Low-Friction Characteristics of Nanostructured Surfaces on Silicon Carbide for Water-Lubricated Seals

This article reports a novel way of in situ formation of ionic liquids (ILs) that are used as lubricant additives for steel/steel contacts. The ILs can be generated simply in base oils by mixing small molecules of 2-oxazolidinone, triglyme, or tetraglyme with lithium bis(trifluoromethane sulfonyl) imide in appropriate molar ratios at room temperature. The said ILs can be formed in polyether, polyester, and polyurea grease and show better solubility in these base oils than commonly used ILs such as 1-methyl-3-hexylimidazolium hexafluorophosphate (L-P106). They can significantly improve the friction-reducing and antiwear properties of the base oils.     

Ionic Liquids as Lubricants of Titanium–Steel Contact

The friction and wear behavior of grade 3 titanium have been studied against AISI 52100 steel at room temperature and at 100 °C, in the presence of six ionic liquid (IL) lubricants, four imidazolium ILs, 1-ethyl-3-methylimidazolium tetrafluoroborate (L102), 1-octyl,-3-methylimidazolium tetrafluoroborate (L108), 1-hexyl, 3-methylimidazolium hexafluorophosphate (L-P106) and 1-benzyl,3-methylimidazolium chloride (ClB), and two quaternary ammonium salts, the chloride derivative AMMOENG™ 101 (AM-101) and the dihydrogenphosphate AMMOENG™ 112 (AM-112), and compared with that of a mineral base oil. At room temperature, all ILs, except L102, give similar mean friction values, below 0.20, with a 60% reduction with respect to the mineral oil. All ILs, except L102, also reduce titanium wear rates. The poor performance of the short alkyl chain tetrafluoroborate L102 is due to tribocorrosion. The best antiwear performance at room temperature is found for the imidazolium chloride (ClB), although corrosion of the AISI 52100 steel ball is observed. At 100 °C, L-P106 maintains the room temperature friction values and shows a 80% wear rate reduction with respect to room temperature. L-108 fails at 100 °C after a sliding distance of 200 m due to decomposition and tribocorrosion. The friction and wear mechanisms and surface interactions are discussed from friction–sliding distance curves, SEM, EDS and XPS analysis, and XRD data.     

Study of the Conductivity and Tribological Performance of Ionic Liquid and Lithium Greases

Ionic liquid (IL) lubricating greases were prepared using 1-hexyl-3-methylimidazolium tetrafluoroborate and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide as base oil and polytetrafluoroethylene (PTFE) as thickener, respectively. Three kinds of lithium greases were also prepared using lithium ILs ([Li(PAG)]X) as base oil and PTFE as thickener. 1-Ethyl-3-methyl imidazolium hexafluorophosphate as an additive was added to the PAG grease, which was prepared using polyalkylene glycol monobutyl ether (PAG) as base oil and PTFE as thickener. The conductivities and tribological properties of the prepared lubricating greases were investigated in detail. Scanning electron microscopy and X-ray photoelectron spectroscopy were employed to explore the friction and wear mechanism. The results showed that the IL and lithium lubricating greases have conductivities and excellent tribological properties. Especially, IL greases have the highest conductivity. The excellent tribological properties are attributed to the formation of boundary films consisting of both tribo-chemical reaction films and physical absorption films, while high conductivities are attributed to the intrinsic electric fields of the ILs.     

Conductive Lubricating Grease Synthesized Using the Ionic Liquid

Two kinds of new conductive lubricating greases were synthesized using 1-octyl-3-methylimidazolium hexafluorophosphate and 1-octyl-3-methylimidazolium tetrafluoroborate as base oil and the polytetrafluoroethylene as thickener. The conductivities of the new conductive lubricating greases are higher than the traditional conductive lubricating greases which contains conductive stuffing. In addition, the physical and tribological properties of the new lubricating greases were investigated in detail. The results show that the new lubricating grease show better friction reducing and anti-wear properties than the lubricating grease based on PAO10 at room temperature and 150 °C. The worn surfaces were observed and analyzed by scanning electron microscope and X-ray photoelectron spectroscope. Also, the possible friction mechanisms for the new lubricating greases are proposed.     

Ionic Liquids as Lubricants of Titanium–Steel Contact. Part 2: Friction, Wear and Surface Interactions at High Temperature

The tribological behaviour and surface interactions of titanium sliding against AISI 52100 steel have been studied at 200 and 300 °C in the presence of two commercial imidazolium room temperature ionic liquid (ILs): 1-octyl-3-methylimidazolium tetrafluoroborate (L108) and 1-hexyl-3-methylimidazolium hexafluorophosphate (LP106). L108 presents the higher thermal stability but gives higher friction coefficients and wear rates than LP106, with long running-in periods and high friction values, both at 200 and 300 °C. Friction and wear rates for LP106 are lower and decrease as the temperature increases from 25 to 200 °C. At 200 °C, LP106 shows a constant friction coefficient, without running-in, produces a mild wear on titanium and no surface damage on steel. LP106 fails at 300 °C, close to its degradation temperature, due to tribochemical decomposition through partial dissociation of the hexafluorophosphate anion, with formation of a phosphorus-rich layer on the steel ball, while the titanium wear track surface is heterogeneous, showing regions with the presence of fluoride and others with the presence of phosphate. When the steel ball is substituted for a ruby sphere under the same conditions at 300 °C, a low friction coefficient and mild wear is observed, due to the higher stability of the LP106 lubricant at the ruby–titanium interface. The friction coefficients, wear mechanisms and surface interactions have been studied by means of friction-distance records, SEM, EDX and XPS.     

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.     

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.     

Comparative study of the tribological properties of ionic liquids as additives of the attapulgite and bentone greases

Three kinds of ionic liquids (1‐butyl‐3‐methylimidazolium hexafluorophosphate (L‐P104), 1‐hexyl‐3‐methyl imidazolium hexafluorophosphate (L‐P106) and 1‐octyl‐3‐methylimidazolium tetrafluoroborate (LB108)) were added to the attapulgite base grease and the bentone base grease to investigate and compare the tribological behaviours of the ionic liquids with the two base greases at room temperature and 150°C. Tribological tests were performed using a ball‐on‐plate reciprocating tribometer. The attapulgite base grease showed better wear resistance properties than that of bentone base grease by adding ionic liquids as additives. At same time, the attapulgite base grease showed excellent friction‐reducing and wear resistance properties at high temperature (150°C). Also, we discussed the tribological mechanism of the attapulgite base grease at both room temperature and 150°C from the aspect of the structure of the grease thicker. Copyright © 2012 John Wiley & Sons, Ltd.     

Tribological behaviour of two imidazolium ionic liquids as lubricant additives for steel/steel contacts

In this paper two room-temperature ionic liquids (ILs), 1-hexyl-3-methylimidazolium tetrafluroborate [HMIM][BF₄] and 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM][PF₆], have been studied as 1%wt. additives of a mineral hydrocracking oil for steel–steel contacts. Rheological properties of the mixtures and base oil were determined over shear rates and temperatures ranging 1–1000 s^?1 and 40–100 °C, respectively. Friction and wear testing was made using a block-on-ring tribometer set for pure sliding contact and XPS was used to analyze wear surfaces. [HMIM][PF₆] and [HMIM][BF₄] increased the viscosity of the base oil and decreased friction and wear. Friction and wear reduction are related to reactivity of the anion of the ionic liquids with surfaces forming FeF₃, B₂O₃, and species such as P₂O₅ or PO₄^3?.     

Imidazolium hexafluorophosphate ionic liquids as high temperature lubricants for steel–steel contacts

A series of long-chain 1,3-dialkyl imidazolium ionic liquids (ILs) were synthesized and evaluated as lubricants for steel–steel contacts both at room temperature and 150 °C. Relationship between the alkyl chain length and the tribological properties of the ILs was investigated in detail. The results indicated that the ILs bearing long alkyl side chains have excellent friction-reducing and anti-wear properties, especially at high temperatures and high loads. The worn surfaces of steel discs were observed and analyzed by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The friction reduction and load carrying capacity were supposed to be due to the formation of high quality boundary films consisting of both tribochemical reaction film and the ordered absorption film.     

Tribological Behavior of Protic Ionic Liquids with Dodecylamine Salts of Dialkyldithiocarbamate as Additives in Lithium Complex Grease

Three kinds of protic ionic liquids with ammonium salts, dodecylamine salt of S-(1-carboxyl)-propyl-N, N-diethyldithiocarbamate (coded as DDED), dodecylamine salt of S-(1-carboxyl)-propyl-N, N-dibutyldithiocarbamate (coded as DDBD), dodecylamine salt of S-(1-carboxyl)-propyl-N, N-dioctyldithiocarbamate (coded as DDOD) were synthesized, characterized, and their tribological behaviors as additives in lithium complex grease were studied for steel/steel contact. The tribological properties were evaluated on an Optimol SRV-I oscillating reciprocating friction and wear tester and a MRS-10A lever-type fourball tester in details. The results of tests demonstrated that the novel additives were able to remarkably improve the extreme pressure, friction-reducing, and anti-wear properties of the base lithium complex grease when added at a low adding concentration (<3?%). Based on the performance comparison of three novel additives with different chain lengths in DTCs groups and a commercial additive with similar DTCs groups but no PILs groups, methylene bis dibutyldithiocarbamate (T323), a number of primary conclusions were drawn. The carboxylic acid ammonium salts, the typical function groups of the PILs existing in the molecule structures of three additives, could not only greatly enhance the physical and/or chemical adsorption on the metal surface to reduce friction of the base grease, and also have better synergism with DTCs groups in improving anti-wear performance of base grease. Based on the characterization and analysis of the worn surface by a PHI-5702 multifunctional X-ray photoelectron spectrometer (XPS) and a JSM-5600LV scanning electron microscope (SEM), a protective film consisting of FeS, organic compound was formed on the surface. The ordered adsorbed film and chemical reactive film on the sliding steels contributed to the main factor in improving the tribological properties of base lithium complex grease.     

Effect of Imidazolium Ionic Liquid Additives on Lubrication Performance of Propylene Carbonate under Different Electrical Potentials

Three different ionic liquids (ILs), 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIm]BF₄), 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIm]PF₆) and 1-decyl-3-methylimidazolium hexafluorophosphate ([DMIm]PF₆), were used as additives in the base ester propylene carbonate (PC) for the lubrication of AISI 4340 steel surfaces. Ball-on-disk friction tests were done under different electrical potentials to investigate the synergetic effect of IL concentration and electrical potential on lubrication performance, and electrochemical and ellipsometric tests were conducted to explore the adsorption of IL additives at different potentials. The friction reduction and anti-wear performance of the tested three IL/PC solutions illustrated similar dependence on electrical potential. In the potential range from ?0.6 to +0.6 V, friction coefficient increases rapidly. When the potential is more negative than ?0.6 V, friction coefficient is at the lower level of about 0.13. When the potential is greater than +0.6 V, friction coefficient is at the higher level of about 0.2. The electrochemical test results show that [DMIm]PF₆/PC solution is the lowest in corrosion against AISI 4340 steel among the three tested lubricants. The wear of steel surface in 0.5 mM [DMIm]PF₆/PC solution is reduced when electrical potential is shifted to ?1.0 V comparing with that at open-circuit potential. The potential-dependent friction and wear behaviors are explained in terms of the variation of the adsorbed ion species and the surface concentration of the adsorbed ions under different additive concentration and electrical potential conditions.     

The Influences of Methyl Group at C2 Position in Imidazolium Ring on Tribological Properties

Tribological properties of two kinds of imidazolium ionic liquids (ILs) of 1,2-dimethyl-3-hexylimidazolium bis(trifluoromethylsulfonyl)imide (L-F116) and 1-dimethyl-3-hexylimidazolium bis(trifluoromethylsulfonyl)imide (L-F106) were evaluated as lubricant additives in poly(ethylene glycol) (PEG) for the steel–steel sliding pair by using an Optimol-SRV oscillating friction and wear test at the room temperature. At the same time, their electrochemical corrosion behaviors were measured by Tafel polarization. The morphologies of the worn surfaces were observed using a scanning electron microscope (SEM). The chemical states of several typical elements on the worn surfaces were examined by means of X-ray photoelectron spectroscopy (XPS). The results show that corrosion phenomena of PEG containing ILs on pure copper are negligible compared to PEG at room temperature. The 2-substituted imidazolium IL L-F116 shows excellent tribological performance and is superior to L-F106 in terms of anti-wear performance and load-carrying capacity. The worn surfaces were characterized to have slight abrasion and the XPS results indicated the formation of tribochemical adsorption and chemical reaction films on the worn surfaces.     

Tribological characteristics of bisphenol S bis(diphenyl phosphate) as a high‐performance antiwear additive in lubricating greases at elevated temperature

Bisphenol S bis(diphenyl phosphate) (BSDP) was synthesised and characterised, and its tribological behaviours as additives in polyurea grease and lithium complex grease were evaluated for steel/steel contact at 200 °C. The results indicated that BSDP could dramatically reduce the friction and wear of sliding pairs in the base grease of polyurea, and the tribological performances of BSDP in polyurea grease were significantly superior to the normally used molybdenum disulfide‐based additive package. Furthermore, BSDP in polyurea grease has better tribological behaviour than that in lithium complex grease at a constant load of 100 N. X‐ray photoelectron spectroscopy analysis indicated that boundary lubrication films composed of Fe(OH)O, Fe₂O₃, Fe₃O₄ and FePO₄ compounds containing the P–O bonds and nitride compounds were formed on the worn surface, which resulted in excellent friction reduction and antiwear performance. Copyright © 2016 John Wiley & Sons, Ltd.     

含纳米CuO锂基润滑脂摩擦学性能研究

为改善锂基润滑脂摩擦学性能,制备不同添加量纳米CuO改性的锂基润滑脂。采用3H-2000PS2比表面及微孔分析仪对纳米CuO粒子进行表征,采用四球摩擦磨损试验机分析纳米CuO添加量对锂基润滑脂摩擦学性能的影响,采用扫描电镜(SEM)和三维形貌分析仪分析试验后钢球磨痕形貌。结果表明:纳米CuO质量分数为0.60%时锂基润滑脂具有最佳的抗磨减摩效果,摩擦因数和磨斑直径较基础脂分别降低24%和12%;一定添加量下,纳米CuO对磨损表面具有修复作用,含质量分数0.60%纳米氧化铜的润滑脂润滑时,磨损表面具有较低的表面粗糙度和较少的犁沟,表现出最佳的抗磨性能。     

Lubrication Mechanism of Phosphonium Phosphate Ionic Liquid Additive in Alkylborane–Imidazole Complexes

The assessment of ionic liquids (ILs) as lubricants in several tribological systems has shown their ability to provide remarkable reduced friction and protection against wear, whether they are used as additives or in the neat form. However, their corrosion and limited solubility in non-polar hydrocarbon oils represent the bottleneck-limiting factors for the use of ILs as lubricants. Therefore, in order to tackle these problems, mixtures of alkylborane–imidazole complexes with one halogen-free IL as additive were used in this study. The knowledge of the additive–surface interactions and hence the understanding of tribological properties are an important issue for lubricant formulations and were also investigated in this work. Thus, combination effects between two ionic liquid additives, a halogenated and a halogen-free one, were evaluated by a ball-on-disc-type tribometer under boundary lubrication conditions. Effective friction reduction and anti-wear properties have been demonstrated in tribological investigations when adding between 0.7 and 3.4 wt% of the halogen-free IL into base fluid composed of alkylborane–imidazole complexes. X-ray photoelectron spectroscopy analyses of the steel specimens were conducted to study the correlation between tribological properties and chemical surface composition of the boundary films formed on the rubbing surface. This work suggests potential applications for using halogen-free ILs as additives for synthetic ionic liquid lubricants.     

油胺修饰镍纳米粒子在锂基脂中的摩擦学性能*

为提高镍纳米粒子作为润滑脂添加剂的减摩和抗磨能力,采用油胺对其进行修饰以减少团聚,通过SEM、FT-IR和XRD对OA-Ni的微观形态和结构进行了表征,利用四球摩擦试验机和TE77往复摩擦试验机考察表面修饰的镍纳米粒子(OA-Ni)对锂基润滑脂摩擦学性能的影响,并探讨其在润滑脂中的减摩抗磨机制。结果表明:制备的油胺修饰镍纳米粒子呈不规则的圆片状,粒径约为100 nm,在润滑脂中有良好的分散性;经油胺表面改性的镍纳米粒子能有效改善锂基脂的摩擦学性能,抗磨和减摩性能分别提升了36.6%和15%。磨损表面分析结果表明,在摩擦过程中油胺修饰的镍纳米粒子在摩擦表面形成了主要成分为Fe2O3、 Fe3O4、NiO、Ni2O3等金属氧化物的摩擦化学膜,提高了锂基脂的摩擦学性能。     

Benzimidazolyl phosphates as anti‐wear additives in poly(ethylene glycol) for steel/steel contacts

Four novel benzimidazolyl phosphates (BPs) were synthesized and evaluated as anti‐wear additives in poly(ethylene glycol) for steel/steel contacts. The friction experiments were carried out on an Optimol SRV‐I oscillating reciprocating friction and wear tester (SRV) both at room temperature and high temperature. The worn surfaces of the steel discs were analysed by JSM‐5600LV scanning electron microscope and PHI‐5702 multifunctional X‐ray photoelectron spectrometer. It was indicated that poly(ethylene glycol) with 2 wt% BP additives had better friction‐reducing and anti‐wear properties than the commercial lubricant additive, tricresyl phosphate. Excellent tribological performance of BPs could be ascribed to the formation of high quality boundary films that consisted of the ordered adsorption films and tribo‐chemical reaction films. Copyright © 2013 John Wiley & Sons, Ltd.     

磁性润滑脂抗磨减摩性能的试验研究

以Fe3O4磁性微粒为添加剂制备了一种磁性润滑脂,在摩擦磨损试验机上考察了其摩擦学特性,并分析了其抗磨减摩机制.结果表明:Fe3O4磁性润滑脂对负荷的适应性较好,特别是在较大载荷、中高转速情况下,具有很好的抗磨性.     

Tribological performance of phosphonium based ionic liquids for an aluminum-on-steel system and opinions on lubrication mechanism

A series of asymmetrical tetraalkylphosphonium ionic liquids were synthesized and evaluated as a new kind of lubricant for the contacts of steel/Al using an Optimol SRV oscillating friction and wear tester in ambient condition. The phosphonium ionic liquid shows excellent tribological performance and is superior to the conventional ionic liquids 1-ethy-3-hexylimidazolium hexafluorophosphate (P206) in terms of anti-wear performance and load-carrying capacity. The chemical compositions of the boundary film generated on different contact surfaces were analyzed on a scanning electron microscope with a Kevex energy dispersive X-ray analyzer attachment (SEM/EDS) and X-ray photoelectron spectrometer (XPS). The friction-reduction and anti-wear mechanism were proposed to originate from the layered structure of ionic liquid under boundary lubrication and the tribochemical reaction of anions with the fresh surface, respectively.