Friction and Wear Properties of Cyanex 302-Modified MoS2 Micro-Sized Spheres as Additive in Liquid Paraffin

The friction and wear properties of MoS ₂ micro-sized spheres (MS-MoS₂) modified by Cyanex 302 (bis(2,4,4-trimethylpentyl) monothiophosphinic acid) as additive in liquid paraffin (LP) were studied and compared with those of commercial colloidal MoS ₂ (CC-MoS ₂ ) on a four-ball tester and an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. The worn surfaces were examined with SEM and XPS, respectively. The results showed that the Cyanex 302-modified MS-MoS ₂ was a better extreme-pressure and antiwear and friction-reducing additive in LP than CC-MoS ₂ . The boundary lubrication mechanism could be deduced as the effective chemical adsorption film formed by the alkyl and active elements (S, O, and P) in Cyanex 302 and tribochemical reaction and deposition film containing MoS ₂ , Fe ₂ O ₃ , and FePO ₄ . Moreover, the coexistence of sliding and rolling frictions in the lubricant of MS-MoS ₂ /LP also contributed to the enhanced tribological properties.     

Preparation and tribological properties of tungsten disulfide hollow spheres assisted by methyltrioctylammonium chloride

In the current paper, tungsten disulfide hollow spheres modified by methyltrioctylammonium chloride with diameters of about 200 nm have been successfully prepared through a solvothermal process. The products were characterized by X-ray power diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, scan electron microscopy and high revolution transmission electron microscopy, respectively. The tribological properties of the as-prepared WS₂ in liquid paraffin (LP) were studied and compared with those of commercial colloidal MoS₂ (CC-MoS₂). The worn surfaces were analyzed by XPS and SEM. Results show that the as-prepared WS₂ hollow sphere is a better anti-wear and friction-reducing additive in LP than CC-MoS₂.     

纳微米硼酸盐添加剂与硫系添加剂复配的摩擦学性能研究

本文研究了纳微米硼酸盐添加剂（简称MB添加剂，下同）与SO复配体系的协同效应及其作用机理。结果表明：MB添加剂与SO复配体系的极压抗磨性具有协同效应。当WMB=0.40%时，极压抗磨性最好；摩擦改进剂ASBT对上述复配体系的抗磨性有较大改善。当WASBT－0．10－0．15％时，复配体系的抗磨性最好。在MB添加剂与SO复配体系油润滑条件下，摩擦表面生成了含元素C、S、B和N复杂摩擦化学反应膜；摩擦改进剂ASBT的加入，改变了摩擦化学反应膜的化学组成和摩擦表面形貌，提高了以应膜的承载能力和耐磨性。     

Tribological investigation of CaF2 nanocrystals as grease additives

Calcium fluoride (CaF₂) nanocrystals with average grain size of 60 nm 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 12 nm. 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.     

Tribological behavior and tribofilm composition in lubricated systems containing surface-capped molybdenum sulfide nanoparticles

The tribological behavior of surface-capped MoS₃ nanoparticles (nano-MoS₃) in hydrocarbon oils was studied both alone and in combination with ZDDP. It was found that the nano-MoS₃ additive alone demonstrates pro-wear properties and decreases the friction coefficient only at high temperatures. The combination with ZDDP demonstrates synergism in antiwear and antifriction activity even at low ZDDP content. X-ray Absorption Near Edge Structure (XANES) spectroscopy at the sulfur, molybdenum and phosphorus edges was used to identify the chemical species in tribochemical films. It was established that the nano-MoS₃-formed tribofilms are composed of oxidized sulfur and molybdenum species while tribofilms formed by combination with ZDDP are composed of phosphate layers incorporating MoS₂-type fragments providing friction reduction.     

Lubricating properties of Cyanex 302-modified MoS2 microspheres in base oil 500SN

The lubricating properties of molybdenum disulphide (MoS2) microspheres modified by Cyanex 302 (bis(2,4,4-trimethylpentyl) monothiophosphinic acid) in base oil 500SN were investigated and compared with those of commercial colloidal MoS2 on a four-ball tester and an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. The worn surfaces of the flat disc lubricated with the additive-containing base oil were analysed by means of X-ray photoelectron spectroscope and scanning electron microscopy. The MoS2 microspheres showed much better extreme pressure properties and anti-wear and friction-reduction properties in 500SN than commercial colloidal MoS2. The effective chemical adsorption and protection film formed by the active elements (S and P) and long chain alkyls in Cyanex 302 and boundary-lubricating transfer film of thin sheets containing the solid lubricant particles (tribochemical products) of the additives could account for the boundary lubrication mechanism. Copyright © 2006 John Wiley & Sons, Ltd.     

Tribological properties of molybdenum disulfide nanosheets by monolayer restacking process as additive in liquid paraffin

Molybdenum disulfide nanosheets were prepared by monolayer restacking process. Results of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM) showed that the obtained MoS₂ nanosheets had a thickness about 30-70 nm. The tribological properties of the so-prepared MoS₂ nanosheets were investigated on a MQ-800 four-ball tribometer. The results showed the base oil with MoS₂ nanosheets had better friction reduction, wear resistance and extreme pressure than those with commercial micro-MoS₂. The good tribological properties of MoS₂ nanosheets were mainly ascribed to the surface effect and the dimension effect of nanoparticles. Moreover, the formation of MoO₃ and FeSO₄ complex film on the rubbed surface also played an important role in friction reduction and wear resistance.     

Synthesis and Tribological Properties of Stearic Acid-Modified Anatase (TiO<Subscript>2</Subscript>) Nanoparticles

Anatase (TiO₂) nanoparticles with an average diameter of 10 nm were synthesized by solvothermal method followed by surface modification with stearic acid (SA). As-prepared, the nanoparticles (SA-TiO₂) were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetry (TGA) and differential scanning calorimetry (DSC). The tribological properties of SA-TiO₂ as an additive of liquid paraffin (LP) were evaluated by a four-ball tester. The results show that LP with SA-TiO₂ exhibited good anti-wear and friction-reduction properties under the all applied loads. Comparing LP with LP-containing SA, LP-containing TiO₂, and LP-containing SA-TiO₂, the LP-containing SA-TiO₂ had the best load-carrying capacity. It was deduced that the boundary lubricating film was mainly composed of TiO₂ deposits and an adsorbing film of SA which contribute to the excellent lubricating effect of SA-TiO₂ in LP.     

Tribological behaviour and wear mechanism of MoS2–Cr coatings sliding against various counterbody

MoS₂–Cr coatings with different Cr contents have been deposited on high speed steel substrates by closed field unbalanced magnetron (CFUBM) sputtering. The tribological properties of the coatings have been tested against different counterbodies under dry conditions using an oscillating friction and wear tester. The coating microstructures, mechanical properties and wear resistance vary according to the Cr metal-content. MoS₂ tribological properties are improved with a Cr metal dopant in the MoS₂ matrix. The optimum Cr content varies with different counterbodies. Showing especially good tribological properties were MoS₂–Cr8% coating sliding against either AISI 1045 steel or AA 6061 aluminum alloy, and MoS₂–Cr5% coating sliding against bronze. Enhanced tribological behavior included low wear depth on coating, low wear width on counterbody, low friction coefficients and long durability.     

Sliding friction and wear performance of Ti6Al4V in the presence of surface-capped copper nanoclusters lubricant

The friction and wear properties of Ti₆Al₄V sliding against AISI52100 steel ball under different lubricative media of surface-capped copper nanoclusters lubricant—Cu nanoparticles capped with O,O′-di-n-octyldithiophosphate (Cu-DTP), rapeseed oil and rapeseed oil containing 1 wt% Cu-DTP was evaluated using an Optimol SRV oscillating friction and wear tester. The wear mechanism was examined using scanning electron microscopy (SEM) and X-ray photoelectron spectrosmeter (XPS). Results indicate that Cu-DTP can act as the best lubricant for Ti₆Al₄V as compared with rapeseed oil and rapeseed oil containing 1 wt% Cu-DTP. The applied load and sliding frequency obviously affected the friction and wear behavior of Ti₆Al₄V under Cu-DTP lubricating. The frictional experiment of the Ti₆Al₄V sliding against AISI52100 cannot continue under the lubricating condition of rapeseed oil or rapeseed oil containing 1 wt% Cu-DTP when the applied load are over 100 N. Surprisingly, the frictional experiment of Ti₆Al₄V sliding against AISI52100 steel can continue at the applied load of 450 N under Cu-DTP lubricating. The tribochemical reaction film containing S and P is responsible for the good wear resistance and friction reduction of Ti₆Al₄V under Cu-DTP at the low applied load. However, a conjunct effect of Cu nanoparticle deposited film and tribochemical reaction film containing S and P contributes to the good tribological properties of Ti₆Al₄V under Cu-DTP at the high-applied load.     

Tribological properties of molybdenum disulphide nanoparticles in soybean oil

Abstract

The tribological properties of soybean oil (SO) with different molybdenum disulfide (MoS₂) additives (hollow nanosphere, nanoplatelet and microplatelet) were investigated. MoS₂ hollow nanospheres remarkably improved the tribological properties of SO. SO with MoS₂ hollow nanospheres decreased abrasive plowing and changed the main wear pattern on the steel friction surfaces into chemical corrosion. The MoS₂ hollow nanospheres easily entered the contact region than the other MoS₂ particles to lubricate the friction pair because of its good dispersibility in SO. The tribochemical reactions among MoS₂ hollow nanospheres, SO and friction material produced a lubricating film composed of MoO₃, Fe₂O₃, carbon containing compounds. Thus, the MoS₂ hollow nanospheres have potential lubricating applications with SO. By contrast, MoS₂ nanoplatelet and microplatelets had lesser effects on the lubricating effect of SO. The MoS₂ nanoplatelets, even with its smaller size and more active chemical properties, had more difficulty in entering into the contact region because of its low dispersibility in the base oil.     

Tribological Behavior of 1-Methyl-3-Hexadecylimidazolium Tetrafluoroborate Ionic Liquid Crystal as a Neat Lubricant and as an Additive of Liquid Paraffin

Ionic liquid crystal (ILC), 1-methyl-3-hexadecylimidazolium tetrafluroborate, was synthesized. The tribological behavior of ILC was evaluated using a four-ball machine at 80 °C. X-ray photoelectron spectroscopic analysis shows that ILC takes part in tribochemical reactions to generate tribochemical products such as B₂O₃, FeF₂, and/or FeF₃, and amine which form a protective film on sliding steel surface, resulting in reduced friction and wear. Besides, ILC 1-methyl-3-hexadecylimidazolium tetrafluoroborate is completely transformed from solid state to liquid crystalline phase at 80 °C, which facilitates the ordered arrangement of its long alkyl chain on sliding steel surface and helps to improve the tribological properties. When the ILC is used as an additive of liquid paraffin (LP), it contributes to reduce friction and wear and increase the load-carrying capacity of the base stock both at room temperature and 80 °C. The reason might lie in that a small amount of F from ILC takes part in tribochemical reactions to generate tribochemical products that form a protective film on sliding steel surface, and friction-induced heat accelerates the transition of as-synthesized ILC to a mesophase and the ordered arrangement of its long alkyl chain on sliding steel surface, both resulting in improved load-carrying capacity and anti-wear ability of the ILC.     

Synergistic Effect of Nano-MoS<Subscript>2</Subscript> and Anatase Nano-TiO<Subscript>2</Subscript> on the Lubrication Properties of MoS<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> Nano-Clusters

A MoS₃ precursor deposited on anatase nano-TiO₂ is heated at 450 °C in an H₂ atmosphere to synthesize MoS₂/TiO₂ nano-clusters. The nano-clusters are then characterized, and their tribological properties are evaluated. MoS₂ is found to be composed of layered structures with 1–10 nm thicknesses, 10–30 nm lengths, and 0.63–0.66 nm layer distances. The MoS₂ sizes in the MoS₂/TiO₂ nano-clusters are smaller and their layer distances are larger than those of pure nano-MoS₂. The MoS₂/TiO₂ nano-clusters also present a lower average friction coefficient than pure nano-MoS₂, but the anti-wear properties of both the nano-clusters and pure nano-MoS₂ are similar. X-ray photoelectron spectroscopy indicates that nano-TiO₂ and the element Mo are transferred to the friction surface from the MoS₂/TiO₂ nano-clusters through a tribochemical reaction. This produces a lubrication film containing TiO₂, MoO₃, and other chemicals. The nano-MoS₂ changes in size and layer distance when combined with nano-TiO₂, producing a synergistic effect. This may further be explained using a micro-cooperation model between MoS₂ nano-platelets and TiO₂ solid nanoparticles.     

The Effect of Morphology on the Tribological Properties of MoS<Subscript>2</Subscript> in Liquid Paraffin

The tribological properties of liquid paraffin (LP) containing molybdenum disulfide (MoS₂) additives, including nano-balls, nano-slices, and bulk 2H-MoS₂, are evaluated using a four-ball tribometer. Results show that all MoS₂ additives used can improve the tribological properties of LP, and that nanosized MoS₂ particles function as lubrication additives in LP better than micro-MoS₂ particles do. The LP with nano-balls presents the best antifriction and antiwear properties at the MoS₂ content of 1.5 wt%. This is ascribed to the chemical stability of the layer-closed spherical structure of nano-balls. The Stribeck curves confirm that the rotation speed of 1,450 rpm used is located at the mixed lubrication region under 300 N. MoS₂ nano-slices have small sizes and easily enter into the interface of the friction pair with a roughness of 0.032 μm, functioning as a lubricant in LP better than nano-balls do at the MoS₂ content of 1.0 wt%. The Stribeck curves also show that the differences between the two nano samples were magnified at high rotation speeds in hydrodynamic lubrication region. The application of nano-slices in high sliding speeds will be more advantageous. This work furthers the understanding of the relationship between the tribological properties and morphology of MoS₂.     

Atomic Force Microscopy and Raman Spectroscopy Investigation of Additive Interactions Responsible for Anti-Wear Film Formation in a Lubricated Contact

Rational formulation of lubricants requires an understanding of additive interactions that impact antiwear film qualities such as thickness, topography, and friction. In an effort to understand the complex additive interactions responsible for formation of anti-wear and friction-reducing films, atomic force microscopy (AFM) in conjunction with Raman microscopy has been used to conduct a nanoscale investigation of the wear tracks formed by a high-frequency reciprocating rig (HFRR) in the presence of various commercial lubricant additives combinations. Of the additives examined, zinc dithiophosphate (ZnDTP)-based additives are found to be solely responsible for the formation of a thick (hundreds of nm) film that exhibits a pitted topography. Addition of a molybdenum-based friction modifier to the lubricant blend reduces the film thickness considerably and reacts to produce MoS ₂ on the surface, suggesting an interaction with the zinc dithiophosphate–based additive that prevents antiwear film formation. Formation of MoS ₂ , found only in the wear track, is consistent with a dramatic reduction of friction coefficient measured in the HFRR. Subsequent addition of borated dispersants to the lubricant reveals a further reduction in friction coefficient and a modest return of anti-wear film. However, addition of detergents to the formulation increases the friction coefficient and also promotes the formation of an anti-wear film. Nanoindentation measurements on the bulk properties of the anti-wear films determined that all of the anti-wear films had similar modulus and hardness measurements which were lower than that of the parent steel material, but did not correlate with the friction measurements obtained from the HFRR. This indicates that nanoscale measurements on material properties of the film are necessary to elucidate friction properties of the interface, and that these properties cannot be determined from macroscale measurements on the bulk film.

     

Tribochemistry of MoS3 Nanoparticle Coatings

The tribology of nanoparticles based on transition metal dichalcogenides has been studied extensively. However, evaluation of metal chalcogenides with other stoichiometries has been lacking. We have studied the friction, endurance, and tribochemistry of bonded molybdenum trisulfide (MoS₃) nanoparticle-based coatings for the first time. A facile aqueous chemistry method was used to fabricate the MoS₃ nanoparticles. Pin-on-disk tribometry of an MoS₃ coating using phenolic resin as the binder was conducted in a dry N₂ atmosphere (0.06 % RH, using normal loads of 5 N and 10 N). The results were compared with two types of commercial bonded coatings based on the solid lubricant molybdenum disulfide (MoS₂), as well as a bonded coating we formulated with commercial MoS₂ nanoparticles. Surprisingly, the MoS₃ coating showed similar lubricating ability to the MoS₂-based coatings, exhibiting average μ _k < 0.05 and endurance greater than a million cycles. To evaluate the tribochemistry occurring in the contact region, tribotesting of an MoS₃ coating was halted when steady-state low friction was achieved (i.e., prefailure). Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction on the surface of this wear track showed that the MoS₃ had undergone a tribochemical reaction to form the solid lubricant MoS₂, which explains the excellent lubricity of the coating. This result opens up the possibility of developing MoS₃ nanoparticle-based solid lubricant coatings and MoS₃ nanoparticle additives for oils and greases that are synthetically easier and lower cost than formulations based on MoS₂ nanoparticles.     

Additives for Rape Seed Oil 1: Preparation and Tribological Behaviour of a Sulphurised Rape Seed Oil Lubricant Additive

A new type of environmentally friendly lubricant additive ‐ a sulphurised rape seed oil additive ‐ was prepared, and the chemical structure characterised using infrared spectroscopy. The tribological properties of the additive in a rape seed base oil were evaluated using a friction tester. The morphologies and tribochemical species of worn surfaces were analysed by means of X‐ray photoelectron spectroscopy. The results show that the additive increased the load‐carrying capacity and improved the antiwear and friction‐reducing properties of the rape seed oil. The inferred lubrication mechanism is that a high‐strength adsorption film and a tribochemical reaction film form on rubbing surfaces due to the carrier effect of the long‐chain rape seed oil molecules, the high reactivity of sulphur, and their synergism.     

Friction and Wear Properties of IF–MoS2 as Additive in Paraffin Oil

Inorganic fullerene-like (IF) MoS₂ nanoparticles with diameters ranging from 70 to 120 nm were synthesized by desulphurizing the MoS₃ precursor and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Tribological properties of the IF–MoS₂, as lubricating oil additive, were evaluated using a MMW-1 four-ball tribotester. The wear scar was examined with an optical microscope and scanning electron microscopy (SEM). The wear resistance of the paraffin oil was improved and the friction coefficient of the oil was decreased by addition of the IF–MoS₂ nanoparticles. The mechanism of friction and wear of the IF–MoS₂ nanoparticles was discussed.     

Antiwear,Antifriction, and Extreme Pressure Properties of Motor Bike Engine Oil Dispersed with Molybdenum Disulfide Nanoparticles

This work presents studies on the antiwear, antifriction, and extreme pressure properties of motor oil dispersed with MoS₂ nanoparticles. Commercial oil (SAE 20W-40 grade) is dispersed with stabilized MoS₂ nanoparticles in 0.25, 0.5, 0.75, and 1 wt%. The test oils are tested for antiwear, antifriction, and extreme pressure properties on a four-ball wear tester. The wear and friction offered by nanolubricants has decreased remarkably compared to the commercial base oil. The weld load and load wear index of oils dispersed with nanoparticles were improved substantially compared to the commercial base oil. Metallographic studies conducted on the wear balls from the extreme pressure test show that nanoparticles are deposited on the worn area along with additives in the oil, thereby preventing welding of the surfaces. An optimum weight fraction is arrived at for best performance. A synergy between the additives in the oil and dispersed nanoparticles has been observed, resulting in less dispersion for best results. It is found that beyond an optimum weight percentage of nanoparticles, the trends tend to reverse, resulting in greater wear and friction.     

Preparation and tribological performance of lanthanum alkoxyborate

Lanthanum isooctoxyborate (LaIOB) was prepared as an additive, and the antiwear and friction‐reducing properties of base oil containing the compound were evaluated with an MS‐800A four‐ball friction tester and HQ‐1 friction machine. The chemical states of tribochemical species on the rubbing surfaces were determined by X‐ray photoelectron spectroscopy (XPS). The results indicate that LaIOB possesses good antiwear and friction‐reducing properties. The XPS analysis shows that LaIOB can be triboreduced to La₂O₃ and B₂O₃ during friction.