Oil-soluble cerium sulfide nanoparticles, methods of synthesis, and use as lubricant additives

Abstract

The application relates to a synthesis method of oil-soluble cerium sulfide nanoparticles, which takes cerium stearate as a cerium source and sulfur powder as a sulfur source, and is stirred at a constant temperature of 300-350 DEG C for 60-80 min in an inert gas atmosphere in the presence of a solvent and a surface modifier; after reaction, solid-liquid separation and washing are carried out, and oil-soluble cerium sulfide nanoparticle flakes are obtained. The oil-soluble cerium sulfide nanoparticles are prepared by a one-pot method, have low energy consumption and low cost, are suitable for batch production, have good dispersibility stability in lubricating oil, can significantly improve the tribological performance of the lubricating oil as a lubricating oil additive, and have a small friction coefficient and a small wear scar diameter.

Description

Technical Field

[0001] This invention belongs to the field of novel functional nanomaterial preparation technology, specifically relating to an oil-soluble flake-shaped cerium sulfide nanoparticle, its synthesis method, and its application as a nano-additive for lubricating oil. Background Technology

[0002] The generation and dissipation of heat during friction wastes a significant amount of energy. Friction-induced wear can lead to serious problems, including surface damage, reduced equipment performance, and decreased reliability.

[0003] Lubricating oil additives are an effective way to improve friction performance. Currently available synthetic lubricating oils typically consist of base oils and additives. Base oils are the main component of lubricants, determining their primary characteristics. Additives constitute a smaller proportion of the formulation, but play a crucial role in imparting new properties or compensating for the shortcomings of base oils.

[0004] Friction reduction and anti-wear properties are important indicators for evaluating lubricant additives. Friction reduction refers to the lubricant's ability to reduce friction between two surfaces during relative motion. This includes reducing friction through the formation of a lubricating film, reducing direct metal-to-metal contact, and improving surface finish, thus making the mechanical system move more smoothly. The main purpose is to reduce dynamic and static friction, reduce energy loss, and improve system efficiency. Anti-wear properties refer to the lubricant's ability to reduce wear on friction surfaces in a mechanical system. It extends the service life of mechanical components by forming a protective film that prevents or slows down surface wear and abrasive particle formation. The main purpose is to reduce wear, prevent surface failure of mechanical components, and thus improve system durability. Anti-wear properties focus on preventing the wear process and protecting mechanical components from the effects of friction and wear. Friction reduction may be more important under high-speed and low-load conditions, while anti-wear properties are more important for applications under high load, low-speed motion, or harsh working conditions.

[0005] Cerium sulfide itself is non-toxic. In some lubrication applications, especially in contact with water or soil, the use of non-toxic lubricants can reduce potential harm to ecosystems. Cerium sulfide has been used as a colorant. For some lubricating oils that require coloring, the addition of nano-cerium sulfide lubricants not only improves the performance of the lubricating oil but also eliminates the need for additional colorants.

[0006] The nano-cerium sulfide lubricant additive of this invention has a sheet-like structure. This structure forms a lubricating film, which slows down or prevents direct contact between friction surfaces, thereby helping to reduce friction, decrease wear on the surface of mechanical parts, and improve the performance of mechanical systems, thus improving the performance of lubricants to a certain extent. The nano-cerium sulfide lubricant additive of this invention exhibits good friction-reducing and anti-wear properties under high temperature and high pressure, improving the stability of friction workpieces in extreme environments. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects of the prior art and provide an oil-soluble flake-shaped cerium sulfide nanoparticle, which is prepared by a one-pot method, consumes less energy, has low cost, and is suitable for mass production; it has good dispersibility and stability in lubricating oil, and as a lubricating oil additive, it can significantly improve the tribological properties of lubricating oil, exhibiting a smaller coefficient of friction and wear scar diameter.

[0008] The present invention also discloses a method for preparing the above-mentioned oil-soluble dispersible flake-shaped cerium sulfide nanoparticles and their application as a lubricating oil additive or anti-wear and friction reducing agent.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for synthesizing oil-soluble cerium sulfide nanoparticles is disclosed, which uses cerium stearate as the cerium source and sulfur powder as the sulfur source. Under the conditions of solvent and surface modifier, the reaction is carried out at a constant temperature of 300-350℃ with stirring for 60-80 min in an inert gas atmosphere (such as argon, nitrogen, etc.). After the reaction is completed, the oil-soluble cerium sulfide nanoparticles are obtained by solid-liquid separation and washing.

[0010] Specifically, the solvent can be octadecene, etc. The surface modifier can be oleylamine, etc.

[0011] Furthermore, the molar ratio of cerium stearate to sulfur powder can be 1:1-3. Both cerium stearate and sulfur used in this invention are powders.

[0012] Further preferably, 20-50 ml of solvent can be added to every 2 g of cerium stearate, and 10-35 ml of surface modifier can be added to every 2 g of cerium stearate.

[0013] This invention provides oil-soluble cerium sulfide nanoparticles synthesized using the above method.

[0014] The present invention also provides the application of the above-mentioned oil-soluble cerium sulfide nanoparticles as a lubricating oil additive or anti-wear and friction reducing agent.

[0015] A preferred method for synthesizing oil-soluble cerium sulfide nanoparticles comprises the following steps: 1) Add cerium stearate and sulfur powder to a three-necked flask, and then add octadecene and oleylamine to obtain a mixed solution; 2) Stir the mixture thoroughly and purge it with argon gas to expel the air from the bottle; 3) The mixed solution was then heated to 300℃. After the reaction was complete, it was centrifuged to obtain a dark red paste with a layer of transparent residue attached. The residue disappeared after washing with anhydrous ethanol. 4) Dry in a vacuum drying oven at 50-80℃ for 10-14 hours to obtain red solid particles, which are oil-soluble cerium sulfide nanoparticles.

[0016] The process route involved in the above-described synthesis method of the present invention is as follows: The nano-cerium sulfide lubricant additive of this invention has a plate-like structure and exhibits excellent friction-reducing and anti-wear properties under high temperature and high pressure, which can improve the stability of friction workpieces in extreme environments. The experimental operation steps of this invention are simple and safe, and the obtained oil-soluble cerium sulfide nanoparticles can be well dispersed in base oil. The oil-soluble cerium sulfide nanoparticles of this invention can be applied to lubricating greases as a lubricating oil additive or an anti-wear and friction-reducing agent. This invention uses a one-pot method, adding oleylamine as a surface modifier to obtain better anti-wear and friction-reducing properties.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The synthesis method of this invention has many advantages, including simple process, inexpensive and readily available raw materials, low cost, environmental friendliness, high yield, and low equipment requirements, making it suitable for large-scale industrial production. The oil-soluble flake-shaped cerium sulfide nanoparticles synthesized by this invention possess various properties and can be well dispersed in base oils. They can be used as a novel lubricating oil additive, effectively improving the friction-reducing and anti-wear properties of lubricating greases, enhancing the load-bearing capacity of friction pairs, and extending the service life of equipment.

[0018] The oil-soluble flake-shaped cerium sulfide nanoparticles provided by this invention are prepared by a one-pot method, which is energy-efficient, low-cost, and suitable for mass production; the process is relatively simple. They exhibit good dispersibility and stability in lubricating oils, and as a lubricating oil additive, they can significantly improve the tribological properties of lubricating oils, exhibiting a smaller coefficient of friction and wear scar diameter. Attached Figure Description

[0019] Figure 1 The Tyndall effect diagram shows the dissolution of oil-soluble cerium sulfide nanoparticles prepared in Example 1 in n-hexane. Figure 2 This is the XRD pattern of the oil-soluble cerium sulfide nanoparticles prepared in Example 1; Figure 3 TEM images of the oil-soluble cerium sulfide nanoparticles prepared in Example 1 dissolved in n-hexane at different sizes (200 nm, 100 nm, 50 nm, 20 nm, 5 nm, 2 nm); Figure 4 This is an XPS image (C, S, Ce elements) of the oil-soluble cerium sulfide nanoparticles prepared in Example 1. Figure 5 The graph shows a comparison of the friction coefficients of PAO6 with 1.0 wt% cerium sulfide additive prepared in Example 1 with that of PAO6; (Experimental conditions: 75℃, 392N, 1200r / min); Figure 6 The wear scar patterns (a) and (b) of PAO6 with 1.0 wt% cerium sulfide additive prepared in Example 1 are shown; (Experimental conditions: 75℃, 392N, 1200r / min); Figure 7 The graph shows a comparison of the friction coefficients of PAO6 with 1.0 wt% cerium sulfide additive prepared in Example 1 with that of PAO6; (Experimental conditions: 50℃, 392N, 1200r / min); Figure 8 The wear scar patterns (a) and (b) of PAO6 with 1.0 wt% cerium sulfide additive prepared in Example 1 are shown; (Experimental conditions: 50℃, 392N, 1200r / min); Figure 9 The graph shows a comparison of the friction coefficients of PAO6 with 1.0 wt% cerium sulfide additive prepared in Example 1 with that of PAO6; (Experimental conditions: 100℃, 392N, 1200r / min); Figure 10 The wear scar patterns (a) and (b) of PAO6 with 1.0 wt% cerium sulfide additive prepared in Example 1 are shown; (Experimental conditions: 100℃, 392N, 1200r / min); Figure 11 The friction coefficient of PAO6 with 1.0 wt% cerium sulfide additive prepared in Example 1 is compared with that of PAO6; (Experimental conditions: 75℃, 200N, 1200r / min); Figure 12 The wear scar patterns (a) and (b) of PAO6 with 1.0 wt% cerium sulfide additive prepared in Example 1 are shown; (Experimental conditions: 75℃, 200N, 1200r / min); Figure 13 The friction coefficient of PAO6 with 1.0 wt% cerium sulfide additive prepared in Example 1 is compared with that of PAO6; (Experimental conditions: 75℃, 500N, 1200r / min); Figure 14 The wear scar patterns (a) and (b) of PAO6 with 1.0 wt% cerium sulfide additive prepared in Example 1 are shown; (Experimental conditions: 75℃, 500N, 1200r / min); Figure 15 The graph shows a comparison of the friction coefficients of PAO6 + 1.0 wt% cerium sulfide additive + 4.9 wt% compound agent prepared in Example 1 with that of PAO6 + 4.9 wt% compound agent; (Experimental conditions: 75℃, 392N, 1200r / min, commercial compound agent was sourced from Lubrizol® 1038, purchased from Lubrizol Additives Ltd.); Figure 16 The images show the wear marks (a) and (b) of PAO6 + 1.0 wt% cerium sulfide additive + 4.9 wt% compound agent prepared in Example 1; (Experimental conditions: 75℃, 392N, 1200r / min, commercial compound agent was sourced from Lubrizol® 1038, purchased from Lubrizol Additives Ltd.). Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0021] Example 1 A method for synthesizing oil-soluble cerium sulfide nanoparticles, the specific steps of which are as follows: 1) Add 1.980g of cerium stearate and 0.096g of sulfur powder to a three-necked flask, then add 30ml of octadecene and 25ml of oleylamine to obtain a mixed solution; 2) Stir the mixture thoroughly and purge it with argon gas to expel the air from the three-necked flask; 3) The mixed solution was then heated to 300℃ and stirred for 70 minutes. After the reaction was complete, it was centrifuged to obtain a dark red paste with a layer of transparent residue attached. The residue disappeared after washing with anhydrous ethanol. 4) Dry in a vacuum drying oven at 70℃ for 12 hours to obtain red solid particles, which are oil-soluble cerium sulfide nanoparticles.

[0022] Figure 1 A Tyndall effect diagram of the oil-soluble cerium sulfide nanoparticles prepared in Example 1 dissolving in n-hexane is given; the diagram proves that the synthesized cerium sulfide is at the nanoscale.

[0023] Figure 2 The XRD pattern of the oil-soluble cerium sulfide nanoparticles prepared in Example 1 is given. It can be seen from the figure that the main diffraction peaks at 29.257°, ​​32.765°, 47.019°, 54.093° and 76.298° correspond to the characteristic diffractions of Ce2S3 phase (220), (310), (420), (510) and (444) (JCPDF card number 27-0104).

[0024] Figure 3 TEM images of the oil-soluble cerium sulfide nanoparticles prepared in Example 1 dissolved in n-hexane are provided. The images show that the synthesized cerium sulfide is in the form of sheet-like nanoparticles, as measured using Digital Micrograph software. Figure 3 The lattice spacing shown is 0.304 nm. The average particle size is 11-13 nm.

[0025] Figure 4 XPS images of the oil-soluble cerium sulfide nanoparticles prepared in Example 1 are given. The figures show that compositional analysis of the cerium sulfide nanosheets described the S2p peak splitting mode. Due to the spin splitting of S2p, the orbital is divided into two parts, 2p1 and 2p3, consisting of two peaks at 162 and 168.6 eV, indicating that S2p is split into two parts. 2- It exists in the form of cerium sulfide. This proves that the material is cerium sulfide.

[0026] Figure 5 A comparison chart of the friction coefficients of PAO6 + 1.0wt% cerium sulfide additive and PAO6 prepared in Example 1 is provided (experimental conditions: 75℃, 392N, 1200r / min). The chart shows that the average friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is 0.051, while that of PAO6 is 0.079. The average friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is reduced by 35.44% compared with that of PAO6 base oil, indicating superior friction reduction performance.

[0027] Figure 6 Wear scar patterns (a) of PAO6 with 1.0 wt% cerium sulfide additive and (b) of PAO6 prepared in Example 1 are shown (experimental conditions: 75℃, 392N, 1200r / min). It can be seen from the figures that the average wear scar diameter of PAO6 with 1.0 wt% cerium sulfide additive is 0.3273 nm, and the average wear scar diameter of PAO6 is 0.6987 nm. The average wear scar diameter of PAO6 with 1.0 wt% cerium sulfide additive is reduced by 53.16% compared with PAO6 base oil, indicating excellent anti-wear performance.

[0028] Figure 7 A comparison chart of the friction coefficients of PAO6 + 1.0wt% cerium sulfide additive and PAO6 prepared in Example 1 is provided (experimental conditions: 50℃, 392N, 1200r / min). The chart shows that the average friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is 0.045, while that of PAO6 is 0.061. The average friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is 26.22% lower than that of PAO6 base oil, indicating good friction reduction performance.

[0029] Figure 8Wear scar patterns (a) of PAO6 with 1.0 wt% cerium sulfide additive and (b) of PAO6 prepared in Example 1 are shown (experimental conditions: 50℃, 392N, 1200r / min). It can be seen from the figures that the average wear scar diameter of PAO6 with 1.0 wt% cerium sulfide additive is 0.5066 nm, and the average wear scar diameter of PAO6 is 0.7752 nm. The average wear scar diameter of PAO6 with 1.0 wt% cerium sulfide additive is reduced by 34.65% compared with PAO6 base oil, indicating excellent anti-wear performance.

[0030] Figure 9 A comparison chart of the friction coefficients of PAO6 + 1.0wt% cerium sulfide additive and PAO6 prepared in Example 1 is provided (experimental conditions: 100℃, 392N, 1200r / min). The chart shows that the average friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is 0.040, while that of PAO6 is 0.077. The average friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is reduced by 48.05% compared with that of PAO6 base oil, indicating superior friction reduction performance.

[0031] Figure 10 The wear scar diagrams (a) of PAO6 with 1.0 wt% cerium sulfide additive and (b) of PAO6 prepared in Example 1 are shown; (experimental conditions: 100℃, 392N, 1200r / min); it can be seen from the figure that the average wear scar diameter of PAO6 with 1.0 wt% cerium sulfide additive is 0.3521 nm, and the average wear scar diameter of PAO6 is 0.6216 nm. The average wear scar diameter of PAO6 with 1.0 wt% cerium sulfide additive is reduced by 43.36% compared with PAO6 base oil, indicating excellent anti-wear performance.

[0032] Depend on Figures 6-10 It can be seen that PAO6 with 1.0wt% cerium sulfide additive exhibits excellent anti-wear and friction reduction properties at different temperatures, and its anti-wear and friction reduction properties are even better at high temperatures, with a more stable coefficient of friction than PAO6 base oil.

[0033] Figure 11 A comparison chart of the friction coefficients of PAO6 + 1.0wt% cerium sulfide additive and PAO6 prepared in Example 1 is provided (experimental conditions: 75℃, 200N, 1200r / min). The chart shows that the average friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is 0.042, while that of PAO6 is 0.049. The average friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is 14.28% lower than that of PAO6 base oil, and the friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is relatively stable.

[0034] Figure 12Wear scar patterns (a) of PAO6 with 1.0 wt% cerium sulfide additive and (b) of PAO6 are shown in Example 1 (experimental conditions: 75℃, 200N, 1200r / min). It can be seen from the figures that the average wear scar diameter of PAO6 with 1.0 wt% cerium sulfide additive is 0.4657 nm, and the average wear scar diameter of PAO6 is 0.6391 nm. The average wear scar diameter of PAO6 with 1.0 wt% cerium sulfide additive is reduced by 27.13% compared with PAO6 base oil, indicating better anti-wear performance.

[0035] Figure 13 A comparison chart of the friction coefficients of PAO6 + 1.0wt% cerium sulfide additive and PAO6 prepared in Example 1 is provided (experimental conditions: 75℃, 500N, 1200r / min). The chart shows that the average friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is 0.054, while that of PAO6 is 0.081. The average friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is reduced by 33.33% compared with that of PAO6 base oil, indicating that PAO6 + 1.0wt% cerium sulfide additive has excellent friction-reducing properties.

[0036] Figure 14 The wear scar diagrams (a) of PAO6 with 1.0 wt% cerium sulfide additive and (b) of PAO6 prepared in Example 1 are shown (experimental conditions: 75℃, 500N, 1200r / min). It can be seen from the figure that the average wear scar diameter of PAO6 with 1.0 wt% cerium sulfide additive is 0.4750 nm, and the average wear scar diameter of PAO6 is 0.7515 nm. The average wear scar diameter of PAO6 with 1.0 wt% cerium sulfide additive is reduced by 36.79% compared with PAO6 base oil, indicating excellent anti-wear performance.

[0037] Depend on Figure 1 , Figure 2 and Figure 11-14 It can be seen that the friction coefficient of PAO6 + 1.0wt% cerium sulfide additive is relatively stable under different loads, and it still exhibits better anti-wear and friction reduction performance under high loads.

[0038] Figure 15 A comparison graph is provided between the friction coefficient of PAO6 + 1.0wt% cerium sulfide additive + 4.9wt% compounding agent prepared in Example 1 and that of PAO6 + 4.9wt% compounding agent; (Experimental conditions: 75℃, 392N, 1200r / min, commercial compounding agent was sourced from Lubrizol® 1038, purchased from Lubrizol Additives Ltd.); The graph shows that after adding the compounding agent, PAO6 + 1.0wt% cerium sulfide additive forms a friction film faster than PAO6 base oil, and the friction coefficient is more stable.

[0039] Figure 16 Wear scar patterns (a) and (b) of PAO6 + 1.0 wt% cerium sulfide additive + 4.9 wt% compound agent prepared in Example 1 are shown; (Experimental conditions: 75℃, 392N, 1200r / min, commercial compound agent was Lubrizol® 1038, purchased from Lubrizol Additives Ltd.). The figures show that compared to PAO6 + 4.9 wt% compound agent, the addition of 1.0 wt% cerium sulfide additive resulted in a certain degree of reduction in wear scar diameter and improved wear resistance.

[0040] Example 2 A method for synthesizing oil-soluble cerium sulfide nanoparticles, the specific steps of which are as follows: 1) Add 1.980g of cerium stearate and 0.128g of sulfur powder to a three-necked flask, then add 30ml of octadecene and 25ml of oleylamine to obtain a mixed solution; 2) Stir the mixture thoroughly and purge it with argon gas to expel the air from the three-necked flask; 3) The mixed solution was then heated to 300℃ and stirred for 70 minutes. After the reaction was complete, it was centrifuged to obtain a dark red paste with a layer of transparent residue attached. The residue disappeared after washing with anhydrous ethanol. 4) Dry in a vacuum drying oven at 70℃ for 12 hours to obtain red solid particles, which are oil-soluble cerium sulfide nanoparticles.

[0041] Example 3 A method for synthesizing oil-soluble cerium sulfide nanoparticles, the specific steps of which are as follows: 1) Add 1.980g of cerium stearate and 0.192g of sulfur powder to a three-necked flask, then add 30ml of octadecene and 25ml of oleylamine to obtain a mixed solution; 2) Stir the mixture thoroughly and purge it with argon gas to expel the air from the three-necked flask; 3) The mixed solution was then heated to 300℃ and stirred for 70 minutes. After the reaction was complete, it was centrifuged to obtain a dark red paste with a layer of transparent residue attached. The residue disappeared after washing with anhydrous ethanol. 4) Dry in a vacuum drying oven at 70℃ for 12 hours to obtain red solid particles, which are oil-soluble cerium sulfide nanoparticles.

[0042] Example 4 A method for synthesizing oil-soluble cerium sulfide nanoparticles, the specific steps of which are as follows: 1) Add 1.980g of cerium stearate and 0.192g of sulfur powder to a three-necked flask, then add 40ml of octadecene and 20ml of oleylamine to obtain a mixed solution; 2) Stir the mixture thoroughly and purge it with argon gas to expel the air from the three-necked flask; 3) The mixed solution was then heated to 300℃ and stirred for 70 minutes. After the reaction was complete, it was centrifuged to obtain a dark red paste with a layer of transparent residue attached. The residue disappeared after washing with anhydrous ethanol. 4) Dry in a vacuum drying oven at 70℃ for 12 hours to obtain red solid particles, which are oil-soluble cerium sulfide nanoparticles.

[0043] Example 5 A method for synthesizing oil-soluble cerium sulfide nanoparticles, the specific steps of which are as follows: 1) Add 1.980g of cerium stearate and 0.128g of sulfur powder to a three-necked flask, then add 20ml of octadecene and 20ml of oleylamine to obtain a mixed solution; 2) Stir the mixture thoroughly and purge it with argon gas to expel the air from the three-necked flask; 3) The mixed solution was then heated to 330℃ and stirred for 70 minutes. After the reaction was complete, it was centrifuged to obtain a dark red paste with a layer of transparent residue attached. The residue disappeared after washing with anhydrous ethanol. 4) Dry in a vacuum drying oven at 70℃ for 12 hours to obtain red solid particles, which are oil-soluble cerium sulfide nanoparticles.

[0044] Comparative Example Referring to Example 1, the surfactant was replaced with oleic acid instead of oleamine. After the reaction was completed, centrifugation did not yield any product. The product obtained after centrifugation with acetone added to the solution was a white paste, not a dark red paste, indicating that oil-soluble cerium sulfide nanoparticles were not synthesized.

[0045] In summary, it can be seen that the oil-soluble cerium sulfide nanoparticles of the present invention, as a lubricating oil additive, can significantly improve the tribological properties of lubricating oil, exhibiting a smaller coefficient of friction and wear scar diameter.

Claims

1. A method for synthesizing oil-soluble cerium sulfide nanoparticles, characterized in that, Using cerium stearate as the cerium source and sulfur powder as the sulfur source, the reaction is carried out in an inert gas atmosphere at 300-350℃ for 60-80 minutes with constant temperature stirring. After the reaction is completed, the product is obtained by solid-liquid separation and washing. The solvent is octadecene; The surface modifier is oleylamine; The molar ratio of cerium stearate to sulfur powder is 1:1-3; The prepared oil-soluble cerium sulfide nanoparticles are sheet-like nanoparticles with an average particle size of 11-13 nm.

2. The method for synthesizing oil-soluble cerium sulfide nanoparticles as described in claim 1, characterized in that, Add 20-50ml of solvent for every 2g of cerium stearate.

3. The method for synthesizing oil-soluble cerium sulfide nanoparticles as described in claim 1, characterized in that, Add 10-35ml of surface modifier for every 2g of cerium stearate.

4. Oil-soluble cerium sulfide nanoparticles synthesized using any one of the methods described in claims 1 to 3.

5. The application of the oil-soluble cerium sulfide nanoparticles as a lubricating oil additive as described in claim 4.

6. The application of the oil-soluble cerium sulfide nanoparticles of claim 4 as an anti-wear and friction-reducing agent.

Images