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The purpose of this study is to reduce the use of Zinc dialkyl dithiophosphates (ZDDP) and improve the frictional properties and thermal oxidation stability of Perfluoropolyether (PFPE) grease by adding antioxidant additives. The addition of antioxidants can reduce the consumption of ZDDP as an antioxidant, thus improving the anti-wear efficiency of ZDDP and reducing the excess phosphorus element in the grease.

In this study, an antioxidant with good comprehensive performance was selected from several antioxidants by tribological tests and high-temperature tests. Then, the effect of its combination additive with ZDDP on PFPE grease was investigated. The anti-wear property, anti-friction property, thermal oxidation stability and extreme pressure property of greases containing different proportions of ZDDP and antioxidant were tested by four-ball tester and synchronous thermal analyzer (STA). The effects of additives on properties of grease were analyzed by SEM, EDS, LSCM, XPS and FT-IR.

The research shows that 2,6-Di-tert-butyl-4-methylphenol (BHT) can be used as an antioxidant in combined additives to reduce the antioxidant reactions of ZDDP, thus improving the anti-wear efficiency of ZDDP and further enhancing the anti-wear performance of the grease. Moreover, BHT and ZDDP have a synergistic effect on the high temperature performance of the PFPE grease due to their different antioxidant mechanisms.

In this paper, the problems related to PFPE grease are studied, which has a certain guiding effect on the industrial application of fluorine grease and the related formulation design.

In this paper, the properties of PFPE grease under different lubricating condition were studied. The synergistic lubrication effect of antioxidant and ZDDP are discussed. It provides experimental and theoretical support for reducing the content of ZDDP and improving the performance of additives.

This paper aims to report the tribological behavior of Ag nanoparticles/reduced graphene oxide nanocomposites (Ag/RGO NCs) and Ag nanoparticles (Ag NPs) as a green additive in oil with different concentration and under different friction conditions.

The Ag/RGO NCs and Ag NPs were both synthesized in a chemical reduction method. The diameter of silver nanoparticles implanted between RGO sheets was about 25 nm and that of silver sol was 70 nm. The morphology and structure of Ag/RGO NC were characterized by TEM, XRD and FTIR. The tribological properties of Ag/RGO NCs and Ag NPs as lubricant oil additive were evaluated by measuring the friction coefficients and wear of the surface in different condition which were tested on UMT-II.

The results indicated that both the additives improved the friction-reduced and anti-wear properties of paraffin oil, and Ag/RGO NCs has better tribological performance than Ag NPs. The excellent tribological properties were attributed to the special structure of Ag/RGO NC and the formation of tribofilm reducing the friction and wear on the shearing surfaces.

It is relatively difficult to observe the morphology of the lubricant film formed on the friction surface and to analyze the chemical composition at different depths of the lubricant film.

It is the first time for Ag/RGO NCs to be applied to improve the friction-reduced and anti-wear properties of lubricant oil as additive.

The purpose of this paper is to study the influence of alkyl chain length and kind of anions of ionic liquids on the tribological properties with different materials as friction pairs (steel-aluminum, steel-copper and steel-Si3N4 ceramic).

Tribological properties were evaluated by an optimol-SRV-IV reciprocation friction tester with a ball-on-block configuration at room temperature and high temperature, respectively. Friction-reducing and anti-wear properties of the ionic liquids for steel/aluminum, steel/copper and steel/ceramic contacts were evaluated on the ball-on-block reciprocating UMT-2MT tribometer. The morphologies of the worn surfaces were observed by a scanning electron microscope. The chemical states of several typical elements on the worn surfaces were examined by X-ray photoelectron spectroscopy.

Both the alkyl chain length and kind of anion influence the tribological properties of ionic liquids, especially for the length of alkyl chains. With the increase of alkyl chain length, the load carrying capacity of ionic liquids is improved at both room temperature and high temperature, and the friction reducing and antiwear behaviors are also significantly enhanced.

The paper presents potentially useful and highly efficient lubricants.

Owing to their good friction-reducing and wear resistance properties, these ionic liquids are promising candidates for versatile applications.

This work might provide a promising research direction for design and application of ionic liquids as lubricants.

This paper aims to determine a suitable anti-wear and friction-reducing compounding additive for lithium greases (LG) by investigating the effects of three single additives potassium borate (PB), zinc dialkyl dithiophosphate and molybdenum dialkyl dithiophosphate (MoDDP) and two compound additives on the friction, wear and extreme pressure properties of LG.

The effects of the above five additives on the friction, wear and extreme pressure properties of LG were investigated using an SRV-5 friction tester. An X-ray photoelectron spectrometer was used to analyze the various elements presented on the wear surface as well as the types of compounds.

The compound additive suitable for grease consists of PB and MoDDP, which have excellent friction reduction, anti-wear and extreme pressure properties. And a boundary protection film consisting of oxide and MoS₂ is formed on the friction surface, thus improving the friction reduction and anti-wear performance of the grease.

This study can improve the anti-wear and friction-reduction performance of greases, which is of great importance in the field of industrial lubrication. The results of this paper are expected to be useful to researchers and academics of grease.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2022-0350/

The purpose of this paper is to investigate that if the lubrication system of a helicopter reducer is compromised, its gears and bearings will be at non-lubricating oil work state, which causes the reducer to be damaged in a very short time.

Various 2 per cent additives were injected and mixed with aeronautical oil to produce 45-min oil/mist lubrication and oil/air lubrication experiments performed upon aeronautical steel tribo-pairs.

The results show that the best anti-wear effect is produced by oil/air lubrication that contains 2 per cent T391. It consumes the least quantity of oil and produces the least wear width, the least rise in temperature and the best surface wear quality.

The technology of oil/air lubrication that contains an extreme-pressure and anti-wear additive is a feasible way to improve the operational ability of a helicopter transmission system that is out of oil.

This paper aims at understanding tribological properties of lubricating oils doped with zinc dithiophosphate(ZDDP) with and without electromagnetic field impact.

The friction and wear properties of the oils formulated with zinc butyloctyl dithiophosphate (T202) or zinc dioctyl dithiophosphate (T203) under electromagnetic field or nonelectromagnetic field were evaluated on a modified four-ball tribotester. The characteristics of the worn surfaces obtained from electromagnetic or nonelectromagnetic field conditions were analyzed by scanning electronic microscopy, energy dispersive spectrometer and X-ray photoelectron spectroscopy. This paper focuses on understanding influence of electromagnetic field on lubrication effect of the ZDDP-formulated oils.

The electromagnetic field could effectively facilitate anti-wear and friction-reducing properties of the oils doped with T202 or T203 as compared to those without electromagnetism affection, and the T203-doped oils were more susceptible to the electromagnetic field. The improvement of anti-wear and friction-reducing abilities of the tested oils were mainly attributed to the promoted tribochemical reactions and the modification of the worn surfaces (forming Zn-Fe solid solution) induced by the electromagnetic field.

This paper has revealed that tribological performances of ZDDP-doped oils could be improved by the electromagnetic field and discussed its lubrication mechanisms. Investigating tribological properties of additives from the viewpoint of electromagnetics is a new attempt, which has significance not only for the choose and designing of additives in electromagnetic condition but also for development of tribological theories and practices.

Thiadiazole compounds and their derivatives have carrying capacity and good lubricating properties. However, their poor oil-solubility limited their wide usage in lubricating oil. The study aims to develop thiadiazole lubricant additives with better oil-solubility. When the hindered phenol antioxidation functional group and alkyl-chain are introduced to thiadiazole, the resulting product could have better oil-solubility and excellent antioxidation resistance, anti-wear and corrosion resistance in the lubricating oil.

One kind of thiadiazole lubricant additive, for the first time, has been synthesized from 2,5-dimercapto-1,3,4-thiadiazole. Its tribological performance has also been evaluated by four-ball test. And, its oxidation resistance has been estimated by rotating pressure vessel oxidation test and pressurized differential scanning calorimetry. The anticorrosion performance of such an additive has been studied by GB/T 5096 standard method test.

The synthesized thiadiazole additive has excellent anti-oxidation capability, good anti-wear and extreme pressure properties and good anticorrosion performance, in comparison with zinc dialkyl dithiophosphate (ZDDP). In base oils, the comprehensive performance of thiadiazole additive is comparable to ZDDP. Mechanistic studies indicate that the S and N active elements were involved in the formation of a boundary film. This may account for the formation of a composite membrane on the metal surface and thus for the tribological performance of such thiadiazole additives.

The thiadiazole derivatives, which are ashless and have environmentally friendly features, are a potential alternative to ZDDP. Because of the film formed on the friction surface, thiadiazole compounds may serve as an excellent anti-wear additive and are expected to reduce friction and wear between metals.

The purpose of this paper is to study the tribological properties of a thiazole derivatives (T561), overbased alkyl benzene calcium sulfonate (T106A) compounded with T561 and overbased alkyl benzene magnesium sulfonate (T107) compounded with T561 in rapeseed oil (RSO).

A four-ball machine was used to evaluate the tribological properties of each compound and their combinations with T561 in RSO. Scanning electron microscopy, EDX and X-ray photoelectron spectroscopy were applied to analyze the tribofilm formed on the worn surfaces.

Results of tribotesting demonstrated that synergistic effects exist between the overbased sulfonates, T106A and T107, and the thiazole derivative, T561. The texts of tribofilm indicated that iron sulfide and iron oxides exist in T561 single agent lubricant film and two composite additives lubricant film, and no sulfates were detected. It suggested that the addition of alkyl benzene sulfonate did not hinder the formation of iron sulfides and iron oxides. Meanwhile, CaSO₄ (MgSO₄) and CaCO₃ (MgCO₃) were detected on the worn surface of the composite additives, which were not detected on the single agent friction surface.

A tribofilm mainly contains CaSO₄ (MgSO₄) and CaCO₃ (MgCO₃) formed on the worn surfaces, which is responsible for excellent extreme pressure and anti-wear properties of the compound agents because of their high melting point and high shear stress.

The purpose of this paper is to study the tribological effect of zinc borate ultrafine powder (ZBUP) oil additive on the running-in quality.

The running-in quality was assessed by friction coefficient and surface topography. Fractal parameters including fractal dimension, the width of multifractal, the multifractal difference, multifractal parameters, phase trajectory and correlation dimension were used to extract the nonlinear characteristics of surface topography and friction coefficient.

When the ZBUP additive was added, the convergence degree of the phase trajectory and the stability of the running in were higher than that of base oil. It indicates that the ZBUP additive can improve the running-in quality of sliding bearing. Besides, the ZBUP additive can shorten the running-in time. A boundary protective film, which has good friction-reducing and anti-wear effects, was generated on the surface when the ZBUP additive was added.

The results have a great significance to improve the running-in quality and prolong the service life of the sliding bearing.

The purpose of this study is to evaluate the effect of water contamination on ageing of lubricants.

The viscosity, total acid number and Fourier transform infrared spectrum of a series of lubricants after ageing with water were studied. The tribological performance (friction and wear) of the aged lubricants was also analyzed, followed by X-ray photoelectron spectroscopy analysis on the selected post test samples to study the tribochemical features of the tribofilm.

The results were also compared with Part I of this study, and it was found that ageing has a different impact on lubricants and tribological performances based on the physical and chemical properties when water is present in the lubricants.

This paper is a continuation of Part I of this study and gives an understanding on the impact of water on the lubricants and related tribological and tribochemical performance.