Alkyl Imidazolium Ionic Liquids as Friction Reduction and Anti-Wear Additive in Polyurea Grease for Steel/Steel Contacts

Five room temperature ionic liquids (ILs), 1-butyl-3-methylimidazolium hexafluorophosphate (L-P104), 1-hexyl-3-methylimidazolium hexafluorophosphate (L-P106), 1-octyl-3-methylimidazolium hexafluorophosphate (L-P108), 1-decyl-3-methylimidazolium hexafluorophosphate (L-P110), and 1-hexyl-3-methylimidazolium tetrafluoroborate (LB106) were studied as 1 wt% additives of polyurea grease for steel/steel contacts. Their tribological behaviors as additives of polyurea grease for steel/steel contacts were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester and an MRS-1J (G) four-ball tester at room and high temperatures. The friction test results showed that the ILs, as 1 wt% additives in polyurea grease for steel/steel contacts, had better friction reduction and anti-wear properties at high temperature than at room temperature, and ILs can significantly improve the friction reduction and anti-wear properties of polyurea grease compared with base grease containing 1 wt% of zinc dialkyldithiophosphate (T204). The excellent tribological properties are attributed to the formation of a surface protective film composed of FeF₂, nitrides, and compound containing the P–O bonding on the lubricated metal surface by a tribochemical reaction. The ordered adsorbed films and good miscibility of ILs with the base grease also contributed to the excellent tribological properties. Wear mechanisms and worn steel surfaces were studied by a PHI-5702 multifunctional X-ray photoelectron spectrometer and a JSM-5600LV scanning electron microscope.     

Oil‐soluble lithium salts as novel lubricant additives towards improving conductivity and tribological performance of bentone grease

The tribological and conductive properties of three kinds of lithium salts (LiBF₄, LiPF₆ and LiNTf₂) as lubricating additives in bentone grease were investigated in detail. As compared with the bentone‐based grease, the lithium salts as its additives not only provide excellent tribological properties but also greatly improve the load‐carrying capacity and electrical conductivity. These benefits are strongly dependent on the formation of a versatile boundary lubricating film and ion diffusion of lithium salts through an external electric field effect. Copyright © 2014 John Wiley & Sons, Ltd.     

Tribological investigation of CaF2 nanocrystals as grease additives

Calcium fluoride (CaF₂) nanocrystals with average grain size of 60 nm were synthesized via a precipitation method. The morphology and structure of nanocrystals were characterized by means of transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). TEM and XRD showed that CaF₂ nanocrystals are cubic particles in submicron scale. The tribological properties of the prepared CaF₂ nanocrystals as an additive in lithium grease were evaluated with a four-ball tester. The results indicated that these nanocrystals exhibit excellent antiwear, friction reduction and extreme pressure (EP) properties. It was also found that the EP and antiwear capabilities of the grease are not proportional to the content of CaF₂ nanocrystals but there existed a certain value. The rubbed surface after friction test was investigated with X-ray photoelectron spectroscopy and scanning electron microscopy to understand the action mechanism. The results show that a boundary film mainly composed of CaF₂, CaO, iron oxide and some organic compounds was formed on the rubbed surface after friction test and the thickness of boundary film was about 12 nm. The disproportion of stoichiometric ratio of Ca and F in boundary lubrication film indicates that tribochemical reaction of CaF₂ nanocrystals occurred on the worn steel surface at severe tribological conditions.     

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。     

混合纳米粒子作为润滑脂添加剂最佳配比的实验研究

在MRH-3型高速环块摩擦磨损试验机上,研究混合纳米粒子Al2O3-Al-Cu和Al2O3-Al-MgO作为润滑脂添加剂的摩擦学性能,通过减摩、表面修复以及抗极压性能实验,确定混合纳米粒子的最佳配比。结果表明:在几种纳米粒子之间的协同作用下,含有混合粒子Al2O3-Al-Cu和Al2O3-Al-MgO的润滑脂具有良好的表面修复、抗极压等摩擦学特性,混合粒子比多数单粒子在减摩方面都具有更好的效果。     

几种纳米粒子作为润滑脂修复添加剂的试验研究

在MRH-3高速环块摩擦磨损实验机上,研究了纳米微粒Cu,Al,Al2O3,MgO加入到通用锂基脂中的摩擦学性能。并采用扫描电子显微镜,能量色散谱仪分析了摩擦表面的形貌和元素组成。结果表明:含有纳米Cu,Al,Al2O3,MgO粒子的润滑脂对摩擦表面均有很好的减摩和修复能力,但各种粒子的效果有所不同,其中Al2O3,Cu,Al3种粒子要比MgO具有更好的效果。     

改性复合磺酸钙基润滑脂的研究

高碱值复合磺酸钙基润滑脂综合性能优异,被称为全新理念的润滑脂,但容易产生硬化问题。对复合磺酸钙基润滑脂进行了改性处理,并且对其硬化机制作了初步分析。结果表明:改性后的复合磺酸钙基润滑脂综合了复合锂基脂、聚脲基脂和复合磺酸钙基脂的性能优势,不仅解决了硬化问题,且该润滑脂具有特殊的纤维结构,从而赋予其极高的滴点、良好的高温极压润滑性能和低的摩擦因数。     

Tribological properties of nano‐calcium borate as lithium grease additive

Nano‐calcium borate (NCB) with an average particle size of about 70 nm was synthesised via ethanol supercritical fluid drying technique, and the morphology and microstructures of as‐prepared particles were characterised by means of scanning electron microscope (SEM, JEOL LTD., Tokyo, Japan) and X‐ray powder diffraction. The friction and wear behaviour of the NCB as additive in lithium grease were evaluated with an Optimol‐SRV IV (Optimol Instruments Prüftechnik GmbH, Munich, Germany) oscillating friction and wear tester (SRV tester). The morphology and surface composition of the worn surfaces of lower discs after SRV test were analysed by SEM and X‐ray photoelectron spectroscopy (XPS, Physical Electronics, Inc., USA). The result demonstrated that the anti‐wear and load‐carrying capacities of the lithium grease were significantly improved, and the friction coefficient of the lithium grease decreased with the addition of NCB additive. The analytical results of XPS indicate that the good tribological performance of NCB is attributable to the formation of a boundary lubrication film composed of deposited NCB and the tribochemical reaction products such as B₂O₃, CaO and iron oxides on the rubbing surface. Copyright © 2013 John Wiley & Sons, Ltd.     

The effect of space irradiation on the lubricating performance of perfluoropolyether greases in simulated space environment

In this paper, 2 kinds of commercial perfluoropolyether (PFPE) greases were coated on the polyimide (PI) blocks, which were placed within simulated space environment including atomic oxygen (AO), proton (Pr), ultraviolet (UV), and electron (El) irradiations, and then the tribological performance has been investigated with a ball‐on‐disc tribometer. Results indicated that the MoS₂‐grease showed better lubrication performance than the PTFE‐grease. The changes in infrared spectroscopy induced by Pr and El irradiations were more obvious than that by AO and UV irradiations. Results of energy dispersive X‐ray spectroscopy indicated that Pr and El irradiations caused carbonation of greases, and AO and UV irradiations induced oxidation of greases. Referred to the tribological properties of PI coated with PFPE oil, PI coated with PFPE greases showed minor changes in friction coefficient and wear rate, and the MoS₂ additives could significantly improve the lubrication properties of PFPE greases in simulated space environment.     

Tribological Performance and Surface Analysis of a Borate Calcium as Additive in Lithium and Polyurea Greases

In this work, a borate calcium additive was added to lithium and polyurea greases to investigate the tribological performance. Friction and wear tests were conducted on a four-ball machine under higher load and a reciprocating tribometer under lower load. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analyses were performed on the worn surface after the tests. It was found that the tribological performance affected the boundary layers formed by the additive and the soap fibers. The boundary films in lithium grease mainly consist of ferrum hydroxide, and more oxide can be found in polyurea-based films. SEM analyses of soap fibers show that the soap fibers in polyurea-based grease were more separated than those in lithium-based grease. Compared to the base grease, the soap shows smaller and shorter fibers.     

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 behaviours of ultrafine Sn/heat treated serpentine powder in grease

Abstract

In order to improve the tribological performance of traditionally based lithium grease, ultrafine serpentine powder of 0·33 μm and Sn powder of 120 nm were prepared by ball mill and direct current arc plasma evaporation respectively. The milled serpentine powder was heat treated at 200, 500, 600 and 800°C in a muffle furnace separately with a four-ball wear test. Then, the tribological behaviours of lithium grease modified with complex powder with different ratios of ultrafine Sn/heat treated serpentine were investigated, and the effects of total concentration and load were discussed too. The optimal performance was achieved by the compound grease with 1 wt-% complex powder and 1∶1 Sn/serpentine powder (heated at 200°C). The friction coefficient and wear scar diameter decreased 25·5 and 42·5% respectively under 392 N compared with pure grease. The compound grease is much more suitable under high load rather than low load.     

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。     

Tribological Behavior of Amorphous and Crystalline Overbased Calcium Sulfonate as Additives in Lithium Complex Grease

The aim of this study was to examine the tribological behavior of amorphous overbased calcium sulfonate (AOBCS) and crystalline overbased calcium sulfonate (COBCS, transformed from the AOBCS) as additives in lithium complex grease. The transformation product of the calcium carbonate polymorph from AOBCS was calcite, as determined by Fourier transform infrared spectroscopy. Tribological properties were evaluated by an oscillating reciprocating friction and wear tester and a four-ball tester. The results showed that the addition of COBCS can dramatically improve both the antiwear performance and the friction-reducing and load-carrying properties of the base grease. However, improvement of the tribological properties of the base grease by AOBCS was highly dependent on the concentrations added and the loads applied. The tribological properties of the base grease were improved more by the addition of COBCS than by the addition of AOBCS. X-ray photoelectron energy spectrometry and thermogravimetric analysis revealed that both AOBCS and COBCS underwent complicated tribochemical reactions in the base grease and that chemically reactive films consisting of CaCO₃, CaO, iron oxide and organic compounds were formed on the worn surfaces. Taken together with the results of the tribo-tests, we suggest that transformation of the calcium carbonate polymorphs was the main factor in improving the tribological properties of lithium complex grease. The transformation of calcium carbonate polymorphs can broaden the application of AOBCS as an extreme pressure/antiwear additive in greases under boundary lubrication conditions.     

Tribological properties of 3 types of MoS2 additives in different base greases

A tribological comparison was conducted among micro‐MoS₂ (m‐MoS₂), platelet‐like nano‐MoS₂, and spherical nano‐MoS₂ in lithium grease, lithium‐calcium grease, and polyurea grease, respectively. Micro‐MoS₂ slightly improved the lubrication of the 3 greases. The 2 nano‐MoS₂ samples had obvious superiority over m‐MoS₂. The tribofilms produced by nano‐MoS₂ contained MoS₂ and MoO₃. However, the tribofilms with m‐MoS₂ did not contain Mo, or Mo only existed in the form of MoO₃. The absence of MoS₂ in tribofilms was the main reason for the poor lubrication of m‐MoS₂ greases. Moreover, the improved lubrication of the spherical nano‐MoS₂ greases than the platelet‐like nano‐MoS₂ ones was ascribed to the lubricating superiority of the spherical structure to the platelet‐like one.     

The Preparation and Tribological Investigation of Ni–P Amorphous Alloy Nanoparticles

Amorphous Ni–P alloy nanoparticles were synthesized by chemical reduction of nickel acetate in water reacted with sodium hypophosphite under stirring. The nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Results of XRD and TEM showed that nanoparticles have an average diameter 100 nm. And XPS analysis indicated that part of the surface of Ni–P amorphous alloy nanoparticles was oxidized. The tribological properties of the prepared Ni–P nanoparticles as an additive in lithium grease were evaluated with a four-ball friction and wear tester. The worn surfaces of the lubricated GCr15 steel were analyzed by means of XPS and scanning electron microscopy (SEM). The lubricating mechanisms were discussed on the basis of XPS and SEM analyses of the worn steel surfaces. The results show that these nanoparticles as a grease additive can effectively enhance the friction-reduction and antiwear ability of lithium grease. Tribochemical reactions were involved for steel–steel frictional pair lubricated with the lithium grease containing amorphous Ni–P alloy nanoparticles, with the formation of a boundary lubricating and protecting film composed of additives of lithium grease and tribochemical reaction products (iron phosphate, iron oxides, nickel oxide, nickel, etc.) of the lubricants. This contributes to improve the tribological properties of the lithium grease.     

Effect of Cu Nanoparticles on the Tribological Performance of Attapulgite Base Grease

This study investigated the effect of Cu nanoparticles on the tribological properties of attapulgite base grease. It was found that the friction reduction ability and antiwear property of the base grease can be improved with the addition of Cu nanoparticles. Under the lubrication of grease containing Cu nanoparticles, a smoother and more compact tribofilm was formed on the rubbing surface. The tribofilm is mainly composed of Cu, FeO, Fe₂O₃, FeOOH, CuO, and SiO. In addition, the content of iron oxides and silicate oxide formed in the tribofilm was increased by the introduction of Cu nanoparticles.     

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.     

表面未修饰及修饰纳米SiO2对锂基脂摩擦学性能的影响

利用四球摩擦磨损试验机考察了表面未修饰及修饰纳米SiO2作为添加剂对锂基脂摩擦学性能的影响;采用扫描电子显微镜观察了钢球磨损表面形貌,并采用X射线光电子能谱仪分析了钢球磨损表面典型元素的化学状态,以探讨2种纳米SiO2添加剂的减摩抗磨作用机理。结果表明,采用化学法和物理法制备的表面修饰及未修饰纳米SiO2作为添加剂均能通过形成复合边界润滑膜而改善锂基脂的减摩抗磨性能,其中采用物理法制备的未修饰纳米SiO2的减摩作用略优,而采用化学法制备的表面修饰纳米SiO2在高载荷下的抗磨作用较优。     

Preparation and tribological properties of the N‐containing heterocyclic borate esters and Cu microparticles as lubricant additives in base oil

In this paper, four kinds of N‐containing heterocyclic borate esters and polyvinyl pyrrolidone‐protected Cu microparticles were synthesised and characterised. Their tribological properties as lubricant additives in industrial white oil were evaluated using a four‐ball tribometer, and their lubrication mechanisms were investigated by X‐ray photoelectron spectroscopy. The results showed that the anti‐friction and anti‐wear performance of the base oil can be significantly improved by the addition of N‐containing borate esters and Cu microparticles, and they present synergistic tribological effect. Moreover, X‐ray photoelectron spectroscopy results showed a lubricating tribochemical reaction film containing B₂O₃, FeB, FeO, Fe₂O₃ and so on is formed on the worn surface. In addition, Cu microparticles as rolling bearings, which transform sliding friction to rolling sliding and the formation of the Cu microparticles deposited film, are probably responsible for the improvement of tribological performance. Copyright © 2017 John Wiley & Sons, Ltd.