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

Recently, inorganic fullerene-like (IF) supramolecules of metal dichalcogenide MX2 (M = Mo, W, etc.; X = S, Se), materials with structures closely related to (nested) carbon fullerenes and nanotubes have been synthesized. The main god of the present work was to study the tribological properties of IF-WS, in comparison to 2H-WS2 and MoS2 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-WS2 particles was 120 nm, while that of 2H-WS2 and 2H-MoS2 was 0.5 mu m and 4 mu m. 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 similar to 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-WS2 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 (WS2). The main advantages of IF nanoparticles lie in their round shape and the absence of dangling bonds. (C) 1999 Published by Elsevier Science S.A. All rights reserved.