Ionic Liquids as Novel Lubricants and Additives for Diesel Engine Applications

The lubricating properties of two ionic liquids (ILs) with the same anion but different cations, one ammonium IL [C₈H₁₇]₃NH.Tf₂N and one imidazolium IL C₁₀mim.Tf₂N, were evaluated both in neat form and as oil additives. Experiments were conducted using a standardized reciprocating sliding test with a segment of a Cr-plated diesel engine piston ring against a gray cast iron flat specimen. The cast iron surface was prepared with simulated honing marks as on a typical internal combustion engine cylinder liner. The selected ILs were benchmarked against conventional hydrocarbon oils. Substantial friction and wear reductions, up to 55% and 34%, respectively, were achieved for the neat ILs compared to a fully formulated 15W40 engine oil. Adding 5 vol% ILs into mineral oil has demonstrated significant improvement in the lubricity. One blend even outperformed the 15W40 engine oil with 9% lower friction and 34% less wear. Lubrication regime modeling, worn surface morphology examination, and surface chemical analysis were conducted to help understand the lubricating mechanisms for ILs. Results suggest great potential for using ionic liquids as base lubricants or lubricant additives for diesel engine applications.     

不同离子液体润滑条件下BCN薄膜摩擦学性能研究

利用中频磁控溅射技术,分别溅射硼靶和石墨靶,在单晶硅衬底上制备BCN薄膜;采用原子力显微镜(AFM)对薄膜的表面形貌进行分析;在1-正丁基-3-甲基咪唑四氟硼酸盐(L104)和1-正己基-3-乙基咪唑六氟磷酸盐(L-P206)离子液体润滑条件下,利用CSM摩擦磨损试验机考察BCN薄膜/钢球摩擦副的摩擦磨损性能;利用电化学腐蚀方法考察薄膜在离子液中的耐腐蚀性能.实验结果表明:所制备的BCN薄膜均匀、致密,表面粗糙度小;在离子液体润滑剂润滑下,BCN薄膜表现出良好的抗磨减摩性能和抗腐蚀性能;与L-P206离子液润滑剂相比,BCN薄膜在L104离子液体润滑剂润滑下的摩擦学性能更好,这可能与L104离子液体自身的分子结构及其腐蚀性弱有关.     

Protic Ionic Liquids with Ammonium Salts as Lubricants for Magnetic Thin Film Media

The newly synthesized perfluoropolyether (PFPE) whose terminal group is an ammonium salt with a carboxylic acid has better frictional and anti-corrosion properties when compared to the conventional PFPEs. The friction is almost independent of the PFPE structure, but depends on the amine structures. This modified PFPE uniformly covers the magnetic surfaces; this is why it not only reduces the friction, but also has an effect on the corrosion resistance.     

Tribological Performance of Halogen-Free Ionic Liquids as Lubricants of Hard Coatings and Ceramics

Ionic liquids are expected to be used as new high-performance lubricants because of their low volatility, high thermal stability, and high oxidation stability. It is well known that halogen-containing ionic liquids exhibit excellent lubricity for metals. However, there is a concern about the corrosiveness of ionic liquids caused by the formation of halides. The lubricity of halogen-free ionic liquids for metals is inferior to that of halogen-containing ionic liquids; however, they do not cause any remarkable corrosion effects. In this study, the lubricity of halogen-free ionic liquids—1-butyl-3-methylimidazolium tricyanomethanide ([BMIM] [TCC]) and 1-ethyl-3-methylimidazolium dicyanamide ([EMIM] [DCN])—for hard coatings and ceramics was evaluated using an SRV oscillating sliding tester. Ionic liquids exhibited excellent lubricity for sintered ceramics. It is supposed that the lubricity of ceramics depends on the chemical interaction between the surface and the ionic liquids. Ionic liquids exhibited different lubricating properties with each nitride coating. [EMIM] [DCN] exhibited a better wear reduction than [BMIM] [TCC] on CrN, and its friction coefficient was higher than that of [BMIM] [TCC]. DLC coatings with [EMIM] [DCN] exhibited better lubricity than with [BMIM] [TCC], and the combination of H-free DLC and [EMIM] [DCN] particularly showed excellent lubricity. XPS analysis showed that two kinds of nitrogen compounds were on the sliding surface of H-free DLC lubricated with [EMIM] [DCN].     

Ionic Liquids as Additives in Water-Based Lubricants: From Surface Adsorption to Tribofilm Formation

Tribology Letters - Thickener plays a significant role on the performance of grease, including rheological property, chemical and thermal stability, colloidal and mechanical stability, and so...     

Tribological Testing and Thermal Analysis of an Alkyl Sulfate Series of Ionic Liquids for Use as Aerospace Lubricants

Due to their low vapor pressures, low melting points, high boiling points, high radiation resistance, and high thermal stability, room-temperature ionic liquids (ILs) appear to be suitable candidates as new aerospace lubricants for the upcoming return to the Moon and eventual Mars missions and for air and rotorcraft applications. In this study, three ILs with the same cation, 1-butyl-3-methylimidazolium, but different sulfate anions were tested using an ultra-high vacuum spiral orbit tribometer (SOT) and their thermal properties were determined by thermogravimetric analysis (TGA). Specifically, 1-butyl-3-methylimidazolium methyl sulfate, 1-butyl-3-methylimidazolium ethyl sulfate, and 1-butyl-3-methylimidazolium octyl sulfate were tested. The SOT experiments revealed that the lifetimes of the three ILs decreased with increasing alkyl substituent length on the sulfate anion. Infrared and Raman spectra were taken to detect unused ILs and graphitic degradation products, respectively, on worn parts. Post-run spectroscopic analysis indicated residual degraded, but still usable, ILs in all runs, coupled with varying amounts of amorphous graphitic material produced as the final degradation product of all ILs. SOT testing indicated that these ILs have lower friction coefficients and lifetimes greater than those of two commonly used perfluoropolyalkylether (PFPE) space lubricants. TGA showed that the methyl sulfate IL had the highest thermal stability in air and nitrogen. The vapor pressure of the methyl sulfate IL is as at least as low as Fomblin 815Z at 20°C.     

Biobased Green Lubricants: Physicochemical,Tribological and Toxicological Properties of Fatty Acid Ionic Liquids

Fatty acid ionic liquids (FAILs) were designed and synthesized by combining quaternary ammonium cations with a range of biobased fatty acid anions. They were found to be good and universal lubricants for steel–steel, steel–copper, and steel–aluminum friction pairs, which possess low corrosivities, moderate viscosity indexes, and thermal stabilities compared to commercially available synthetic oil polyalphaolefin (PAO) 10 and traditional ionic liquid (IL) L-F104. Among them, N₁₄₄₄Oct and N₄₄₄₄Oct were found to have far lower toxicity than L-F104. Investigation of the lubricating mechanism revealed that firm and effective physical adsorption and tribochemical reaction films can be easily formed on the sliding surface due to the polarity of the fatty acid anions and the aliphatic tails, which prevent metal–metal contact and further antiwear and reduce friction.     

Tribological Performance of Room-Temperature Ionic Liquids as Lubricant

The tribological performance of room-temperature ionic liquid of alkylimidazolium tetrafluoroborate was evaluated using an Optimol SRV oscillating friction and wear tester in air and a CZM vacuum friction tester in vacuum (1×10^-3 Pa) using a steel/steel (SAE52100) contact. From the results, the ionic liquid exhibits excellent friction-reduction, antiwear proprieties, both in air and vacuum, which are superior to phosphazene (X-1P) and perfluoropolyether (PFPE). During friction, the ionic liquid forms a surface protective film mainly composed of FeF₂ and B₂O₃, which contributes to low friction and wear.     

Ionic Liquid Lubricants: Basics and Applications

Interest in the tribological performance of ionic liquids (ILs) has increased significantly since they were first introduced as lubricants in 2001. The primary advantages of ILs over conventional lubricants lie in their better ability to form tribofilms, higher thermal stability, environmental friendliness, and adaptability to various applications. A remarkable reduction in friction and wear has been observed after the addition of ILs in oil- or water-based media and in grease, suggesting that ILs are promising candidate materials as neat lubricants as well as lubricant additives. Despite the relatively common utilization of ILs as lubricating media, their wider use is limited by their high cost and corrosive properties. This article provides a brief introduction to relevant IL structures and properties, focusing on recent applications of the materials in engineering tribology.     

Transition in Wear Performance for Ionic Liquid Lubricants under Increasing Load

The effect of ionic liquid (IL) lubrication for aluminium/steel systems is highly dependant on the applied load and the IL structure. This study illustrates that a change in anion of an IL lubricant results in different physicochemical properties that will alter its performance at a given load. As the load is increased there is a shift in lubricant performance and mechanism of the IL. Up to a load of 30 N the lowest wear coefficient was achieved by a phosphonium diphenylphosphate IL, whilst above 30 N a phosphonium bis(trifluoromethanesulfonyl)amide IL was able to form a more tenacious tribolayer that resulted in the lowest wear.     

普通离子液体润滑剂的润滑成膜性能研究

目前离子液体在机械润滑研究领域受到重视,但对离子液体润滑成膜能力的研究还不多.利用纳米级膜厚测量仪考察几种具有不同阳离子侧链长度的普通磷酸盐离子液体在不同压力下的成膜能力,同时利用相近粘度的硅油作为对比对象,探讨离子液体的润滑失效及抗压能力.结果表明,在卷吸速度较高时,这几种离子液体的润滑行为符合弹流润滑规律,而在较低...     

Green Ionic Liquid Lubricants Prepared from Anti-Inflammatory Drug

Tribology Letters - Head wear of thermal flying height control sliders is studied experimentally by (a) comparing the touch-down power before and after a wear test consisting of 300 consecutive...     

Conductive and Tribological Properties of Lithium-Based Ionic Liquids as Grease Base Oil

This article reports several conductive greases prepared by ionic liquids (ILs) that are synthesized by mixing lithium tetrafluoroborate (LiBF₄) or lithium bis(trifluoromethane-sulfonyl) imide (LiNTf₂) in diglyme (G2) and tetraglyme (G4) with appropriate weight ratios at room temperature (RT). The ILs have good solution in poly(ethylene glycol-ran-propylene glycol) monobutyl ether (PAG) and thus can be used as a base oil for preparing grease for steel–steel contacts. The electrical conductive properties of the grease prepared with the mixed oil of PAG plus ILs were evaluated using the DDSJ-308A conductivity tester, GEST-121 volume surface resistance tester, and HLY-200A circuit resistance tester. Combining the free volume with viscosity, the conductivity is inversely proportional to viscosity. The tribological properties were investigated using an MFT-R4000 reciprocating friction and wear tester. The results demonstrated that the prepared greases possess better conductive and tribological properties than the commercial grease with Cu powder as an additive.     

Electrical Sliding Friction Lubricated with Ionic Liquids

Lubrication is one of the most important methods for maintaining and improving the reliability of electric contact components. In view of the conductivity, the lubrication performances of ionic liquids under electric contact have been investigated by using a reciprocating sliding tribometer. Compared with dry friction condition, ionic liquids present an excellent lubrication property. Meanwhile, under the low-load condition, the contact resistance as well as electrical power consumption decreased obviously when lubricated with ionic liquids. And the stronger current strength it is, the higher coefficient and lower contact resistance it shows. The reason could be ascribed to the current-induced fracture of the ion-adsorbed film, especially those in the asperities. And the transformation of the direct contacts, in turn, affects the friction coefficient and contact resistance.     

两种离子液体的摩擦学行为研究

合成了1-丁基-3-甲基咪唑四氟硼酸盐([Bm im]BF4)及1-羟乙基-3-甲基咪唑四氟硼酸盐([C2OHm im]BF4)2种室温离子液体。在四球摩擦机上研究了这2种离子液体的摩擦学性能,用SEM和XPS对磨痕表面的形貌和元素组成进行了表征,并分析了2种离子液体不同的润滑机制。结果表明,由于[C2OHm im]BF4上的功能化基团容易吸附在摩擦副表面,其在中低载荷下有更好的减摩抗磨性能。     

系列磷酸酯水溶性离子液体在水中摩擦学行为研究

基于分子设计的理念,将辛醇、十二醇、十八醇分别与五氧化二磷反应得到不同链长的磷酸酯,再与二乙醇胺反应制备出3种水溶性离子液体润滑添加剂。采用红外光谱分析定性确认添加剂的结构,并应用热重分析3种添加剂的热稳定性。通过四球摩擦磨损试验机评价3种添加剂在水体系中的摩擦学性能。采用扫描电子显微镜(SEM)和X射线光电子能谱(XPS)对磨损表面进行表征分析,探讨其摩擦化学机制。结果表明:3种添加剂的热分解温度较高,分别为130、165、178℃;3种添加剂均能显著提高水体系的减摩抗磨和耐极压性能,且其抗磨和耐极压性能随着链长的增加而增强,这可能与添加剂的吸附能力和反应活性有关,烷基链较长的添加剂更容易吸附在金属表面,高载荷下能更快地与金属发生反应形成边界润滑膜;添加剂在表面形成的反应膜主要由铁氧化物,磷酸铁构成;边界润滑膜的存在提高了水体系的摩擦学性能,丰富了水作为润滑介质的使用场合。     

Tribological Performance and Mechanism of Phosphate Ionic Liquids as Additives in Three Base Oils for Steel-on-aluminum Contact

Butylammonium dibutylphosphate and tetrabutylammonium dibutylphosphate ionic liquids (ILs) were evaluated as antiwear additives for steel-on-aluminum contact in three different base oils, a polyalphaolefin, an ester oil and an IL 1-methy-3-hexylimidazolium hexafluorophosphate, respectively, with similar viscosity and different polarities. The friction experiments were carried out on an Optimal SRV-IV oscillating reciprocating friction and wear tester at room temperature. Results indicate phosphate ILs can effectively improve the tribological properties of the base oil, especially the antiwear property, as additives for steel/aluminum contacts. For the base oils PAO10 and PAO40 with different viscosities, the higher viscosity of PAO40 can be beneficial to reducing the friction coefficient. The worn surface morphologies and chemical compositions of wear scars were analyzed by a JSM-5600LV scanning electron microscope and PHI-5702 multifunctional X-ray photoelectron spectrometer (XPS). The XPS analysis results illustrate that the phosphate IL additives in the base oils with different polarities exhibit the same tribological mechanism. A synergy exists between the adsorbed layers and boundary-lubricating films generated from the tribochemical reaction of IL and the substrate surface, which may reduce the friction coefficient and wear volume of the friction pairs.     

A Review of Ionic Liquids for Green Molecular Lubrication in Nanotechnology

Common industrial lubricants include natural and synthetic hydrocarbons and perfluoropolyethers (PFPEs), where the latter is widely used in commercial applications requiring extreme operating conditions due to their high temperature stability and extremely low vapor pressure. However, PFPEs exhibit low electrical conductivity, making them undesirable in some nanotechnology applications. Ionic liquids (ILs) have been explored as lubricants for various device applications due to their excellent electrical conductivity as well as good thermal conductivity, where the latter allows frictional heating dissipation. Since they do not emit volatile organic compounds, they are regarded as “green” lubricants. In this article, we review the different types of ILs and their physical properties responsible for lubrication. We also discuss their suitability as lubricants, since the long-term performance of ILs as lubricants may be affected by issues such as corrosion, oxidation, tribochemical reactions, and toxicity. We present nanotribological, electrical, and spectroscopic studies of IL films along with conventional tribological investigations, recognizing that understanding the tribological performance at various length scales is a crucial step in selecting and designing effective lubricants.