Using a new quartz-made reactor, large amounts of fullerene-like (IF) MoS 2 nanoparticles were synthesized by reacting MoO 3 vapor with H 2 S 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) MoS 2 and IF-WS 2 . These tests indicated that under high pressure and relatively low humidity, the IF-MoS 2 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-WS 2 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.

Inorganic fullerene-(IF)-like nanoparticles made of metal dichalcogenides (IF-MoS 2 , IF-WS 2 ) 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-MoS 2 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-MoS 2 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-MoS 2 nanolayers and the iron/iron oxide has been proposed as an explanation for the adhesion of this tribofilm. The tribochemical mechanism of the IF-MoS 2 nanoparticles is discussed in this article.

WS(2) belongs to a family of layered metal dichalcogenide compounds that are known to form cylindrical (inorganic nanotubes-INT) and polyhedral nanostructures--onion or nested fullerene-like (IF) particles. The outermost layers of these IF nanoparticles can be peeled under shear stress, thus IF nanoparticles have been studied for their use as solid lubricants. However, the IF nanoparticles tend to agglomerate, presumably because of surface structural defects induced by elastic strain and curvature, a fact that has a deleterious effect on their tribological properties. In the present work, chemical modification of the IF-WS(2) surface with alkyl-silane molecules is reported. The surface-modified IF nanoparticles display improved dispersion in oil-based suspensions. The alkyl-silane coating reduces the IF-WS(2) nanoparticles' tendency to agglomerate and consequently improves the long-term tribological behavior of oil formulated with the IF additive.

Inorganic fullerene-like (IF) MoS 2 and WS 2 nanoparticles were found to be good friction modifiers and anti-wear additives when dispersed in a lubricant. Their tribological performance seems to be related to the structure, size, and shape of these nanomaterials. The present study describes the tribological properties of a new inorganic fullerene IF-Mo x W 1-x S 2 containing both molybdenum and tungsten disulfide under boundary lubrication. Mo x W 1-x S 2 amorphous inorganic fullerene nanostructures were synthesized by means of MOCVD using an induction furnace setup. The average diameters range from 25 to 45 nm. Upon variation of the amounts of precursors and S, various solid solutions of IF-Mo x W 1-x S 2 were obtained. In addition, a morphological, chemical, and structural analysis of the samples was performed using high resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD). Friction experiments were carried out with a ball-on-flat contact using an environmental tribometer. The results show interesting friction reducing and wear properties of these nanomaterials. The change in the molecule stoichiometry, which led to a variation of particles size but also to a variation of the crystallinity of the particles, affects the tribological performance.

Organosulphur compounds have been long known to be effective antiwear (AW) and extreme pressure (EP) additives in a wide range of metalworking applications. Several interpretations to explain the properties of these compounds have been proposed, but the mechanisms and surface reaction products are still largely unknown. To understand the tribochemistry of these additives, especially thiols and polysulphides, a new device called 'environmentally controlled tribometer' was developed. It permits to simulate the action of the additives using gases having the same chemical function. After friction experiments, surface analyses were carried out on the tribofilm in order to understand the tribochemical mechanism. The evolution of the friction coefficient versus partial pressure of gaseous additive and sample temperature allowed clear differentiation of organosulphur compounds reactivity. The studies showed that the lubricating properties of the additives depend both on the quantity of sulphur and on the carbon chain length. The results for thiols series showed an increasing of EP and AW efficiency with increasing carbon chain length. The comparison between the liquid phase lubrication and the gas phase lubrication results validates this methodology.