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OVER the years lithium soap greases have earned a reputation of providing excellent service under a wide variety of operating conditions. Since their introduction in the early 1950s, lithium soap greases have served the market well, being especially suitable for both automotive and industrial multipurpose applications. Their performance has enabled them to grow in commercial importance to the point where they now account for over half the grease volume manufactured in the United States.

This paper aims to improve the tribological properties of lithium complex greases using nanoparticles to investigate the tribological behavior of single additives (nano-TiO₂ or nano-CeO₂) and composite additives (nano-TiO₂–CeO₂) in lithium complex greases and to analyze the mechanism of their influence using a variety of characterization tools.

The morphology and microstructure of the nanoparticles were characterized by scanning electron microscopy and an X-ray diffractometer. The tribological properties of different nanoparticles, as well as compounded nanoparticles as greases, were evaluated. Average friction coefficients and wear diameters were analyzed. Scanning electron microscopy and three-dimensional topography were used to analyze the surface topography of worn steel balls. The elements present on the worn steel balls’ surface were analyzed using energy-dispersive spectroscopy and X-ray photoelectron spectroscopy.

The results showed that the coefficient of friction (COF) of grease with all three nanoparticles added was low. The grease-containing composite nanoparticles exhibited a lower COF and superior anti-wear properties. The sample displayed its optimal tribological performance when the ratio of TiO₂ to CeO₂ was 6:4, resulting in a 30.5% reduction in the COF and a 29.2% decrease in wear spot diameter compared to the original grease. Additionally, the roughness of the worn spot surface and the maximum depth of the wear mark were significantly reduced.

The main innovation of this study is the first mixing of nano-TiO₂ and nano-CeO₂ with different sizes and properties as compound lithium grease additives to significantly enhance the anti-wear and friction reduction properties of this grease. The results of friction experiments with a single additive are used as a basis to explore the synergistic lubrication mechanism of the compounded nanoparticles. This innovative approach provides a new reference and direction for future research and development of grease additives.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2023-0291/

The purpose of this paper is to formulate heavy-duty lithium complex grease using low molecular weight poly tetra fluoro ethylene (PTFE) micro-particles as extreme pressure (EP) additive manufactured by E-beam scissoring and ultra-high speed grinding process of pre-sintered PTFE scrap.

Lithium complex grease is formulated with PTFE micro-particles, and optimum treat rate was studied by standard bench tests by ASTM D 2266 and IP-239 for tribological properties and compared with commercially available Molybdenum Di sulphide (Moly)-based lithium complex grease. The performance of the grease was further evaluated by a cyclic load test at varying speeds and loads to simulate the operational field conditions.

The lithium complex PTFE grease was manufactured using PTFE micro-particles as EP additive. The PTFE micro-particles dispersed in the lithium complex grease significantly improve the anti-wear performance and load bearing properties. Further, when the product was tested under a cyclic load conditions on standard tribological bench test against commercially available Moly lithium complex grease, shows stable anti-wear properties and reduced coefficient of friction.

The low molecular weight PTFE micro-particles, manufactured in the in-house electron beam (E-beam) and ultra-high speed micronizer facility from a pre-sintered PTFE scrap has been used as EP additive for grease applications for the first time. The results on the cyclic load tests indicate significant performance improvement in retaining the anti-wear and friction properties. Thus, value addition is done in formulating superior performance grease and evaluating under cyclic load conditions similar to field operating conditions and also in creating value added additives by converting the pre-sintered PTFE scarp which is environmental hazard due to poor biodegradability, creating a cyclic economy and a sustainable concept.

A joint paper by G. L. HARTING, of Exxon Research and Engineering Company and T. C. WILSON, Exxon Company of USA present a joint paper at the National Lubricating Grease Institute annual general meeting.

Describes the structure and rheological characteristics of soap based greases and how the thickener retains the oil phase. Illustrates the thixotropic behaviour and effect of time of shearing on friction, film thickness, noise energy loss in grease lubricated contacts. Shows how friction can be less with grease than with oil.

This study aims to probe the applicability of 2-mercaptobenzothiazole (MBT) functionalized ionic liquids (ILs) as additives in lithium complex grease (LCG) by researching the corrosion inhibiting, rheological and tribological performances.

Electrochemical tests such as electrochemical impedance spectroscopy and potentiodynamic polarization curves were used on Gamry electrochemical workstation to research the corrosion inhibition properties of ILs in 1.0 M HCl corrosive solution. The rheological properties of different grease samples were tested on a rheometer. The tribological properties were investigated on SRV-V oscillating reciprocating friction and wear tester. Scanning electron microscope, X-ray spectrometer and X-ray photoelectron spectrometer were used to characterize the lubricating mechanism.

The 2-MBT functionalized ILs have excellent corrosion inhibition properties. When used as additives in LCG, they both exhibited enhancing effects on thermostability, colloid stability and structural recoverability, and furthermore, outstanding friction-reducing and antiwear properties were also obtained. Surface analysis indicated that the superior lubricating performances of 2-MBT functionalized ILs were mainly ascribed to the formation of tribochemical products on wear tracks, including organic compounds with C–O bond, Fe₂O₃ and FeS₂.

The 2-MBT-based ILs synthesized in this study were multifunctional additives with excellent corrosion inhibiting and tribological properties, which would have a very broad application prospect in lubricating grease industry.

The purpose of this paper is to synthesize a kind of core-shell Ag@polyaniline (Ag@PAN) as a lubricant additive to improve the friction reduction and anti-wear abilities of lithium-based complex grease.

The core-shell Ag@PAN was prepared by a simple method and was introduced into the lithium-based complex grease. The typical properties of Ag@PAN were investigated by scanning electron microscopy (SEM), Fourier transforms infrared spectrometer and thermal gravimetric analyzer. The tribological properties were evaluated under different conditions. After the tribological test, the worn surface was analyzed by SEM and X-ray photoelectron spectroscopy to probe the lubrication mechanisms.

The prepared Ag@PAN could greatly improve the friction reduction and wear resistance of the friction pair under different conditions. The preferable tribological performances were mainly attributed to the synergism of various lubrication mechanisms including “mending effect,” “rolling effect” and lubricating protective film, and so on.

This study synthesizes a new kind of core-shell Ag@PAN as a lubricant additive, and it possesses preferable friction reduction and anti-wear abilities.

The purpose of this paper is to synthesize a new kind of conductive grease which possesses a prominent conductive capacity and good tribological properties.

A two-step method was used to prepare complex lithium-based grease. Ketjen black (KB), acetylene black (AB) and carbon black (CB) were characterized by transmission electron microscope and used as lubricant additives to prepare conductive greases. Conductive capacity was evaluated by a conductivity meter, a surface volume resistivity meter and a circuit resistance meter. Tribological properties were investigated by a reciprocating friction and wear tester (MFT-R4000). The worn surfaces were analyzed by a scanning electron microscope, Raman spectroscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscope.

The conductive grease prepared with KB has a prominent conductive capacity at room temperature, 100°C and 150°C. Further, this conductive grease also possesses better tribological properties than AB and KB greases. When the concentration of KB is 1.8 Wt.%, the coefficient of friction and wear width reduced by 11 and 14 per cent, respectively.

This work is a new application of nanometer KB as a lubricant additive in grease, which provides a direction for preparing conductive grease. The conductivity and tribology experiments have been carried out though the variation of experiment conductions.

Nanoparticles as the grease additives play an important role in anti-wear and friction-reducing property during the mechanical operation. To improve the lubrication action of grease, the tribological behavior of lithium-based greases with single (nanometer Al₂O₃ or nanometer ZnO) and composite additives (Al₂O₃–ZnO nanoparticles) were investigated in this paper.

The morphology and microstructure of nanoparticles were characterized by means of transmission electron microscope and X-ray diffraction. Tribological properties of different nanoparticles as additives in lithium-based greases were evaluated using a universal friction and wear testing machine. In addition, the friction coefficient (COF) and wear scar diameter were analyzed. The surface morphology and element overlay of the worn steel surface were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), respectively.

The results show that the greases with nanometer Al₂O₃ or nanometer ZnO and the composite nanoparticles additives both exhibit lower COFs and wear scar diameters than those of base grease. And the grease with Al₂O₃–ZnO composite nanoparticles possesses much lower COF and shows much better wear resistance than greases with single additives. When the additives contents are 0.4 Wt.% Al₂O₃ and 0.6 Wt.% ZnO, the composite nanoparticles-based grease exhibits the lowest mean COF (0.04) and wear scar diameter (0.65 mm), which is about 160% and 28% lower than those of base grease, respectively.

The main innovative thought of this work lies in dealing with the grease using single or composite nanoparticles. And through a serial contrast experiments, the anti-wear and friction-reducing property with different nanoparticles additives in lithium grease are evaluated.

This paper aims to contrastively investigate the antioxidant behavior and tribological performance of a novel multifunctional additive (PBT) and dialkyldithiophosphate (ZDDP) in complex lithium grease (CLG).

PBT was successfully synthesized through esterification reaction. The antioxidant behavior of PBT and ZDDP was investigated by thermal analysis, and meanwhile, their tribological performance was evaluated by Optimol SRV-IV oscillating reciprocating friction and wear tester (SRV-IV test) and MRS-1J four-ball tester (Four-ball test). Furthermore, their anticorrosion ability was determined by copper strip corrosion test.

Four-ball tests showed that the extreme pressure property of PBT was a little inferior to that of ZDDP. Besides, all the other results demonstrated that PBT showed more superior antioxidation stability, friction-reduction and antiwear ability, as well as anticorrosion performance than ZDDP.

This work provides a study of hindered phenol derivative as a multifunctional additive in lubricant grease, which can contribute to the development of substitution of ZDDP.