

[0045] Mix the aqueous dispersion of MXenes, the first base oil and dodecyl phosphoric acid, adjust the pH value to 2-2.5, modify the MXenes, and perform solid-liquid separation to obtain the solid component as dodecyl phosphoric acid-modified MXenes;

[0046] Mix the dodecyl phosphoric acid-modified MXenes with the second base oil to obtain the MXenes nanofluid.

[0047] In the present invention, the mass ratio of MXenes to the amount of substance of dodecyl phosphoric acid is preferably 1 g: 2.4-4.2 mmol, and in specific embodiments, it can be 1 g: 2.4 mmol, 1 g: 2.5 mmol, 1 g: 2.8 mmol, 1 g: 3 mmol, 1 g: 3.2 mmol, 1 g: 3.5 mmol, 1 g: 3.8 mmol, 1 g: 4 mmol or 1 g: 4.2 mmol.

[0048] In the present invention, the optional types of the first base oil and the second base oil are the same as the optional types in the MXenes nanofluid, which will not be elaborated here. Preferably, it includes one or more of mineral oil, hydrocarbon oil, ester oil and polyether lubricating oil. In the present invention, the mineral oil preferably includes one or more of 150N, 150SN and 300N. In the present invention, the hydrocarbon oil preferably includes one or more of polyalphaolefin, paraffin oil, naphthenic oil and aromatic oil. In the present invention, the ester oil preferably includes one or more of trimethylolpropane oleate, ditrimethylolpropane ester and diol fatty acid ester. In the present invention, the polyether lubricating oil preferably includes one or more of OSP46, OSP68 and OSP150. In the present invention, the kinematic viscosity of the base oil at 40 °C is preferably 28-62 mm 2 / s, and in specific embodiments, it can be 28 mm 2 / s, 30 mm 2 / s, 35 mm 2 / s, 40 mm 2 / s, 45 mm 2 / s, 50 mm 2 / s, 55 mm 2 / s, 60 mm 2 / s or 62 mm 2 / s. The purpose of adding base oil in the preparation process of MXenes nanofluid in the present invention is to directly convert hydrophilic MXenes into hydrophobic MXenes through surface modification and one-step phase transfer method, so that it can be stably dispersed in the base oil, and then prepare MXenes nanofluid containing dodecyl phosphate modified MXenes and base oil.

[0049] In the present invention, the mass ratio of the MXenes to the first base oil is preferably 8-20:1000, and in the specific embodiments, it can be 8:1000, 10:1000, 12:1000, 15:1000, 18:1000 or 20:1000.

[0050] In the present invention, the concentration of the aqueous dispersion of the MXenes is preferably 8-20 g / L, and in the specific embodiments, it can be 8 g / L, 10 g / L, 12 g / L, 15 g / L, 18 g / L or 20 g / L.

[0051] In the present invention, the pH value is preferably 2, 2.1, 2.2, 2.3, 2.4 or 2.5. In the present invention, the acid used to adjust the pH value preferably includes hydrochloric acid; there is no special limitation on the concentration of the acid in the present invention, as long as it can adjust the pH value of the system to 2-2.5.

[0052] In the present invention, the temperature of the modification is preferably room temperature, and the time of the modification is preferably 12-48 h, and in the specific embodiments, it can be 12 h, 15 h, 18 h, 20 h, 24 h, 28 h, 30 h, 35 h, 40 h, 45 h or 48 h. Dodecyl phosphate (C 12 PA) is used as a surface modifier and a phase transfer medium. After being modified by dodecyl phosphate, the dodecyl phosphate modified MXenes are changed from hydrophilic to hydrophobic, and the MXenes are transferred from the aqueous phase to the base oil by a one-step phase transfer method and can be uniformly dispersed in the base oil.

[0053] In the present invention, the solid-liquid separation preferably includes: washing the modified liquid obtained by the modification with water, standing for layering, centrifuging the obtained oil phase, and centrifuging and washing the obtained solid component with a third base oil, and the obtained solid component is MXenes modified with dodecyl phosphoric acid. In the present invention, the rotation speeds of the centrifugation and the centrifugal washing are independently preferably 5000-10000 r / min, and can be 5000 r / min, 6000 r / min, 7000 r / min, 8000 r / min, 9000 r / min or 10000 r / min in specific embodiments; the time is independently preferably 5-20 min, and can be 5 min, 10 min, 15 min or 20 min in specific embodiments. In the present invention, the optional types of the third base oil are the same as those in the MXenes nanofluid, which will not be elaborated here; the purpose of centrifuging and washing with the third base oil is to remove the excess dodecyl phosphoric acid.

[0054] The present invention has no special limitation on the mixing of the MXenes modified with dodecyl phosphoric acid and the second base oil, and it is only necessary to mix the raw materials evenly.

[0055] The present invention also provides the application of the MXenes nanofluid described in the above technical solution or the MXenes nanofluid prepared by the preparation method described in the above technical solution in grease.

[0056] The present invention also provides a high-load grease. Calculated by mass percentage, the preparation raw materials include 84-94% of MXenes nanofluid and 6-16% of thickener; the base oil and / or thickener in the MXenes nanofluid contain carbonyl groups.

[0057] Calculated by mass percentage, the preparation raw materials of the high-load grease provided by the present invention include 84-94% of MXenes nanofluid, and can be 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93% or 94% in specific embodiments.

[0058] Calculated by mass percentage, the preparation raw materials of the high-load grease provided by the present invention include 6-16% of thickener, and can be 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or 16% in specific embodiments.

[0059] In the present invention, the thickener includes an organic thickener and / or an inorganic thickener; the organic thickener includes a polyurea thickener and / or a metal soap. In the present invention, the inorganic thickener preferably includes one or more of bentonite, silica, attapulgite, aluminum silicate and boron nitride. In the present invention, the metal soap preferably includes one or more of lithium soap, calcium soap, aluminum soap and barium soap.

[0060] In the present invention, the polyurea thickener preferably includes a polyurea thickener obtained by the reaction of a monoamine, a diamine, and a diisocyanate. In the present invention, the monoamine preferably includes one or more of octadecylamine, monoethanolamine, aniline, piperazine, and isobutyramide. In the present invention, the diamine preferably includes one or more of ethylenediamine, N,N-diethylethanolamine, p-phenylenediamine, and 4,4'-methylenedianiline. In the present invention, the diisocyanate preferably includes one or more of toluene diisocyanate, methane diisocyanate, 1,6-hexamethylene diisocyanate, and 4,4'-diphenylmethane diisocyanate. The present invention has no special limitation on the preparation method of the polyurea thickener, and the preparation method of the polyurea thickener well-known to those skilled in the art can be adopted.

[0061] In the present invention, the MXenes nanofluid is the MXenes nanofluid described in the above technical solution or the MXenes nanofluid prepared by the preparation method described in the above technical solution. In the MXenes nanofluid used in the present invention, the MXenes modified with dodecyl phosphoric acid has lipophilicity and can be stably dispersed in the base oil, improving the distribution uniformity of the MXenes modified with the additive dodecyl phosphoric acid. Further, the prepared grease is uniformly stressed and has a high load-carrying capacity. At the same time, the MXenes modified with dodecyl phosphoric acid carries surface hydroxyl groups and can interact with soap fibers and / or polar base oils, improving the structural stability of the lubricating oil composition; the MXenes nanofluid and the thickener act synergistically to form a surface friction film, making the grease have excellent anti-load-carrying performance.

[0062] The present invention also provides a preparation method of the high-load-carrying grease described in the above technical solution, including the following steps: mixing the preparation raw materials, and sequentially performing heat dispersion, refining, and cooling to obtain the high-load-carrying grease.

[0063] In the present invention, the temperature of the heat dispersion is 125-135°C, and in specific embodiments, it can be 125°C, 128°C, 130°C, 132°C, or 135°C; the heat dispersion is preferably carried out under stirring conditions.

[0064] In the present invention, the temperature of the refining is preferably 160-180°C, and in specific embodiments, it can be 160°C, 162°C, 165°C, 168°C, 170°C, 172°C, 175°C, 178°C, or 180°C; the time of the refining is preferably 10-20 min, and in specific embodiments, it can be 10 min, 12 min, 15 min, 18 min, or 20 min; the refining is preferably carried out under stirring conditions.

[0065] In the present invention, the cooling time is preferably 0.5 - 2 h, and in specific embodiments, it can be 0.5 h, 1 h, 1.5 h, or 2 h. In the present invention, the cooling is preferably carried out by ice - water bath cooling; the cooling is preferably carried out under stirring conditions. The present invention cools under the above - mentioned conditions, promoting the base oil to accelerate into the thickener network structure during rapid cooling to prepare a high - performance grease.

[0066] After completing the cooling, the present invention preferably further includes: grinding the system obtained by cooling to obtain the high - load - bearing grease.

[0067] The present invention also provides the application of the high - load - bearing grease described in the above technical solution or the high - load - bearing grease prepared by the preparation method described in the above technical solution as a lubricating grease for mechanical equipment. In the present invention, the high - load - bearing grease is preferably used as a lubricating grease for bearings, and more preferably used as a lubricating grease for bearings under extreme pressure conditions.

[0068] To further illustrate the present invention, the following examples are used to describe in detail the MXenes nanofluid provided by the present invention, its preparation method and application, the high - load - bearing grease and its preparation method and application, but they should not be construed as limiting the protection scope of the present invention.

[0069] The thickener used in the following examples and comparative examples: Yiderun DPU - AS prefabricated polyurea thickener, which is a reaction product of octadecylamine, 4,4 - methylenedianiline and toluene diisocyanate.

[0070] Example 1

[0071] Preparation of MXenes nanofluid (see Figure 1 ): At room temperature, mix 10 g / L MXenes (specifically Ti 3 C 2 T x ) aqueous dispersion and OSP46 in equal mass, add dodecyl phosphoric acid (C 12 PA), adjust the pH = 2.5 with hydrochloric acid, mix and stir evenly, wash with deionized water, mix well, let stand and layer, take the upper oil phase and place it in a centrifuge for centrifugation. The obtained solid component is washed by centrifugation with OSP46. The solid component is dodecyl phosphoric acid - modified MXenes. Mix the dodecyl phosphoric acid - modified MXenes and OSP46 evenly to prepare MXenes nanofluids with MXenes contents of 0.5 wt%, 1.0 wt%, 2.0 wt%, and 4.0 wt% respectively. Among them, the centrifuge speed is 8000 r / min, and the centrifugation time for each time is 10 min. The dosage ratio of MXenes and dodecyl phosphoric acid is 1 g:3 mmol.

[0072] Comparative Example 1

[0073] Raw materials for preparing urea-based grease: 92 wt% OSP46 and 8 wt% thickening agent.

[0074] The thickening agent and OSP46 are evenly mixed, heated to 130 °C and stirred for dispersion, then heated to 160 ± 5 °C and kept warm for refining for 10 ± 1 min, heating is stopped, and it is stirred and cooled with an ice-water bath for 1 h, and then ground to obtain the grease (denoted as base grease).

[0075] Example 2

[0076] Raw materials for preparing high-load urea-based grease (denoted as +0.5 wt% P-M): 92 wt% MXenes nanofluid (MXenes content is 0.5 wt%) and 8 wt% thickening agent.

[0077] The MXenes nanofluid and the thickening agent are mixed evenly, heated to 130 °C and stirred for dispersion, then heated to 160 ± 5 °C and kept warm for refining for 10 ± 1 min, heating is stopped, and it is stirred and cooled with an ice-water bath for 1 h, and then ground to obtain the high-load urea-based grease.

[0078] Example 3

[0079] Raw materials for preparing high-load urea-based grease (denoted as +1.0 wt% P-M): 92 wt% MXenes nanofluid (MXenes content is 1.0 wt%) and 8 wt% thickening agent.

[0080] The preparation method of the high-load urea-based grease is the same as that of Example 2.

[0081] Example 4

[0082] Raw materials for preparing high-load urea-based grease (denoted as +2.0 wt% P-M): 92 wt% MXenes nanofluid (MXenes content is 2.0 wt%) and 8 wt% thickening agent.

[0083] The preparation method of the high-load urea-based grease is the same as that of Example 2.

[0084] Example 5

[0085] Raw materials for preparing high-load urea-based grease (denoted as +4.0 wt% P-M): 92 wt% MXenes nanofluid (MXenes content is 4.0 wt%) and 8 wt% thickening agent.

[0086] The preparation method of the high-load urea-based grease is the same as that of Example 2.

[0087] Test Example 1

[0088] The structures and properties of the urea-based greases prepared in Comparative Example 1 and Examples 2 - 5

[0089] (1) Uniformity

[0090] The macro morphology of the urea - based grease was photographed using the 50 - megapixel super - converging camera of Huawei Pura70 PRO, and the results are shown in Figure 2 . From Figure 2 It can be seen that the base grease and the urea - based grease with added MXenes nanofluid are solid pastes at normal temperature and pressure and can maintain their morphology without flowing. The base grease is light yellow and has no particle feeling; the urea - based grease with added MXenes nanofluid is black and has no particle feeling when the concentration is low, indicating that the MXenes additive is evenly dispersed. When the MXenes concentration reaches 4wt%, it has a slight particle feeling, indicating that its addition amount is relatively large.

[0091] (2) Rheological properties

[0092] The rheological properties of the urea - based grease with added MXenes were tested using an Anton - paar MCR302 rotational rheometer from Austria. The test rotor used was a PP25 / TG plate measurement module, and the test gap was 1 mm. Figure 3 shows the thixotropy test results of the urea - based grease. The thixotropy of the urea - based grease is an important index reflecting the fluidity and stability of the urea - based grease. From Figure 3 the change of viscosity with the shear rate, it can be seen that as the shear rate increases, the structure of the urea - based grease is gradually destroyed under the action of shear force, the flow resistance in the body decreases, the shear stress decreases, and the viscosity decreases; when the shear gradually stops, the viscosity gradually increases with the decrease of the shear rate, and the structure of the urea - based grease gradually recovers, but its viscosity does not return to the value before shear, indicating that the structure of the urea - based grease is not completely recovered. From Figure 3 the comparison of the columnar diagrams of the thixotropy loop area of the urea - based grease in, it can be seen that as the addition amount of the MXenes nanofluid increases, the thixotropy loop area of the urea - based grease shows a gradually increasing trend, the energy required to destroy the structure of the urea - based grease is larger, and the structure is more stable. However, the urea - based grease with 4wt% added MXenes nanofluid has agglomeration due to the excessive addition of the additive, which affects its structural stability, and the structural stability of the urea - based grease prepared in Comparative Example 1 is relatively low.

[0093] The urea - based grease with 2wt% added MXenes nanofluid has the highest structural stability, and its microscopic morphology and tribological properties are analyzed.

[0094] (3) Microscopic morphology of urea - based grease

[0095] The microscopic morphology and element distribution of the urea - based grease with 2wt% added MXenes were further characterized using a JEOL JSM - 7900F field - emission scanning electron microscope from Japan, and the results are as Figure 4Among them, the N element is the characteristic element of the urea-based grease, and the Ti element is the characteristic element of MXenes. According to its SEM and EDS structures, it can be seen that the MXenes nanosheet particles in the prepared urea-based grease are relatively small, being flaky with a size of hundreds of nanometers. The soap fibers have a three-dimensional network structure, distributed around the MXenes nanosheets, and some are longer than the MXenes nanosheets, indicating that there is an interaction between the MXenes nanosheets and the soap fibers, which is helpful for the structural stability.

[0096] (4) Friction and wear test

[0097] (4.1) Coefficient of friction

[0098] The SRV-V micro-friction and wear testing machine produced by German optimol Oelwerke GmbH was used to test the coefficient of friction (COF) change of the urea-based grease compositions prepared in Comparative Example 1 and Examples 2 to 5 at 50 °C, a frequency of 25 Hz, a reciprocating distance of 1 mm, an initial load set at 50 N, and the load was increased by 50 N every 3 min of operation until the COF showed large-scale fluctuations multiple times under this load, and then the friction experiment was stopped, from which the extreme pressure and anti-wear performance of the urea-based grease could be known. The steel ball used in the test was a GCr15 bearing steel with Φ = 10 mm, and the lower specimen was a GCr15 steel block with Φ24 × 7.9 mm. The results are shown in Figure 5 . It can be seen from Figure 5 that the urea-based grease added with 2 wt% MXenes nanofluid (Example 4) has excellent extreme pressure performance, reaching 900 N, far exceeding the load-carrying capacity of traditional urea-based grease (Comparative Example 1).

[0099] The SRV-V micro-friction and wear testing machine produced by German optimol Oelwerke GmbH was used to test the coefficient of friction of the urea-based greases prepared in Comparative Example 1 and Examples 2 to 5 at a fixed temperature of 50 °C and a fixed frequency of 25 Hz, while changing the load and making it run for 30 min under different loads. The steel ball used in the test was a GCr15 bearing steel with Φ = 10 mm, and the lower specimen was a GCr15 steel block with Φ24 × 7.9 mm. The results are shown in Figure 6 , the left figure is the curve of the coefficient of friction change of the urea-based grease prepared in Comparative Example 1 under different loads, and the right figure is the curve of the coefficient of friction change of the urea-based grease added with 2 wt% MXenes nanofluid in Example 4 under different loads. It can be seen from Figure 6It can be seen that under the condition of lower load (100 N), the friction coefficient of the urea-based grease system with 2 wt% MXenes nanofluid is not much different in magnitude from that of the urea-based grease prepared in Comparative Example 1, but is relatively stable as a whole; when the load increases, the friction coefficient of the urea-based grease prepared in Comparative Example 1 is unstable. When the load reaches 300 N, there are multiple severe jumps, the friction film ruptures, and the lubrication fails briefly. However, the urea-based grease with 2 wt% MXenes nanofluid has a lower and more stable friction coefficient under different loads. Until the load reaches as high as 500 N, there is a relatively obvious jump in its friction coefficient, indicating that the urea-based grease with 2 wt% MXenes nanofluid has excellent anti-friction performance under higher loads.

[0100] (4.2) Wear amount

[0101] The three-dimensional morphology and wear volume of the wear scars of the urea-based greases prepared in Comparative Example 1 and Examples 2 - 5 were tested using a MicroXAM 3D non-contact surface tester at a temperature of 50 °C, a frequency of 25 Hz, a stroke of 1 mm, and under different load conditions for 30 min of long-term wear, as shown respectively in Figures 7 - 8 . The results show that under different loads, the urea-based grease prepared in Comparative Example 1 has relatively severe wear and a large wear volume. When the urea-based grease with 2 wt% MXenes nanofluid is used as the lubricating phase, the wear on the wear scar surface is greatly alleviated, the wear depth is shallower, and the wear volume is smaller, having excellent anti-wear performance.

[0102] (4.3) Wear surface analysis

[0103] The microscopic morphology and element distribution of the friction surface were further characterized using a JEOL JSM-7900F field emission scanning electron microscope from Japan. Taking a temperature of 50 °C, a frequency of 25 Hz, a stroke of 1 mm, and a load of 200 N as an example, the wear scar surfaces of the urea-based greases in Comparative Example 1 and Examples 2 - 5 when used as the lubricating phase were analyzed, and the results are as shown in Figure 9 . Under this friction condition, when the urea-based grease prepared in Comparative Example 1 is used as the lubricating phase, the wear marks on the wear scar surface are deeper and more obvious, and spalling pits appear, indicating relatively severe wear; when the urea-based grease with 2 wt% MXenes nanofluid prepared in Example 4 is used as the lubricating phase, the wear surface is relatively smooth, and the distributions of C, N, O, Ti, and Fe on the wear surface are relatively uniform. The Ti element has an obvious distribution along the scratch direction, and the surface contains the characteristic element N of soap fibers, indicating that MXenes and soap fibers have a synergistic lubrication effect, generating a friction film and having an anti-friction and anti-wear effect.

[0104] In summary, when the addition amount of MXenes nanofluid is 2 wt%, the urea-based grease has both extreme pressure and anti-wear properties and friction-reducing and anti-wear properties, and has excellent high load-carrying performance, which helps to ensure the smooth operation of bearings under extreme pressure conditions.

[0105] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Application of dodecylphosphoric acid-modified MXenes as additives in lubricating greases.

2. A MXenes nanofluid comprising MXenes modified with dodecyl phosphoric acid and a base oil.

3. The MXenes nanofluid according to claim 1, characterized in that: The mass content of MXenes in the MXenes nanofluid is 0.2-5%.

4. The method for preparing the MXenes nanofluid according to claim 2 or 3, comprising the following steps: The aqueous dispersion of MXenes, the first base oil and dodecyl phosphoric acid are mixed, the pH value is adjusted to 2 to 2.5, the MXenes are modified, and the solid-liquid separation is performed to obtain a solid component which is the MXenes modified with dodecyl phosphoric acid; The dodecyl phosphoric acid-modified MXenes are mixed with a second base oil to obtain a MXenes nanofluid.

5. The preparation method according to claim 4, characterized in that: The mass ratio of the MXenes to the amount of dodecyl phosphoric acid is 1 g: 2.4-4.2 mmol; The first base oil and the second base oil include one or more of mineral oil, hydrocarbon oil, ester oil and polyether lubricating oil; The mass ratio of the MXenes to the first base oil is 8 to 20:1000.

6. Use of the MXenes nanofluid according to claim 2 or 3 or the MXenes nanofluid prepared by the preparation method according to claim 4 or 5 in lubricating grease.

7. A high load-bearing grease, characterized in that: In terms of mass percentage, the preparation raw materials include 84-94% of MXenes nanofluid and 6-16% of thickener; The base oil and / or thickener in the MXenes nanofluid contains a carbonyl group; The MXenes nanofluid is the MXenes nanofluid according to claim 2 or 3 or the MXenes nanofluid prepared by the preparation method according to claim 4 or 5; The thickener includes an organic thickener and / or an inorganic thickener; the organic thickener includes a polyurea thickener and / or a metal soap.

8. The high load-bearing grease according to claim 7, characterized in that: The polyurea thickener includes a polyurea thickener obtained by reacting a monoamine, a diamine and a diisocyanate; The metal soap includes one or more of lithium soap, calcium soap, aluminum soap and barium soap; The inorganic thickener includes one or more of bentonite, silicon dioxide, attapulgite, aluminum silicate and boron nitride.

9. The method for preparing the high-load bearing grease according to any one of claims 7 or 8, characterized in that: The following steps are involved: The prepared raw materials are mixed, and are heated, dispersed, refined and cooled in sequence to obtain the high-load grease.

10. Use of the high-load lubricating grease according to claim 7 or 8 or the high-load lubricating grease prepared by the preparation method according to claim 9 as lubricating grease for mechanical equipment.

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