Inorganic fullerene-like material as additives to lubricants: structure–function relationship

Abstract

Recently, inorganic fullerene-like (IF) supramolecules of metal dichalcogenide MX 2 (M=Mo, W, etc.; X=S, Se), materials with structures closely related to (nested) carbon fullerenes and nanotubes have been synthesized. The main goal of the present work was to study the tribological properties of IF–WS 2 in comparison to 2H–WS 2 and MoS 2 platelets over a wide range of loads and sliding velocities. The size and shape distributions of the nanoparticles were studied by transmission electron microscopy (TEM). The average size of the IF–WS 2 particles was 120 nm, while that of 2H–WS 2 and 2H–MoS 2 was 0.5 μm and 4 μm. The chemical reactivity of the different powders in an oxygenated atmosphere was verified by heating the powders in ambient atmosphere. The friction experiments were performed in laboratory atmosphere (humidity ∼50%) using a ring-block tester. Complementary information on the state of wear of the powders in the lubricating fluid and on the metal surfaces of the specimens was obtained using a combination of TEM, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It has been established that IF–WS 2 nanoparticles appear to have excellent tribological properties in definite loading range in comparison to typical metal dichalcogenides. The oxidation of the IF particles and the wear track was essentially less than with solid lubricants made of platelets of the same chemical compound (WS 2). The main advantages of IF nanoparticles lie in their round shape and the absence of dangling bonds.