Fullerene-like WS2 Nanoparticles Research Articles

A new way to feed nanoparticles to friction interfaces

Fullerene-like WS2 (MoS2) nanoparticles (IF) have been studied in the past. Their efficacy as additives for lubrication fluids has been demonstrated. It was shown that the IF nanoparticles are usually delaminated in the inlet of the smooth contact. Thin sheets of broken IF nanoparticles can be entrapped between the rubbed surfaces and thus favorably affect the friction and the wear. Friction pairs at real mechanical macrosystems are often subjected to friction-induced vibrations. It was shown that the mechanical excitations can improve the supplying and preservation of fluid lubricant film in the interface. It can be hypothesized that under vibrations in a definite range of frequencies and amplitudes, the probability for small IF aggregates to be entrapped into the interface is increased. The main goal of this work was to study the effect of artificial mechanical excitations on the friction and wear of contact pairs rubbed with nanoparticles. In order to avoid friction-induced excitations, a new ball-on-flat friction device was developed. The frequency and the amplitude of the ball were varied using a motion of miniature micromotor attached to the ball holder. The behavior of IF nanoparticles in friction tests with and without external mechanical excitations was compared with the tribological behavior of the contact pair lubricated with pure paraffin oil. It was found that the external mechanical excitation of the mechanical parts rubbed with nanoparticles allows a penetration of these nanoparticles into interface. This effect leads to a remarkable shortening of the run-in period and improves the tribological properties of contact pairs. From the present results it may be anticipated that the accidental friction-induced vibrations, which are determined by the stiffness and damping force of the device, lead to preferential penetration of the IF nanoparticles into the contact area, affecting thereby the tribological behavior of the interface.

Pressure-induced exfoliation of inorganic fullerene-like WS2 particles in a Hertzian contact

Nanoparticles are potential additives for the improvement of lubricant properties, because of the structural modifications they undergo under high pressures in mechanical contacts. The behavior of inorganic fullerene-like WS2 nanoparticles (IF-WS2) under high isotropic pressures of up to 20GPa generated in a diamond anvil cell was studied and compared to the response of the lamellar 2H phase of WS2. The same materials were then subjected to static uniaxial pressures in a Hertzian contact in the GPa range. The evolution of the particles as a function of pressure was studied by in situ Raman spectroscopy and transmission electron microscopy at the end of the test. Data analysis shows that IF-WS2 particles resist high hydrostatic pressures well, but they are totally exfoliated by uniaxial compression in a Hertzian contact under low pressure. These results explain the excellent tribological properties at ambient temperature of IF-WS2 nanolubricant that have previously been attributed to the nested nanospheres during the friction process but whose origin had not been clearly identified.

Friction and wear of fullerene-like WS2 under severe contact conditions: friction of ceramic materials

Recently, the behavior of inorganic fullerene-like (IF) WS2 nanoparticles in the interface of steel-on-steel pair has been analyzed. It was shown that originally when the gap between the contact surfaces is smaller than the size of the IF nanoparticles, there is no effect of the nanoparticles on the friction force. During the test stiff IF nanoparticles can plough the surface of hard steel samples and penetrate into the interface under friction. Molecular sheets of WS2 from the delaminated IF nanoparticles, which reside in the valleys of the rough surfaces cover the contact spots and thus decrease the number of adhered spots at the transition to seizure. The goal of the present work was to study the behavior of IF nanoparticles in the interface of ceramic surfaces. The friction tests were performed using a ball-on-flat device. A silicon nitride ball was slid against an alumina flat with maximum contact pressure close to 2 GPa. SEM, TEM and AFM techniques have been used in order to assess the behavior of IF nanoparticles in the interface. The behavior of IF nanoparticles in the much harder ceramic interfaces was found to be appreciably different from the steel pair. The pristine IF nanoparticles are damaged in the inlet of the contact during the first few cycles and thin shells of broken nanoparticles gradually cover the middle range of the contact surface. Different modes of deformation and destruction of the IF nanoparticles are exhibited when going from the middle to edge area of the contact. While aggregates of the pristine nanoparticles are formed at the edge of the contact, thin shells of broken IF nanoparticles are observed in the middle area where contact pressure is maximum. Mechanical stability and damage of IF nanoparticles in the ceramic interface are discussed.

Ultralow-friction and wear properties of IF-WS2 under boundary lubrication

Tested in boundary lubrication, inorganic fullerene-like WS2 nanoparticles used as additives in oil present interesting friction reducing and anti-wear properties. A dispersion with only 1 wt% of particles leads, from a contact pressure of 0.83 GPa, to a drastic decrease of the friction coefficient below 0.04 and to very low wear. High resolution transmission electron microscopy (HRTEM), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Raman Spectroscopy and video imaging were used to explain the lubrication mechanisms. A structural modification of fullerene-like nanoparticles into sheets during the friction test was evidenced to be the main effect at the origin of these properties.

The Effect of WS2Nanoparticles on Friction Reduction in Various Lubrication Regimes

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.

Slow Release of Fullerene-like WS2 Nanoparticles from Fe−Ni Graphite Matrix: A Self-Lubricating Nanocomposite

Densified iron−nickel−graphite blocks were prepared by powder metallurgy processes and subsequently impregnated with a few percent of fullerene-like WS2 nanoparticles (<150 nm), synthesized in a fluidized bed reactor. Using the disc-block setup, the friction coefficient; critical load for seizure, and wear rates were measured. Substantial improvements in all of the tribological parameters were measured with the addition of the fullerene-like nanoparticldes. This behavior is attributed to a slow release of the nanoparticles from the porous matrix onto the block surface and their excellent tribological behavior.

Slow Release of Fullerene-Like WS2 Nanoparticles as a Superior Solid Lubrication Mechanism in Composite Matrices

Slow Release of Fullerene-Like WS2 Nanoparticles as a Superior Solid Lubrication Mechanism in Composite Matrices

Slow Release of Fullerene-Like WS2 Nanoparticles as a Superior Solid Lubrication Mechanism in Composite Matrices

Slow Release of Fullerene-Like WS2 Nanoparticles as a Superior Solid Lubrication Mechanism in Composite Matrices