Preparation method and application of high-performance lithium-based lubricating grease based on branched-chain butyl octyl ZDDP modification

Abstract

The invention discloses a preparation method and application of high-performance lithium-based lubricating grease modified based on branched-chain butyl octyl ZDDP, general lithium-based lubricating grease is used as base grease, the high-performance lithium-based lubricating grease comprises a ZDDP additive, the ZDDP additive is branched-chain alkyl ZDDP, and the addition amount of the ZDDP additive is 0.4-0.6 wt%. According to the invention, through systematic and creative research, butyl octyl ZDDP (T202) with a medium carbon chain branched chain structure is screened as an optimal additive, and through a concentration gradient experiment, the optimal use concentration range of ZDDP in lithium-based grease is accurately determined.

Description

Technical Field

[0001] This invention relates to the field of lubricating materials technology, specifically to a method for preparing high-performance lithium-based grease based on branched butyryl ZDDP modification and its application. Background Technology

[0002] Grease, as an important semi-solid lubricating material, is widely used in critical friction pairs such as bearings and gears in mechanical equipment. Among them, general-purpose lithium-based greases dominate the market due to their mature manufacturing process, low cost, and good overall performance. However, traditional lithium-based greases suffer from problems such as insufficient lubricating film strength, easy rupture, and a sharp decline in anti-wear performance under harsh conditions such as high temperature, high load, and high speed, leading to premature failure of friction pairs and severely restricting their application in high-performance equipment. How to make the performance of general-purpose lithium-based greases approach or surpass that of high-priced specialty greases through low-cost and efficient additive compounding technology is an important research direction in this field.

[0003] To improve the extreme pressure and anti-wear properties of lubricating greases, the industry typically uses functional additives such as sulfur-phosphorus additives (e.g., zinc dialkyl dithiophosphate, ZDDP) or organic molybdenum compounds (e.g., molybdenum dialkyl dithiocarbamate, MODTC). ZDDP can thermally decompose on the friction surface to generate a protective film composed of zinc phosphate, zinc sulfide, etc., effectively preventing surface adhesion and wear.

[0004] However, the following technical problems urgently need to be solved in the existing technology: 1. Unclear selection and compatibility of additives: ZDDP with different carbon chain structures (such as straight chain, branched chain, aryl) has significant differences in reactivity, film-forming efficiency and final anti-wear effect in grease systems. Existing technologies lack the optimization rules for ZDDP molecular structure for lithium-based grease thickener systems, resulting in blind selection of additives and failure to achieve optimal performance.

[0005] 2. The effect of additive concentration is unclear: When the additive concentration is too low, a continuous and effective protective film cannot be formed; when the concentration is too high, it may damage the colloidal structure of the grease, leading to a decrease in consistency, a weakening of the oil film's carrying capacity, or even aggravating abrasive wear due to an excessively thick and porous reaction film. Existing technologies lack systematic research on the optimal concentration window of ZDDP in lithium-based greases.

[0006] Therefore, there is an urgent need in this field for a modification scheme based on scientific formulation and precise process, which can clarify the structure-property relationship between the molecular structure and concentration of ZDDP and the anti-wear properties of lithium-based grease, and develop a high-performance lithium-based grease that has excellent friction reduction, anti-wear and high stability to meet the requirements of modern industry for long equipment life and high reliability. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a high-performance lithium-based grease modified with ZDDP and its preparation method. Through systematic and creative research, the synergistic relationship between the structure, concentration, and performance of specific additives in a specific grease system (general-purpose lithium-based grease) was revealed. Butyl-octyl ZDDP (T202) with a medium carbon chain branched structure was selected as the optimal additive, and the optimal concentration range of ZDDP in lithium-based grease was accurately determined through concentration gradient experiments.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a high-performance lithium-based grease modified with branched butyryl ZDDP, which uses general lithium-based grease as a base grease and contains ZDDP additives, wherein the ZDDP additives are branched alkyl ZDDPs.

[0009] Furthermore, the branched alkyl ZDDP is zinc butyryldialkyldithiophosphate (T202).

[0010] Furthermore, the amount of the ZDDP additive added is 0.4-0.6 wt%.

[0011] Preferably, the amount of ZDDP additive added is 0.5 wt%.

[0012] A second aspect of the present invention provides a method for preparing the above-mentioned high-performance lithium-based grease modified with branched butyryl ZDDP, comprising the following steps: S1. Heat and soften the weighed general-purpose lithium-based grease. S2. Weigh out the ZDDP additive according to the target addition amount, dissolve it in an appropriate amount of base oil, and prepare a uniform premix. S3. Slowly add the premixed liquid dropwise to the softened general-purpose lithium-based grease. After initial stirring and dispersion, the mixture is then emulsified at high speed to obtain a uniformly dispersed and stably distributed grease system. S4. After dispersion, allow the grease sample to cool naturally and stand to remove bubbles, then finally pack it into a sample bottle and seal it for storage.

[0013] Further, in step S1, the general-purpose lithium-based grease is heated and softened in an oil bath at 70-90°C for 20-40 minutes. The purpose of this stage is to reduce the consistency of the grease to the most suitable apparent viscosity range for subsequent mixing without damaging the lithium-based soap fiber structure, thereby facilitating subsequent operations and ensuring the colloidal stability of the final product.

[0014] In step S2, the weighed additive is premixed with the same type of mineral base oil. The mixture is stirred until a uniform, sediment-free, transparent or semi-transparent premixed liquid is formed. In this step, the surface energy of the additive system is effectively reduced by pre-dispersion, and its possible micellar aggregation structure is initially destroyed, laying the foundation for highly uniform dispersion in the lipid matrix in the future.

[0015] Furthermore, in step S3, while maintaining a temperature of 70-90°C, the premixed liquid is added dropwise to the softened general-purpose lithium-based grease. During the initial stirring and dispersion process, the stirring speed is 400-600 rpm and the stirring and mixing time is 5-15 min.

[0016] Further, in step S3, the mixture is transferred to a high-shear emulsifier for high-speed emulsification, with a stirring speed of 2500-3500 rpm and a shear dispersion time of 10-20 min.

[0017] Step S3 employs a unique two-step method: "low-speed penetration followed by high-speed shearing." First, the premix is ​​added dropwise to the softened general-purpose lithium-based grease for initial stirring and dispersion. The purpose of this stage is to allow the premix to fully wet and penetrate the three-dimensional soap fiber network of the grease under low shear stress, achieving a macroscopically uniform distribution of the additives and avoiding excessively high local concentrations. Subsequently, the premixed material is rapidly transferred to a high-shear emulsifier or homogenizer for strong shear dispersion at high speed. This stage generates powerful cavitation, impact, and shear effects, which can break the additive clusters down to the micron or even submicron level and firmly anchor them to the surface and network gaps of the soap fibers through physical encapsulation and chemical adsorption, forming an extremely stable and uniform dispersion system.

[0018] Finally, in step S4, after dispersion is complete, heating is stopped, and the grease mixture is allowed to cool naturally to room temperature under undisturbed conditions for at least 2 hours. Subsequently, the sample is sealed and allowed to mature for at least 24 hours. This stage is crucial, as it allows the soap fiber network disrupted under high-speed shear to slowly rebuild and stabilize, while simultaneously giving additive molecules sufficient time for interfacial migration and orientation, thus achieving optimal performance. Finally, the matured grease undergoes vacuum degassing to remove air bubbles entrained during stirring, ensuring the product's density and performance.

[0019] A third aspect of the present invention provides an application of the above-mentioned high-performance lithium-based grease modified with branched butyryl ZDDP, wherein the high-performance lithium-based grease modified with branched butyryl ZDDP is used in the field of lubrication under high-speed, heavy-load, and harsh service environments.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) Traditionally, ZDDP is considered an effective anti-wear agent. However, different molecular structures (such as T202, T203, T205, and T214) exhibit significant differences in anti-wear and friction-reducing performance within complex lithium-based grease thickener systems, and there is a lack of clear guiding principles. This invention, through comparative experiments, reveals for the first time that zinc butyryldialkyldithiophosphate (T202), with a medium-sized carbon chain branched structure, demonstrates significantly superior anti-wear and friction-reducing performance in general-purpose lithium-based greases compared to other structures (T205 with a long straight chain structure, T203 with a highly branched structure, and T214 with a mixed aryl chain structure). The fundamental reason for this is that the branched structure of T202 provides an optimal balance between reactivity and steric hindrance, enabling it to decompose rapidly and uniformly on the friction surface, forming a dense and strongly adherent phosphate / sulfide protective film.

[0021] (2) The present invention also precisely determined the optimal addition concentration of ZDDP in lithium-based grease. Specifically, through concentration gradient experiments, it was first systematically determined that for medium carbon chain branched ZDDP (T202), there is a narrow and efficient "optimal concentration window" (0.4-0.6 wt%) in general lithium-based grease, especially 0.5 wt%. Within the above-mentioned optimal concentration range, a uniform and dense friction protective film with significantly increased S, P and Zn element content can be formed, achieving an order-of-magnitude improvement in anti-wear performance. This quantitative discovery provides a precise formulation basis for industrial production. Attached Figure Description

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0023] Figure 1 The friction coefficient curves of general-purpose lithium-based grease under different loads; Figure 2 The wear track profiles of general-purpose lithium-based grease under different loads; Figure 3 The volumetric wear rate of general-purpose lithium-based grease under different loads; Figure 4 Curves showing the change in friction coefficient over time after adding ZDDP with different carbon chain structures to general-purpose lithium-based greases; Figure 5 The wear track profile (a) and volumetric wear rate (b) of general lithium-ZDDP with different carbon chain lengths; Figure 6 The friction coefficient curves of general-purpose lithium with different concentrations of T2O2 are shown. Figure 7 The wear track profiles (a) and volumetric wear rates (b) of general-purpose lithium-T2O2 with different concentrations are shown. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Experimental materials: Using 45# steel as the base material, the base material was cut into circular samples with a radius of 30mm using wire cutting. The metal discs were then polished and ground sequentially with metallographic sandpaper and polishing compound until the surface roughness Ra=0.1. Finally, they were cleaned in an ultrasonic cleaner for 10-15 minutes to remove surface organic matter. The base oil of the No. 3 general-purpose lithium-based grease was mineral oil, the thickener was lithium soap, and the additives mainly included antioxidants and preservatives.

[0026] The basic components of the grease are provided by Wuxi PetroChina Grease Co., Ltd., and the specific elemental composition is shown in Table 1, which lists the basic properties and main elemental contents of the grease.

[0027] Table 1. Basic properties and main element content of two types of greases I. Preparation method of high-performance lithium-based grease modified with branched butyryl-octyl ZDDP All ZDDP modified grease samples in this study were prepared using #3 general-purpose lithium-based grease as the base grease and a combination of mechanical stirring and high-shear dispersion.

[0028] The specific steps are as follows: First, place the weighed base grease in an 80°C oil bath for 30 minutes to soften it, thereby reducing its viscosity and facilitating subsequent mixing.

[0029] Subsequently, a certain amount of ZDDP additives (T202, T203, T205, T214) were weighed according to the target addition amount (mass fraction) and dissolved in an appropriate amount of base oil to prepare a uniform premix.

[0030] The premix was slowly added dropwise to the softened grease, and initially mixed for 10 minutes at 500 rpm using a magnetic stirrer to allow the additive to initially disperse in the grease matrix. The mixture was then transferred to a high-speed emulsification device and sheared dispersed for 15 minutes at 3000 rpm to ensure that the additive was uniformly dispersed and stably distributed in the grease system.

[0031] After dispersion, the grease sample is allowed to cool naturally and stand to degas. Finally, it is placed in a clean sample bottle, sealed, and stored at room temperature in the dark for later use.

[0032] Regarding the above preparation process: First, in step S1, the general-purpose lithium-based grease is heated and softened in an oil bath at 70-90°C for 20-40 minutes. The purpose of this stage is to reduce the consistency of the grease to the most suitable apparent viscosity range for subsequent mixing without damaging the lithium-based soap fiber structure, thereby facilitating subsequent operations and ensuring the colloidal stability of the final product.

[0033] Subsequently, in step S2, the weighed additive is premixed with the same type of mineral base oil. The mixture is stirred until a uniform, sediment-free, transparent or semi-transparent premixed liquid is formed. In this step, the surface energy of the additive system is effectively reduced through pre-dispersion, and its possible micellar aggregation structure is initially destroyed, laying the foundation for highly uniform dispersion in the lipid matrix in the future.

[0034] Then, step S3 employs a unique two-step method of "low-speed penetration followed by high-speed shearing": First, the premix is ​​added dropwise to the softened general-purpose lithium-based grease for initial stirring and dispersion. The purpose of this stage is to allow the premix to fully wet and penetrate the three-dimensional soap fiber network of the grease under low shear stress, achieving a macroscopically uniform distribution of the additives and avoiding excessively high local concentrations. Subsequently, the initially mixed material is rapidly transferred to a high-shear emulsifier or homogenizer for strong shear dispersion at high speed. This stage generates powerful cavitation, impact, and shear effects, which can break the additive clusters down to the micron or even submicron level and firmly anchor them to the surface and network gaps of the soap fibers through physical encapsulation and chemical adsorption, forming an extremely stable and uniform dispersion system.

[0035] Finally, in step S4, after dispersion is complete, heating is stopped, and the grease mixture is allowed to cool naturally to room temperature under undisturbed conditions for at least 2 hours. Subsequently, the sample is sealed and allowed to mature for at least 24 hours. This stage is crucial, as it allows the soap fiber network disrupted under high-speed shear to slowly rebuild and stabilize, while simultaneously giving additive molecules sufficient time for interfacial migration and orientation, thus achieving optimal performance. Finally, the matured grease undergoes vacuum degassing to remove air bubbles entrained during stirring, ensuring the product's density and performance.

[0036] The samples prepared in the following research processes include the following categories: Samples were prepared by adding different types of ZDDP (T202, T203, T205, T214) at an amount of 0.25 wt%. Using T202 as a representative additive, modified samples were prepared with addition amounts of 0.25wt%, 0.50wt%, 0.75wt%, and 1.00wt%, respectively, and named as "General Lithium – x%T202", where x is the mass fraction of the additive.

[0037] T202, chemically named butoctyl ZDDP or butoctyldialkylzinc dithiophosphate, has a branched structure with a medium carbon chain length. T203, chemically named sec-octyl ZDDP, also has a branched structure. T205, chemically named beroctyl ZDDP, has a long-chain linear structure. T214, chemically named octyl / aryl mixed-chain zinc dithiophosphate, has a mixed-chain structure.

[0038] II. Friction Testing Methods and Lubricating Grease Performance Characterization The tribological properties of modified grease were evaluated on a reciprocating friction and wear tester. The upper sample was a GCr15 steel ball (9 mm in diameter, HRC-58 hardness), and the lower sample was a 45# steel circular sample with a diameter of 30 mm. The friction test load of the base grease was set to 10-30 N, and the friction test load of the modified grease was set to 20 N. The sliding speed was 3 mm / s, the reciprocating distance was 3 mm, and the test time was 30 min. Before and after the test, the steel ball and the disc sample were ultrasonically cleaned in anhydrous ethanol for 10 min and then dried to remove oil stains, wear debris and other impurities from the surface. After the test, the wear track profile of the disc sample was measured using a roughness measuring instrument, and the volumetric wear rate was calculated based on the wear track profile. To reduce the measurement error, the average value was taken after 3 measurements. The formula for calculating the volumetric wear rate is shown in formula (1). The morphology of the wear area of ​​the substrate was observed using a scanning electron microscope, and the elemental distribution of the wear surface was measured by an EDS energy dispersive spectroscopy instrument to analyze the wear mechanism. （1）

[0039] In the formula, W is the volumetric wear rate (mm). 3 ·(Nm) -1 V represents the wear volume (mm). 3 P is the load (N); S is the sliding displacement (m).

[0040] III. Basal Fat Test Results 3.1 Tribological Properties Analysis of Base Grease under Different Loads Figure 1 The friction coefficient curves of the substrate under different load conditions using general-purpose lithium-based grease are shown. From Figure 1It can be seen that the friction coefficient curve of the general-purpose lithium-based grease under a 10N load is relatively stable. Initially, the friction coefficient rapidly rises to 0.14, then quickly decreases to 0.12 after a short break-in period, with an average friction coefficient of approximately 0.120. In contrast, under 20N and 30N loads, the friction coefficient curves fluctuate significantly, with similar trends. The maximum fluctuation is approximately 0.1, and the average friction coefficients are 0.150 and 0.188, respectively, which are 1.25 times and 1.57 times that under the 10N load condition. After 1200 seconds, both groups gradually enter a stable wear stage, with friction coefficients stabilizing at 0.15 and 0.20, respectively. This indicates that under lower loads (10N), the general-purpose lithium-based grease can form a relatively uniform lubricating film. However, under higher loads of 20N and 30N, the lubricating film thickness thins or even ruptures due to uneven pressure, resulting in a lack of lubrication for the friction pair and causing significant fluctuations in the friction coefficient.

[0041] Figure 2 The wear track profiles of the substrate under 10N, 20N, and 30N loads using general-purpose lithium-based grease are shown. Under 10N load, the wear track width and depth of the general-purpose lithium-based grease are 235μm and 1.64μm, respectively, with a wear protrusion approximately 44μm wide and 0.7μm high in the center of the wear track. In contrast, under 20N and 30N loads, the general-purpose lithium-based grease experienced lubrication failure, leading to severe wear of the substrate. Under 20N load, the wear track width and depth are 412.4μm and 3.82μm, respectively, with a furrow approximately 54μm wide and 2.52μm deep in the center of the wear track. Compared to the 10N load, the wear track width increased by 177.4μm and the depth increased by 2.18μm under the 20N load. Under a 30N load, the wear was more severe, with the wear track width and depth reaching 529.6μm and 4.86μm, respectively, increases of 117.2μm and 1.04μm compared to the 20N load. Furthermore, more pronounced wear protrusions and grooves appeared in the central area of ​​the wear track. This indicates that excessive load can lead to uneven or even ruptured grease film in the friction area, further exacerbating wear. In addition, higher loads may also cause the grease temperature to rise, accelerating grease degradation and further reducing its lubricating performance.

[0042] Figure 3 The volumetric wear rate of the substrate under loads of 10N, 20N, and 30N using general-purpose lithium-based grease is given. The volumetric wear rate under a 10N load is 7.11 × 10⁻⁶. -6 mm 3 / N·m. The volumetric wear rates of general-purpose lithium-based grease under 20N and 30N loads are 12.4 × 10⁻⁶ N·m. -6 mm 3 / N·m and 10.81×10 -6 mm 3 / N·m. Under lubrication failure, the volumetric wear rate of the substrate under 20N and 30N loads is 1.73 times and 1.52 times that under 10N load, respectively. It can be seen that when the load reaches 20N, the wear volume of the substrate using general lithium-based grease increases significantly, which indicates that excessive load will lead to a significant deterioration of the wear condition between the friction pairs.

[0043] 3.2 Wear Mechanism Analysis As shown in Table 2, the Fe content gradually decreases with increasing load, from 87.5% (measurement point 1) under 10N conditions to 75.2% (measurement point 1) under 30N conditions, indicating that the matrix material wear is more severe under high loads. Furthermore, the O content increases significantly with increasing load, reaching a maximum of 14.7% (measurement point 2) under 30N conditions, and several dark areas similar to the measurement points are observed, indicating severe oxidative wear during friction. The Cr and Mn contents remain relatively stable, indicating that the matrix composition has not changed significantly. Overall, under low load (10N), the lubrication state is mainly elastohydrodynamic lubrication, and the wear mechanism is slight abrasive wear; under medium load (20N), it enters a mixed lubrication stage, with oxidative wear and slight spalling acting synergistically; under high load (30N), the lubrication state transforms into boundary lubrication, with significant coupling effects of oxidative wear, adhesive wear, and fatigue spalling.

[0044] Table 2. Element content (wt%) of general-purpose lithium-10N, 20N, and 30N friction surfaces. IV. The Influence of ZDDP Molecular Structure on the Anti-wear Properties of Lithium-based Grease 4.1 Tribological Properties Study of Modified Greases with Different Additives Figure 4The graphs show the coefficient of friction versus time for modified general-purpose lithium-based greases with a concentration of 0.25 wt% after adding ZDDPs (T202, T203, T205, T214) with different carbon chain structures in a reciprocating friction test. The graphs reveal significant differences in the friction-reducing performance of the greases due to the addition of ZDDPs with different carbon chain structures (T202, T203, T205, T214). In the initial friction phase (0-300 s), the coefficient of friction for all samples increases rapidly, mainly because the lubricating film has not yet fully formed, and the grease is in a boundary lubrication state. Subsequently, in the stable friction phase, the performance differences between the samples gradually become apparent. Sample T202 exhibits the best performance, with the lowest stable coefficient of friction (approximately 0.10–0.11) and minimal fluctuation, indicating good lubricating film formation and friction-reducing effect under these conditions. Samples T203 and T214 exhibited similar friction coefficients in the steady-state phase, slightly higher than T202, demonstrating moderate friction-reducing performance. Sample T205, however, consistently showed a high friction coefficient (approximately 0.12–0.13) with significant fluctuations, indicating relatively poor lubricant film formation and stability. Considering the ZDDP molecular structure, T202, with its medium-sized carbon chain branched structure, exhibits high reactivity and readily forms a dense phosphate film on metal surfaces. In contrast, T205, with its long-chain straight structure, has limited reactivity, resulting in slow film formation at medium and low temperatures and consequently, less than ideal friction-reducing performance. These results demonstrate that the carbon chain structure of ZDDP additives significantly influences lubrication performance, and branched medium-carbon ZDDPs (such as T202) are more suitable for anti-wear and friction-reducing modification of general-purpose lithium-based greases.

[0045] Figure 5 The effects of four ZDDP additives (T202, T203, T205, and T214) with different structures on the friction wear profile (a) and volumetric wear rate (b) of a general-purpose lithium-based grease under the same operating conditions (additive concentration 0.25 wt%, test time 30 min, speed 10 mm / s). Figure 5 As shown in (a), the wear track depth and width vary significantly among different types of ZDDP additives. Sample T202 exhibits the shallowest and narrowest wear track, indicating the formation of a relatively complete and stable lubricating film during friction, effectively reducing surface wear. T205 is next, with a slightly wider but generally symmetrical and smooth wear track. T203 and T214 show significantly deeper wear tracks, especially T214, which exhibits deep grooves with irregular edges, indicating weak lubricating film protection and susceptibility to micro-cutting and ploughing damage on the material surface.

[0046] Volume wear rate data such as Figure 5 As shown in (b), the observations from the profile diagram are further validated. Sample T202 exhibited the lowest volumetric wear rate, at only 4.44 × 10⁻⁶. -6 mm 3 / N·m, much lower than that of sample T214 (8.19×10 -6 mm 3 / N·m) and T203 sample (7.64×10 -6 mm 3 The T205 sample showed stronger wear resistance (N·m / N), indicating a volumetric wear rate of 5.00 × 10⁻⁶. -6 mm 3 / N·m, which is between the two.

[0047] This result is consistent with the aforementioned friction coefficient analysis, indicating that the carbon chain structure of the ZDDP molecule has a significant impact on its friction-reducing and wear-resistant properties. T202, with its short alkyl chain (butyl-octyl), rapidly decomposes under frictional heat, releasing active sulfur and phosphorus elements, which react with the metal surface to form a continuous sulfur-phosphorus composite film. This process can be completed in the early stages of friction, reducing severe wear during the "break-in period." While T214 contains aromatic ring groups, its longer chain length reduces its decomposition activity, leading to delayed film formation. Before film formation, significant wear has already occurred on the metal surface, increasing the depth of wear tracks and volume loss.

[0048] 4.2 Influence of Additive Carbon Chain Length on Grease Wear Mechanism Table 3 shows the effect of different additives (T202, T203, T205, T214) at a 0.25 wt% addition rate on the elemental composition of the wear surface of general-purpose lithium-based grease. The grease with 0.25 wt% T202 additive has average P, S, and Zn contents of 0.15%, 0.55%, and 0.05%, respectively, while its C and O contents are only 6.7% and 4.7%, respectively. This indicates that this grease has a good anti-friction effect. The low C and O contents indicate that grease failure and oxidative wear on the substrate surface are effectively suppressed. The high P and Zn contents indicate the formation of a phosphate and zinc oxide protective film in the lubricating film, which helps improve anti-wear performance. The moderate S content indicates that there are still some sulfide components in the lubricating film, which helps reduce friction. The grease with 0.25 wt% T203 differs from T202 in the elemental composition of the wear surface, with an O content as high as 5.3%, a P content of 0.05%, a S content of 0.25%, and a Zn content of 0.1%. Compared to T202, T203 exhibits more severe oxidative wear. The slightly lower P and Zn content indicates that a phosphate and zinc oxide protective film still forms in the lubricating film, but its stability is worse. In the 0.25wt% T205 additive grease, the C content is 7.05%, O content is 4.8%, P content is 0.2%, S content is 0.55%, and Zn content is 0.15%. Compared to T202, T205 has slightly higher P, S, and Zn contents, indicating the formation of more phosphate and zinc oxide protective films, but the C and O content is also higher, resulting in compromised lubrication performance. The 0.25wt% T214 grease on the wear-marked surface has a C content of 7.0%, an O content of 5.2%, a P content of 0.1%, an S content of 0.15%, and a Zn content of 0.2%. The higher C and O content indicates that the lubricating film is easily oxidized. The low content of P, S, and Zn results in a lack of phosphate and zinc oxide components in the lubricating film, leading to insufficient protective ability of the lubricating film.

[0049] Table 3. Element content (wt.%) of friction surfaces of general-purpose lithium-based greases + 0.25% T202, T203, T205, and T214. V. The Influence of Additive Concentration on the Anti-wear Properties of Lithium-Based Grease 5.1 Study on Tribological Properties under Concentration Gradients of Phosphorus-Based Additives Figure 6Friction coefficient curves obtained by adding different concentrations of ZDDP additive to general-purpose lithium-based greases are shown in the figure. As can be seen from the figure, the friction coefficient of higher dosages improves both stability and average value compared to the 0.25wt% content. The 0.5wt% T202 exhibits the lowest average friction coefficient, at approximately 0.09. Its friction coefficient rapidly increases to approximately 0.15 in the initial stage of the test, then stabilizes at approximately 0.1 after a small fluctuation of about 200s, and subsequently continues to decrease. Compared to 0.25wt% T202, 0.5wt% T202 exhibits a more stable friction coefficient because the higher dosage of additive provides a more uniform and stable phosphate protective layer and significantly improves the load-bearing capacity of the lubricating oil film. Compared to 0.5wt%T202, 0.75wt%T202 has a longer initial break-in period (approximately 100s) and enters the stable wear stage after 100s. During the stable wear stage, the overall trends of both greases are largely similar, with an average coefficient of friction of approximately 0.1. 1.0wt%T202 has the most stable coefficient of friction and the longest break-in period (approximately 250s), but its coefficient of friction curve shows a gradually increasing trend during the stable wear stage, resulting in its highest average coefficient of friction (approximately 0.11). This phenomenon may be due to an excessive amount of phosphorus-based additives, which impair the film-forming properties of the lithium-based grease itself.

[0050] Figure 7 The figures show the wear track profiles and volumetric wear rates obtained from lithium-based greases with different concentrations of T202 additive. Figure 7 (a) It can be seen that the 0.5wt%T202 sample has a smaller wear track width and depth compared to the 0.25wt%T202 sample, indicating that the load-carrying capacity and oil film integrity of the grease are significantly improved with increasing concentration. Simultaneously, the 0.5wt%T202 sample is also the smoothest among all samples. Compared to 0.5wt%T202, the 0.75wt%T202 sample shows a slight increase in wear track width and a significant increase in wear track depth (approximately 1.5μm), with a substantial increase in surface grooves and wear protrusions. With increasing T202 concentration, the film-forming properties and load-carrying capacity of the grease are compromised. As the additive concentration reaches 1.0wt%T202, the surface roughness of the worn surface increases significantly, with the wear track width and depth reaching 0.211mm and 5μm, respectively. Furthermore, many deep grooves and edge plastic deformation deposits were found on the surface of the 1.0wt%T202 sample, indicating that the wear modes mainly include severe abrasive wear and adhesive wear.

[0051] exist Figure 7 In (b), the volumetric wear rate exhibits a similar trend to that described above with increasing T202 addition. Specifically, the volumetric wear rate with 0.25 wt% T202 is 4.44 × 10⁻⁶. -6mm³ / N·m. As the amount of T202 added increases, the volumetric wear rate initially rises and then decreases, with 0.5wt% T202 exhibiting the lowest volumetric wear rate of approximately (0.48 × 10⁻⁶). -6 With additive content reaching 0.75 wt% and 1.0 wt%, the volumetric wear rate increased to 1.53 × 10⁻⁶ mm³ / N·m, respectively. -6 mm³ / N·m and 5.29×10 -6 mm³ / N·m indicates that high concentrations of T202 additive may lead to a decline in lubrication effect, further proving that excessive additives cause instability or excessively thin film in the lubricating film, thereby reducing lubrication performance.

[0052] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-performance lithium-based grease modified with branched butyryl-octyl ZDDP, characterized in that, It uses general-purpose lithium-based grease as its base grease and contains ZDDP additive, which is a branched alkyl ZDDP.

2. The high-performance lithium-based grease based on branched butyryl ZDDP modification according to claim 1, characterized in that, The branched alkyl ZDDP is zinc butyryldialkyldithiophosphate.

3. The high-performance lithium-based grease based on branched butyryl ZDDP modification according to claim 2, characterized in that, The amount of ZDDP additive added is 0.4-0.6 wt%.

4. The high-performance lithium-based grease based on branched butyryl ZDDP modification according to claim 3, characterized in that, The amount of ZDDP additive added is 0.5 wt%.

5. A method for preparing a high-performance lithium-based grease modified with branched butyryl ZDDP as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Heat and soften the weighed general-purpose lithium-based grease. S2. Weigh out the ZDDP additive according to the target addition amount, dissolve it in an appropriate amount of base oil, and prepare a uniform premix. S3. Slowly add the premixed liquid dropwise to the softened general-purpose lithium-based grease. After initial stirring and dispersion, the mixture is then emulsified at high speed to obtain a uniformly dispersed and stably distributed grease system. S4. After dispersion, allow the grease sample to cool naturally and stand to remove bubbles, then finally pack it into a sample bottle and seal it for storage.

6. The method for preparing high-performance lithium-based grease modified with branched butyryl-octyl ZDDP according to claim 5, characterized in that, In step S1, the general-purpose lithium-based grease is placed in an oil bath at 70-90°C for 20-40 minutes to soften it.

7. The method for preparing high-performance lithium-based grease modified with branched butyryl-octyl ZDDP according to claim 5, characterized in that, In step S3, while maintaining a temperature of 70-90°C, the premixed liquid is added dropwise to the softened general-purpose lithium-based grease. During the initial stirring and dispersion process, the stirring speed is 400-600 rpm and the stirring and mixing time is 5-15 min.

8. The method for preparing high-performance lithium-based grease modified with branched butyryl-octyl ZDDP according to claim 5, characterized in that, In step S3, the mixture is transferred to a high-shear emulsifier for high-speed emulsification, with a stirring speed of 2500-3500 rpm and a shear dispersion time of 10-20 min.

9. The application of a high-performance lithium-based grease modified with branched butyryl ZDDP as described in any one of claims 1-4, characterized in that, The high-performance lithium-based grease modified with branched butyryl ZDDP is used for lubrication in high-speed, heavy-load, and harsh service environments.

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