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Abstract: Calcium fluoride (CaF2) nanocrystals with average grain size of 60nm were synthesized via a precipitation method. The morphology and structure of nanocrystals were characterized by means of transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). TEM and XRD showed that CaF2 nanocrystals are cubic particles in submicron scale. The tribological properties of the prepared CaF2 nanocrystals as an additive in lithium grease were evaluated with a four-ball tester. The results indicated that these nanocrystals exhibit excellent antiwear, friction reduction and extreme pressure (EP) properties. It was also found that the EP and antiwear capabilities of the grease are not proportional to the content of CaF2 nanocrystals but there existed a certain value. The rubbed surface after friction test was investigated with X-ray photoelectron spectroscopy and scanning electron microscopy to understand the action mechanism. The results show that a boundary film mainly composed of CaF2, CaO, iron oxide and some organic compounds was formed on the rubbed surface after friction test and the thickness of boundary film was about 12nm. The disproportion of stoichiometric ratio of Ca and F in boundary lubrication film indicates that tribochemical reaction of CaF2 nanocrystals occurred on the worn steel surface at severe tribological conditions. [Copyright &y& Elsevier]

Abstract: A series of asymmetrical tetraalkylphosphonium ionic liquids were synthesized and evaluated as a new kind of lubricant for the contacts of steel/Al using an Optimol SRV oscillating friction and wear tester in ambient condition. The phosphonium ionic liquid shows excellent tribological performance and is superior to the conventional ionic liquids 1-ethy-3-hexylimidazolium hexafluorophosphate (P206) in terms of anti-wear performance and load-carrying capacity. The chemical compositions of the boundary film generated on different contact surfaces were analyzed on a scanning electron microscope with a Kevex energy dispersive X-ray analyzer attachment (SEM/EDS) and X-ray photoelectron spectrometer (XPS). The friction-reduction and anti-wear mechanism were proposed to originate from the layered structure of ionic liquid under boundary lubrication and the tribochemical reaction of anions with the fresh surface, respectively. [Copyright &y& Elsevier]

A series of S, P-containing triazine derivatives, 2,4-bis-(diethylamino)-6-(O,O′-dialkyl dithiophosphate)-s-1,3,5-triazine, which are potential environmentally friendly lubricating oil additives, were synthesized. The tribological properties as lubricating oil additives in vegetable oil were evaluated using a four-ball tester. The results show that the series of triazine derivatives possess good antiwear performance, excellent load-carrying capacity. These compounds also show good friction-reducing properties. The action mechanism was estimated through analysis of the worn surface with X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). [Copyright &y& Elsevier]

The ionic liquid 1-ethyl-3-hexylimidazolium-bis(trifluoromethylsulfonyl)-imide was synthesized and evaluated as lubricant for the contact of steel/steel. The tribological properties of the ionic liquid as lubricant were investigated on an Optimol SRV oscillating friction and wear tester in ambient condition. The synthetic ionic liquid shows excellent tribological performance and is superior to the ionic liquid of alkylimidazolium tetrafluoroborate and the conventional high temperature lubricants X-1P and PFPE in terms of antiwear performance and load-carrying capacity. The elemental composition and chemical nature of the boundary film generated on the steel surface were analyzed on a scanning electron microscope with a Kevex energy dispersive X-ray analyzer attachment (SEM/EDS) and X-ray photoelectron spectrometer (XPS), and the XPS results indicate the occurrence of a complicated tribochemical reaction of ionic liquid with iron on the rubbing surface during the sliding process, with the formation of FeS, organic fluoride, inorganic fluoride, etc. [Copyright &y& Elsevier]

Three novel ashless triazine–dithiocarbamate derivatives, which are potential environmentally friendly oil additives, were synthesized. Their tribological properties as additives in rapeseed oil (RSO) were evaluated using a four-ball tester. Their anticorrosive properties and thermal stabilities were also investigated. The results indicate that the three novel triazine–dithiocarbamate compounds possess excellent load-carrying capacity, good corrosion inhibiting performance and high thermal stability. Although these additives show friction-reducing property at high additive concentration (5 wt.%), they have friction increase and wear promote natures in most cases. The elemental composition and chemical state of the antiwear films generated on steel counterface were investigated with scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and X-ray photoelectron spectroscopy (XPS). It was found that the synthetic additives reacted with the counterface metal and generated a surface protective film consisting of sulfate, FeS and absorbed compounds containing organic-N. [Copyright &y& Elsevier]

Polyimide (PI) nanocomposites with different proportions of nanoparticle Al2O3 were made by compression molding at elevated temperature. The mechanical and tribological properties of the resulting PI-based nanocomposites were investigated. The bending strength and microhardness of the nanocomposite specimens were determined, and the tribological behavior of the nanocomposite blocks in dry sliding against a plain carbon steel ring was evaluated on an M-2000 friction and wear tester. The morphologies of the worn nanocomposite surfaces and transfer films on the counterpart steel ring were observed on a scanning electron microscope. Results indicated that the PI-based nanocomposites with appropriate proportions of nanometer Al2O3 exhibited lower friction coefficient and wear volume loss than PI under the same testing conditions. The nanocomposite containing 3.0wt.%–4.0wt.% nanometer Al2O3 registered the lowest wear volume loss under a relatively high load. The differences in the friction and wear behaviors of PI and PI–Al2O3 nanocomposites were attributed to the differences in their worn surface morphologies, transfer film characteristics, and wear debris features. The agglomerated abrasives on the worn composite and transfer film surfaces contributed to increase the wear volume loss of the nanocomposites of higher mass fractions of nanometer Al2O3. [Copyright &y& Elsevier]

Amorphous carbon (a-C) films were deposited on a single-crystal silicon substrate by direct current magnetron sputtering system. The effect of Cr+ ion-implantation on the structure and tribological properties of the sputtered a-C films were investigated by means of Raman spectrometric analysis, X-ray photoelectron spectroscopic analysis, and friction and wear measurements. The morphology of the worn film surfaces was observed with a scanning electron microscope (SEM). The structure of a-C tended to be disordered and had a growth of sp3 content at high implantation doses. The sputtering depth profiles of the films by X-ray photoelectron spectroscopy indicate that chromium carbide is formed at the film–substrate interface where the implanted Cr+ has a higher concentration. The interface between Si and C is widened by ion-implantation. Thus the anti-wear behavior of the ion-implanted film is improved. The brittleness of the a-C film is increased after implantation with Cr+ at a larger dose. This is attributed to the generation of chromium carbide from the reaction of carbon and Cr. Subsequently the film implanted with Cr+ at a relatively low dose is characterized by adhesive wear, while that implanted at a higher dose characterized by abrasive wear. [Copyright &y& Elsevier]

Three S-(1H-benzotriazole-1-yl) methyl N,N-dialkyldithiocarbamates were synthesized and their tribological behaviors as additives in rapeseed oil (RSO) were evaluated using a four-ball tester. Thermal degradation tests were conducted to identify their thermal stabilities using thermogravimetric analyzer (TGA). The worn surface of the steel ball was investigated by X-ray photoelectron spectroscopy (XPS). The results indicate that the additives possess excellent load-carrying abilities and high thermal stabilities, but have no antiwear and friction-reducing properties. Based on the results of XPS analysis, it can be seen that tribochemical reactions occur between the synthesized compounds and metal surfaces during the sliding process. [Copyright &y& Elsevier]

Ester oils (1,4,5,8-4C n) were synthesized through esterification of naphthalene-1,4,5,8-tetracarboxylic acid with aliphatic alcohols. The molecular structures were confirmed with 1H NMR, 13C NMR, FT-IR and elemental analysis. Their KV, VI, FP, PP, oxidation and thermal stabilities, friction reducing and anti-wear performances were measured. The results demonstrate that the 1,4,5,8-4C n have obviously higher thermal and oxidation stabilities than the existing esters DOS, PIS and Phe-3C i8. They also have predominant tribological behavior at both 50 °C and 120 °C. Analyzing from the results of ECR, QCM and XPS, it could be concluded that strongly and orderly physicochemical adsorption of the 1,4,5,8-4C n molecules on the sliding surfaces is the critical factor for these oils to demonstrate excellent tribological performance for steel contacts. • Naphthoate oils were prepared and evaluated as lubricants for steel/steel contact. • The oils have high thermal and oxidation stabilities. • The oils exhibited predominant tribological property. • The predominant property owns to physiochemically adsorbed film formation. [ABSTRACT FROM AUTHOR]

A novel and simple method for the preparation of two-component gel lubricant and some evaluation of its physicochemical and lubricating properties are reported. The addition of two-component gelator including bis(2-ethylhexyl) sulfosuccinate and cholesterol to white oil can result in self-assembly to form a gel. The gelation mechanism was characterized by the combination of atomistic molecular dynamics simulation and experiment. It not only has excellent thermal stability, but also possesses thermal reversibility, creep recovery and thixotropic properties. Noticeably, the gel can significantly enhance lubricous and AW performances of base oil. Obtained by FIB-TEM, EDS, XPS and QCM characterization, we speculate that the gelator forms an effective adsorption and tribochemical reaction film, so it can protect the contact surface from being worn. Image 1 • The manuscript reports a novel, simple and low cost method for the preparation of two-component gel lubricant. • The AOT and cholesterol added to food grade white oil can result in self-assembly to form a gel. • The obtained gel lubricants have excellent lubricity, wear resistance and higher load carrying capacity. • The gel lubricants are green and non-toxic, provide potential application in the field of food or drug processing. [ABSTRACT FROM AUTHOR]