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1.
Inorganic fullerene-(IF)-like nanoparticles made of metal dichalcogenides (IF-MoS2, IF-WS2) have been known to be effective as anti-wear and friction modifier additives under boundary lubrication. The lubrication mechanism of these nanoparticles has been widely investigated in the past and even if the exfoliation and third body transfer of molecular sheets onto the asperities constitute the prevalent mechanism for the improved tribological behavior of IF nanoparticles, it has also been suggested that a rolling friction process could also play a role for well crystallized and spherical particles. In this study, in situ Transmission Electron Microscopy (TEM) observations of the behavior of single IF-MoS2 nanoparticles were conducted using a sample holder that combines TEM and Atomic Force Microscopy (AFM) which simultaneously can apply normal and shear loads. It was shown that depending on the test conditions, either a rolling process or a sliding of the fullerenes could be possible. These in situ TEM observations are the first carried out with IF nanoparticles.  相似文献   

2.
Direct observation of the behaviour of individual inorganic fullerenes (IF)‐MoS2 nanoparticles in a sliding interface is essential for the understanding of the influence of the intrinsic characteristics of the nanoparticles on their lubrication mechanisms, when they are used as additives in lubricant oil. In this work, in situ transmission electron microscopy sliding tests were performed on two different types of MoS2 nanoparticles synthesised by two different methods. It is shown that the IF‐MoS2 nanoparticles having perfect structure with a high crystalline order and without defects are able to roll and to slide under the combined effect of pressure and shear stress, whereas the IF‐MoS2 nanoparticles containing many defects exfoliate immediately in the same conditions to deliver MoS2 layers covering the mating surfaces. A link between these results, the lubrication mechanisms of the nanoparticles and their tribological properties at the macro‐scale was established, proving that the lubrication mechanisms of fullerenes depend on their intrinsic characteristics. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

3.
Using a new quartz-made reactor, large amounts of fullerene-like (IF) MoS2 nanoparticles were synthesized by reacting MoO3 vapor with H2S in a reducing atmosphere. The nanoparticles were found to be of high crystalline order; with an average size of 70 nm and consist of more than 30 closed shells. Extensive tribological testing of the nanoparticles in two types of synthetic oils- poly-alpha olefins (PAO)- was carried out and compared to that of bulk (2H platelets) MoS2 and IF-WS2. These tests indicated that under high pressure and relatively low humidity, the IF-MoS2 exhibited a friction coefficient as low as 0.03 and the smallest wear rate of the measured systems. However, its performance was found to be lower in comparison to IF-WS2 after 2500 cycles, due probably to its inferior chemical stability. This study indicates that the tribological performance of the IF nanoparticles depends strongly on their crystalline order and size.  相似文献   

4.
Inorganic fullerene-(IF)-like nanoparticles made of metal dichalcogenides (IF-MoS2, IF-WS2) have been known to be effective as anti-wear and friction modifier additives under boundary lubrication. The lubrication mechanism of these nanoparticles has been widely investigated in the past and it is now admitted that their lubrication properties are attributed to a gradual exfoliation of the external sheets of the particles during the friction process leading to their transfer onto the asperities of the reciprocating surfaces. However, the chemical interaction between these molecular sheets and the rubbing surfaces has so far never been investigated in detail. In this study, the tribochemistry of the IF nanoparticles was carefully investigated. A series of friction test experiments on different rubbing surfaces (Steel, Alumina, Diamond-Like Carbon) were performed with IF-MoS2 nanoparticles. High-resolution transmission electron microscopy, scanning electron microscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the tribostressed areas on rubbing surfaces. A tribofilm composed of hexagonal 2H-MoS2 nanosheets was only observed on the steel surface. This transfer film was found to be incorporated into an iron oxide layer. A tribochemical reaction between the 2H-MoS2 nanolayers and the iron/iron oxide has been proposed as an explanation for the adhesion of this tribofilm. The tribochemical mechanism of the IF-MoS2 nanoparticles is discussed in this article.  相似文献   

5.
Inorganic fullerene-like molybdenum disulfide (IF-MoS2) nanoparticles are known to exhibit great friction and wear-reducing abilities in severe boundary lubrication regimes, when added to a base oil alone. Their use in fully formulated lubricants was investigated in this study, and the tribological benefits attributed to the IF-MoS2 nanoparticles were found to be lost in the presence of dispersants. Various experimental techniques were used on three reference oils (base oil containing only IF-MoS2, only dispersants and both IF-MoS2 and dispersants) in order to understand the effect of succinimide-based dispersants on the three phases needed for effective nanoparticle-based lubrication, namely (1) the passing of the nanoparticles through the contact (2) the exfoliation of the IF-MoS2 inside the contact and (3) the adhesion of the released MoS2 platelets on the friction surfaces. The dispersants were shown to improve the dispersion of the nanoparticles in the oil by reducing their agglomeration, but prevented the adhesion of a low-friction MoS2 tribofilm on the steel surfaces. In-situ contact visualization revealed that the well-dispersed nanoparticles passed through the contact and exfoliated nanoparticles were observed after tribological testing. These results imply that nanoparticle dispersion itself does not seem to be an issue concerning nanoparticle effectiveness, even though the reduced agglomerate size and inertia may have affected nanoparticle flow near the contact, as well as entrapment and exfoliation conditions inside the contact. The use of succinimide-based dispersants may, however, have affected the tribochemistry of the contact, by an excessive adsorption on the steel surfaces and/or by encapsulating the released MoS2 platelets, preventing tribofilm adhesion. A balance was finally found between nanoparticle dispersion and friction reduction, but for very low dispersant concentrations and after a running-in period. The role of succinimide-based dispersants and their effect on nanoparticle lubrication were discussed in the light of these results.  相似文献   

6.
The tribological properties of rhenium-doped inorganic fullerene-like MoS2 nanoparticles were studied in poly alpha olefin oil, and compared to inorganic fullerene-like (IF) MS2 (M=Mo,W) nanoparticles and 2H-MoS2 platelets. For this purpose a rotational disc tribometer was used. Different regimes in the Stribeck curve, i.e., boundary, mixed and elasto-hydrodynamic lubrication conditions were studied. A precipitous reduction in friction and wear of oil suspensions with nanoparticles were observed for the entire IF samples. However, Re-doped IF exhibited the best results, presumably due to their reduced tribocharging and agglomeration. The various tribological mechanisms of solid state additives are discussed.  相似文献   

7.
Seed-assisted solution synthesis of hollow IF-MoS2 nanoparticles allows independent control of particles size and MoS2 slabs crystallinity. Variations of the reaction mixture composition influence the particle size in the range 50–150 nm. As demonstrated by Rietvelt refinement of the X-ray diffraction patterns, the sulfide crystallinity depends only on the post-treatment temperature (350–750 °C) and not on the particle size. The tribological properties of new MoS2 nanoparticles prepared by seed-assisted solution technique were investigated and showed a strong decrease in the friction coefficient and wear compared with base oil. Small particles of 50–60-nm size showed the best results. The particle size above 100 nm is deleterious for the lubrication properties since it hinders particles penetration into the contact zone. MoS2 slabs crystallinity had lesser influence on the lubrication efficiency. However, less-crystallized samples treated at 350 °C showed better lubrication, apparently because of easier exfoliation of the individual MoS2 slabs, leading to more efficient formation of tribofilm.  相似文献   

8.
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.  相似文献   

9.
Fullerene-like WS2 (MoS2) nanoparticles (IF) have been studied in the past as solid lubricants. Using the tribological ball-on-flat experiments, it was shown that the size of the aggregates and their distribution determine the penetration and entrapping of the IF nanoparticles at the interface. It is expected that the wedge clearance at the inlet of the contact, i.e., the oblique-angle entrance to the contact zone between the two mating tribological surfaces, as well as the average surface roughness, can limit the supply of the lubricant into the interface in, e.g., the block-on-ring experiment. In the present series of experiments, the Stribeck curve was designed first using a linear loading scheme and pure oil. It was concluded that a wedge clearance (oblique-angle) in the inlet of the contact zone leads to entrapment of the IF nanoparticles and their compaction, which hamper the supply of the fluid lubricant into the interface. A ball-on-flat and flat block-on-ring friction devices with wedge clearance in the inlet of the contact can distort the efficacy of IF. Procedures for improving the supply of the IF nanoparticles to the contact zone and improving thereby their efficacy are considered.  相似文献   

10.
The electrostatic effects in tribological systems have been studied in the past, especially with regards to data storage media. Nanoparticles (NP) of WS2 and MoS2 with fullerene-like structure (IF) have been studied in the past and showed very good tribological behavior. Being semiconductors, their electrical properties can be controlled by, e.g., substituting the lattice Mo (W) atoms with Re (n-type conductivity) and Nb (p-type conductivity) atoms. In this study doping of IF-MoS2, and to a lesser degree IF-WS2, NP with small amounts (< 1 at.%) of rhenium atoms has been studied. For this purpose two new synthetic approaches have been pursued. The doped nanoparticles were characterized by various techniques. In particular, the doping density was determined by ICP-MS technique. The resistivity of the nanoparticles was shown to decrease significantly with increasing doping level. In contrast to the undoped nanoparticles, the doped NP were shown to exhibit reduced agglomeration and produce stable suspensions in PAO-4 and PAO-6 oils. Extensive tribological measurements with these PAO oils formulated with 1 wt % of the doped NP showed friction coefficients as low as 0.01 in mixed lubrication conditions and negligible wear. Microscopy analysis of the tribological surfaces reveal very smooth but discontinuous and dense film of the doped NP on the tribological surfaces. It is proposed that the doped NP are negatively charged at their surface eliciting mutual repulsion, which has a remarkable influence on their rheological properties and their tribological behavior.  相似文献   

11.
Fe3Si, Fe3Si alloys containing Cu were fabricated by arc melting followed by hot-pressing. The friction and wear behaviors of Fe3Si based alloys with and without Cu addition against Si3N4 ball in water-lubrication were investigated. The friction coefficient and the wear rates of Fe3Si based alloys decreased as the load increased. The wear rate of Fe3Si was higher than that of AISI 304. The addition of Cu can significantly improve the friction and wear properties of Fe3Si based alloys and substantially reduce the wear rates of Si3N4 ball. The wear rate of Fe3Si–10%Cu was 2.56 × 10−6 mm3 N−1 m−1 at load of 20 N and decreased to 1.64 × 10−6 mm3 N−1 m−1 at load of 90 N. The wear rate of Si3N4 ball against Fe3Si–10%Cu was 1.41 × 10−6 mm3 N−1 m−1, while the wear rate of Si3N4 ball against AISI 304 was 5.20 × 10−6 mm3 N−1 m−1 at load of 90 N. The wear mechanism was dominated by micro-ploughing. The combination of mechanical action (i.e., shear, smear and transference of Cu) and tribochemical reaction of Si3N4 with water was responsible for the improved tribological behavior of Fe3Si alloys containing Cu under high loads.  相似文献   

12.
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.  相似文献   

13.
Greenberg  R.  Halperin  G.  Etsion  I.  Tenne  R. 《Tribology Letters》2004,17(2):179-186
A study of the tribological behavior of nested inorganic fullerene-like (IF) nanoparticles of WS2, as a potential additive to base oils is presented. Friction measurement results obtained from three different test rigs over a wide range of normal loads and sliding velocities are shown. Stribeck curves are used to reveal the lubrication regimes where the IF are most effective. It is found that the addition of IF-WS2 nanoparticles to the base oils results in up to 50% reduction in friction coefficient in the mixed lubrication regime. The mechanism of improved friction and wear behavior with the IF additive is discussed.  相似文献   

14.
MoS x /MoS x -Mo multi-layer films consisted of several bilayers and a surface layer on steel substrate were deposited by d.c. magnetron sputtering at different deposition pressures. Each bilayer contained a MoS x layer with 80 nm in thickness and a MoS x -Mo composite layer with 20 nm in thickness. With the increase of deposition pressure, the perpendicular orientation of the basal plane prevailed while the parallel orientation decreased. The tribological properties of the multi-layer films were investigated by using a ball-on-disk tribometer both in vacuum and in humid air. The multi-layer film deposited at 0.24 Pa had a compact, consistent layered structure with high intensity of (002) plane and low S content compared to the others deposited at 0.32 and 0.40 Pa, and showed the lowest friction coefficient and wear rate in humid air.  相似文献   

15.
MoS2 coatings exhibit low coefficient of friction (COF) when sliding against aluminum; however, the magnitudes of their COF show high sensitivity to environmental conditions. Ti could reduce the sensitivity of the frictional behavior of MoS2 coatings to moisture. This study examines the tribological properties of Ti containing MoS2 coating (Ti–MoS2) tested against an aluminum alloy (Al-6.5% Si) in ambient air (58% relative humidity, RH), dry oxygen, dry air and dry N2 (< 4% RH) atmospheres. The Ti–MoS2 coating exhibited similar COF values under an ambient (0.14), dry oxygen (0.15) and dry air (0.16) atmospheres. It was found that oxidation of MoS2 to MoO3 was responsible for high COF under these testing conditions as revealed by Energy-dispersive X-ray Spectroscopy (EDS) and micro-Raman spectroscopy. However, a low and stable COF of 0.07 was observed under a dry N2 condition. This work further showed that the tests performed at elevated temperatures, up to 400 °C in a dry N2 atmosphere sustained the low and stable COF of the Ti–MoS2 coatings. The sliding tests performed under a dry N2 atmosphere prevented the formation of MoO3 and as a result, the Ti–MoS2 coatings maintained low COF values. Low COF values were also attributed to the formation of MoS2 transfer layers.  相似文献   

16.
Pulsed laser deposition (PLD) was employed to grow MoS x –WSe y composite films, where x = 1.18, y = 0.78. Scanning electron micrographs show that the films have a dense granular morphology. Crystallization, d-spacing and hexagonal sheet curvature within the film were studied with X-ray diffraction, electron diffraction and transmission electron microscopy. A predominant hexagonal MoS x phase was formed but contained W and Se, which were most likely present as substituents for Mo and S. There was no evidence for two separate crystalline phases. MoS x –WSe y composite films exhibited a larger expansion along the c-axis (d-spacing between basal planes) than PLD MoS2 and WSe2 films grown by laser ablation of pure targets. The lattice spacing along the a-axis was expanded in comparison to the MoS2 film, and compressed in comparison to the WSe2 film. X-ray photoelectron spectroscopy showed a significant sulfur deficiency, and verified both of S and Se bonding in the film. High-resolution electron microscope images exhibited significant curvatures of the (002) basal planes in the films. The bending behavior of basal planes was explained by S vacancies and Se substitution on the atomic site of S layers. The tribological properties of the composite films were measured in dry and wet conditions using a ball-on-disc tribometer. The reduced friction was correlated with the increased crystallinity and increased separation of basal planes in the composite films.  相似文献   

17.
The tribological behaviors of three silicon-based materials (low temperature silicon oxide (LTO), polysilicon (Poly Si) and silicon nitride (Si3N4) films) under ion liquids (ILs) lubrication have been investigated by varying the applied load and the sliding velocity. An atomic force microscope and a nanoindentor were used to characterize the deposited films, and the worn surfaces after frictional tests were analyzed by an optical microscope, a scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS) and an X-ray photoelectron spectrometer (XPS). The results show the best lubricating properties of the IL lubricants are obtained at the intermediate load of 150 g for the three tribo-pairs. For the Si3N4/Si3N4 tribo-pair, the coefficients of friction (COFs) and the wear rates under ILs lubrication are larger than those under dry friction. The COF values decrease with sliding velocity, and the COFs of the Si3N4/Si3N4 tribo-pair are greater than the ones of the other two tribo-pairs (LTO/Si3N4 and Poly Si/Si3N4) at low velocities. The COF of 1-ethyl-3-methylimidazolium tetrafluoroborate is nearly 3 times larger than the other two IL lubricants (1-butyl-2,3-dimethylimidazolium tetrafluoroborate and N-butylpyridinium tetrafluoroborate) for the Si3N4/Si3N4 tribo-pair. The differences in COFs between the latter two lubricants for the three tribo-pairs are negligible. Different mechanisms of these results have been analyzed in the paper.  相似文献   

18.
Abstract

For several years different types of nanoparticles have been considered and studied as potential friction modifying lubricant additives. Some nanoparticles can reduce the friction coefficient by 30–70%, depending on the base oil and the experimental conditions. In the present study, an experimental analysis on tribological properties of inorganic fullerene-like metal dichalcogenides was performed in comparison with MoS2 2H layered structures. Tribological tests were carried out on a pin on disc tribometer in ambient air. Several contact conditions are analysed in order to realise boundary and mixed lubrication regimes. The experimental study was performed on a mineral base oil, and particle concentration effects were analysed. Antifriction properties were evaluated by measuring the friction coefficient and are presented as generalised Stribeck diagrams. Inorganic fullerene-like WS2 and MoS2 nanoparticles present interesting friction reduction properties when tested in boundary and mixed lubrication.  相似文献   

19.
Synthesis and tribological evaluation of three tetraalkylammonium thiomolybdate (R4N)2MoS4 (R = methyl, propyl, or ammonia) aqueous-based lubricant additives on a ball-on-disk tribometer was carried out for a steel–aluminum contact. Tests were performed at the same conditions of load, entrainment speed, sliding distance, temperature, and concentration of MoS2 to compare the activity (lubrication effect) of the thiomolybdates prepared. A friction reduction is observed for the three salts compared to pure water; however, significant differences in friction coefficient are observed depending on the alkyl group. SEM/EDAX and Raman analysis of the wear tracks reveal the in-contact formation of a MoS2-lubricating film, rich in molybdenum and sulfur.  相似文献   

20.
The deformation and degradation behavior of single inorganic fullerenes nanoparticles of MoS2 under compression and shear has been observed in real time using a high-resolution transmission electron microscope equipped with a nanoindentation holder. The MoS2 nanoparticles were compressed using a nanoindenter and a truncated diamond tip. For the first time, real time imaging of the deformation of individual nanoparticles clearly shows first orientation changes in the particle shape during loading process followed by a large deformation and the exfoliation of the outer sheets of the fullerene nested structure. Exfoliation was observed for a contact pressure estimated at 1 GPa. Additional sliding tests performed with the nanoindenter gave evidence for a rolling process for lower contact pressures up to 100 MPa.  相似文献   

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