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Purpose – The purpose of this paper is to study the influences of test conditions to the tribological behavior of LaF3 nanoparticles as an additive to a polyalphaolefin (PAO). Design/methodology/approach – An Optimol-SRV4 oscillating friction and wear tester (SRV) were used to investigate the tribological properties of LaF3 nanoparticles as an additive in a polyalphaolefin (PAO). The 3-D morphologies and wear loss volume of the worn scar were measured using a surface profilometer. The chemical state and the intensity of La and F elements on worn surface after friction test was investigated with X-ray photoelectron spectroscopy to interpret the possible mechanisms of friction-reduction and anti-wear with LaF3 nanoparticles. Findings – The experimental results show that LaF3 nanoparticles added to PAO exhibit excellent load-carrying capacity, anti-wear and friction-reduction properties. LaF3 nanoparticles deposited on the worn surface under lower test temperature during the friction test, and higher applied load, higher test frequency and longer test duration are propitious to the deposition of LaF3 nanoparticles accumulated on the rubbing surface. Under higher temperature, a complicated tribo-chemical reaction occurred during the friction process, the tribo-chemical reaction product of La2O3 deposit on worn surface, which also exhibits good lubricating performance. Originality/value – This paper investigates the tribological properties of LaF3 nanoparticles as green oil additive in poly-alpha-olefin (PAO) under variable temperature, applied load, sliding speed and sliding duration. The results could be very helpful for the further applications of LaF3 nanoparticles additives in industry. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to study the tribological performance of tri(hydroxymethyl)propane esters containing boron and nitrogen as lubricant additives in rapeseed oil. Design/methodology/approach – Thermal degradation tests were performed to analyze their thermal stability using a thermo-gravimetric analyzer. Two four-ball testers were used to measure the tribological properties of tri(hydroxymethyl)propane esters containing boron and nitrogen as lubricant additives in rapeseed oil. The worn surfaces of steel balls were investigated by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Findings – The results show that the tri(hydroxymethyl)propane esters containing boron and nitrogen have excellent thermal stability, good antiwear performance, improve the load-carrying capacity, and possess friction-reducing behavior especially at 98 N when they are used as additives in rapeseed oil. The results of XPS show that the adsorption and tribochemical reactions have been occurred to form a complex boundary lubrication film. Originality/value – The paper illustrates two novel tri(hydroxymethyl)propane esters which contain B and N elements used as additives in rapeseed oil. The results are useful for further applications in advanced environment friendly lubricating oils and additives. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to prepare water-soluble TiO2 nanoparticles and evaluate the tribological properties as additives in water. Design/methodology/approach – Nanoparticles present excellent friction-reducing and antiwear properties as additives in base oils. However, there are seldom literatures about the nanoparticles as additives in water as yet. In this work, water-soluble TiO2 nanoparticles were prepared by sol-gel method and characterized with transmission electron microscopy and selected area electron diffraction. The tribological properties as additives in water were investigated by SRV and the surface analysis by scanning electron microscope and X-ray photon electron spectroscope. Findings – TiO2 nanoparticles modified with polyethylene glycol have uniform size about 10 nm and easily dissolve in water. The tribological experiments showed TiO2 nanoparticles exhibit excellent friction-reducing and antiwear properties. Research limitations/implications – The paper is restricted to only TiO2 nanoparticles. Some other water-soluble nanoparticles also should be prepared and their tribological properties investigated. Practical implications – Water-soluble TiO2 nanoparticles could be used as water additives and improve the tribological properties. Originality/value – This paper emphasises that the water-soluble nanoparticles are prepared and could be used as water additives. [ABSTRACT FROM AUTHOR]

Purpose – 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. Design/methodology/approach – 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. Findings – The results indicate that the four-ball PD 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. Research limitations/implications – 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. Practical implications – These results may be useful for the researchers to formulate some high EP industrial oils. Originality/value – 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. [ABSTRACT FROM AUTHOR]

Purpose – 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. [ABSTRACT FROM AUTHOR]

Purpose – In order to formulate ashless GL-5 gear oils and high-pressure antiwear hydraulic oils, the performances of extreme-pressure (EP) and antiwear (AW), and the thermal and hydrolytic stability of series ashless P-containing additives with different chemical structures are investigated by four-ball EP test, high-temperature oxidation test and hydrolytic stability test.Design/methodology/approach – Series ashless P-containing EP and AW additives with different chemical structures were designed and selected, their EP and AW performances, high-temperature oxidation, hydrolytic stability compared with the traditional zinc dialkyldithiophosphate (ZDDP) additive were investigated according to relative testing standards, and their applied performances compared with the traditional ZDDP additive were investigated using the CRC L-37 gear oil rear axle test, Deniso T-5D Vane Pump test and Deniso P-46 Piston Pump test.Findings – The results indicate that two ashless neutral thiophosphate esters exhibit excellent EP and AW performances, high-temperature oxidation and hydrolytic stability. The application performance of these P-containing additives is also examined by CRC L-37 rear axle test. The results show that only the oil samples with the addition of neutral thiophosphate esters correspondingly to API GL-5 automotive gear oil can pass the CRC L-37 gear oil rear axle test successfully. The results of further Deniso T-5D Vane Pump and Deniso P-46 Piston Pump tests prove that the ashless neutral thiophosphate ester is a very effective EP/AW additive for high-pressure antiwear hydraulic oil. In one sentence, the neutral thiophosphate ester is the excellent ashless EP/AW additive and the useful substitute for ZDDP.Research limitations/implications – From the results, the neutral thiophosphate ester is the excellent ashless EP/AW additive and the useful substitute for ZDDP, however, their tribological mechanicsm and their synergic effect with the other additives used in the test base oil for the applied performance tests may be done in the future works.Practical implications – These results may be useful for the researchers to formulate some ashless high EP/AW industrial oils.Originality/value – This paper proves that the two ashless neutral thiophosphate esters exhibit excellent EP and AW performances, high-temperature oxidation and hydrolytic stability, and is the useful substitute for ZDDP for formulating ashless GL-5 gear oils and high-pressure AW hydraulic oils. [ABSTRACT FROM AUTHOR]