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Ultra-high molecular weight polyethylene (UHMWPE) has an excellent performance and application value; however, as a tribological material, its main drawback is its poor performance under dry friction, impacting its ability to work in high-speed dry friction conditions. Modification of UHMWPE can be carried out to overcome these issues. A significant number of inorganic materials have been used to modify UHMWPE and provide it with good tribological performance. However, thus far, there has been no systematic investigation into the methodology of modifying UHMWPE. The authors take a quantitative approach to determine the structure tribo-ability relationship and basic principles of screening of inorganic compounds suited to modify UHMWPE.

The tribological properties of modified UHMWPE using a series of inorganic additives have been qualitatively studied by the authors’ research group previously. In this study, basic quantitative structure tribo-ability relationships (QSTRs) of inorganic additives for modifying UHMWPE were studied to predict tribological properties. A set of 15 inorganic compounds and their tribological data were used to study the predictive capability of QSTR towards inorganic additives properties.

The results show that the anti-wear and friction-reducing properties of these inorganic compounds correlate with the calculated parameters of entropy and dipole moment. Increased entropy and smaller dipole moment can effectively improve the anti-wear and friction-reducing ability of inorganic compounds as UHMWPE additives. Additives with larger molecular weight, lower hardness and lower melting and boiling points provide good tribological properties for UHMWPE. For inorganic compounds to act as UHMWPE additives, the chemical bond should be less covalent and have more ionic character.

Only 15 inorganic compounds and their tribological data were used to study the predictive capability of QSTR towards inorganic additives properties. If the samples number is more than 30, the other QSTR methodology can be used to study the modified UHMWPE, and the models finding can be more precise.

A QSTR model for modified UHMWPE has been studied systematically. While the results are not more precise and detailed, the model provides a new way to explore the modified UHMWPE characteristics and to reveal new insight into the friction and wear process.

Because the method of studying tribological materials is entirely different from others, the authors want to present the works and discuss it with colleagues.

The paper presents a new method to study the modified UHMWPE. A QSTR is used to study the tribology capability of compounds from calculated structure descriptors. This study uses the Hartree–Fock ab initio method to establish a QSTR prediction model to estimate the ability of 15 inorganic compounds to act as anti-wear and friction-reducing additives for UHMWPE.

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/

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 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.

The purpose of this paper is to understand the impacts of oleoyl glycine on biodegradation, friction and wear performances of a mineral lubricating oil.

The biodegradabilities of a neat oil and its formulations with oleoyl glycine were evaluated on a biodegradation tester and the microbial characters in the biodegradation sewage observed through a microscope. Also, the friction and wear performances of neat oil and the formulated oil were determined on a four‐ball tribometer. The morphologies and tribochemical features of the worn surfaces were analyzed by scanning electron microscopy and X‐ray photoelectron spectroscopy.

Oleoyl glycine markedly enhanced biodegradation of unreadily biodegradable mineral oil and effectively improved its anti‐wear and friction‐reducing abilities. The enhancement of biodegradability of the mineral oil was preliminarily ascribed to the increment of microbial populations in the biodegradation processes, while the improvement of anti‐wear and friction‐reducing abilities was mainly attributed to the formation of a boundary adsorption film of oleoyl glycine on the friction surfaces.

Oleoyl glycine is a biodegradable and low eco‐toxic compound. The authors' work has shown that oleoyl glycine is effective in improving biodegradability and tribological performances of mineral lubricants. Enhancing biodegradability of petroleum‐based lubricants by additives is a new attempt. The paper has significance for improving ecological and tribological performances of mineral lubricants, even for developing petroleum‐based biodegradable lubricants.

The purpose of this paper is to understand the effect of base media on the tribological performance and tribochemistry of bismuth thiophosphate additive.

The oil‐water double soluble additive bismuth dithiophosphate was prepared and identified. The contributions of the two base media on the additive tribological behavior and the tribofilm components were comparatively studied.

The extreme pressure (EP) and friction‐reducing properties are remarkably improved with water substituted for paraffin as the base medium. The EP performance of the lubricating media containing this additive mainly results from the tribochemical reaction film on the rubbing surface, not from the viscosity of the base media. In water or paraffin medium, the adsorption process of this additive from the lubricant bulk onto the rubbing surface and the components and the properties of the tribochemical reaction films formed are different, which have important effect on the tribological performance.

The paper mainly focuses on how the water medium with polarity and the liquid paraffin base medium with non‐polarity affect on the tribological performance of the bismuth thiophosphate additive.

The research has found a water‐oil double soluble lubrication additive with outstanding EP and friction‐reducing performance.

The designed experiment provides a new approach to further learn the action mechanism of thiophosphate additive.

The purpose of this paper is to test two kinds of rare earth complexes of Lanthanum Dialkyldithiophosphate (LaDDP) and Lanthanum Dialkylphosphate (LaDP) as lubricant additives in liquid paraffin for the untreated 60Si2Mn steel and laser‐cladding Ni35A coating on 60Si2Mn steel sliding pairs which are a potential substitute for Zinc Dialkldithiophosphate (ZnDDP).

Tribological properties were evaluated by an Optimol‐SRV oscillating friction and wear test. The morphologies of the worn surfaces were observed by a scanning electron microscope (SEM), and the chemical states of several typical elements on the worn surfaces were examined by means of X‐ray photoelectron spectroscopy (XPS).

Treated laser cladding coatings of steel can improve its hardness and strength and the coated steel possess higher load‐carrying capacity than that of 60Si2Mn; The rare earth complexes of LaDDP and LaDP possess good oil‐solubility, friction‐reducing and wear resistance properties. Those rare earth complexes as additives in liquid paraffin during the friction process can form a protective film containing rare earth oxide, sulfate and sulfur‐containing compound during the friction process.

The paper presents two kinds of potentially useful, environmentally‐friendly and highly efficient substitutes for the ZnDDP additives in lubricants.

Owing to their good friction‐reducing and wear resistance properties, LaDDP and LaDP are two optimum and promising industry lubrication additives.

This work is a new application of rare earth complex as lubricant additive in liquid paraffin, which provides a new direction for designing friction pairs and lubricant additive. The tribology experiments have been carried out through the variation of experiment conditions.

The purpose of this paper is to prove the self‐repairing Cu film of Cu‐DDP additive in base lubricating oil.

Cu nanoparticles coated with dialkydithiophosphate (Coded as Cu‐DDP) were synthesized in situ by redox method. The size and structure of Cu‐DDP were characterized using transmission electronic microscopy (TEM) and electronic diffraction (ED) analysis. The self‐repairing performance of Cu‐DDP as additive in base lubricating oil was evaluated by MRH‐3 stock‐on‐ring testing machine. Scanning electronic microscopy (SEM), UMT‐2 tribometer, X‐ray photoelectron spectroscopy (XPS), and energy‐dispersive spectrum (EDS) were used to study the self‐repairing Cu film on the stock.

The test results showed that the modified Cu‐DDP additive in base lubricating oil exhibited excellent anti‐wear and friction‐reducing properties, as well as good self‐repairing performance.

The thickness of the self‐repairing Cu film was unknown, and the relationship between thickness of the Cu film and load, time, rotation velocity was still necessary to investigate.

The Cu‐DDP additive was involved P and S elements, therefore, it is still promising to seek environment friendly additive without P and S elements.

For the first time, MRH‐3 stock‐on‐ring testing machine, Scanning electronic microscopy (SEM), UMT‐2 tribometer, X‐ray photoelectron spectroscopy (XPS), and energy‐dispersive spectrum (EDS) were widely used to study the self‐repairing Cu film on the stock.

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.

The purpose of this paper is to investigate the tribological properties of novel phosphorous-nitrogen (P-N) type additives in water.

The tribological properties of the novel P-N additives in water are compared with a commercial lubricant additive of the P-N type using a four-ball machine. The tribological mechanism was investigated by X-ray absorption near-edge structure (XANES) spectroscopy.

The experimental results indicate that the phosphoramidate derivatives possess good anti-wear and friction-reducing properties. The XANES analysis shows that the prepared compounds can form a protective film containing phosphate and/or polyphosphate that affects the tribological behavior.

The purpose of this paper is to investigate the tribological properties of the novel P-N type additives in water.