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The purpose of this paper is to investigate the tribological performance of graphene oxide (GO) sheets as water-based lubricant additive when ultra-high molecular weight polyethylene (UHMWPE) plates slid against 316L stainless steel ball using a reciprocating tribometre.

The factors influencing the tribological performance were considered, including the viscosity of the GO dispersion, normal load, sliding velocity and the roughness of UHMWPE. The surface microstructure and properties of UHMWPE were studied by means of scanning electron microscopy, laser confocal microscopy, Raman spectroscopy and contact angle measurements.

The results revealed that the GO dispersion reduced friction and sliding-wear. The surface images of the wear UHMWPE plates indicated that GO sheets were prone to adsorption on the surface and form a thin physical tribofilms at the substrate.

Based on the experimental findings for the evolution of the microstructure morphology and the development of subsurface cracks, less debris and cracking can be observed in the UHMWPE plates lubricated by GO dispersion.

This paper sets out to study tribological properties, anticorrosive performances and thermal stabilities of two novel S‐N type triazinyl‐containing polysulfides {Bis[2,4‐bis(diethylamino)‐s‐triazin‐6‐yl] polysulfide (BBET‐PS) and Bis[2,4‐bis(di‐n‐butylamino)‐s‐triazin‐6‐yl] polysulfide (BBBT‐PS)} as additives in biodegradable grease, and to estimate the tribochemical mechanism.

Extreme pressure (EP) and anti‐wear (AW) properties of two compounds at different addition concentration were evaluated using a four‐ball machine. Their wear scar was analyzed with X‐ray photoelectron spectroscopy (XPS) and a scanning electron microscope.

Two novel S‐N type triazinyl‐containing polysulfides possess excellent load‐carrying capacity, good AW and show good corrosion‐inhibiting performance. The thermal stability of BBB‐PS is better than that of BBE‐PS. According to the XPS results, the triazinyl‐containing polysulfides react with the metal to generate a surface protective film consisting of sulfate, FeS and absorbed compounds containing organic‐N.

The antioxidant and biodegradability of the two novel compounds were not investigated.

Two effective EP and AW additives were synthesized, and maybe potentially industrial applied lubricating grease additives.

The achievement of this study is the synthesis of two triazinyl‐containing polysulfides, which can be effective additives to improve the tribological performance of biodegradable grease.

The purpose of the research was to test whether the novel synthesized additive TEAT can be a substitution for the traditional additive ZDDP partly or entirely in mineral oil.

The extreme pressure, antiwear (AW) and friction reducing property of TEAT was examined, the tribological property of the combination of TEAT and ZDDP was also examined. The worn surfaces of the steel balls were observed using a polarizing optical microscope and x‐ray absorption near edge structure spectroscopy.

The results show that: TEAT can enhance the P_B value of the base oil obviously; TEAT shows better AW performance than ZDDP in high load and a wide range of concentration, it shows better friction‐reducing performance than ZDDP in high load and all the concentration tested; TEAT alone can provide a better AW and friction reducing property than ZDDP and the combination of TEAT and ZDDP; and the tribochemical reaction occurs between novel compound and metallic surface, generating sulfur containing layer mainly exists in the form of FeS.

These findings indicate that TEAT presents better tribological properties than ZDDP in a wide range of practical conditions. TEAT may be a substitute for ZDDP in the future.

To study some tribochemical properties of tetrazole derivatives, n‐hexadecanyl (1H‐tetrazol‐1‐yl) acetate (HTA) and 1‐phenyl‐5‐(octylthio)‐tetrazole (PCT) as lubricating oil additives in hydrogenised oil, and estimate the action mechanism.Design/methodology/approach – The two tetrazole compounds were synthesized, and added them in hydrogenised oil with different concentrations. Their anti‐wear properties were evaluated with a four‐ball machine, the wear scar was analyzed with a X‐ray photoelectron spectroscopy (XPS).Findings – The novel compounds possess good anti‐wear, friction reduction properties and good load‐carrying capacity. According to the XPS results, the novel compounds were migrated onto the surface of the steel balls and adsorbed on the surface. The two additive compounds, themselves, and their decomposers contributed to the corresponding tribological performances. With S element contained in the compound PCT, the influence on the load‐carrying capacity of the base oil was enhanced. It may be due to the formation of S²⁻ and SO₄²⁻ compounds on the worn surface which could form a protective film.Research limitations/implications – Their antioxidant, anticorrosion, anti‐wear properties are not estimated.Practical implications – Two useful EP and AW lubricating oil additives were synthesized, and maybe it is the potential industrial applied lubricating oil additives.Originality/value – This paper provided a study way of some N‐containing heterocyclic compounds as lubricating oil additives.

The aim of this paper is to study the tribological performance and self-repairing performance of surface-modified nanoscale serpentine powders as lubricant additives in the mineral base oil (5-CST).

Fourier transform infrared spectroscopy spectra and thermo-gravimetric analysis of both modified and unmodified serpentine were performed to analyse their grafting ratio and suspension after modified using a long-chain naphthene aliphatic acid. The tribological properties of surface-modified serpentine as lubricant additives in 5-CST were evaluated and the worn surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES).

The results show that the serpentine particles have high grafting ratio, improving the dispersity in 5-CST. When the serpentine concentration of 1.00 weight per cent is used as additives in 5-CST, friction coefficient reduces by 14.80 per cent under 294 N and wear scar diameter (WSD) decreases by 11.82 per cent. The results of X-ray absorption near edge structure and XANES show that the adsorption and tribochemical reactions occur to form self-repairing lubrication films.

The paper illustrates a tribofilm form on the rubbed surface, which is responsible for the decrease in friction and wear, mainly containing iron oxides, silicon oxides, magnesium oxides and organic compounds. The results are useful for further applications in advanced environmental friendly lubricating oils and additives.

Nanoparticles are not well dispersed in non‐polar organic solvents due to their hydrophilic property which limits their applications in lubricant oils. To improve the oil‐solubility of nanoparticles, a novel technology was used to prepare a kind of lubricant containing calcium borate nanoparticles.

The microstructures of the prepared nanoparticles were characterized by transmission electron microscope (TEM) and infrared spectra (IR). Tribological properties of calcium borate nanoparticles used as additive in base oil were evaluated using four‐ball tribotester and SRV tribotester, and the worn surface of the steel ball was investigated by Polarized microscope (PM) and X‐ray photoelectron spectroscopy (XPS). In addition, the dispersing stability and antioxidation property of lubricant containing nanoparticles were also studied.

The results indicate that the average size of the prepared nanoparticles is in the range of 50‐100 nm, and the surface of the nanoparticles was altered from hydrophilicity to hydrophobicity. At the same time, the nanoparticles can be well dispersed in the base oil totally under novel process which has no significantly negative effect on the antioxidation property. The results of tribological tests show that calcium borate nanoparticles under the novel process (CBNN) show better antiwear property and friction‐reducing property in base oil compared to calcium borate nanoparticles under tradition process (CBNT). Based on the results of PM and XPS, it can be deduced that a continuous resistance film containing depositions and the tribochemical reaction products such as B₂O₃, FeB, Fe₂O₃ and CaO formed during the sliding process.

The main innovative thought of this work lies in dealing with the oil‐solubility problem through the combination effect of surface modification and special blend process of lubricating oil, and this method was first used to prepare lubricant containing calcium borate nanoparticles. It should be helpful for the borate nanoparticles used as additives in engine oil, gear oil and other industrial lubricants.

As multifunctional additives, ZDDP, which provides excellent oxidation resistance and superior antiwear properties, has been used widely in lubricants, however, it shows oppositional effect with friction modifiers when used together. In this paper, an attempt is made to find a novel kind of borate ester which can be used as potential substitute for ZDDP.

A novel borate ester containing dialkylthiophosphate group was prepared and characterized. Its tribological properties as an additive in synthetic ester were evaluated using a four‐ball tribometer and antioxidative ability tested by pressurized differential scanning calorimetry (PDSC). Thermal degradation tests were conducted to identify its thermal stabilities using thermogravimetric analyzer (TGA). The worn surface of the steel ball was investigated by X‐ray photoelectron spectroscopy (XPS) and the antiwear mechanism of the additive was preliminarily discussed.

Results show the additive possesses outstanding loading‐carrying and friction‐reducing properties, compared with ZDDP, and can improve antiwear properties of the base oil dramatically. Moreover, it also has excellent antioxidation performance and thermal stability.

This paper provides a multifunctional ashless additive which possesses excellent tribological properties, and gives another selection for industrial applications in which ZDDP is needed.

Sulfurized olefins have been extensively used in many kinds of gear lubricants as EP additives. However, their commercial applications are not totally satisfactory because of the pungent, obnoxious odor and corrosion of copper and copper alloys. The purpose of this paper is to investigate the synergistic effects of one type of calcium borate nanoparticles modified by oleic acid (code to CaBN) and sulfurized olefin, in a kind of mineral base oil MVIS 250, in order to find a potential substitute for sulfurized olefins.

One kind of calcium borate nanoparticle modified by oleic acid (CaBN) was prepared, and its structures were characterized by inductively coupled plasma atomic emission spectroscopy (ICP‐AES), X‐ray power diffraction (XRD) and transmission electron microscope (TEM). The tribological properties of the complex of CaBN with sulfurized olefins (T321) in base oil were evaluated using four‐ball tribotester and compared with CaBN or T321 as individual component. The worn surfaces were investigated by scanning electron microscope (SEM) and X‐ray photoelectron spectroscopy (XPS). In addition, the corrosion‐inhibiting properties of additives were also studied.

The results of tests show that there are significant synergistic effects on tribological properties between two kinds of additives. Based on the results of SEM and XPS, it can be deduced that a wear resistance film containing B₂O₃, FeS, FeS₂ and CaO was formed on the worn surfaces during the sliding process. Moreover, CaBN and T321 also show excellent synergistic effect on the corrosion‐inhibiting property.

This paper provides a kind of “green” nanoparticle which possesses excellent synergic effect with sulfurized olefins, and gives another selection for industrial applications in which T321 is needed.

In order to develop novel high EP S‐containing additives and to meet the need of formulating GL‐5 gear oil or other high EP lubricating oils, aims to investigate the tribological behaviors and mechanism of a di(iso‐butyl)polysulfide (DIBPS), which was synthesized from some cheap materials at low temperature and under normal atmospheric pressure, as an additive in some mineral base oils compared with the traditional sulfurized olefin (SO) additive.

The DIBPS additive was designed and synthesized, of which the main composition is the di(iso‐butyl)trisulfide. Its load‐carrying capacity, anti‐wear and friction reduction properties as additive in some mineral base oils, compared with the traditional SO additive, were investigated using a four‐ball machine and a Timken tester according to relative testing standards. The tribological mechanism was discussed according to the SEM and XPS analytical data.

The results indicate that the four‐ball P_D value and the Timken OK value of the prepared DIBPS in VHVIS500 is clearly better than that of the traditional SO; the anti‐wear property of DIBPS is equivalent to the traditional SO and the friction reduction effect of DIBPS is better than that of the traditional SO. The SEM and XPS data show that the DIBPS additive experiences different tribochemical reaction during tribological process compared with the traditional SO. The S active element of DIBPS reacted with surface metal mainly to form FeSO₄ and/or Fe₂(SO₄)₃ inorganic film, but the S active element of the traditional SO reacted with the surface metal mainly to form FeS inorganic film. This may be the chief reason why the prepared DIBPS possesses better EP properties than the SO.

The results show that the polysulfide additive (DIBPS) possesses better extreme pressure property than the traditional SO. However, more experimental study such as the synergic effect with other additives must be performed, from which it will be clearly shown whether the novel polysulfide can be applied in industrial oils.

These results may be useful for the researchers to formulate some high EP industrial oils.

This paper proves that the designed polysulfide additive, of which the main composition is the trisulfide, possesses better extreme pressure property than the traditional SO, and its tribological mechanicsm is also different with that of SO. It is noticed that the preparative method of this novel polysulfide additive has some superiorities, such as: low‐experimental temperature, low‐experimental pressure and cheap materials.

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.