Preparation method of liquid metal / ionic liquid composite lubricating functional additive with three-layer core-shell structure

Abstract

A method for preparing a liquid metal / ionic liquid composite lubricating functional additive with a three-layer core-shell structure belongs to the field of high-performance lubricating materials under extreme working conditions. The present invention utilizes the advantages of liquid metal such as low melting point, high temperature resistance, and easy flow, and adopts a simple ultrasonic dispersion method to prepare a liquid metal / ionic liquid composite lubricating functional additive. The present invention characterizes the surface condition of liquid metal modified by ionic liquid, and explores the extreme pressure performance and anti-wear and friction reduction properties of ionic liquid with different addition amounts of liquid metal. The results show that the ionic liquid improves the liquid metal particles to present a core-shell structure, and a layer of ionic liquid film adheres to the surface of the liquid metal. After adding LM, the organic groups attached to the surface of the friction pair can effectively protect the interface of the friction pair. At the same time, the boundary lubrication film generated by the friction-induced chemical reaction can effectively improve the load-bearing capacity and anti-wear and friction reduction performance of the lubricant. Its excellent lubrication performance makes it more widely used in existing fields or unknown fields.

Description

Technical Field

[0001] The present invention belongs to the field of high-performance lubricating materials under extreme working conditions, and specifically relates to a method for preparing a liquid metal / ionic liquid composite lubricating functional additive with a three-layer core-shell structure. Background Art

[0002] Liquid metal (LM) refers to an alloy material primarily composed of gallium and containing other metallic elements. LM also boasts a low melting point, high temperature resistance, high electrical and thermal conductivity, biocompatibility, low volatility, and fluidity. LM has been widely studied in the field of tribology and can be added to grease, polyalphaolefin (PAO), water and polyimide (PI) to improve the lubrication properties of composites [Yin, F., Zhao, Y., Li, Z., & Li, T. (2022). Study on external influencing factors of gallium based liquid metal as lubricant. Journal of Functional Materials, 53(2), 2043-2049. https: / / doi.org / 10.3969 / j.issn.1001-9731.2022.02.007] [Xiao, R., Yao, M., Cheng, J., et al. (2024). Lubrication properties of gallium-based liquid metals by doping bismuth. Tribology International, 195, 109653]

[0003] Tian et al. added gallium-based liquid metal to grease in varying proportions and investigated the tribological properties of the composites using a four-ball friction tester. The addition of liquid metal significantly improved the extreme pressure lubrication capability of the grease, but the anti-wear performance under low loads was not significantly improved [Bai, PP, Li, SW, Jia, WP, et al. (2018). Tribological properties of liquid-metal galinstan as a novel additive in lithium grease. Tribology International, 128, 181-189]. Academician Liu Weimin's research group studied the effects of aluminum doping in liquid metal on its tribological behavior. At the same time, the changes in the lubrication properties of liquid metals under high load conditions have also been explored [Cheng, J., Yu, Y., Guo, J., Wang, S., Zhu, S., Ye, Q., Yang, J., & Liu, W. (2019). Ga-based liquid metal with good self-lubricity and high load-carrying capacity. Tribology International, 129, 1-4.]. In summary, liquid metals have good anti-wear properties. However, liquid metal alloys are expensive and have poor lubricity under low loads.

[0004] Ionic liquids (ILs) have similar physical and chemical properties to liquid metals, such as low volatility and good lubrication properties [Xiao, H., Guo, D., Liu, S., Pan, G., & Lu, X. (2011). Film thickness of ionic liquids under high contact pressures as a function of alkyl chain length. Tribology Letters, 41(2), 471–477.]. Ionic liquids are usually organic salts composed of several anions and organic cations. Their melting point is generally below 100°C, they are semi-fluid, non-toxic, and non-volatile. They can be used as lubricating additives, especially lubricating additives under extreme working conditions [Guo, H., & Iglesias, P. (2021). Ionic liquids as high-performance lubricants and lubricant additives. In IntechOpen. https: / / doi.org / 10.5772 / intechopen.96428].

[0005] Musavi et al. attempted to use ionic liquids as a green, cutting fluid-compatible additive for grinding. Compared with mineral-based additives, ionic liquid additives can reduce grinding forces and improve workpiece surface integrity. The reason can be attributed to the fact that compared with mineral-based fluids, liquid molecules are more inclined to adhere to the surface of high-temperature alloys, forming a strong lubricating layer with a lower static contact angle, thereby creating stable lubrication conditions in the high-stress grinding-affected area [Musavi, SH, Razfar, M., & DomiriGanji, D. (2024). New application of ionic liquid as a green-efficient lubricant. Results in Engineering, 21, 101773]. It can be found in the literature that phosphates can be adsorbed on the surface of metal oxide layers and modify the surface of particles [Li, MX, Liu, JY, Xu, YF, et al. (2016). Phosphate adsorption on metal oxides and metal hydroxides: A comparative review. 24 (3), 319-332].

[0006] Given these properties, it's conceivable that core-shell microparticles prepared by adsorbing ionic liquid components onto liquid metal interfaces could serve as lubricating additives. However, limited research has been reported on this approach. Therefore, the successful preparation of this composite additive could lead to the development of a lubricating additive that performs well under extreme operating conditions, providing a fundamental guarantee for the smooth operation of high-end equipment. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a functional additive with good lubrication effect and can meet the lubrication requirements under extreme working conditions. Therefore, the present invention proposes a preparation method of a three-layer core-shell structured liquid metal / ionic liquid composite lubricating functional additive.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for preparing a liquid metal / ionic liquid composite lubricating functional additive with a three-layer core-shell structure, comprising the following steps:

[0010] 1) Gallium, indium, and tin are weighed separately and placed in a container. The mixture is heated and stirred until all the metals are fully mixed. The heating is stopped and the mixture is cooled to room temperature to obtain a Ga-In-Sn ternary alloy, which is liquid metal (LM).

[0011] 2) Take a certain mass of liquid metal (LM), place it in 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6), stir it for a period of time, and then place it in a CNC ultrasonic cleaning machine for water bath ultrasonication to obtain a liquid metal / ionic liquid composite lubricating functional additive with a three-layer core-shell structure.

[0012] As a preferred technical solution of the present invention, in the preparation method:

[0013] In step 1), the mass ratio of gallium, indium, and tin is 68.5-80:21.5-30:10-20. The heating temperature during stirring is 80-160°C. The resulting Ga-In-Sn ternary alloy, after cooling to room temperature, is directly used in the continuous preparation in step 2. If continuous preparation is not possible, it needs to be stored in an alkaline solution.

[0014] In step 2), the amount of liquid metal (LM) added is 0.1% to 1% of the mass of 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6). The liquid metal (LM) and 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6) are mixed and first mechanically stirred for 3-6 hours, and then placed in a CNC ultrasonic cleaning machine for 3-6 hours in a water bath.

[0015] This invention leverages the advantages of liquid metal, such as its low melting point, high temperature resistance, and fluidity, to prepare a liquid metal / ionic liquid composite lubricating additive using a simple ultrasonic dispersion method. The surface condition of the ionic liquid-modified liquid metal was characterized using scanning electron microscopy and accompanying energy spectrum. A four-ball friction tester was used to investigate the extreme pressure performance and anti-wear and friction-reducing properties of ionic liquids with varying amounts of liquid metal added. Compared to existing technologies, this invention demonstrates the following advantages:

[0016] 1) The liquid metal / ionic liquid composite lubricating additive prepared by the present invention has a diameter of approximately 500 nm, and a layer of ionic liquid film adheres to the surface of the liquid metal. Analysis of the worn surface of steel balls shows that the organic groups attached to the friction pair surface after the addition of LM effectively protect the friction pair interface. At the same time, the boundary lubrication film generated by the friction-induced chemical reaction effectively improves the lubricant's load-bearing capacity and anti-wear and friction-reducing properties. Its excellent lubrication performance makes it suitable for a wider range of applications in existing and uncharted fields.

[0017] 2) The present invention utilizes an ultrasonic preparation method, which is simple, easy, and low-cost. It also allows for uniform distribution of LM particles in [HMIM]PF6, thereby further enhancing the lubricity of the composite lubricant additive. The proposed preparation method is pollution-free, resulting in an environmentally friendly, green composite lubricant additive. LM exhibits excellent dispersibility in [HMIM]PF6 and can be stored for long periods at room temperature. Furthermore, the preparation process utilizes readily available, inexpensive instruments, resulting in low production costs and suitability for industrial-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a transmission image of the liquid metal / ionic liquid composite lubricating functional additive prepared by the present invention dispersed in dichloromethane. As shown in the figure, the LM particles have a clear core-shell structure, and a transparent coating layer of about 20nm is clearly visible on their surface. The element distribution diagram shows that the surface elements are mainly composed of C, O, F, and P, indicating that a layer of [HMIM]PF6 is self-assembled on the surface of the LM particles.

[0019] Figure 2 This is a transmission image of the liquid metal / ionic liquid composite lubricating functional additive prepared by the present invention dispersed in anhydrous ethanol. It can be clearly seen that most of the surface-coated [HMIM]PF6 has been detached and agglomerated together. Figure 2 In (b), where the [HMIM]PF6 coating is lost, there is still an oxide layer of about 5nm. Figure 1 Because of the [HMIM]PF6 coating, it cannot be clearly observed. Figure 1 and Figure 2It can be seen that the liquid metal / ionic liquid composite lubricating functional additive prepared by the present invention has a three-layer core-shell structure as a whole. Its core is a liquid alloy composed of three metal elements: gallium, indium and tin. The middle layer is an oxide layer formed by natural oxidation of the liquid alloy, and its outermost layer is 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6) adsorbed on the oxide layer.

[0020] Figures 3 to 6 Anti-wear and friction reduction tests were conducted on several composite lubricating additives of different concentrations prepared according to the present invention at loads of 392N, 784N, 1568N, and 1960N in comparison with the commercial additive ZDDP.

[0021] Depend on Figure 3 (a) It can be seen that the friction coefficient curve of [HMIM]PF6 with 0.2wt% LM and 0.3wt% LM added under a load of 392N is at the lowest position among several samples, and remains stable around 0.06; the friction coefficient curve of [HMIM]PF6 with 1wt% commercial additive ZDDP is higher, around 0.07; Figure 3 (b) shows the average coefficient of friction (ACOF) and average wear spot diameter (AWSD) of [HMIM]PF6 under different LM addition amounts. It can be seen that under a load of 392N, as the amount of LM added increases, the ACOF and AWSD of [HMIM]PF6 also increase. Adding 0.2wt% and 0.3wt% LM can effectively improve the anti-wear and friction reduction properties of [HMIM]PF6, among which the addition amount of 0.2wt% has the best effect. After adding 0.2wt% LM, the ACOF decreased by 16.9% from 0.071 to 0.059, and the wear spot diameter decreased by 31.3% from 454.274μm to 311.97μm. Figure 4 It can be seen that the minimum ACOF is achieved by adding 0.3wt% LM under a load of 784N, which decreases from 0.057 to 0.054, a decrease of 5.3%; the minimum AWSD is achieved by adding 0.2wt% LM, which decreases from 529.789μm to 479.438μm, a decrease of 9.5%. Figure 5 The results show that adding different amounts of LM has little effect on the anti-wear properties of [HMIM]PF6, with the AWSD of the steel ball remaining almost unchanged at various addition levels. However, adding 0.3wt% of LM under this load effectively reduces the ACOF of [HMIM]PF6, from 0.055 to 0.046, a decrease of 16.4%. Figure 6 It shows that the ACOF and AWSD of steel ball achieved the lowest values ​​when LM was added in an amount of 0.3wt%, decreasing by 10.6% (from 0.066 to 0.059) and 11.9% (from 885.401μm to 779.763μm), respectively. DETAILED DESCRIPTION

[0022] Example 1

[0023] This example provides a liquid metal / ionic liquid composite lubricating functional additive, and the specific steps are as follows:

[0024] 1) Gallium, indium, and tin are weighed in a mass ratio of 68.5:21.5:10 and placed in a beaker. The beaker is then placed on an electric hot plate and heated at 80°C while stirring with a glass rod. Heating is stopped after all the metals are thoroughly mixed. After cooling, sodium hydroxide solution is added to remove oxides produced during heating to obtain a Ga-In-Sn ternary alloy (LM).

[0025] 2) 0.03 g of LM was added to 30 g of 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM]PF6, and the mixture was mechanically stirred for 3 h using an electric stirrer.

[0026] 3) Place the stirred solution in a CNC ultrasonic cleaning machine and ultrasonicate it in a water bath for 3 hours to obtain the prepared three-layer core-shell structure LM / [HMIM]PF6 composite lubricating additive. (The appearance, morphology, lubrication performance and other tests are similar to Figure 1-6 shown).

[0027] Example 2

[0028] This example provides a liquid metal / ionic liquid composite lubricating functional additive, and the specific steps are as follows:

[0029] 1) Gallium, indium, and tin are weighed in a mass ratio of 68.5:21.5:10 and placed in a beaker. The beaker is then placed on an electric hot plate and heated at 105°C while stirring with a glass rod. Heating is stopped after all the metals are thoroughly mixed. After cooling, sodium hydroxide solution is added to remove oxides produced during heating to obtain a Ga-In-Sn ternary alloy (LM).

[0030] 2) 0.06 g of LM was added to 30 g of 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM]PF6, and the mixture was mechanically stirred for 3.5 h using an electric stirrer.

[0031] 3) Place the stirred solution in a CNC ultrasonic cleaning machine and ultrasonicate it in a water bath for 3.5 hours to obtain the prepared three-layer core-shell structure LM / [HMIM]PF6 composite lubricating additive. (The appearance, morphology, lubrication performance and other tests are similar to Figure 1-6 shown).

[0032] Example 3

[0033] This example provides a liquid metal / ionic liquid composite lubricating functional additive, and the specific steps are as follows:

[0034] 1) Gallium, indium, and tin are weighed in a mass ratio of 68.5:21.5:10 and placed in a beaker. The beaker is then placed on an electric hot plate and heated at 120°C while stirring with a glass rod. Heating is stopped after all the metals are thoroughly mixed. After cooling, sodium hydroxide solution is added to remove oxides produced during heating to obtain a Ga-In-Sn ternary alloy (LM).

[0035] 2) 0.09 g of LM was added to 30 g of 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM]PF6, and the mixture was mechanically stirred for 5 h using an electric stirrer.

[0036] 3) Place the stirred solution in a CNC ultrasonic cleaning machine and ultrasonicate it in a water bath for 4 hours to obtain the prepared three-layer core-shell structure LM / [HMIM]PF6 composite lubricating additive. (The appearance, morphology, lubrication performance and other tests are similar to Figure 1-6 shown).

[0037] Example 4

[0038] This example provides a liquid metal / ionic liquid composite lubricating functional additive, and the specific steps are as follows:

[0039] 1) Gallium, indium, and tin are weighed in a mass ratio of 68.5:21.5:10 and placed in a beaker. The beaker is then placed on an electric hot plate and heated at 130°C while stirring with a glass rod. Heating is stopped after all the metals are thoroughly mixed. After cooling, sodium hydroxide solution is added to remove oxides produced during heating to obtain a Ga-In-Sn ternary alloy (LM).

[0040] 2) 0.12 g of LM was added to 30 g of 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM]PF6, and the mixture was mechanically stirred for 4 h using an electric stirrer.

[0041] 3) Place the stirred solution in a CNC ultrasonic cleaning machine and ultrasonicate it in a water bath for 5 hours to obtain the prepared three-layer core-shell structure LM / [HMIM]PF6 composite lubricating additive. (The appearance, morphology, lubrication performance and other tests are similar to Figure 1-6 shown).

[0042] The above content is merely an example and explanation of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a three-layer core-shell structured liquid metal / ionic liquid composite lubricating functional additive, characterized in that: Here are the steps: 1) Gallium, indium, and tin are weighed separately and placed in a container, and the temperature is raised while stirring; the mass ratio of the gallium, indium, and tin metals is 68.5-80:21.5-30:10-20, and the heating temperature during stirring is 80-160°C; after all the metals are fully mixed, heating is stopped; and after cooling to room temperature, a Ga-In-Sn ternary alloy is obtained, which is liquid metal; 2) Take a certain mass of liquid metal and place it in 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6). The amount of liquid metal added is 0.1% to 1% of the mass of 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6). After the liquid metal and 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6) are mixed, they are first mechanically stirred for 3 to 6 hours and then placed in a CNC ultrasonic cleaning machine for water bath ultrasonication for 3 to 6 hours to obtain a liquid metal / ionic liquid composite lubricating functional additive with a three-layer core-shell structure.

2. The preparation method according to claim 1, wherein The Ga-In-Sn ternary alloy obtained by cooling to room temperature in step 1) is directly used for continuous preparation in step 2). If continuous preparation is not possible, it needs to be stored in alkaline solution.

3. The liquid metal / ionic liquid composite lubricating functional additive prepared by the method according to claim 1 or 2, characterized in that: The overall structure is a three-layer core-shell structure. The core is a liquid alloy composed of three metal elements: gallium, indium and tin. The middle layer is an oxide layer formed by the natural oxidation of the liquid alloy, and the outermost layer is 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6) adsorbed on the oxide layer.

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